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25  
26  package java.net;
27  
28  import java.io.IOException;
29  import java.io.InvalidObjectException;
30  import java.io.ObjectInputStream;
31  import java.io.ObjectOutputStream;
32  import java.io.Serializable;
33  import java.nio.ByteBuffer;
34  import java.nio.CharBuffer;
35  import java.nio.charset.CharsetDecoder;
36  import java.nio.charset.CharsetEncoder;
37  import java.nio.charset.CoderResult;
38  import java.nio.charset.CodingErrorAction;
39  import java.nio.charset.CharacterCodingException;
40  import java.text.Normalizer;
41  import sun.nio.cs.ThreadLocalCoders;
42  
43  import java.lang.Character;             // for javadoc
44  import java.lang.NullPointerException;  // for javadoc
45  
46  
47  /**
48   * Represents a Uniform Resource Identifier (URI) reference.
49   *
50   * <p> Aside from some minor deviations noted below, an instance of this
51   * class represents a URI reference as defined by
52   * <a href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform
53   * Resource Identifiers (URI): Generic Syntax</i></a>, amended by <a
54   * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for
55   * Literal IPv6 Addresses in URLs</i></a>. The Literal IPv6 address format
56   * also supports scope_ids. The syntax and usage of scope_ids is described
57   * <a href="Inet6Address.html#scoped">here</a>.
58   * This class provides constructors for creating URI instances from
59   * their components or by parsing their string forms, methods for accessing the
60   * various components of an instance, and methods for normalizing, resolving,
61   * and relativizing URI instances.  Instances of this class are immutable.
62   *
63   *
64   * <h3> URI syntax and components </h3>
65   *
66   * At the highest level a URI reference (hereinafter simply "URI") in string
67   * form has the syntax
68   *
69   * <blockquote>
70   * [<i>scheme</i><b>{@code :}</b>]<i>scheme-specific-part</i>[<b>{@code #}</b><i>fragment</i>]
71   * </blockquote>
72   *
73   * where square brackets [...] delineate optional components and the characters
74   * <b>{@code :}</b> and <b>{@code #}</b> stand for themselves.
75   *
76   * <p> An <i>absolute</i> URI specifies a scheme; a URI that is not absolute is
77   * said to be <i>relative</i>.  URIs are also classified according to whether
78   * they are <i>opaque</i> or <i>hierarchical</i>.
79   *
80   * <p> An <i>opaque</i> URI is an absolute URI whose scheme-specific part does
81   * not begin with a slash character ({@code '/'}).  Opaque URIs are not
82   * subject to further parsing.  Some examples of opaque URIs are:
83   *
84   * <blockquote><table cellpadding=0 cellspacing=0 summary="layout">
85   * <tr><td>{@code mailto:java-net@java.sun.com}<td></tr>
86   * <tr><td>{@code news:comp.lang.java}<td></tr>
87   * <tr><td>{@code urn:isbn:096139210x}</td></tr>
88   * </table></blockquote>
89   *
90   * <p> A <i>hierarchical</i> URI is either an absolute URI whose
91   * scheme-specific part begins with a slash character, or a relative URI, that
92   * is, a URI that does not specify a scheme.  Some examples of hierarchical
93   * URIs are:
94   *
95   * <blockquote>
96   * {@code http://java.sun.com/j2se/1.3/}<br>
97   * {@code docs/guide/collections/designfaq.html#28}<br>
98   * {@code ../../../demo/jfc/SwingSet2/src/SwingSet2.java}<br>
99   * {@code file:///~/calendar}
100  * </blockquote>
101  *
102  * <p> A hierarchical URI is subject to further parsing according to the syntax
103  *
104  * <blockquote>
105  * [<i>scheme</i><b>{@code :}</b>][<b>{@code //}</b><i>authority</i>][<i>path</i>][<b>{@code ?}</b><i>query</i>][<b>{@code #}</b><i>fragment</i>]
106  * </blockquote>
107  *
108  * where the characters <b>{@code :}</b>, <b>{@code /}</b>,
109  * <b>{@code ?}</b>, and <b>{@code #}</b> stand for themselves.  The
110  * scheme-specific part of a hierarchical URI consists of the characters
111  * between the scheme and fragment components.
112  *
113  * <p> The authority component of a hierarchical URI is, if specified, either
114  * <i>server-based</i> or <i>registry-based</i>.  A server-based authority
115  * parses according to the familiar syntax
116  *
117  * <blockquote>
118  * [<i>user-info</i><b>{@code @}</b>]<i>host</i>[<b>{@code :}</b><i>port</i>]
119  * </blockquote>
120  *
121  * where the characters <b>{@code @}</b> and <b>{@code :}</b> stand for
122  * themselves.  Nearly all URI schemes currently in use are server-based.  An
123  * authority component that does not parse in this way is considered to be
124  * registry-based.
125  *
126  * <p> The path component of a hierarchical URI is itself said to be absolute
127  * if it begins with a slash character ({@code '/'}); otherwise it is
128  * relative.  The path of a hierarchical URI that is either absolute or
129  * specifies an authority is always absolute.
130  *
131  * <p> All told, then, a URI instance has the following nine components:
132  *
133  * <blockquote><table summary="Describes the components of a URI:scheme,scheme-specific-part,authority,user-info,host,port,path,query,fragment">
134  * <tr><th><i>Component</i></th><th><i>Type</i></th></tr>
135  * <tr><td>scheme</td><td>{@code String}</td></tr>
136  * <tr><td>scheme-specific-part&nbsp;&nbsp;&nbsp;&nbsp;</td><td>{@code String}</td></tr>
137  * <tr><td>authority</td><td>{@code String}</td></tr>
138  * <tr><td>user-info</td><td>{@code String}</td></tr>
139  * <tr><td>host</td><td>{@code String}</td></tr>
140  * <tr><td>port</td><td>{@code int}</td></tr>
141  * <tr><td>path</td><td>{@code String}</td></tr>
142  * <tr><td>query</td><td>{@code String}</td></tr>
143  * <tr><td>fragment</td><td>{@code String}</td></tr>
144  * </table></blockquote>
145  *
146  * In a given instance any particular component is either <i>undefined</i> or
147  * <i>defined</i> with a distinct value.  Undefined string components are
148  * represented by {@code null}, while undefined integer components are
149  * represented by {@code -1}.  A string component may be defined to have the
150  * empty string as its value; this is not equivalent to that component being
151  * undefined.
152  *
153  * <p> Whether a particular component is or is not defined in an instance
154  * depends upon the type of the URI being represented.  An absolute URI has a
155  * scheme component.  An opaque URI has a scheme, a scheme-specific part, and
156  * possibly a fragment, but has no other components.  A hierarchical URI always
157  * has a path (though it may be empty) and a scheme-specific-part (which at
158  * least contains the path), and may have any of the other components.  If the
159  * authority component is present and is server-based then the host component
160  * will be defined and the user-information and port components may be defined.
161  *
162  *
163  * <h4> Operations on URI instances </h4>
164  *
165  * The key operations supported by this class are those of
166  * <i>normalization</i>, <i>resolution</i>, and <i>relativization</i>.
167  *
168  * <p> <i>Normalization</i> is the process of removing unnecessary {@code "."}
169  * and {@code ".."} segments from the path component of a hierarchical URI.
170  * Each {@code "."} segment is simply removed.  A {@code ".."} segment is
171  * removed only if it is preceded by a non-{@code ".."} segment.
172  * Normalization has no effect upon opaque URIs.
173  *
174  * <p> <i>Resolution</i> is the process of resolving one URI against another,
175  * <i>base</i> URI.  The resulting URI is constructed from components of both
176  * URIs in the manner specified by RFC&nbsp;2396, taking components from the
177  * base URI for those not specified in the original.  For hierarchical URIs,
178  * the path of the original is resolved against the path of the base and then
179  * normalized.  The result, for example, of resolving
180  *
181  * <blockquote>
182  * {@code docs/guide/collections/designfaq.html#28}
183  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
184  * &nbsp;&nbsp;&nbsp;&nbsp;(1)
185  * </blockquote>
186  *
187  * against the base URI {@code http://java.sun.com/j2se/1.3/} is the result
188  * URI
189  *
190  * <blockquote>
191  * {@code http://docs.oracle.com/javase/1.3/docs/guide/collections/designfaq.html#28}
192  * </blockquote>
193  *
194  * Resolving the relative URI
195  *
196  * <blockquote>
197  * {@code ../../../demo/jfc/SwingSet2/src/SwingSet2.java}&nbsp;&nbsp;&nbsp;&nbsp;(2)
198  * </blockquote>
199  *
200  * against this result yields, in turn,
201  *
202  * <blockquote>
203  * {@code http://java.sun.com/j2se/1.3/demo/jfc/SwingSet2/src/SwingSet2.java}
204  * </blockquote>
205  *
206  * Resolution of both absolute and relative URIs, and of both absolute and
207  * relative paths in the case of hierarchical URIs, is supported.  Resolving
208  * the URI {@code file:///~calendar} against any other URI simply yields the
209  * original URI, since it is absolute.  Resolving the relative URI (2) above
210  * against the relative base URI (1) yields the normalized, but still relative,
211  * URI
212  *
213  * <blockquote>
214  * {@code demo/jfc/SwingSet2/src/SwingSet2.java}
215  * </blockquote>
216  *
217  * <p> <i>Relativization</i>, finally, is the inverse of resolution: For any
218  * two normalized URIs <i>u</i> and&nbsp;<i>v</i>,
219  *
220  * <blockquote>
221  *   <i>u</i>{@code .relativize(}<i>u</i>{@code .resolve(}<i>v</i>{@code )).equals(}<i>v</i>{@code )}&nbsp;&nbsp;and<br>
222  *   <i>u</i>{@code .resolve(}<i>u</i>{@code .relativize(}<i>v</i>{@code )).equals(}<i>v</i>{@code )}&nbsp;&nbsp;.<br>
223  * </blockquote>
224  *
225  * This operation is often useful when constructing a document containing URIs
226  * that must be made relative to the base URI of the document wherever
227  * possible.  For example, relativizing the URI
228  *
229  * <blockquote>
230  * {@code http://docs.oracle.com/javase/1.3/docs/guide/index.html}
231  * </blockquote>
232  *
233  * against the base URI
234  *
235  * <blockquote>
236  * {@code http://java.sun.com/j2se/1.3}
237  * </blockquote>
238  *
239  * yields the relative URI {@code docs/guide/index.html}.
240  *
241  *
242  * <h4> Character categories </h4>
243  *
244  * RFC&nbsp;2396 specifies precisely which characters are permitted in the
245  * various components of a URI reference.  The following categories, most of
246  * which are taken from that specification, are used below to describe these
247  * constraints:
248  *
249  * <blockquote><table cellspacing=2 summary="Describes categories alpha,digit,alphanum,unreserved,punct,reserved,escaped,and other">
250  *   <tr><th valign=top><i>alpha</i></th>
251  *       <td>The US-ASCII alphabetic characters,
252  *        {@code 'A'}&nbsp;through&nbsp;{@code 'Z'}
253  *        and {@code 'a'}&nbsp;through&nbsp;{@code 'z'}</td></tr>
254  *   <tr><th valign=top><i>digit</i></th>
255  *       <td>The US-ASCII decimal digit characters,
256  *       {@code '0'}&nbsp;through&nbsp;{@code '9'}</td></tr>
257  *   <tr><th valign=top><i>alphanum</i></th>
258  *       <td>All <i>alpha</i> and <i>digit</i> characters</td></tr>
259  *   <tr><th valign=top><i>unreserved</i>&nbsp;&nbsp;&nbsp;&nbsp;</th>
260  *       <td>All <i>alphanum</i> characters together with those in the string
261  *        {@code "_-!.~'()*"}</td></tr>
262  *   <tr><th valign=top><i>punct</i></th>
263  *       <td>The characters in the string {@code ",;:$&+="}</td></tr>
264  *   <tr><th valign=top><i>reserved</i></th>
265  *       <td>All <i>punct</i> characters together with those in the string
266  *        {@code "?/[]@"}</td></tr>
267  *   <tr><th valign=top><i>escaped</i></th>
268  *       <td>Escaped octets, that is, triplets consisting of the percent
269  *           character ({@code '%'}) followed by two hexadecimal digits
270  *           ({@code '0'}-{@code '9'}, {@code 'A'}-{@code 'F'}, and
271  *           {@code 'a'}-{@code 'f'})</td></tr>
272  *   <tr><th valign=top><i>other</i></th>
273  *       <td>The Unicode characters that are not in the US-ASCII character set,
274  *           are not control characters (according to the {@link
275  *           java.lang.Character#isISOControl(char) Character.isISOControl}
276  *           method), and are not space characters (according to the {@link
277  *           java.lang.Character#isSpaceChar(char) Character.isSpaceChar}
278  *           method)&nbsp;&nbsp;<i>(<b>Deviation from RFC 2396</b>, which is
279  *           limited to US-ASCII)</i></td></tr>
280  * </table></blockquote>
281  *
282  * <p><a name="legal-chars"></a> The set of all legal URI characters consists of
283  * the <i>unreserved</i>, <i>reserved</i>, <i>escaped</i>, and <i>other</i>
284  * characters.
285  *
286  *
287  * <h4> Escaped octets, quotation, encoding, and decoding </h4>
288  *
289  * RFC 2396 allows escaped octets to appear in the user-info, path, query, and
290  * fragment components.  Escaping serves two purposes in URIs:
291  *
292  * <ul>
293  *
294  *   <li><p> To <i>encode</i> non-US-ASCII characters when a URI is required to
295  *   conform strictly to RFC&nbsp;2396 by not containing any <i>other</i>
296  *   characters.  </p></li>
297  *
298  *   <li><p> To <i>quote</i> characters that are otherwise illegal in a
299  *   component.  The user-info, path, query, and fragment components differ
300  *   slightly in terms of which characters are considered legal and illegal.
301  *   </p></li>
302  *
303  * </ul>
304  *
305  * These purposes are served in this class by three related operations:
306  *
307  * <ul>
308  *
309  *   <li><p><a name="encode"></a> A character is <i>encoded</i> by replacing it
310  *   with the sequence of escaped octets that represent that character in the
311  *   UTF-8 character set.  The Euro currency symbol ({@code '\u005Cu20AC'}),
312  *   for example, is encoded as {@code "%E2%82%AC"}.  <i>(<b>Deviation from
313  *   RFC&nbsp;2396</b>, which does not specify any particular character
314  *   set.)</i> </p></li>
315  *
316  *   <li><p><a name="quote"></a> An illegal character is <i>quoted</i> simply by
317  *   encoding it.  The space character, for example, is quoted by replacing it
318  *   with {@code "%20"}.  UTF-8 contains US-ASCII, hence for US-ASCII
319  *   characters this transformation has exactly the effect required by
320  *   RFC&nbsp;2396. </p></li>
321  *
322  *   <li><p><a name="decode"></a>
323  *   A sequence of escaped octets is <i>decoded</i> by
324  *   replacing it with the sequence of characters that it represents in the
325  *   UTF-8 character set.  UTF-8 contains US-ASCII, hence decoding has the
326  *   effect of de-quoting any quoted US-ASCII characters as well as that of
327  *   decoding any encoded non-US-ASCII characters.  If a <a
328  *   href="../nio/charset/CharsetDecoder.html#ce">decoding error</a> occurs
329  *   when decoding the escaped octets then the erroneous octets are replaced by
330  *   {@code '\u005CuFFFD'}, the Unicode replacement character.  </p></li>
331  *
332  * </ul>
333  *
334  * These operations are exposed in the constructors and methods of this class
335  * as follows:
336  *
337  * <ul>
338  *
339  *   <li><p> The {@linkplain #URI(java.lang.String) single-argument
340  *   constructor} requires any illegal characters in its argument to be
341  *   quoted and preserves any escaped octets and <i>other</i> characters that
342  *   are present.  </p></li>
343  *
344  *   <li><p> The {@linkplain
345  *   #URI(java.lang.String,java.lang.String,java.lang.String,int,java.lang.String,java.lang.String,java.lang.String)
346  *   multi-argument constructors} quote illegal characters as
347  *   required by the components in which they appear.  The percent character
348  *   ({@code '%'}) is always quoted by these constructors.  Any <i>other</i>
349  *   characters are preserved.  </p></li>
350  *
351  *   <li><p> The {@link #getRawUserInfo() getRawUserInfo}, {@link #getRawPath()
352  *   getRawPath}, {@link #getRawQuery() getRawQuery}, {@link #getRawFragment()
353  *   getRawFragment}, {@link #getRawAuthority() getRawAuthority}, and {@link
354  *   #getRawSchemeSpecificPart() getRawSchemeSpecificPart} methods return the
355  *   values of their corresponding components in raw form, without interpreting
356  *   any escaped octets.  The strings returned by these methods may contain
357  *   both escaped octets and <i>other</i> characters, and will not contain any
358  *   illegal characters.  </p></li>
359  *
360  *   <li><p> The {@link #getUserInfo() getUserInfo}, {@link #getPath()
361  *   getPath}, {@link #getQuery() getQuery}, {@link #getFragment()
362  *   getFragment}, {@link #getAuthority() getAuthority}, and {@link
363  *   #getSchemeSpecificPart() getSchemeSpecificPart} methods decode any escaped
364  *   octets in their corresponding components.  The strings returned by these
365  *   methods may contain both <i>other</i> characters and illegal characters,
366  *   and will not contain any escaped octets.  </p></li>
367  *
368  *   <li><p> The {@link #toString() toString} method returns a URI string with
369  *   all necessary quotation but which may contain <i>other</i> characters.
370  *   </p></li>
371  *
372  *   <li><p> The {@link #toASCIIString() toASCIIString} method returns a fully
373  *   quoted and encoded URI string that does not contain any <i>other</i>
374  *   characters.  </p></li>
375  *
376  * </ul>
377  *
378  *
379  * <h4> Identities </h4>
380  *
381  * For any URI <i>u</i>, it is always the case that
382  *
383  * <blockquote>
384  * {@code new URI(}<i>u</i>{@code .toString()).equals(}<i>u</i>{@code )}&nbsp;.
385  * </blockquote>
386  *
387  * For any URI <i>u</i> that does not contain redundant syntax such as two
388  * slashes before an empty authority (as in {@code file:///tmp/}&nbsp;) or a
389  * colon following a host name but no port (as in
390  * {@code http://java.sun.com:}&nbsp;), and that does not encode characters
391  * except those that must be quoted, the following identities also hold:
392  * <pre>
393  *     new URI(<i>u</i>.getScheme(),
394  *             <i>u</i>.getSchemeSpecificPart(),
395  *             <i>u</i>.getFragment())
396  *     .equals(<i>u</i>)</pre>
397  * in all cases,
398  * <pre>
399  *     new URI(<i>u</i>.getScheme(),
400  *             <i>u</i>.getUserInfo(), <i>u</i>.getAuthority(),
401  *             <i>u</i>.getPath(), <i>u</i>.getQuery(),
402  *             <i>u</i>.getFragment())
403  *     .equals(<i>u</i>)</pre>
404  * if <i>u</i> is hierarchical, and
405  * <pre>
406  *     new URI(<i>u</i>.getScheme(),
407  *             <i>u</i>.getUserInfo(), <i>u</i>.getHost(), <i>u</i>.getPort(),
408  *             <i>u</i>.getPath(), <i>u</i>.getQuery(),
409  *             <i>u</i>.getFragment())
410  *     .equals(<i>u</i>)</pre>
411  * if <i>u</i> is hierarchical and has either no authority or a server-based
412  * authority.
413  *
414  *
415  * <h4> URIs, URLs, and URNs </h4>
416  *
417  * A URI is a uniform resource <i>identifier</i> while a URL is a uniform
418  * resource <i>locator</i>.  Hence every URL is a URI, abstractly speaking, but
419  * not every URI is a URL.  This is because there is another subcategory of
420  * URIs, uniform resource <i>names</i> (URNs), which name resources but do not
421  * specify how to locate them.  The {@code mailto}, {@code news}, and
422  * {@code isbn} URIs shown above are examples of URNs.
423  *
424  * <p> The conceptual distinction between URIs and URLs is reflected in the
425  * differences between this class and the {@link URL} class.
426  *
427  * <p> An instance of this class represents a URI reference in the syntactic
428  * sense defined by RFC&nbsp;2396.  A URI may be either absolute or relative.
429  * A URI string is parsed according to the generic syntax without regard to the
430  * scheme, if any, that it specifies.  No lookup of the host, if any, is
431  * performed, and no scheme-dependent stream handler is constructed.  Equality,
432  * hashing, and comparison are defined strictly in terms of the character
433  * content of the instance.  In other words, a URI instance is little more than
434  * a structured string that supports the syntactic, scheme-independent
435  * operations of comparison, normalization, resolution, and relativization.
436  *
437  * <p> An instance of the {@link URL} class, by contrast, represents the
438  * syntactic components of a URL together with some of the information required
439  * to access the resource that it describes.  A URL must be absolute, that is,
440  * it must always specify a scheme.  A URL string is parsed according to its
441  * scheme.  A stream handler is always established for a URL, and in fact it is
442  * impossible to create a URL instance for a scheme for which no handler is
443  * available.  Equality and hashing depend upon both the scheme and the
444  * Internet address of the host, if any; comparison is not defined.  In other
445  * words, a URL is a structured string that supports the syntactic operation of
446  * resolution as well as the network I/O operations of looking up the host and
447  * opening a connection to the specified resource.
448  *
449  *
450  * @author Mark Reinhold
451  * @since 1.4
452  *
453  * @see <a href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC&nbsp;2279: UTF-8, a
454  * transformation format of ISO 10646</i></a>, <br><a
455  * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IPv6 Addressing
456  * Architecture</i></a>, <br><a
457  * href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform
458  * Resource Identifiers (URI): Generic Syntax</i></a>, <br><a
459  * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for
460  * Literal IPv6 Addresses in URLs</i></a>, <br><a
461  * href="URISyntaxException.html">URISyntaxException</a>
462  */
463 
464 public final class URI
465     implements Comparable<URI>, Serializable
466 {
467 
468     // Note: Comments containing the word "ASSERT" indicate places where a
469     // throw of an InternalError should be replaced by an appropriate assertion
470     // statement once asserts are enabled in the build.
471 
472     static final long serialVersionUID = -6052424284110960213L;
473 
474 
475     // -- Properties and components of this instance --
476 
477     // Components of all URIs: [<scheme>:]<scheme-specific-part>[#<fragment>]
478     private transient String scheme;            // null ==> relative URI
479     private transient String fragment;
480 
481     // Hierarchical URI components: [//<authority>]<path>[?<query>]
482     private transient String authority;         // Registry or server
483 
484     // Server-based authority: [<userInfo>@]<host>[:<port>]
485     private transient String userInfo;
486     private transient String host;              // null ==> registry-based
487     private transient int port = -1;            // -1 ==> undefined
488 
489     // Remaining components of hierarchical URIs
490     private transient String path;              // null ==> opaque
491     private transient String query;
492 
493     // The remaining fields may be computed on demand
494 
495     private volatile transient String schemeSpecificPart;
496     private volatile transient int hash;        // Zero ==> undefined
497 
498     private volatile transient String decodedUserInfo = null;
499     private volatile transient String decodedAuthority = null;
500     private volatile transient String decodedPath = null;
501     private volatile transient String decodedQuery = null;
502     private volatile transient String decodedFragment = null;
503     private volatile transient String decodedSchemeSpecificPart = null;
504 
505     /**
506      * The string form of this URI.
507      *
508      * @serial
509      */
510     private volatile String string;             // The only serializable field
511 
512 
513 
514     // -- Constructors and factories --
515 
516     private URI() { }                           // Used internally
517 
518     /**
519      * Constructs a URI by parsing the given string.
520      *
521      * <p> This constructor parses the given string exactly as specified by the
522      * grammar in <a
523      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
524      * Appendix&nbsp;A, <b><i>except for the following deviations:</i></b> </p>
525      *
526      * <ul>
527      *
528      *   <li><p> An empty authority component is permitted as long as it is
529      *   followed by a non-empty path, a query component, or a fragment
530      *   component.  This allows the parsing of URIs such as
531      *   {@code "file:///foo/bar"}, which seems to be the intent of
532      *   RFC&nbsp;2396 although the grammar does not permit it.  If the
533      *   authority component is empty then the user-information, host, and port
534      *   components are undefined. </p></li>
535      *
536      *   <li><p> Empty relative paths are permitted; this seems to be the
537      *   intent of RFC&nbsp;2396 although the grammar does not permit it.  The
538      *   primary consequence of this deviation is that a standalone fragment
539      *   such as {@code "#foo"} parses as a relative URI with an empty path
540      *   and the given fragment, and can be usefully <a
541      *   href="#resolve-frag">resolved</a> against a base URI.
542      *
543      *   <li><p> IPv4 addresses in host components are parsed rigorously, as
544      *   specified by <a
545      *   href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>: Each
546      *   element of a dotted-quad address must contain no more than three
547      *   decimal digits.  Each element is further constrained to have a value
548      *   no greater than 255. </p></li>
549      *
550      *   <li> <p> Hostnames in host components that comprise only a single
551      *   domain label are permitted to start with an <i>alphanum</i>
552      *   character. This seems to be the intent of <a
553      *   href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>
554      *   section&nbsp;3.2.2 although the grammar does not permit it. The
555      *   consequence of this deviation is that the authority component of a
556      *   hierarchical URI such as {@code s://123}, will parse as a server-based
557      *   authority. </p></li>
558      *
559      *   <li><p> IPv6 addresses are permitted for the host component.  An IPv6
560      *   address must be enclosed in square brackets ({@code '['} and
561      *   {@code ']'}) as specified by <a
562      *   href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>.  The
563      *   IPv6 address itself must parse according to <a
564      *   href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>.  IPv6
565      *   addresses are further constrained to describe no more than sixteen
566      *   bytes of address information, a constraint implicit in RFC&nbsp;2373
567      *   but not expressible in the grammar. </p></li>
568      *
569      *   <li><p> Characters in the <i>other</i> category are permitted wherever
570      *   RFC&nbsp;2396 permits <i>escaped</i> octets, that is, in the
571      *   user-information, path, query, and fragment components, as well as in
572      *   the authority component if the authority is registry-based.  This
573      *   allows URIs to contain Unicode characters beyond those in the US-ASCII
574      *   character set. </p></li>
575      *
576      * </ul>
577      *
578      * @param  str   The string to be parsed into a URI
579      *
580      * @throws  NullPointerException
581      *          If {@code str} is {@code null}
582      *
583      * @throws  URISyntaxException
584      *          If the given string violates RFC&nbsp;2396, as augmented
585      *          by the above deviations
586      */
587     public URI(String str) throws URISyntaxException {
588         new Parser(str).parse(false);
589     }
590 
591     /**
592      * Constructs a hierarchical URI from the given components.
593      *
594      * <p> If a scheme is given then the path, if also given, must either be
595      * empty or begin with a slash character ({@code '/'}).  Otherwise a
596      * component of the new URI may be left undefined by passing {@code null}
597      * for the corresponding parameter or, in the case of the {@code port}
598      * parameter, by passing {@code -1}.
599      *
600      * <p> This constructor first builds a URI string from the given components
601      * according to the rules specified in <a
602      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
603      * section&nbsp;5.2, step&nbsp;7: </p>
604      *
605      * <ol>
606      *
607      *   <li><p> Initially, the result string is empty. </p></li>
608      *
609      *   <li><p> If a scheme is given then it is appended to the result,
610      *   followed by a colon character ({@code ':'}).  </p></li>
611      *
612      *   <li><p> If user information, a host, or a port are given then the
613      *   string {@code "//"} is appended.  </p></li>
614      *
615      *   <li><p> If user information is given then it is appended, followed by
616      *   a commercial-at character ({@code '@'}).  Any character not in the
617      *   <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
618      *   categories is <a href="#quote">quoted</a>.  </p></li>
619      *
620      *   <li><p> If a host is given then it is appended.  If the host is a
621      *   literal IPv6 address but is not enclosed in square brackets
622      *   ({@code '['} and {@code ']'}) then the square brackets are added.
623      *   </p></li>
624      *
625      *   <li><p> If a port number is given then a colon character
626      *   ({@code ':'}) is appended, followed by the port number in decimal.
627      *   </p></li>
628      *
629      *   <li><p> If a path is given then it is appended.  Any character not in
630      *   the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
631      *   categories, and not equal to the slash character ({@code '/'}) or the
632      *   commercial-at character ({@code '@'}), is quoted.  </p></li>
633      *
634      *   <li><p> If a query is given then a question-mark character
635      *   ({@code '?'}) is appended, followed by the query.  Any character that
636      *   is not a <a href="#legal-chars">legal URI character</a> is quoted.
637      *   </p></li>
638      *
639      *   <li><p> Finally, if a fragment is given then a hash character
640      *   ({@code '#'}) is appended, followed by the fragment.  Any character
641      *   that is not a legal URI character is quoted.  </p></li>
642      *
643      * </ol>
644      *
645      * <p> The resulting URI string is then parsed as if by invoking the {@link
646      * #URI(String)} constructor and then invoking the {@link
647      * #parseServerAuthority()} method upon the result; this may cause a {@link
648      * URISyntaxException} to be thrown.  </p>
649      *
650      * @param   scheme    Scheme name
651      * @param   userInfo  User name and authorization information
652      * @param   host      Host name
653      * @param   port      Port number
654      * @param   path      Path
655      * @param   query     Query
656      * @param   fragment  Fragment
657      *
658      * @throws URISyntaxException
659      *         If both a scheme and a path are given but the path is relative,
660      *         if the URI string constructed from the given components violates
661      *         RFC&nbsp;2396, or if the authority component of the string is
662      *         present but cannot be parsed as a server-based authority
663      */
664     public URI(String scheme,
665                String userInfo, String host, int port,
666                String path, String query, String fragment)
667         throws URISyntaxException
668     {
669         String s = toString(scheme, null,
670                             null, userInfo, host, port,
671                             path, query, fragment);
672         checkPath(s, scheme, path);
673         new Parser(s).parse(true);
674     }
675 
676     /**
677      * Constructs a hierarchical URI from the given components.
678      *
679      * <p> If a scheme is given then the path, if also given, must either be
680      * empty or begin with a slash character ({@code '/'}).  Otherwise a
681      * component of the new URI may be left undefined by passing {@code null}
682      * for the corresponding parameter.
683      *
684      * <p> This constructor first builds a URI string from the given components
685      * according to the rules specified in <a
686      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
687      * section&nbsp;5.2, step&nbsp;7: </p>
688      *
689      * <ol>
690      *
691      *   <li><p> Initially, the result string is empty.  </p></li>
692      *
693      *   <li><p> If a scheme is given then it is appended to the result,
694      *   followed by a colon character ({@code ':'}).  </p></li>
695      *
696      *   <li><p> If an authority is given then the string {@code "//"} is
697      *   appended, followed by the authority.  If the authority contains a
698      *   literal IPv6 address then the address must be enclosed in square
699      *   brackets ({@code '['} and {@code ']'}).  Any character not in the
700      *   <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
701      *   categories, and not equal to the commercial-at character
702      *   ({@code '@'}), is <a href="#quote">quoted</a>.  </p></li>
703      *
704      *   <li><p> If a path is given then it is appended.  Any character not in
705      *   the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
706      *   categories, and not equal to the slash character ({@code '/'}) or the
707      *   commercial-at character ({@code '@'}), is quoted.  </p></li>
708      *
709      *   <li><p> If a query is given then a question-mark character
710      *   ({@code '?'}) is appended, followed by the query.  Any character that
711      *   is not a <a href="#legal-chars">legal URI character</a> is quoted.
712      *   </p></li>
713      *
714      *   <li><p> Finally, if a fragment is given then a hash character
715      *   ({@code '#'}) is appended, followed by the fragment.  Any character
716      *   that is not a legal URI character is quoted.  </p></li>
717      *
718      * </ol>
719      *
720      * <p> The resulting URI string is then parsed as if by invoking the {@link
721      * #URI(String)} constructor and then invoking the {@link
722      * #parseServerAuthority()} method upon the result; this may cause a {@link
723      * URISyntaxException} to be thrown.  </p>
724      *
725      * @param   scheme     Scheme name
726      * @param   authority  Authority
727      * @param   path       Path
728      * @param   query      Query
729      * @param   fragment   Fragment
730      *
731      * @throws URISyntaxException
732      *         If both a scheme and a path are given but the path is relative,
733      *         if the URI string constructed from the given components violates
734      *         RFC&nbsp;2396, or if the authority component of the string is
735      *         present but cannot be parsed as a server-based authority
736      */
737     public URI(String scheme,
738                String authority,
739                String path, String query, String fragment)
740         throws URISyntaxException
741     {
742         String s = toString(scheme, null,
743                             authority, null, null, -1,
744                             path, query, fragment);
745         checkPath(s, scheme, path);
746         new Parser(s).parse(false);
747     }
748 
749     /**
750      * Constructs a hierarchical URI from the given components.
751      *
752      * <p> A component may be left undefined by passing {@code null}.
753      *
754      * <p> This convenience constructor works as if by invoking the
755      * seven-argument constructor as follows:
756      *
757      * <blockquote>
758      * {@code new} {@link #URI(String, String, String, int, String, String, String)
759      * URI}{@code (scheme, null, host, -1, path, null, fragment);}
760      * </blockquote>
761      *
762      * @param   scheme    Scheme name
763      * @param   host      Host name
764      * @param   path      Path
765      * @param   fragment  Fragment
766      *
767      * @throws  URISyntaxException
768      *          If the URI string constructed from the given components
769      *          violates RFC&nbsp;2396
770      */
771     public URI(String scheme, String host, String path, String fragment)
772         throws URISyntaxException
773     {
774         this(scheme, null, host, -1, path, null, fragment);
775     }
776 
777     /**
778      * Constructs a URI from the given components.
779      *
780      * <p> A component may be left undefined by passing {@code null}.
781      *
782      * <p> This constructor first builds a URI in string form using the given
783      * components as follows:  </p>
784      *
785      * <ol>
786      *
787      *   <li><p> Initially, the result string is empty.  </p></li>
788      *
789      *   <li><p> If a scheme is given then it is appended to the result,
790      *   followed by a colon character ({@code ':'}).  </p></li>
791      *
792      *   <li><p> If a scheme-specific part is given then it is appended.  Any
793      *   character that is not a <a href="#legal-chars">legal URI character</a>
794      *   is <a href="#quote">quoted</a>.  </p></li>
795      *
796      *   <li><p> Finally, if a fragment is given then a hash character
797      *   ({@code '#'}) is appended to the string, followed by the fragment.
798      *   Any character that is not a legal URI character is quoted.  </p></li>
799      *
800      * </ol>
801      *
802      * <p> The resulting URI string is then parsed in order to create the new
803      * URI instance as if by invoking the {@link #URI(String)} constructor;
804      * this may cause a {@link URISyntaxException} to be thrown.  </p>
805      *
806      * @param   scheme    Scheme name
807      * @param   ssp       Scheme-specific part
808      * @param   fragment  Fragment
809      *
810      * @throws  URISyntaxException
811      *          If the URI string constructed from the given components
812      *          violates RFC&nbsp;2396
813      */
814     public URI(String scheme, String ssp, String fragment)
815         throws URISyntaxException
816     {
817         new Parser(toString(scheme, ssp,
818                             null, null, null, -1,
819                             null, null, fragment))
820             .parse(false);
821     }
822 
823     /**
824      * Creates a URI by parsing the given string.
825      *
826      * <p> This convenience factory method works as if by invoking the {@link
827      * #URI(String)} constructor; any {@link URISyntaxException} thrown by the
828      * constructor is caught and wrapped in a new {@link
829      * IllegalArgumentException} object, which is then thrown.
830      *
831      * <p> This method is provided for use in situations where it is known that
832      * the given string is a legal URI, for example for URI constants declared
833      * within in a program, and so it would be considered a programming error
834      * for the string not to parse as such.  The constructors, which throw
835      * {@link URISyntaxException} directly, should be used situations where a
836      * URI is being constructed from user input or from some other source that
837      * may be prone to errors.  </p>
838      *
839      * @param  str   The string to be parsed into a URI
840      * @return The new URI
841      *
842      * @throws  NullPointerException
843      *          If {@code str} is {@code null}
844      *
845      * @throws  IllegalArgumentException
846      *          If the given string violates RFC&nbsp;2396
847      */
848     public static URI create(String str) {
849         try {
850             return new URI(str);
851         } catch (URISyntaxException x) {
852             throw new IllegalArgumentException(x.getMessage(), x);
853         }
854     }
855 
856 
857     // -- Operations --
858 
859     /**
860      * Attempts to parse this URI's authority component, if defined, into
861      * user-information, host, and port components.
862      *
863      * <p> If this URI's authority component has already been recognized as
864      * being server-based then it will already have been parsed into
865      * user-information, host, and port components.  In this case, or if this
866      * URI has no authority component, this method simply returns this URI.
867      *
868      * <p> Otherwise this method attempts once more to parse the authority
869      * component into user-information, host, and port components, and throws
870      * an exception describing why the authority component could not be parsed
871      * in that way.
872      *
873      * <p> This method is provided because the generic URI syntax specified in
874      * <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>
875      * cannot always distinguish a malformed server-based authority from a
876      * legitimate registry-based authority.  It must therefore treat some
877      * instances of the former as instances of the latter.  The authority
878      * component in the URI string {@code "//foo:bar"}, for example, is not a
879      * legal server-based authority but it is legal as a registry-based
880      * authority.
881      *
882      * <p> In many common situations, for example when working URIs that are
883      * known to be either URNs or URLs, the hierarchical URIs being used will
884      * always be server-based.  They therefore must either be parsed as such or
885      * treated as an error.  In these cases a statement such as
886      *
887      * <blockquote>
888      * {@code URI }<i>u</i>{@code  = new URI(str).parseServerAuthority();}
889      * </blockquote>
890      *
891      * <p> can be used to ensure that <i>u</i> always refers to a URI that, if
892      * it has an authority component, has a server-based authority with proper
893      * user-information, host, and port components.  Invoking this method also
894      * ensures that if the authority could not be parsed in that way then an
895      * appropriate diagnostic message can be issued based upon the exception
896      * that is thrown. </p>
897      *
898      * @return  A URI whose authority field has been parsed
899      *          as a server-based authority
900      *
901      * @throws  URISyntaxException
902      *          If the authority component of this URI is defined
903      *          but cannot be parsed as a server-based authority
904      *          according to RFC&nbsp;2396
905      */
906     public URI parseServerAuthority()
907         throws URISyntaxException
908     {
909         // We could be clever and cache the error message and index from the
910         // exception thrown during the original parse, but that would require
911         // either more fields or a more-obscure representation.
912         if ((host != null) || (authority == null))
913             return this;
914         defineString();
915         new Parser(string).parse(true);
916         return this;
917     }
918 
919     /**
920      * Normalizes this URI's path.
921      *
922      * <p> If this URI is opaque, or if its path is already in normal form,
923      * then this URI is returned.  Otherwise a new URI is constructed that is
924      * identical to this URI except that its path is computed by normalizing
925      * this URI's path in a manner consistent with <a
926      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
927      * section&nbsp;5.2, step&nbsp;6, sub-steps&nbsp;c through&nbsp;f; that is:
928      * </p>
929      *
930      * <ol>
931      *
932      *   <li><p> All {@code "."} segments are removed. </p></li>
933      *
934      *   <li><p> If a {@code ".."} segment is preceded by a non-{@code ".."}
935      *   segment then both of these segments are removed.  This step is
936      *   repeated until it is no longer applicable. </p></li>
937      *
938      *   <li><p> If the path is relative, and if its first segment contains a
939      *   colon character ({@code ':'}), then a {@code "."} segment is
940      *   prepended.  This prevents a relative URI with a path such as
941      *   {@code "a:b/c/d"} from later being re-parsed as an opaque URI with a
942      *   scheme of {@code "a"} and a scheme-specific part of {@code "b/c/d"}.
943      *   <b><i>(Deviation from RFC&nbsp;2396)</i></b> </p></li>
944      *
945      * </ol>
946      *
947      * <p> A normalized path will begin with one or more {@code ".."} segments
948      * if there were insufficient non-{@code ".."} segments preceding them to
949      * allow their removal.  A normalized path will begin with a {@code "."}
950      * segment if one was inserted by step 3 above.  Otherwise, a normalized
951      * path will not contain any {@code "."} or {@code ".."} segments. </p>
952      *
953      * @return  A URI equivalent to this URI,
954      *          but whose path is in normal form
955      */
956     public URI normalize() {
957         return normalize(this);
958     }
959 
960     /**
961      * Resolves the given URI against this URI.
962      *
963      * <p> If the given URI is already absolute, or if this URI is opaque, then
964      * the given URI is returned.
965      *
966      * <p><a name="resolve-frag"></a> If the given URI's fragment component is
967      * defined, its path component is empty, and its scheme, authority, and
968      * query components are undefined, then a URI with the given fragment but
969      * with all other components equal to those of this URI is returned.  This
970      * allows a URI representing a standalone fragment reference, such as
971      * {@code "#foo"}, to be usefully resolved against a base URI.
972      *
973      * <p> Otherwise this method constructs a new hierarchical URI in a manner
974      * consistent with <a
975      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
976      * section&nbsp;5.2; that is: </p>
977      *
978      * <ol>
979      *
980      *   <li><p> A new URI is constructed with this URI's scheme and the given
981      *   URI's query and fragment components. </p></li>
982      *
983      *   <li><p> If the given URI has an authority component then the new URI's
984      *   authority and path are taken from the given URI. </p></li>
985      *
986      *   <li><p> Otherwise the new URI's authority component is copied from
987      *   this URI, and its path is computed as follows: </p>
988      *
989      *   <ol>
990      *
991      *     <li><p> If the given URI's path is absolute then the new URI's path
992      *     is taken from the given URI. </p></li>
993      *
994      *     <li><p> Otherwise the given URI's path is relative, and so the new
995      *     URI's path is computed by resolving the path of the given URI
996      *     against the path of this URI.  This is done by concatenating all but
997      *     the last segment of this URI's path, if any, with the given URI's
998      *     path and then normalizing the result as if by invoking the {@link
999      *     #normalize() normalize} method. </p></li>
1000      *
1001      *   </ol></li>
1002      *
1003      * </ol>
1004      *
1005      * <p> The result of this method is absolute if, and only if, either this
1006      * URI is absolute or the given URI is absolute.  </p>
1007      *
1008      * @param  uri  The URI to be resolved against this URI
1009      * @return The resulting URI
1010      *
1011      * @throws  NullPointerException
1012      *          If {@code uri} is {@code null}
1013      */
1014     public URI resolve(URI uri) {
1015         return resolve(this, uri);
1016     }
1017 
1018     /**
1019      * Constructs a new URI by parsing the given string and then resolving it
1020      * against this URI.
1021      *
1022      * <p> This convenience method works as if invoking it were equivalent to
1023      * evaluating the expression {@link #resolve(java.net.URI)
1024      * resolve}{@code (URI.}{@link #create(String) create}{@code (str))}. </p>
1025      *
1026      * @param  str   The string to be parsed into a URI
1027      * @return The resulting URI
1028      *
1029      * @throws  NullPointerException
1030      *          If {@code str} is {@code null}
1031      *
1032      * @throws  IllegalArgumentException
1033      *          If the given string violates RFC&nbsp;2396
1034      */
1035     public URI resolve(String str) {
1036         return resolve(URI.create(str));
1037     }
1038 
1039     /**
1040      * Relativizes the given URI against this URI.
1041      *
1042      * <p> The relativization of the given URI against this URI is computed as
1043      * follows: </p>
1044      *
1045      * <ol>
1046      *
1047      *   <li><p> If either this URI or the given URI are opaque, or if the
1048      *   scheme and authority components of the two URIs are not identical, or
1049      *   if the path of this URI is not a prefix of the path of the given URI,
1050      *   then the given URI is returned. </p></li>
1051      *
1052      *   <li><p> Otherwise a new relative hierarchical URI is constructed with
1053      *   query and fragment components taken from the given URI and with a path
1054      *   component computed by removing this URI's path from the beginning of
1055      *   the given URI's path. </p></li>
1056      *
1057      * </ol>
1058      *
1059      * @param  uri  The URI to be relativized against this URI
1060      * @return The resulting URI
1061      *
1062      * @throws  NullPointerException
1063      *          If {@code uri} is {@code null}
1064      */
1065     public URI relativize(URI uri) {
1066         return relativize(this, uri);
1067     }
1068 
1069     /**
1070      * Constructs a URL from this URI.
1071      *
1072      * <p> This convenience method works as if invoking it were equivalent to
1073      * evaluating the expression {@code new URL(this.toString())} after
1074      * first checking that this URI is absolute. </p>
1075      *
1076      * @return  A URL constructed from this URI
1077      *
1078      * @throws  IllegalArgumentException
1079      *          If this URL is not absolute
1080      *
1081      * @throws  MalformedURLException
1082      *          If a protocol handler for the URL could not be found,
1083      *          or if some other error occurred while constructing the URL
1084      */
1085     public URL toURL()
1086         throws MalformedURLException {
1087         if (!isAbsolute())
1088             throw new IllegalArgumentException("URI is not absolute");
1089         return new URL(toString());
1090     }
1091 
1092     // -- Component access methods --
1093 
1094     /**
1095      * Returns the scheme component of this URI.
1096      *
1097      * <p> The scheme component of a URI, if defined, only contains characters
1098      * in the <i>alphanum</i> category and in the string {@code "-.+"}.  A
1099      * scheme always starts with an <i>alpha</i> character. <p>
1100      *
1101      * The scheme component of a URI cannot contain escaped octets, hence this
1102      * method does not perform any decoding.
1103      *
1104      * @return  The scheme component of this URI,
1105      *          or {@code null} if the scheme is undefined
1106      */
1107     public String getScheme() {
1108         return scheme;
1109     }
1110 
1111     /**
1112      * Tells whether or not this URI is absolute.
1113      *
1114      * <p> A URI is absolute if, and only if, it has a scheme component. </p>
1115      *
1116      * @return  {@code true} if, and only if, this URI is absolute
1117      */
1118     public boolean isAbsolute() {
1119         return scheme != null;
1120     }
1121 
1122     /**
1123      * Tells whether or not this URI is opaque.
1124      *
1125      * <p> A URI is opaque if, and only if, it is absolute and its
1126      * scheme-specific part does not begin with a slash character ('/').
1127      * An opaque URI has a scheme, a scheme-specific part, and possibly
1128      * a fragment; all other components are undefined. </p>
1129      *
1130      * @return  {@code true} if, and only if, this URI is opaque
1131      */
1132     public boolean isOpaque() {
1133         return path == null;
1134     }
1135 
1136     /**
1137      * Returns the raw scheme-specific part of this URI.  The scheme-specific
1138      * part is never undefined, though it may be empty.
1139      *
1140      * <p> The scheme-specific part of a URI only contains legal URI
1141      * characters. </p>
1142      *
1143      * @return  The raw scheme-specific part of this URI
1144      *          (never {@code null})
1145      */
1146     public String getRawSchemeSpecificPart() {
1147         defineSchemeSpecificPart();
1148         return schemeSpecificPart;
1149     }
1150 
1151     /**
1152      * Returns the decoded scheme-specific part of this URI.
1153      *
1154      * <p> The string returned by this method is equal to that returned by the
1155      * {@link #getRawSchemeSpecificPart() getRawSchemeSpecificPart} method
1156      * except that all sequences of escaped octets are <a
1157      * href="#decode">decoded</a>.  </p>
1158      *
1159      * @return  The decoded scheme-specific part of this URI
1160      *          (never {@code null})
1161      */
1162     public String getSchemeSpecificPart() {
1163         if (decodedSchemeSpecificPart == null)
1164             decodedSchemeSpecificPart = decode(getRawSchemeSpecificPart());
1165         return decodedSchemeSpecificPart;
1166     }
1167 
1168     /**
1169      * Returns the raw authority component of this URI.
1170      *
1171      * <p> The authority component of a URI, if defined, only contains the
1172      * commercial-at character ({@code '@'}) and characters in the
1173      * <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, and <i>other</i>
1174      * categories.  If the authority is server-based then it is further
1175      * constrained to have valid user-information, host, and port
1176      * components. </p>
1177      *
1178      * @return  The raw authority component of this URI,
1179      *          or {@code null} if the authority is undefined
1180      */
1181     public String getRawAuthority() {
1182         return authority;
1183     }
1184 
1185     /**
1186      * Returns the decoded authority component of this URI.
1187      *
1188      * <p> The string returned by this method is equal to that returned by the
1189      * {@link #getRawAuthority() getRawAuthority} method except that all
1190      * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>
1191      *
1192      * @return  The decoded authority component of this URI,
1193      *          or {@code null} if the authority is undefined
1194      */
1195     public String getAuthority() {
1196         if (decodedAuthority == null)
1197             decodedAuthority = decode(authority);
1198         return decodedAuthority;
1199     }
1200 
1201     /**
1202      * Returns the raw user-information component of this URI.
1203      *
1204      * <p> The user-information component of a URI, if defined, only contains
1205      * characters in the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, and
1206      * <i>other</i> categories. </p>
1207      *
1208      * @return  The raw user-information component of this URI,
1209      *          or {@code null} if the user information is undefined
1210      */
1211     public String getRawUserInfo() {
1212         return userInfo;
1213     }
1214 
1215     /**
1216      * Returns the decoded user-information component of this URI.
1217      *
1218      * <p> The string returned by this method is equal to that returned by the
1219      * {@link #getRawUserInfo() getRawUserInfo} method except that all
1220      * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>
1221      *
1222      * @return  The decoded user-information component of this URI,
1223      *          or {@code null} if the user information is undefined
1224      */
1225     public String getUserInfo() {
1226         if ((decodedUserInfo == null) && (userInfo != null))
1227             decodedUserInfo = decode(userInfo);
1228         return decodedUserInfo;
1229     }
1230 
1231     /**
1232      * Returns the host component of this URI.
1233      *
1234      * <p> The host component of a URI, if defined, will have one of the
1235      * following forms: </p>
1236      *
1237      * <ul>
1238      *
1239      *   <li><p> A domain name consisting of one or more <i>labels</i>
1240      *   separated by period characters ({@code '.'}), optionally followed by
1241      *   a period character.  Each label consists of <i>alphanum</i> characters
1242      *   as well as hyphen characters ({@code '-'}), though hyphens never
1243      *   occur as the first or last characters in a label. The rightmost
1244      *   label of a domain name consisting of two or more labels, begins
1245      *   with an <i>alpha</i> character. </li>
1246      *
1247      *   <li><p> A dotted-quad IPv4 address of the form
1248      *   <i>digit</i>{@code +.}<i>digit</i>{@code +.}<i>digit</i>{@code +.}<i>digit</i>{@code +},
1249      *   where no <i>digit</i> sequence is longer than three characters and no
1250      *   sequence has a value larger than 255. </p></li>
1251      *
1252      *   <li><p> An IPv6 address enclosed in square brackets ({@code '['} and
1253      *   {@code ']'}) and consisting of hexadecimal digits, colon characters
1254      *   ({@code ':'}), and possibly an embedded IPv4 address.  The full
1255      *   syntax of IPv6 addresses is specified in <a
1256      *   href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IPv6
1257      *   Addressing Architecture</i></a>.  </p></li>
1258      *
1259      * </ul>
1260      *
1261      * The host component of a URI cannot contain escaped octets, hence this
1262      * method does not perform any decoding.
1263      *
1264      * @return  The host component of this URI,
1265      *          or {@code null} if the host is undefined
1266      */
1267     public String getHost() {
1268         return host;
1269     }
1270 
1271     /**
1272      * Returns the port number of this URI.
1273      *
1274      * <p> The port component of a URI, if defined, is a non-negative
1275      * integer. </p>
1276      *
1277      * @return  The port component of this URI,
1278      *          or {@code -1} if the port is undefined
1279      */
1280     public int getPort() {
1281         return port;
1282     }
1283 
1284     /**
1285      * Returns the raw path component of this URI.
1286      *
1287      * <p> The path component of a URI, if defined, only contains the slash
1288      * character ({@code '/'}), the commercial-at character ({@code '@'}),
1289      * and characters in the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>,
1290      * and <i>other</i> categories. </p>
1291      *
1292      * @return  The path component of this URI,
1293      *          or {@code null} if the path is undefined
1294      */
1295     public String getRawPath() {
1296         return path;
1297     }
1298 
1299     /**
1300      * Returns the decoded path component of this URI.
1301      *
1302      * <p> The string returned by this method is equal to that returned by the
1303      * {@link #getRawPath() getRawPath} method except that all sequences of
1304      * escaped octets are <a href="#decode">decoded</a>.  </p>
1305      *
1306      * @return  The decoded path component of this URI,
1307      *          or {@code null} if the path is undefined
1308      */
1309     public String getPath() {
1310         if ((decodedPath == null) && (path != null))
1311             decodedPath = decode(path);
1312         return decodedPath;
1313     }
1314 
1315     /**
1316      * Returns the raw query component of this URI.
1317      *
1318      * <p> The query component of a URI, if defined, only contains legal URI
1319      * characters. </p>
1320      *
1321      * @return  The raw query component of this URI,
1322      *          or {@code null} if the query is undefined
1323      */
1324     public String getRawQuery() {
1325         return query;
1326     }
1327 
1328     /**
1329      * Returns the decoded query component of this URI.
1330      *
1331      * <p> The string returned by this method is equal to that returned by the
1332      * {@link #getRawQuery() getRawQuery} method except that all sequences of
1333      * escaped octets are <a href="#decode">decoded</a>.  </p>
1334      *
1335      * @return  The decoded query component of this URI,
1336      *          or {@code null} if the query is undefined
1337      */
1338     public String getQuery() {
1339         if ((decodedQuery == null) && (query != null))
1340             decodedQuery = decode(query);
1341         return decodedQuery;
1342     }
1343 
1344     /**
1345      * Returns the raw fragment component of this URI.
1346      *
1347      * <p> The fragment component of a URI, if defined, only contains legal URI
1348      * characters. </p>
1349      *
1350      * @return  The raw fragment component of this URI,
1351      *          or {@code null} if the fragment is undefined
1352      */
1353     public String getRawFragment() {
1354         return fragment;
1355     }
1356 
1357     /**
1358      * Returns the decoded fragment component of this URI.
1359      *
1360      * <p> The string returned by this method is equal to that returned by the
1361      * {@link #getRawFragment() getRawFragment} method except that all
1362      * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>
1363      *
1364      * @return  The decoded fragment component of this URI,
1365      *          or {@code null} if the fragment is undefined
1366      */
1367     public String getFragment() {
1368         if ((decodedFragment == null) && (fragment != null))
1369             decodedFragment = decode(fragment);
1370         return decodedFragment;
1371     }
1372 
1373 
1374     // -- Equality, comparison, hash code, toString, and serialization --
1375 
1376     /**
1377      * Tests this URI for equality with another object.
1378      *
1379      * <p> If the given object is not a URI then this method immediately
1380      * returns {@code false}.
1381      *
1382      * <p> For two URIs to be considered equal requires that either both are
1383      * opaque or both are hierarchical.  Their schemes must either both be
1384      * undefined or else be equal without regard to case. Their fragments
1385      * must either both be undefined or else be equal.
1386      *
1387      * <p> For two opaque URIs to be considered equal, their scheme-specific
1388      * parts must be equal.
1389      *
1390      * <p> For two hierarchical URIs to be considered equal, their paths must
1391      * be equal and their queries must either both be undefined or else be
1392      * equal.  Their authorities must either both be undefined, or both be
1393      * registry-based, or both be server-based.  If their authorities are
1394      * defined and are registry-based, then they must be equal.  If their
1395      * authorities are defined and are server-based, then their hosts must be
1396      * equal without regard to case, their port numbers must be equal, and
1397      * their user-information components must be equal.
1398      *
1399      * <p> When testing the user-information, path, query, fragment, authority,
1400      * or scheme-specific parts of two URIs for equality, the raw forms rather
1401      * than the encoded forms of these components are compared and the
1402      * hexadecimal digits of escaped octets are compared without regard to
1403      * case.
1404      *
1405      * <p> This method satisfies the general contract of the {@link
1406      * java.lang.Object#equals(Object) Object.equals} method. </p>
1407      *
1408      * @param   ob   The object to which this object is to be compared
1409      *
1410      * @return  {@code true} if, and only if, the given object is a URI that
1411      *          is identical to this URI
1412      */
1413     public boolean equals(Object ob) {
1414         if (ob == this)
1415             return true;
1416         if (!(ob instanceof URI))
1417             return false;
1418         URI that = (URI)ob;
1419         if (this.isOpaque() != that.isOpaque()) return false;
1420         if (!equalIgnoringCase(this.scheme, that.scheme)) return false;
1421         if (!equal(this.fragment, that.fragment)) return false;
1422 
1423         // Opaque
1424         if (this.isOpaque())
1425             return equal(this.schemeSpecificPart, that.schemeSpecificPart);
1426 
1427         // Hierarchical
1428         if (!equal(this.path, that.path)) return false;
1429         if (!equal(this.query, that.query)) return false;
1430 
1431         // Authorities
1432         if (this.authority == that.authority) return true;
1433         if (this.host != null) {
1434             // Server-based
1435             if (!equal(this.userInfo, that.userInfo)) return false;
1436             if (!equalIgnoringCase(this.host, that.host)) return false;
1437             if (this.port != that.port) return false;
1438         } else if (this.authority != null) {
1439             // Registry-based
1440             if (!equal(this.authority, that.authority)) return false;
1441         } else if (this.authority != that.authority) {
1442             return false;
1443         }
1444 
1445         return true;
1446     }
1447 
1448     /**
1449      * Returns a hash-code value for this URI.  The hash code is based upon all
1450      * of the URI's components, and satisfies the general contract of the
1451      * {@link java.lang.Object#hashCode() Object.hashCode} method.
1452      *
1453      * @return  A hash-code value for this URI
1454      */
1455     public int hashCode() {
1456         if (hash != 0)
1457             return hash;
1458         int h = hashIgnoringCase(0, scheme);
1459         h = hash(h, fragment);
1460         if (isOpaque()) {
1461             h = hash(h, schemeSpecificPart);
1462         } else {
1463             h = hash(h, path);
1464             h = hash(h, query);
1465             if (host != null) {
1466                 h = hash(h, userInfo);
1467                 h = hashIgnoringCase(h, host);
1468                 h += 1949 * port;
1469             } else {
1470                 h = hash(h, authority);
1471             }
1472         }
1473         hash = h;
1474         return h;
1475     }
1476 
1477     /**
1478      * Compares this URI to another object, which must be a URI.
1479      *
1480      * <p> When comparing corresponding components of two URIs, if one
1481      * component is undefined but the other is defined then the first is
1482      * considered to be less than the second.  Unless otherwise noted, string
1483      * components are ordered according to their natural, case-sensitive
1484      * ordering as defined by the {@link java.lang.String#compareTo(Object)
1485      * String.compareTo} method.  String components that are subject to
1486      * encoding are compared by comparing their raw forms rather than their
1487      * encoded forms.
1488      *
1489      * <p> The ordering of URIs is defined as follows: </p>
1490      *
1491      * <ul>
1492      *
1493      *   <li><p> Two URIs with different schemes are ordered according the
1494      *   ordering of their schemes, without regard to case. </p></li>
1495      *
1496      *   <li><p> A hierarchical URI is considered to be less than an opaque URI
1497      *   with an identical scheme. </p></li>
1498      *
1499      *   <li><p> Two opaque URIs with identical schemes are ordered according
1500      *   to the ordering of their scheme-specific parts. </p></li>
1501      *
1502      *   <li><p> Two opaque URIs with identical schemes and scheme-specific
1503      *   parts are ordered according to the ordering of their
1504      *   fragments. </p></li>
1505      *
1506      *   <li><p> Two hierarchical URIs with identical schemes are ordered
1507      *   according to the ordering of their authority components: </p>
1508      *
1509      *   <ul>
1510      *
1511      *     <li><p> If both authority components are server-based then the URIs
1512      *     are ordered according to their user-information components; if these
1513      *     components are identical then the URIs are ordered according to the
1514      *     ordering of their hosts, without regard to case; if the hosts are
1515      *     identical then the URIs are ordered according to the ordering of
1516      *     their ports. </p></li>
1517      *
1518      *     <li><p> If one or both authority components are registry-based then
1519      *     the URIs are ordered according to the ordering of their authority
1520      *     components. </p></li>
1521      *
1522      *   </ul></li>
1523      *
1524      *   <li><p> Finally, two hierarchical URIs with identical schemes and
1525      *   authority components are ordered according to the ordering of their
1526      *   paths; if their paths are identical then they are ordered according to
1527      *   the ordering of their queries; if the queries are identical then they
1528      *   are ordered according to the order of their fragments. </p></li>
1529      *
1530      * </ul>
1531      *
1532      * <p> This method satisfies the general contract of the {@link
1533      * java.lang.Comparable#compareTo(Object) Comparable.compareTo}
1534      * method. </p>
1535      *
1536      * @param   that
1537      *          The object to which this URI is to be compared
1538      *
1539      * @return  A negative integer, zero, or a positive integer as this URI is
1540      *          less than, equal to, or greater than the given URI
1541      *
1542      * @throws  ClassCastException
1543      *          If the given object is not a URI
1544      */
1545     public int compareTo(URI that) {
1546         int c;
1547 
1548         if ((c = compareIgnoringCase(this.scheme, that.scheme)) != 0)
1549             return c;
1550 
1551         if (this.isOpaque()) {
1552             if (that.isOpaque()) {
1553                 // Both opaque
1554                 if ((c = compare(this.schemeSpecificPart,
1555                                  that.schemeSpecificPart)) != 0)
1556                     return c;
1557                 return compare(this.fragment, that.fragment);
1558             }
1559             return +1;                  // Opaque > hierarchical
1560         } else if (that.isOpaque()) {
1561             return -1;                  // Hierarchical < opaque
1562         }
1563 
1564         // Hierarchical
1565         if ((this.host != null) && (that.host != null)) {
1566             // Both server-based
1567             if ((c = compare(this.userInfo, that.userInfo)) != 0)
1568                 return c;
1569             if ((c = compareIgnoringCase(this.host, that.host)) != 0)
1570                 return c;
1571             if ((c = this.port - that.port) != 0)
1572                 return c;
1573         } else {
1574             // If one or both authorities are registry-based then we simply
1575             // compare them in the usual, case-sensitive way.  If one is
1576             // registry-based and one is server-based then the strings are
1577             // guaranteed to be unequal, hence the comparison will never return
1578             // zero and the compareTo and equals methods will remain
1579             // consistent.
1580             if ((c = compare(this.authority, that.authority)) != 0) return c;
1581         }
1582 
1583         if ((c = compare(this.path, that.path)) != 0) return c;
1584         if ((c = compare(this.query, that.query)) != 0) return c;
1585         return compare(this.fragment, that.fragment);
1586     }
1587 
1588     /**
1589      * Returns the content of this URI as a string.
1590      *
1591      * <p> If this URI was created by invoking one of the constructors in this
1592      * class then a string equivalent to the original input string, or to the
1593      * string computed from the originally-given components, as appropriate, is
1594      * returned.  Otherwise this URI was created by normalization, resolution,
1595      * or relativization, and so a string is constructed from this URI's
1596      * components according to the rules specified in <a
1597      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
1598      * section&nbsp;5.2, step&nbsp;7. </p>
1599      *
1600      * @return  The string form of this URI
1601      */
1602     public String toString() {
1603         defineString();
1604         return string;
1605     }
1606 
1607     /**
1608      * Returns the content of this URI as a US-ASCII string.
1609      *
1610      * <p> If this URI does not contain any characters in the <i>other</i>
1611      * category then an invocation of this method will return the same value as
1612      * an invocation of the {@link #toString() toString} method.  Otherwise
1613      * this method works as if by invoking that method and then <a
1614      * href="#encode">encoding</a> the result.  </p>
1615      *
1616      * @return  The string form of this URI, encoded as needed
1617      *          so that it only contains characters in the US-ASCII
1618      *          charset
1619      */
1620     public String toASCIIString() {
1621         defineString();
1622         return encode(string);
1623     }
1624 
1625 
1626     // -- Serialization support --
1627 
1628     /**
1629      * Saves the content of this URI to the given serial stream.
1630      *
1631      * <p> The only serializable field of a URI instance is its {@code string}
1632      * field.  That field is given a value, if it does not have one already,
1633      * and then the {@link java.io.ObjectOutputStream#defaultWriteObject()}
1634      * method of the given object-output stream is invoked. </p>
1635      *
1636      * @param  os  The object-output stream to which this object
1637      *             is to be written
1638      */
1639     private void writeObject(ObjectOutputStream os)
1640         throws IOException
1641     {
1642         defineString();
1643         os.defaultWriteObject();        // Writes the string field only
1644     }
1645 
1646     /**
1647      * Reconstitutes a URI from the given serial stream.
1648      *
1649      * <p> The {@link java.io.ObjectInputStream#defaultReadObject()} method is
1650      * invoked to read the value of the {@code string} field.  The result is
1651      * then parsed in the usual way.
1652      *
1653      * @param  is  The object-input stream from which this object
1654      *             is being read
1655      */
1656     private void readObject(ObjectInputStream is)
1657         throws ClassNotFoundException, IOException
1658     {
1659         port = -1;                      // Argh
1660         is.defaultReadObject();
1661         try {
1662             new Parser(string).parse(false);
1663         } catch (URISyntaxException x) {
1664             IOException y = new InvalidObjectException("Invalid URI");
1665             y.initCause(x);
1666             throw y;
1667         }
1668     }
1669 
1670 
1671     // -- End of public methods --
1672 
1673 
1674     // -- Utility methods for string-field comparison and hashing --
1675 
1676     // These methods return appropriate values for null string arguments,
1677     // thereby simplifying the equals, hashCode, and compareTo methods.
1678     //
1679     // The case-ignoring methods should only be applied to strings whose
1680     // characters are all known to be US-ASCII.  Because of this restriction,
1681     // these methods are faster than the similar methods in the String class.
1682 
1683     // US-ASCII only
1684     private static int toLower(char c) {
1685         if ((c >= 'A') && (c <= 'Z'))
1686             return c + ('a' - 'A');
1687         return c;
1688     }
1689 
1690     // US-ASCII only
1691     private static int toUpper(char c) {
1692         if ((c >= 'a') && (c <= 'z'))
1693             return c - ('a' - 'A');
1694         return c;
1695     }
1696 
1697     private static boolean equal(String s, String t) {
1698         if (s == t) return true;
1699         if ((s != null) && (t != null)) {
1700             if (s.length() != t.length())
1701                 return false;
1702             if (s.indexOf('%') < 0)
1703                 return s.equals(t);
1704             int n = s.length();
1705             for (int i = 0; i < n;) {
1706                 char c = s.charAt(i);
1707                 char d = t.charAt(i);
1708                 if (c != '%') {
1709                     if (c != d)
1710                         return false;
1711                     i++;
1712                     continue;
1713                 }
1714                 if (d != '%')
1715                     return false;
1716                 i++;
1717                 if (toLower(s.charAt(i)) != toLower(t.charAt(i)))
1718                     return false;
1719                 i++;
1720                 if (toLower(s.charAt(i)) != toLower(t.charAt(i)))
1721                     return false;
1722                 i++;
1723             }
1724             return true;
1725         }
1726         return false;
1727     }
1728 
1729     // US-ASCII only
1730     private static boolean equalIgnoringCase(String s, String t) {
1731         if (s == t) return true;
1732         if ((s != null) && (t != null)) {
1733             int n = s.length();
1734             if (t.length() != n)
1735                 return false;
1736             for (int i = 0; i < n; i++) {
1737                 if (toLower(s.charAt(i)) != toLower(t.charAt(i)))
1738                     return false;
1739             }
1740             return true;
1741         }
1742         return false;
1743     }
1744 
1745     private static int hash(int hash, String s) {
1746         if (s == null) return hash;
1747         return s.indexOf('%') < 0 ? hash * 127 + s.hashCode()
1748                                   : normalizedHash(hash, s);
1749     }
1750 
1751 
1752     private static int normalizedHash(int hash, String s) {
1753         int h = 0;
1754         for (int index = 0; index < s.length(); index++) {
1755             char ch = s.charAt(index);
1756             h = 31 * h + ch;
1757             if (ch == '%') {
1758                 /*
1759                  * Process the next two encoded characters
1760                  */
1761                 for (int i = index + 1; i < index + 3; i++)
1762                     h = 31 * h + toUpper(s.charAt(i));
1763                 index += 2;
1764             }
1765         }
1766         return hash * 127 + h;
1767     }
1768 
1769     // US-ASCII only
1770     private static int hashIgnoringCase(int hash, String s) {
1771         if (s == null) return hash;
1772         int h = hash;
1773         int n = s.length();
1774         for (int i = 0; i < n; i++)
1775             h = 31 * h + toLower(s.charAt(i));
1776         return h;
1777     }
1778 
1779     private static int compare(String s, String t) {
1780         if (s == t) return 0;
1781         if (s != null) {
1782             if (t != null)
1783                 return s.compareTo(t);
1784             else
1785                 return +1;
1786         } else {
1787             return -1;
1788         }
1789     }
1790 
1791     // US-ASCII only
1792     private static int compareIgnoringCase(String s, String t) {
1793         if (s == t) return 0;
1794         if (s != null) {
1795             if (t != null) {
1796                 int sn = s.length();
1797                 int tn = t.length();
1798                 int n = sn < tn ? sn : tn;
1799                 for (int i = 0; i < n; i++) {
1800                     int c = toLower(s.charAt(i)) - toLower(t.charAt(i));
1801                     if (c != 0)
1802                         return c;
1803                 }
1804                 return sn - tn;
1805             }
1806             return +1;
1807         } else {
1808             return -1;
1809         }
1810     }
1811 
1812 
1813     // -- String construction --
1814 
1815     // If a scheme is given then the path, if given, must be absolute
1816     //
1817     private static void checkPath(String s, String scheme, String path)
1818         throws URISyntaxException
1819     {
1820         if (scheme != null) {
1821             if ((path != null)
1822                 && ((path.length() > 0) && (path.charAt(0) != '/')))
1823                 throw new URISyntaxException(s,
1824                                              "Relative path in absolute URI");
1825         }
1826     }
1827 
1828     private void appendAuthority(StringBuffer sb,
1829                                  String authority,
1830                                  String userInfo,
1831                                  String host,
1832                                  int port)
1833     {
1834         if (host != null) {
1835             sb.append("//");
1836             if (userInfo != null) {
1837                 sb.append(quote(userInfo, L_USERINFO, H_USERINFO));
1838                 sb.append('@');
1839             }
1840             boolean needBrackets = ((host.indexOf(':') >= 0)
1841                                     && !host.startsWith("[")
1842                                     && !host.endsWith("]"));
1843             if (needBrackets) sb.append('[');
1844             sb.append(host);
1845             if (needBrackets) sb.append(']');
1846             if (port != -1) {
1847                 sb.append(':');
1848                 sb.append(port);
1849             }
1850         } else if (authority != null) {
1851             sb.append("//");
1852             if (authority.startsWith("[")) {
1853                 // authority should (but may not) contain an embedded IPv6 address
1854                 int end = authority.indexOf("]");
1855                 String doquote = authority, dontquote = "";
1856                 if (end != -1 && authority.indexOf(":") != -1) {
1857                     // the authority contains an IPv6 address
1858                     if (end == authority.length()) {
1859                         dontquote = authority;
1860                         doquote = "";
1861                     } else {
1862                         dontquote = authority.substring(0 , end + 1);
1863                         doquote = authority.substring(end + 1);
1864                     }
1865                 }
1866                 sb.append(dontquote);
1867                 sb.append(quote(doquote,
1868                             L_REG_NAME | L_SERVER,
1869                             H_REG_NAME | H_SERVER));
1870             } else {
1871                 sb.append(quote(authority,
1872                             L_REG_NAME | L_SERVER,
1873                             H_REG_NAME | H_SERVER));
1874             }
1875         }
1876     }
1877 
1878     private void appendSchemeSpecificPart(StringBuffer sb,
1879                                           String opaquePart,
1880                                           String authority,
1881                                           String userInfo,
1882                                           String host,
1883                                           int port,
1884                                           String path,
1885                                           String query)
1886     {
1887         if (opaquePart != null) {
1888             /* check if SSP begins with an IPv6 address
1889              * because we must not quote a literal IPv6 address
1890              */
1891             if (opaquePart.startsWith("//[")) {
1892                 int end =  opaquePart.indexOf("]");
1893                 if (end != -1 && opaquePart.indexOf(":")!=-1) {
1894                     String doquote, dontquote;
1895                     if (end == opaquePart.length()) {
1896                         dontquote = opaquePart;
1897                         doquote = "";
1898                     } else {
1899                         dontquote = opaquePart.substring(0,end+1);
1900                         doquote = opaquePart.substring(end+1);
1901                     }
1902                     sb.append (dontquote);
1903                     sb.append(quote(doquote, L_URIC, H_URIC));
1904                 }
1905             } else {
1906                 sb.append(quote(opaquePart, L_URIC, H_URIC));
1907             }
1908         } else {
1909             appendAuthority(sb, authority, userInfo, host, port);
1910             if (path != null)
1911                 sb.append(quote(path, L_PATH, H_PATH));
1912             if (query != null) {
1913                 sb.append('?');
1914                 sb.append(quote(query, L_URIC, H_URIC));
1915             }
1916         }
1917     }
1918 
1919     private void appendFragment(StringBuffer sb, String fragment) {
1920         if (fragment != null) {
1921             sb.append('#');
1922             sb.append(quote(fragment, L_URIC, H_URIC));
1923         }
1924     }
1925 
1926     private String toString(String scheme,
1927                             String opaquePart,
1928                             String authority,
1929                             String userInfo,
1930                             String host,
1931                             int port,
1932                             String path,
1933                             String query,
1934                             String fragment)
1935     {
1936         StringBuffer sb = new StringBuffer();
1937         if (scheme != null) {
1938             sb.append(scheme);
1939             sb.append(':');
1940         }
1941         appendSchemeSpecificPart(sb, opaquePart,
1942                                  authority, userInfo, host, port,
1943                                  path, query);
1944         appendFragment(sb, fragment);
1945         return sb.toString();
1946     }
1947 
1948     private void defineSchemeSpecificPart() {
1949         if (schemeSpecificPart != null) return;
1950         StringBuffer sb = new StringBuffer();
1951         appendSchemeSpecificPart(sb, null, getAuthority(), getUserInfo(),
1952                                  host, port, getPath(), getQuery());
1953         if (sb.length() == 0) return;
1954         schemeSpecificPart = sb.toString();
1955     }
1956 
1957     private void defineString() {
1958         if (string != null) return;
1959 
1960         StringBuffer sb = new StringBuffer();
1961         if (scheme != null) {
1962             sb.append(scheme);
1963             sb.append(':');
1964         }
1965         if (isOpaque()) {
1966             sb.append(schemeSpecificPart);
1967         } else {
1968             if (host != null) {
1969                 sb.append("//");
1970                 if (userInfo != null) {
1971                     sb.append(userInfo);
1972                     sb.append('@');
1973                 }
1974                 boolean needBrackets = ((host.indexOf(':') >= 0)
1975                                     && !host.startsWith("[")
1976                                     && !host.endsWith("]"));
1977                 if (needBrackets) sb.append('[');
1978                 sb.append(host);
1979                 if (needBrackets) sb.append(']');
1980                 if (port != -1) {
1981                     sb.append(':');
1982                     sb.append(port);
1983                 }
1984             } else if (authority != null) {
1985                 sb.append("//");
1986                 sb.append(authority);
1987             }
1988             if (path != null)
1989                 sb.append(path);
1990             if (query != null) {
1991                 sb.append('?');
1992                 sb.append(query);
1993             }
1994         }
1995         if (fragment != null) {
1996             sb.append('#');
1997             sb.append(fragment);
1998         }
1999         string = sb.toString();
2000     }
2001 
2002 
2003     // -- Normalization, resolution, and relativization --
2004 
2005     // RFC2396 5.2 (6)
2006     private static String resolvePath(String base, String child,
2007                                       boolean absolute)
2008     {
2009         int i = base.lastIndexOf('/');
2010         int cn = child.length();
2011         String path = "";
2012 
2013         if (cn == 0) {
2014             // 5.2 (6a)
2015             if (i >= 0)
2016                 path = base.substring(0, i + 1);
2017         } else {
2018             StringBuffer sb = new StringBuffer(base.length() + cn);
2019             // 5.2 (6a)
2020             if (i >= 0)
2021                 sb.append(base.substring(0, i + 1));
2022             // 5.2 (6b)
2023             sb.append(child);
2024             path = sb.toString();
2025         }
2026 
2027         // 5.2 (6c-f)
2028         String np = normalize(path);
2029 
2030         // 5.2 (6g): If the result is absolute but the path begins with "../",
2031         // then we simply leave the path as-is
2032 
2033         return np;
2034     }
2035 
2036     // RFC2396 5.2
2037     private static URI resolve(URI base, URI child) {
2038         // check if child if opaque first so that NPE is thrown
2039         // if child is null.
2040         if (child.isOpaque() || base.isOpaque())
2041             return child;
2042 
2043         // 5.2 (2): Reference to current document (lone fragment)
2044         if ((child.scheme == null) && (child.authority == null)
2045             && child.path.equals("") && (child.fragment != null)
2046             && (child.query == null)) {
2047             if ((base.fragment != null)
2048                 && child.fragment.equals(base.fragment)) {
2049                 return base;
2050             }
2051             URI ru = new URI();
2052             ru.scheme = base.scheme;
2053             ru.authority = base.authority;
2054             ru.userInfo = base.userInfo;
2055             ru.host = base.host;
2056             ru.port = base.port;
2057             ru.path = base.path;
2058             ru.fragment = child.fragment;
2059             ru.query = base.query;
2060             return ru;
2061         }
2062 
2063         // 5.2 (3): Child is absolute
2064         if (child.scheme != null)
2065             return child;
2066 
2067         URI ru = new URI();             // Resolved URI
2068         ru.scheme = base.scheme;
2069         ru.query = child.query;
2070         ru.fragment = child.fragment;
2071 
2072         // 5.2 (4): Authority
2073         if (child.authority == null) {
2074             ru.authority = base.authority;
2075             ru.host = base.host;
2076             ru.userInfo = base.userInfo;
2077             ru.port = base.port;
2078 
2079             String cp = (child.path == null) ? "" : child.path;
2080             if ((cp.length() > 0) && (cp.charAt(0) == '/')) {
2081                 // 5.2 (5): Child path is absolute
2082                 ru.path = child.path;
2083             } else {
2084                 // 5.2 (6): Resolve relative path
2085                 ru.path = resolvePath(base.path, cp, base.isAbsolute());
2086             }
2087         } else {
2088             ru.authority = child.authority;
2089             ru.host = child.host;
2090             ru.userInfo = child.userInfo;
2091             ru.host = child.host;
2092             ru.port = child.port;
2093             ru.path = child.path;
2094         }
2095 
2096         // 5.2 (7): Recombine (nothing to do here)
2097         return ru;
2098     }
2099 
2100     // If the given URI's path is normal then return the URI;
2101     // o.w., return a new URI containing the normalized path.
2102     //
2103     private static URI normalize(URI u) {
2104         if (u.isOpaque() || (u.path == null) || (u.path.length() == 0))
2105             return u;
2106 
2107         String np = normalize(u.path);
2108         if (np == u.path)
2109             return u;
2110 
2111         URI v = new URI();
2112         v.scheme = u.scheme;
2113         v.fragment = u.fragment;
2114         v.authority = u.authority;
2115         v.userInfo = u.userInfo;
2116         v.host = u.host;
2117         v.port = u.port;
2118         v.path = np;
2119         v.query = u.query;
2120         return v;
2121     }
2122 
2123     // If both URIs are hierarchical, their scheme and authority components are
2124     // identical, and the base path is a prefix of the child's path, then
2125     // return a relative URI that, when resolved against the base, yields the
2126     // child; otherwise, return the child.
2127     //
2128     private static URI relativize(URI base, URI child) {
2129         // check if child if opaque first so that NPE is thrown
2130         // if child is null.
2131         if (child.isOpaque() || base.isOpaque())
2132             return child;
2133         if (!equalIgnoringCase(base.scheme, child.scheme)
2134             || !equal(base.authority, child.authority))
2135             return child;
2136 
2137         String bp = normalize(base.path);
2138         String cp = normalize(child.path);
2139         if (!bp.equals(cp)) {
2140             if (!bp.endsWith("/"))
2141                 bp = bp + "/";
2142             if (!cp.startsWith(bp))
2143                 return child;
2144         }
2145 
2146         URI v = new URI();
2147         v.path = cp.substring(bp.length());
2148         v.query = child.query;
2149         v.fragment = child.fragment;
2150         return v;
2151     }
2152 
2153 
2154 
2155     // -- Path normalization --
2156 
2157     // The following algorithm for path normalization avoids the creation of a
2158     // string object for each segment, as well as the use of a string buffer to
2159     // compute the final result, by using a single char array and editing it in
2160     // place.  The array is first split into segments, replacing each slash
2161     // with '\0' and creating a segment-index array, each element of which is
2162     // the index of the first char in the corresponding segment.  We then walk
2163     // through both arrays, removing ".", "..", and other segments as necessary
2164     // by setting their entries in the index array to -1.  Finally, the two
2165     // arrays are used to rejoin the segments and compute the final result.
2166     //
2167     // This code is based upon src/solaris/native/java/io/canonicalize_md.c
2168 
2169 
2170     // Check the given path to see if it might need normalization.  A path
2171     // might need normalization if it contains duplicate slashes, a "."
2172     // segment, or a ".." segment.  Return -1 if no further normalization is
2173     // possible, otherwise return the number of segments found.
2174     //
2175     // This method takes a string argument rather than a char array so that
2176     // this test can be performed without invoking path.toCharArray().
2177     //
2178     static private int needsNormalization(String path) {
2179         boolean normal = true;
2180         int ns = 0;                     // Number of segments
2181         int end = path.length() - 1;    // Index of last char in path
2182         int p = 0;                      // Index of next char in path
2183 
2184         // Skip initial slashes
2185         while (p <= end) {
2186             if (path.charAt(p) != '/') break;
2187             p++;
2188         }
2189         if (p > 1) normal = false;
2190 
2191         // Scan segments
2192         while (p <= end) {
2193 
2194             // Looking at "." or ".." ?
2195             if ((path.charAt(p) == '.')
2196                 && ((p == end)
2197                     || ((path.charAt(p + 1) == '/')
2198                         || ((path.charAt(p + 1) == '.')
2199                             && ((p + 1 == end)
2200                                 || (path.charAt(p + 2) == '/')))))) {
2201                 normal = false;
2202             }
2203             ns++;
2204 
2205             // Find beginning of next segment
2206             while (p <= end) {
2207                 if (path.charAt(p++) != '/')
2208                     continue;
2209 
2210                 // Skip redundant slashes
2211                 while (p <= end) {
2212                     if (path.charAt(p) != '/') break;
2213                     normal = false;
2214                     p++;
2215                 }
2216 
2217                 break;
2218             }
2219         }
2220 
2221         return normal ? -1 : ns;
2222     }
2223 
2224 
2225     // Split the given path into segments, replacing slashes with nulls and
2226     // filling in the given segment-index array.
2227     //
2228     // Preconditions:
2229     //   segs.length == Number of segments in path
2230     //
2231     // Postconditions:
2232     //   All slashes in path replaced by '\0'
2233     //   segs[i] == Index of first char in segment i (0 <= i < segs.length)
2234     //
2235     static private void split(char[] path, int[] segs) {
2236         int end = path.length - 1;      // Index of last char in path
2237         int p = 0;                      // Index of next char in path
2238         int i = 0;                      // Index of current segment
2239 
2240         // Skip initial slashes
2241         while (p <= end) {
2242             if (path[p] != '/') break;
2243             path[p] = '\0';
2244             p++;
2245         }
2246 
2247         while (p <= end) {
2248 
2249             // Note start of segment
2250             segs[i++] = p++;
2251 
2252             // Find beginning of next segment
2253             while (p <= end) {
2254                 if (path[p++] != '/')
2255                     continue;
2256                 path[p - 1] = '\0';
2257 
2258                 // Skip redundant slashes
2259                 while (p <= end) {
2260                     if (path[p] != '/') break;
2261                     path[p++] = '\0';
2262                 }
2263                 break;
2264             }
2265         }
2266 
2267         if (i != segs.length)
2268             throw new InternalError();  // ASSERT
2269     }
2270 
2271 
2272     // Join the segments in the given path according to the given segment-index
2273     // array, ignoring those segments whose index entries have been set to -1,
2274     // and inserting slashes as needed.  Return the length of the resulting
2275     // path.
2276     //
2277     // Preconditions:
2278     //   segs[i] == -1 implies segment i is to be ignored
2279     //   path computed by split, as above, with '\0' having replaced '/'
2280     //
2281     // Postconditions:
2282     //   path[0] .. path[return value] == Resulting path
2283     //
2284     static private int join(char[] path, int[] segs) {
2285         int ns = segs.length;           // Number of segments
2286         int end = path.length - 1;      // Index of last char in path
2287         int p = 0;                      // Index of next path char to write
2288 
2289         if (path[p] == '\0') {
2290             // Restore initial slash for absolute paths
2291             path[p++] = '/';
2292         }
2293 
2294         for (int i = 0; i < ns; i++) {
2295             int q = segs[i];            // Current segment
2296             if (q == -1)
2297                 // Ignore this segment
2298                 continue;
2299 
2300             if (p == q) {
2301                 // We're already at this segment, so just skip to its end
2302                 while ((p <= end) && (path[p] != '\0'))
2303                     p++;
2304                 if (p <= end) {
2305                     // Preserve trailing slash
2306                     path[p++] = '/';
2307                 }
2308             } else if (p < q) {
2309                 // Copy q down to p
2310                 while ((q <= end) && (path[q] != '\0'))
2311                     path[p++] = path[q++];
2312                 if (q <= end) {
2313                     // Preserve trailing slash
2314                     path[p++] = '/';
2315                 }
2316             } else
2317                 throw new InternalError(); // ASSERT false
2318         }
2319 
2320         return p;
2321     }
2322 
2323 
2324     // Remove "." segments from the given path, and remove segment pairs
2325     // consisting of a non-".." segment followed by a ".." segment.
2326     //
2327     private static void removeDots(char[] path, int[] segs) {
2328         int ns = segs.length;
2329         int end = path.length - 1;
2330 
2331         for (int i = 0; i < ns; i++) {
2332             int dots = 0;               // Number of dots found (0, 1, or 2)
2333 
2334             // Find next occurrence of "." or ".."
2335             do {
2336                 int p = segs[i];
2337                 if (path[p] == '.') {
2338                     if (p == end) {
2339                         dots = 1;
2340                         break;
2341                     } else if (path[p + 1] == '\0') {
2342                         dots = 1;
2343                         break;
2344                     } else if ((path[p + 1] == '.')
2345                                && ((p + 1 == end)
2346                                    || (path[p + 2] == '\0'))) {
2347                         dots = 2;
2348                         break;
2349                     }
2350                 }
2351                 i++;
2352             } while (i < ns);
2353             if ((i > ns) || (dots == 0))
2354                 break;
2355 
2356             if (dots == 1) {
2357                 // Remove this occurrence of "."
2358                 segs[i] = -1;
2359             } else {
2360                 // If there is a preceding non-".." segment, remove both that
2361                 // segment and this occurrence of ".."; otherwise, leave this
2362                 // ".." segment as-is.
2363                 int j;
2364                 for (j = i - 1; j >= 0; j--) {
2365                     if (segs[j] != -1) break;
2366                 }
2367                 if (j >= 0) {
2368                     int q = segs[j];
2369                     if (!((path[q] == '.')
2370                           && (path[q + 1] == '.')
2371                           && (path[q + 2] == '\0'))) {
2372                         segs[i] = -1;
2373                         segs[j] = -1;
2374                     }
2375                 }
2376             }
2377         }
2378     }
2379 
2380 
2381     // DEVIATION: If the normalized path is relative, and if the first
2382     // segment could be parsed as a scheme name, then prepend a "." segment
2383     //
2384     private static void maybeAddLeadingDot(char[] path, int[] segs) {
2385 
2386         if (path[0] == '\0')
2387             // The path is absolute
2388             return;
2389 
2390         int ns = segs.length;
2391         int f = 0;                      // Index of first segment
2392         while (f < ns) {
2393             if (segs[f] >= 0)
2394                 break;
2395             f++;
2396         }
2397         if ((f >= ns) || (f == 0))
2398             // The path is empty, or else the original first segment survived,
2399             // in which case we already know that no leading "." is needed
2400             return;
2401 
2402         int p = segs[f];
2403         while ((p < path.length) && (path[p] != ':') && (path[p] != '\0')) p++;
2404         if (p >= path.length || path[p] == '\0')
2405             // No colon in first segment, so no "." needed
2406             return;
2407 
2408         // At this point we know that the first segment is unused,
2409         // hence we can insert a "." segment at that position
2410         path[0] = '.';
2411         path[1] = '\0';
2412         segs[0] = 0;
2413     }
2414 
2415 
2416     // Normalize the given path string.  A normal path string has no empty
2417     // segments (i.e., occurrences of "//"), no segments equal to ".", and no
2418     // segments equal to ".." that are preceded by a segment not equal to "..".
2419     // In contrast to Unix-style pathname normalization, for URI paths we
2420     // always retain trailing slashes.
2421     //
2422     private static String normalize(String ps) {
2423 
2424         // Does this path need normalization?
2425         int ns = needsNormalization(ps);        // Number of segments
2426         if (ns < 0)
2427             // Nope -- just return it
2428             return ps;
2429 
2430         char[] path = ps.toCharArray();         // Path in char-array form
2431 
2432         // Split path into segments
2433         int[] segs = new int[ns];               // Segment-index array
2434         split(path, segs);
2435 
2436         // Remove dots
2437         removeDots(path, segs);
2438 
2439         // Prevent scheme-name confusion
2440         maybeAddLeadingDot(path, segs);
2441 
2442         // Join the remaining segments and return the result
2443         String s = new String(path, 0, join(path, segs));
2444         if (s.equals(ps)) {
2445             // string was already normalized
2446             return ps;
2447         }
2448         return s;
2449     }
2450 
2451 
2452 
2453     // -- Character classes for parsing --
2454 
2455     // RFC2396 precisely specifies which characters in the US-ASCII charset are
2456     // permissible in the various components of a URI reference.  We here
2457     // define a set of mask pairs to aid in enforcing these restrictions.  Each
2458     // mask pair consists of two longs, a low mask and a high mask.  Taken
2459     // together they represent a 128-bit mask, where bit i is set iff the
2460     // character with value i is permitted.
2461     //
2462     // This approach is more efficient than sequentially searching arrays of
2463     // permitted characters.  It could be made still more efficient by
2464     // precompiling the mask information so that a character's presence in a
2465     // given mask could be determined by a single table lookup.
2466 
2467     // Compute the low-order mask for the characters in the given string
2468     private static long lowMask(String chars) {
2469         int n = chars.length();
2470         long m = 0;
2471         for (int i = 0; i < n; i++) {
2472             char c = chars.charAt(i);
2473             if (c < 64)
2474                 m |= (1L << c);
2475         }
2476         return m;
2477     }
2478 
2479     // Compute the high-order mask for the characters in the given string
2480     private static long highMask(String chars) {
2481         int n = chars.length();
2482         long m = 0;
2483         for (int i = 0; i < n; i++) {
2484             char c = chars.charAt(i);
2485             if ((c >= 64) && (c < 128))
2486                 m |= (1L << (c - 64));
2487         }
2488         return m;
2489     }
2490 
2491     // Compute a low-order mask for the characters
2492     // between first and last, inclusive
2493     private static long lowMask(char first, char last) {
2494         long m = 0;
2495         int f = Math.max(Math.min(first, 63), 0);
2496         int l = Math.max(Math.min(last, 63), 0);
2497         for (int i = f; i <= l; i++)
2498             m |= 1L << i;
2499         return m;
2500     }
2501 
2502     // Compute a high-order mask for the characters
2503     // between first and last, inclusive
2504     private static long highMask(char first, char last) {
2505         long m = 0;
2506         int f = Math.max(Math.min(first, 127), 64) - 64;
2507         int l = Math.max(Math.min(last, 127), 64) - 64;
2508         for (int i = f; i <= l; i++)
2509             m |= 1L << i;
2510         return m;
2511     }
2512 
2513     // Tell whether the given character is permitted by the given mask pair
2514     private static boolean match(char c, long lowMask, long highMask) {
2515         if (c == 0) // 0 doesn't have a slot in the mask. So, it never matches.
2516             return false;
2517         if (c < 64)
2518             return ((1L << c) & lowMask) != 0;
2519         if (c < 128)
2520             return ((1L << (c - 64)) & highMask) != 0;
2521         return false;
2522     }
2523 
2524     // Character-class masks, in reverse order from RFC2396 because
2525     // initializers for static fields cannot make forward references.
2526 
2527     // digit    = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
2528     //            "8" | "9"
2529     private static final long L_DIGIT = lowMask('0', '9');
2530     private static final long H_DIGIT = 0L;
2531 
2532     // upalpha  = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
2533     //            "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |
2534     //            "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
2535     private static final long L_UPALPHA = 0L;
2536     private static final long H_UPALPHA = highMask('A', 'Z');
2537 
2538     // lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" |
2539     //            "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" |
2540     //            "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
2541     private static final long L_LOWALPHA = 0L;
2542     private static final long H_LOWALPHA = highMask('a', 'z');
2543 
2544     // alpha         = lowalpha | upalpha
2545     private static final long L_ALPHA = L_LOWALPHA | L_UPALPHA;
2546     private static final long H_ALPHA = H_LOWALPHA | H_UPALPHA;
2547 
2548     // alphanum      = alpha | digit
2549     private static final long L_ALPHANUM = L_DIGIT | L_ALPHA;
2550     private static final long H_ALPHANUM = H_DIGIT | H_ALPHA;
2551 
2552     // hex           = digit | "A" | "B" | "C" | "D" | "E" | "F" |
2553     //                         "a" | "b" | "c" | "d" | "e" | "f"
2554     private static final long L_HEX = L_DIGIT;
2555     private static final long H_HEX = highMask('A', 'F') | highMask('a', 'f');
2556 
2557     // mark          = "-" | "_" | "." | "!" | "~" | "*" | "'" |
2558     //                 "(" | ")"
2559     private static final long L_MARK = lowMask("-_.!~*'()");
2560     private static final long H_MARK = highMask("-_.!~*'()");
2561 
2562     // unreserved    = alphanum | mark
2563     private static final long L_UNRESERVED = L_ALPHANUM | L_MARK;
2564     private static final long H_UNRESERVED = H_ALPHANUM | H_MARK;
2565 
2566     // reserved      = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |
2567     //                 "$" | "," | "[" | "]"
2568     // Added per RFC2732: "[", "]"
2569     private static final long L_RESERVED = lowMask(";/?:@&=+$,[]");
2570     private static final long H_RESERVED = highMask(";/?:@&=+$,[]");
2571 
2572     // The zero'th bit is used to indicate that escape pairs and non-US-ASCII
2573     // characters are allowed; this is handled by the scanEscape method below.
2574     private static final long L_ESCAPED = 1L;
2575     private static final long H_ESCAPED = 0L;
2576 
2577     // uric          = reserved | unreserved | escaped
2578     private static final long L_URIC = L_RESERVED | L_UNRESERVED | L_ESCAPED;
2579     private static final long H_URIC = H_RESERVED | H_UNRESERVED | H_ESCAPED;
2580 
2581     // pchar         = unreserved | escaped |
2582     //                 ":" | "@" | "&" | "=" | "+" | "$" | ","
2583     private static final long L_PCHAR
2584         = L_UNRESERVED | L_ESCAPED | lowMask(":@&=+$,");
2585     private static final long H_PCHAR
2586         = H_UNRESERVED | H_ESCAPED | highMask(":@&=+$,");
2587 
2588     // All valid path characters
2589     private static final long L_PATH = L_PCHAR | lowMask(";/");
2590     private static final long H_PATH = H_PCHAR | highMask(";/");
2591 
2592     // Dash, for use in domainlabel and toplabel
2593     private static final long L_DASH = lowMask("-");
2594     private static final long H_DASH = highMask("-");
2595 
2596     // Dot, for use in hostnames
2597     private static final long L_DOT = lowMask(".");
2598     private static final long H_DOT = highMask(".");
2599 
2600     // userinfo      = *( unreserved | escaped |
2601     //                    ";" | ":" | "&" | "=" | "+" | "$" | "," )
2602     private static final long L_USERINFO
2603         = L_UNRESERVED | L_ESCAPED | lowMask(";:&=+$,");
2604     private static final long H_USERINFO
2605         = H_UNRESERVED | H_ESCAPED | highMask(";:&=+$,");
2606 
2607     // reg_name      = 1*( unreserved | escaped | "$" | "," |
2608     //                     ";" | ":" | "@" | "&" | "=" | "+" )
2609     private static final long L_REG_NAME
2610         = L_UNRESERVED | L_ESCAPED | lowMask("$,;:@&=+");
2611     private static final long H_REG_NAME
2612         = H_UNRESERVED | H_ESCAPED | highMask("$,;:@&=+");
2613 
2614     // All valid characters for server-based authorities
2615     private static final long L_SERVER
2616         = L_USERINFO | L_ALPHANUM | L_DASH | lowMask(".:@[]");
2617     private static final long H_SERVER
2618         = H_USERINFO | H_ALPHANUM | H_DASH | highMask(".:@[]");
2619 
2620     // Special case of server authority that represents an IPv6 address
2621     // In this case, a % does not signify an escape sequence
2622     private static final long L_SERVER_PERCENT
2623         = L_SERVER | lowMask("%");
2624     private static final long H_SERVER_PERCENT
2625         = H_SERVER | highMask("%");
2626     private static final long L_LEFT_BRACKET = lowMask("[");
2627     private static final long H_LEFT_BRACKET = highMask("[");
2628 
2629     // scheme        = alpha *( alpha | digit | "+" | "-" | "." )
2630     private static final long L_SCHEME = L_ALPHA | L_DIGIT | lowMask("+-.");
2631     private static final long H_SCHEME = H_ALPHA | H_DIGIT | highMask("+-.");
2632 
2633     // uric_no_slash = unreserved | escaped | ";" | "?" | ":" | "@" |
2634     //                 "&" | "=" | "+" | "$" | ","
2635     private static final long L_URIC_NO_SLASH
2636         = L_UNRESERVED | L_ESCAPED | lowMask(";?:@&=+$,");
2637     private static final long H_URIC_NO_SLASH
2638         = H_UNRESERVED | H_ESCAPED | highMask(";?:@&=+$,");
2639 
2640 
2641     // -- Escaping and encoding --
2642 
2643     private final static char[] hexDigits = {
2644         '0', '1', '2', '3', '4', '5', '6', '7',
2645         '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
2646     };
2647 
2648     private static void appendEscape(StringBuffer sb, byte b) {
2649         sb.append('%');
2650         sb.append(hexDigits[(b >> 4) & 0x0f]);
2651         sb.append(hexDigits[(b >> 0) & 0x0f]);
2652     }
2653 
2654     private static void appendEncoded(StringBuffer sb, char c) {
2655         ByteBuffer bb = null;
2656         try {
2657             bb = ThreadLocalCoders.encoderFor("UTF-8")
2658                 .encode(CharBuffer.wrap("" + c));
2659         } catch (CharacterCodingException x) {
2660             assert false;
2661         }
2662         while (bb.hasRemaining()) {
2663             int b = bb.get() & 0xff;
2664             if (b >= 0x80)
2665                 appendEscape(sb, (byte)b);
2666             else
2667                 sb.append((char)b);
2668         }
2669     }
2670 
2671     // Quote any characters in s that are not permitted
2672     // by the given mask pair
2673     //
2674     private static String quote(String s, long lowMask, long highMask) {
2675         int n = s.length();
2676         StringBuffer sb = null;
2677         boolean allowNonASCII = ((lowMask & L_ESCAPED) != 0);
2678         for (int i = 0; i < s.length(); i++) {
2679             char c = s.charAt(i);
2680             if (c < '\u0080') {
2681                 if (!match(c, lowMask, highMask)) {
2682                     if (sb == null) {
2683                         sb = new StringBuffer();
2684                         sb.append(s.substring(0, i));
2685                     }
2686                     appendEscape(sb, (byte)c);
2687                 } else {
2688                     if (sb != null)
2689                         sb.append(c);
2690                 }
2691             } else if (allowNonASCII
2692                        && (Character.isSpaceChar(c)
2693                            || Character.isISOControl(c))) {
2694                 if (sb == null) {
2695                     sb = new StringBuffer();
2696                     sb.append(s.substring(0, i));
2697                 }
2698                 appendEncoded(sb, c);
2699             } else {
2700                 if (sb != null)
2701                     sb.append(c);
2702             }
2703         }
2704         return (sb == null) ? s : sb.toString();
2705     }
2706 
2707     // Encodes all characters >= \u0080 into escaped, normalized UTF-8 octets,
2708     // assuming that s is otherwise legal
2709     //
2710     private static String encode(String s) {
2711         int n = s.length();
2712         if (n == 0)
2713             return s;
2714 
2715         // First check whether we actually need to encode
2716         for (int i = 0;;) {
2717             if (s.charAt(i) >= '\u0080')
2718                 break;
2719             if (++i >= n)
2720                 return s;
2721         }
2722 
2723         String ns = Normalizer.normalize(s, Normalizer.Form.NFC);
2724         ByteBuffer bb = null;
2725         try {
2726             bb = ThreadLocalCoders.encoderFor("UTF-8")
2727                 .encode(CharBuffer.wrap(ns));
2728         } catch (CharacterCodingException x) {
2729             assert false;
2730         }
2731 
2732         StringBuffer sb = new StringBuffer();
2733         while (bb.hasRemaining()) {
2734             int b = bb.get() & 0xff;
2735             if (b >= 0x80)
2736                 appendEscape(sb, (byte)b);
2737             else
2738                 sb.append((char)b);
2739         }
2740         return sb.toString();
2741     }
2742 
2743     private static int decode(char c) {
2744         if ((c >= '0') && (c <= '9'))
2745             return c - '0';
2746         if ((c >= 'a') && (c <= 'f'))
2747             return c - 'a' + 10;
2748         if ((c >= 'A') && (c <= 'F'))
2749             return c - 'A' + 10;
2750         assert false;
2751         return -1;
2752     }
2753 
2754     private static byte decode(char c1, char c2) {
2755         return (byte)(  ((decode(c1) & 0xf) << 4)
2756                       | ((decode(c2) & 0xf) << 0));
2757     }
2758 
2759     // Evaluates all escapes in s, applying UTF-8 decoding if needed.  Assumes
2760     // that escapes are well-formed syntactically, i.e., of the form %XX.  If a
2761     // sequence of escaped octets is not valid UTF-8 then the erroneous octets
2762     // are replaced with '\uFFFD'.
2763     // Exception: any "%" found between "[]" is left alone. It is an IPv6 literal
2764     //            with a scope_id
2765     //
2766     private static String decode(String s) {
2767         if (s == null)
2768             return s;
2769         int n = s.length();
2770         if (n == 0)
2771             return s;
2772         if (s.indexOf('%') < 0)
2773             return s;
2774 
2775         StringBuffer sb = new StringBuffer(n);
2776         ByteBuffer bb = ByteBuffer.allocate(n);
2777         CharBuffer cb = CharBuffer.allocate(n);
2778         CharsetDecoder dec = ThreadLocalCoders.decoderFor("UTF-8")
2779             .onMalformedInput(CodingErrorAction.REPLACE)
2780             .onUnmappableCharacter(CodingErrorAction.REPLACE);
2781 
2782         // This is not horribly efficient, but it will do for now
2783         char c = s.charAt(0);
2784         boolean betweenBrackets = false;
2785 
2786         for (int i = 0; i < n;) {
2787             assert c == s.charAt(i);    // Loop invariant
2788             if (c == '[') {
2789                 betweenBrackets = true;
2790             } else if (betweenBrackets && c == ']') {
2791                 betweenBrackets = false;
2792             }
2793             if (c != '%' || betweenBrackets) {
2794                 sb.append(c);
2795                 if (++i >= n)
2796                     break;
2797                 c = s.charAt(i);
2798                 continue;
2799             }
2800             bb.clear();
2801             int ui = i;
2802             for (;;) {
2803                 assert (n - i >= 2);
2804                 bb.put(decode(s.charAt(++i), s.charAt(++i)));
2805                 if (++i >= n)
2806                     break;
2807                 c = s.charAt(i);
2808                 if (c != '%')
2809                     break;
2810             }
2811             bb.flip();
2812             cb.clear();
2813             dec.reset();
2814             CoderResult cr = dec.decode(bb, cb, true);
2815             assert cr.isUnderflow();
2816             cr = dec.flush(cb);
2817             assert cr.isUnderflow();
2818             sb.append(cb.flip().toString());
2819         }
2820 
2821         return sb.toString();
2822     }
2823 
2824 
2825     // -- Parsing --
2826 
2827     // For convenience we wrap the input URI string in a new instance of the
2828     // following internal class.  This saves always having to pass the input
2829     // string as an argument to each internal scan/parse method.
2830 
2831     private class Parser {
2832 
2833         private String input;           // URI input string
2834         private boolean requireServerAuthority = false;
2835 
2836         Parser(String s) {
2837             input = s;
2838             string = s;
2839         }
2840 
2841         // -- Methods for throwing URISyntaxException in various ways --
2842 
2843         private void fail(String reason) throws URISyntaxException {
2844             throw new URISyntaxException(input, reason);
2845         }
2846 
2847         private void fail(String reason, int p) throws URISyntaxException {
2848             throw new URISyntaxException(input, reason, p);
2849         }
2850 
2851         private void failExpecting(String expected, int p)
2852             throws URISyntaxException
2853         {
2854             fail("Expected " + expected, p);
2855         }
2856 
2857         private void failExpecting(String expected, String prior, int p)
2858             throws URISyntaxException
2859         {
2860             fail("Expected " + expected + " following " + prior, p);
2861         }
2862 
2863 
2864         // -- Simple access to the input string --
2865 
2866         // Return a substring of the input string
2867         //
2868         private String substring(int start, int end) {
2869             return input.substring(start, end);
2870         }
2871 
2872         // Return the char at position p,
2873         // assuming that p < input.length()
2874         //
2875         private char charAt(int p) {
2876             return input.charAt(p);
2877         }
2878 
2879         // Tells whether start < end and, if so, whether charAt(start) == c
2880         //
2881         private boolean at(int start, int end, char c) {
2882             return (start < end) && (charAt(start) == c);
2883         }
2884 
2885         // Tells whether start + s.length() < end and, if so,
2886         // whether the chars at the start position match s exactly
2887         //
2888         private boolean at(int start, int end, String s) {
2889             int p = start;
2890             int sn = s.length();
2891             if (sn > end - p)
2892                 return false;
2893             int i = 0;
2894             while (i < sn) {
2895                 if (charAt(p++) != s.charAt(i)) {
2896                     break;
2897                 }
2898                 i++;
2899             }
2900             return (i == sn);
2901         }
2902 
2903 
2904         // -- Scanning --
2905 
2906         // The various scan and parse methods that follow use a uniform
2907         // convention of taking the current start position and end index as
2908         // their first two arguments.  The start is inclusive while the end is
2909         // exclusive, just as in the String class, i.e., a start/end pair
2910         // denotes the left-open interval [start, end) of the input string.
2911         //
2912         // These methods never proceed past the end position.  They may return
2913         // -1 to indicate outright failure, but more often they simply return
2914         // the position of the first char after the last char scanned.  Thus
2915         // a typical idiom is
2916         //
2917         //     int p = start;
2918         //     int q = scan(p, end, ...);
2919         //     if (q > p)
2920         //         // We scanned something
2921         //         ...;
2922         //     else if (q == p)
2923         //         // We scanned nothing
2924         //         ...;
2925         //     else if (q == -1)
2926         //         // Something went wrong
2927         //         ...;
2928 
2929 
2930         // Scan a specific char: If the char at the given start position is
2931         // equal to c, return the index of the next char; otherwise, return the
2932         // start position.
2933         //
2934         private int scan(int start, int end, char c) {
2935             if ((start < end) && (charAt(start) == c))
2936                 return start + 1;
2937             return start;
2938         }
2939 
2940         // Scan forward from the given start position.  Stop at the first char
2941         // in the err string (in which case -1 is returned), or the first char
2942         // in the stop string (in which case the index of the preceding char is
2943         // returned), or the end of the input string (in which case the length
2944         // of the input string is returned).  May return the start position if
2945         // nothing matches.
2946         //
2947         private int scan(int start, int end, String err, String stop) {
2948             int p = start;
2949             while (p < end) {
2950                 char c = charAt(p);
2951                 if (err.indexOf(c) >= 0)
2952                     return -1;
2953                 if (stop.indexOf(c) >= 0)
2954                     break;
2955                 p++;
2956             }
2957             return p;
2958         }
2959 
2960         // Scan a potential escape sequence, starting at the given position,
2961         // with the given first char (i.e., charAt(start) == c).
2962         //
2963         // This method assumes that if escapes are allowed then visible
2964         // non-US-ASCII chars are also allowed.
2965         //
2966         private int scanEscape(int start, int n, char first)
2967             throws URISyntaxException
2968         {
2969             int p = start;
2970             char c = first;
2971             if (c == '%') {
2972                 // Process escape pair
2973                 if ((p + 3 <= n)
2974                     && match(charAt(p + 1), L_HEX, H_HEX)
2975                     && match(charAt(p + 2), L_HEX, H_HEX)) {
2976                     return p + 3;
2977                 }
2978                 fail("Malformed escape pair", p);
2979             } else if ((c > 128)
2980                        && !Character.isSpaceChar(c)
2981                        && !Character.isISOControl(c)) {
2982                 // Allow unescaped but visible non-US-ASCII chars
2983                 return p + 1;
2984             }
2985             return p;
2986         }
2987 
2988         // Scan chars that match the given mask pair
2989         //
2990         private int scan(int start, int n, long lowMask, long highMask)
2991             throws URISyntaxException
2992         {
2993             int p = start;
2994             while (p < n) {
2995                 char c = charAt(p);
2996                 if (match(c, lowMask, highMask)) {
2997                     p++;
2998                     continue;
2999                 }
3000                 if ((lowMask & L_ESCAPED) != 0) {
3001                     int q = scanEscape(p, n, c);
3002                     if (q > p) {
3003                         p = q;
3004                         continue;
3005                     }
3006                 }
3007                 break;
3008             }
3009             return p;
3010         }
3011 
3012         // Check that each of the chars in [start, end) matches the given mask
3013         //
3014         private void checkChars(int start, int end,
3015                                 long lowMask, long highMask,
3016                                 String what)
3017             throws URISyntaxException
3018         {
3019             int p = scan(start, end, lowMask, highMask);
3020             if (p < end)
3021                 fail("Illegal character in " + what, p);
3022         }
3023 
3024         // Check that the char at position p matches the given mask
3025         //
3026         private void checkChar(int p,
3027                                long lowMask, long highMask,
3028                                String what)
3029             throws URISyntaxException
3030         {
3031             checkChars(p, p + 1, lowMask, highMask, what);
3032         }
3033 
3034 
3035         // -- Parsing --
3036 
3037         // [<scheme>:]<scheme-specific-part>[#<fragment>]
3038         //
3039         void parse(boolean rsa) throws URISyntaxException {
3040             requireServerAuthority = rsa;
3041             int ssp;                    // Start of scheme-specific part
3042             int n = input.length();
3043             int p = scan(0, n, "/?#", ":");
3044             if ((p >= 0) && at(p, n, ':')) {
3045                 if (p == 0)
3046                     failExpecting("scheme name", 0);
3047                 checkChar(0, L_ALPHA, H_ALPHA, "scheme name");
3048                 checkChars(1, p, L_SCHEME, H_SCHEME, "scheme name");
3049                 scheme = substring(0, p);
3050                 p++;                    // Skip ':'
3051                 ssp = p;
3052                 if (at(p, n, '/')) {
3053                     p = parseHierarchical(p, n);
3054                 } else {
3055                     int q = scan(p, n, "", "#");
3056                     if (q <= p)
3057                         failExpecting("scheme-specific part", p);
3058                     checkChars(p, q, L_URIC, H_URIC, "opaque part");
3059                     p = q;
3060                 }
3061             } else {
3062                 ssp = 0;
3063                 p = parseHierarchical(0, n);
3064             }
3065             schemeSpecificPart = substring(ssp, p);
3066             if (at(p, n, '#')) {
3067                 checkChars(p + 1, n, L_URIC, H_URIC, "fragment");
3068                 fragment = substring(p + 1, n);
3069                 p = n;
3070             }
3071             if (p < n)
3072                 fail("end of URI", p);
3073         }
3074 
3075         // [//authority]<path>[?<query>]
3076         //
3077         // DEVIATION from RFC2396: We allow an empty authority component as
3078         // long as it's followed by a non-empty path, query component, or
3079         // fragment component.  This is so that URIs such as "file:///foo/bar"
3080         // will parse.  This seems to be the intent of RFC2396, though the
3081         // grammar does not permit it.  If the authority is empty then the
3082         // userInfo, host, and port components are undefined.
3083         //
3084         // DEVIATION from RFC2396: We allow empty relative paths.  This seems
3085         // to be the intent of RFC2396, but the grammar does not permit it.
3086         // The primary consequence of this deviation is that "#f" parses as a
3087         // relative URI with an empty path.
3088         //
3089         private int parseHierarchical(int start, int n)
3090             throws URISyntaxException
3091         {
3092             int p = start;
3093             if (at(p, n, '/') && at(p + 1, n, '/')) {
3094                 p += 2;
3095                 int q = scan(p, n, "", "/?#");
3096                 if (q > p) {
3097                     p = parseAuthority(p, q);
3098                 } else if (q < n) {
3099                     // DEVIATION: Allow empty authority prior to non-empty
3100                     // path, query component or fragment identifier
3101                 } else
3102                     failExpecting("authority", p);
3103             }
3104             int q = scan(p, n, "", "?#"); // DEVIATION: May be empty
3105             checkChars(p, q, L_PATH, H_PATH, "path");
3106             path = substring(p, q);
3107             p = q;
3108             if (at(p, n, '?')) {
3109                 p++;
3110                 q = scan(p, n, "", "#");
3111                 checkChars(p, q, L_URIC, H_URIC, "query");
3112                 query = substring(p, q);
3113                 p = q;
3114             }
3115             return p;
3116         }
3117 
3118         // authority     = server | reg_name
3119         //
3120         // Ambiguity: An authority that is a registry name rather than a server
3121         // might have a prefix that parses as a server.  We use the fact that
3122         // the authority component is always followed by '/' or the end of the
3123         // input string to resolve this: If the complete authority did not
3124         // parse as a server then we try to parse it as a registry name.
3125         //
3126         private int parseAuthority(int start, int n)
3127             throws URISyntaxException
3128         {
3129             int p = start;
3130             int q = p;
3131             URISyntaxException ex = null;
3132 
3133             boolean serverChars;
3134             boolean regChars;
3135 
3136             if (scan(p, n, "", "]") > p) {
3137                 // contains a literal IPv6 address, therefore % is allowed
3138                 serverChars = (scan(p, n, L_SERVER_PERCENT, H_SERVER_PERCENT) == n);
3139             } else {
3140                 serverChars = (scan(p, n, L_SERVER, H_SERVER) == n);
3141             }
3142             regChars = (scan(p, n, L_REG_NAME, H_REG_NAME) == n);
3143 
3144             if (regChars && !serverChars) {
3145                 // Must be a registry-based authority
3146                 authority = substring(p, n);
3147                 return n;
3148             }
3149 
3150             if (serverChars) {
3151                 // Might be (probably is) a server-based authority, so attempt
3152                 // to parse it as such.  If the attempt fails, try to treat it
3153                 // as a registry-based authority.
3154                 try {
3155                     q = parseServer(p, n);
3156                     if (q < n)
3157                         failExpecting("end of authority", q);
3158                     authority = substring(p, n);
3159                 } catch (URISyntaxException x) {
3160                     // Undo results of failed parse
3161                     userInfo = null;
3162                     host = null;
3163                     port = -1;
3164                     if (requireServerAuthority) {
3165                         // If we're insisting upon a server-based authority,
3166                         // then just re-throw the exception
3167                         throw x;
3168                     } else {
3169                         // Save the exception in case it doesn't parse as a
3170                         // registry either
3171                         ex = x;
3172                         q = p;
3173                     }
3174                 }
3175             }
3176 
3177             if (q < n) {
3178                 if (regChars) {
3179                     // Registry-based authority
3180                     authority = substring(p, n);
3181                 } else if (ex != null) {
3182                     // Re-throw exception; it was probably due to
3183                     // a malformed IPv6 address
3184                     throw ex;
3185                 } else {
3186                     fail("Illegal character in authority", q);
3187                 }
3188             }
3189 
3190             return n;
3191         }
3192 
3193 
3194         // [<userinfo>@]<host>[:<port>]
3195         //
3196         private int parseServer(int start, int n)
3197             throws URISyntaxException
3198         {
3199             int p = start;
3200             int q;
3201 
3202             // userinfo
3203             q = scan(p, n, "/?#", "@");
3204             if ((q >= p) && at(q, n, '@')) {
3205                 checkChars(p, q, L_USERINFO, H_USERINFO, "user info");
3206                 userInfo = substring(p, q);
3207                 p = q + 1;              // Skip '@'
3208             }
3209 
3210             // hostname, IPv4 address, or IPv6 address
3211             if (at(p, n, '[')) {
3212                 // DEVIATION from RFC2396: Support IPv6 addresses, per RFC2732
3213                 p++;
3214                 q = scan(p, n, "/?#", "]");
3215                 if ((q > p) && at(q, n, ']')) {
3216                     // look for a "%" scope id
3217                     int r = scan (p, q, "", "%");
3218                     if (r > p) {
3219                         parseIPv6Reference(p, r);
3220                         if (r+1 == q) {
3221                             fail ("scope id expected");
3222                         }
3223                         checkChars (r+1, q, L_ALPHANUM, H_ALPHANUM,
3224                                                 "scope id");
3225                     } else {
3226                         parseIPv6Reference(p, q);
3227                     }
3228                     host = substring(p-1, q+1);
3229                     p = q + 1;
3230                 } else {
3231                     failExpecting("closing bracket for IPv6 address", q);
3232                 }
3233             } else {
3234                 q = parseIPv4Address(p, n);
3235                 if (q <= p)
3236                     q = parseHostname(p, n);
3237                 p = q;
3238             }
3239 
3240             // port
3241             if (at(p, n, ':')) {
3242                 p++;
3243                 q = scan(p, n, "", "/");
3244                 if (q > p) {
3245                     checkChars(p, q, L_DIGIT, H_DIGIT, "port number");
3246                     try {
3247                         port = Integer.parseInt(substring(p, q));
3248                     } catch (NumberFormatException x) {
3249                         fail("Malformed port number", p);
3250                     }
3251                     p = q;
3252                 }
3253             }
3254             if (p < n)
3255                 failExpecting("port number", p);
3256 
3257             return p;
3258         }
3259 
3260         // Scan a string of decimal digits whose value fits in a byte
3261         //
3262         private int scanByte(int start, int n)
3263             throws URISyntaxException
3264         {
3265             int p = start;
3266             int q = scan(p, n, L_DIGIT, H_DIGIT);
3267             if (q <= p) return q;
3268             if (Integer.parseInt(substring(p, q)) > 255) return p;
3269             return q;
3270         }
3271 
3272         // Scan an IPv4 address.
3273         //
3274         // If the strict argument is true then we require that the given
3275         // interval contain nothing besides an IPv4 address; if it is false
3276         // then we only require that it start with an IPv4 address.
3277         //
3278         // If the interval does not contain or start with (depending upon the
3279         // strict argument) a legal IPv4 address characters then we return -1
3280         // immediately; otherwise we insist that these characters parse as a
3281         // legal IPv4 address and throw an exception on failure.
3282         //
3283         // We assume that any string of decimal digits and dots must be an IPv4
3284         // address.  It won't parse as a hostname anyway, so making that
3285         // assumption here allows more meaningful exceptions to be thrown.
3286         //
3287         private int scanIPv4Address(int start, int n, boolean strict)
3288             throws URISyntaxException
3289         {
3290             int p = start;
3291             int q;
3292             int m = scan(p, n, L_DIGIT | L_DOT, H_DIGIT | H_DOT);
3293             if ((m <= p) || (strict && (m != n)))
3294                 return -1;
3295             for (;;) {
3296                 // Per RFC2732: At most three digits per byte
3297                 // Further constraint: Each element fits in a byte
3298                 if ((q = scanByte(p, m)) <= p) break;   p = q;
3299                 if ((q = scan(p, m, '.')) <= p) break;  p = q;
3300                 if ((q = scanByte(p, m)) <= p) break;   p = q;
3301                 if ((q = scan(p, m, '.')) <= p) break;  p = q;
3302                 if ((q = scanByte(p, m)) <= p) break;   p = q;
3303                 if ((q = scan(p, m, '.')) <= p) break;  p = q;
3304                 if ((q = scanByte(p, m)) <= p) break;   p = q;
3305                 if (q < m) break;
3306                 return q;
3307             }
3308             fail("Malformed IPv4 address", q);
3309             return -1;
3310         }
3311 
3312         // Take an IPv4 address: Throw an exception if the given interval
3313         // contains anything except an IPv4 address
3314         //
3315         private int takeIPv4Address(int start, int n, String expected)
3316             throws URISyntaxException
3317         {
3318             int p = scanIPv4Address(start, n, true);
3319             if (p <= start)
3320                 failExpecting(expected, start);
3321             return p;
3322         }
3323 
3324         // Attempt to parse an IPv4 address, returning -1 on failure but
3325         // allowing the given interval to contain [:<characters>] after
3326         // the IPv4 address.
3327         //
3328         private int parseIPv4Address(int start, int n) {
3329             int p;
3330 
3331             try {
3332                 p = scanIPv4Address(start, n, false);
3333             } catch (URISyntaxException x) {
3334                 return -1;
3335             } catch (NumberFormatException nfe) {
3336                 return -1;
3337             }
3338 
3339             if (p > start && p < n) {
3340                 // IPv4 address is followed by something - check that
3341                 // it's a ":" as this is the only valid character to
3342                 // follow an address.
3343                 if (charAt(p) != ':') {
3344                     p = -1;
3345                 }
3346             }
3347 
3348             if (p > start)
3349                 host = substring(start, p);
3350 
3351             return p;
3352         }
3353 
3354         // hostname      = domainlabel [ "." ] | 1*( domainlabel "." ) toplabel [ "." ]
3355         // domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
3356         // toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
3357         //
3358         private int parseHostname(int start, int n)
3359             throws URISyntaxException
3360         {
3361             int p = start;
3362             int q;
3363             int l = -1;                 // Start of last parsed label
3364 
3365             do {
3366                 // domainlabel = alphanum [ *( alphanum | "-" ) alphanum ]
3367                 q = scan(p, n, L_ALPHANUM, H_ALPHANUM);
3368                 if (q <= p)
3369                     break;
3370                 l = p;
3371                 if (q > p) {
3372                     p = q;
3373                     q = scan(p, n, L_ALPHANUM | L_DASH, H_ALPHANUM | H_DASH);
3374                     if (q > p) {
3375                         if (charAt(q - 1) == '-')
3376                             fail("Illegal character in hostname", q - 1);
3377                         p = q;
3378                     }
3379                 }
3380                 q = scan(p, n, '.');
3381                 if (q <= p)
3382                     break;
3383                 p = q;
3384             } while (p < n);
3385 
3386             if ((p < n) && !at(p, n, ':'))
3387                 fail("Illegal character in hostname", p);
3388 
3389             if (l < 0)
3390                 failExpecting("hostname", start);
3391 
3392             // for a fully qualified hostname check that the rightmost
3393             // label starts with an alpha character.
3394             if (l > start && !match(charAt(l), L_ALPHA, H_ALPHA)) {
3395                 fail("Illegal character in hostname", l);
3396             }
3397 
3398             host = substring(start, p);
3399             return p;
3400         }
3401 
3402 
3403         // IPv6 address parsing, from RFC2373: IPv6 Addressing Architecture
3404         //
3405         // Bug: The grammar in RFC2373 Appendix B does not allow addresses of
3406         // the form ::12.34.56.78, which are clearly shown in the examples
3407         // earlier in the document.  Here is the original grammar:
3408         //
3409         //   IPv6address = hexpart [ ":" IPv4address ]
3410         //   hexpart     = hexseq | hexseq "::" [ hexseq ] | "::" [ hexseq ]
3411         //   hexseq      = hex4 *( ":" hex4)
3412         //   hex4        = 1*4HEXDIG
3413         //
3414         // We therefore use the following revised grammar:
3415         //
3416         //   IPv6address = hexseq [ ":" IPv4address ]
3417         //                 | hexseq [ "::" [ hexpost ] ]
3418         //                 | "::" [ hexpost ]
3419         //   hexpost     = hexseq | hexseq ":" IPv4address | IPv4address
3420         //   hexseq      = hex4 *( ":" hex4)
3421         //   hex4        = 1*4HEXDIG
3422         //
3423         // This covers all and only the following cases:
3424         //
3425         //   hexseq
3426         //   hexseq : IPv4address
3427         //   hexseq ::
3428         //   hexseq :: hexseq
3429         //   hexseq :: hexseq : IPv4address
3430         //   hexseq :: IPv4address
3431         //   :: hexseq
3432         //   :: hexseq : IPv4address
3433         //   :: IPv4address
3434         //   ::
3435         //
3436         // Additionally we constrain the IPv6 address as follows :-
3437         //
3438         //  i.  IPv6 addresses without compressed zeros should contain
3439         //      exactly 16 bytes.
3440         //
3441         //  ii. IPv6 addresses with compressed zeros should contain
3442         //      less than 16 bytes.
3443 
3444         private int ipv6byteCount = 0;
3445 
3446         private int parseIPv6Reference(int start, int n)
3447             throws URISyntaxException
3448         {
3449             int p = start;
3450             int q;
3451             boolean compressedZeros = false;
3452 
3453             q = scanHexSeq(p, n);
3454 
3455             if (q > p) {
3456                 p = q;
3457                 if (at(p, n, "::")) {
3458                     compressedZeros = true;
3459                     p = scanHexPost(p + 2, n);
3460                 } else if (at(p, n, ':')) {
3461                     p = takeIPv4Address(p + 1,  n, "IPv4 address");
3462                     ipv6byteCount += 4;
3463                 }
3464             } else if (at(p, n, "::")) {
3465                 compressedZeros = true;
3466                 p = scanHexPost(p + 2, n);
3467             }
3468             if (p < n)
3469                 fail("Malformed IPv6 address", start);
3470             if (ipv6byteCount > 16)
3471                 fail("IPv6 address too long", start);
3472             if (!compressedZeros && ipv6byteCount < 16)
3473                 fail("IPv6 address too short", start);
3474             if (compressedZeros && ipv6byteCount == 16)
3475                 fail("Malformed IPv6 address", start);
3476 
3477             return p;
3478         }
3479 
3480         private int scanHexPost(int start, int n)
3481             throws URISyntaxException
3482         {
3483             int p = start;
3484             int q;
3485 
3486             if (p == n)
3487                 return p;
3488 
3489             q = scanHexSeq(p, n);
3490             if (q > p) {
3491                 p = q;
3492                 if (at(p, n, ':')) {
3493                     p++;
3494                     p = takeIPv4Address(p, n, "hex digits or IPv4 address");
3495                     ipv6byteCount += 4;
3496                 }
3497             } else {
3498                 p = takeIPv4Address(p, n, "hex digits or IPv4 address");
3499                 ipv6byteCount += 4;
3500             }
3501             return p;
3502         }
3503 
3504         // Scan a hex sequence; return -1 if one could not be scanned
3505         //
3506         private int scanHexSeq(int start, int n)
3507             throws URISyntaxException
3508         {
3509             int p = start;
3510             int q;
3511 
3512             q = scan(p, n, L_HEX, H_HEX);
3513             if (q <= p)
3514                 return -1;
3515             if (at(q, n, '.'))          // Beginning of IPv4 address
3516                 return -1;
3517             if (q > p + 4)
3518                 fail("IPv6 hexadecimal digit sequence too long", p);
3519             ipv6byteCount += 2;
3520             p = q;
3521             while (p < n) {
3522                 if (!at(p, n, ':'))
3523                     break;
3524                 if (at(p + 1, n, ':'))
3525                     break;              // "::"
3526                 p++;
3527                 q = scan(p, n, L_HEX, H_HEX);
3528                 if (q <= p)
3529                     failExpecting("digits for an IPv6 address", p);
3530                 if (at(q, n, '.')) {    // Beginning of IPv4 address
3531                     p--;
3532                     break;
3533                 }
3534                 if (q > p + 4)
3535                     fail("IPv6 hexadecimal digit sequence too long", p);
3536                 ipv6byteCount += 2;
3537                 p = q;
3538             }
3539 
3540             return p;
3541         }
3542 
3543     }
3544 
3545 }