/*

 * Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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 *

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package java.net;

import java.io.IOException;

import java.io.InvalidObjectException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.io.Serializable;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.charset.CharsetDecoder;

import java.nio.charset.CharsetEncoder;

import java.nio.charset.CoderResult;

import java.nio.charset.CodingErrorAction;

import java.nio.charset.CharacterCodingException;

import java.text.Normalizer;

import sun.nio.cs.ThreadLocalCoders;

import java.lang.Character;             // for javadoc

import java.lang.NullPointerException;  // for javadoc

/**

 * Represents a Uniform Resource Identifier (URI) reference.

 *

 * <p> Aside from some minor deviations noted below, an instance of this

 * class represents a URI reference as defined by

 * <a href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform

 * Resource Identifiers (URI): Generic Syntax</i></a>, amended by <a

 * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for

 * Literal IPv6 Addresses in URLs</i></a>. The Literal IPv6 address format

 * also supports scope_ids. The syntax and usage of scope_ids is described

 * <a href="Inet6Address.html#scoped">here</a>.

 * This class provides constructors for creating URI instances from

 * their components or by parsing their string forms, methods for accessing the

 * various components of an instance, and methods for normalizing, resolving,

 * and relativizing URI instances.  Instances of this class are immutable.

 *

 *

 * <h3> URI syntax and components </h3>

 *

 * At the highest level a URI reference (hereinafter simply "URI") in string

 * form has the syntax

 *

 * <blockquote>

 * [<i>scheme</i><b>{@code :}</b>]<i>scheme-specific-part</i>[<b>{@code #}</b><i>fragment</i>]

 * </blockquote>

 *

 * where square brackets [...] delineate optional components and the characters

 * <b>{@code :}</b> and <b>{@code #}</b> stand for themselves.

 *

 * <p> An <i>absolute</i> URI specifies a scheme; a URI that is not absolute is

 * said to be <i>relative</i>.  URIs are also classified according to whether

 * they are <i>opaque</i> or <i>hierarchical</i>.

 *

 * <p> An <i>opaque</i> URI is an absolute URI whose scheme-specific part does

 * not begin with a slash character ({@code '/'}).  Opaque URIs are not

 * subject to further parsing.  Some examples of opaque URIs are:

 *

 * <blockquote><table cellpadding=0 cellspacing=0 summary="layout">

 * <tr><td>{@code mailto:java-net@java.sun.com}<td></tr>

 * <tr><td>{@code news:comp.lang.java}<td></tr>

 * <tr><td>{@code urn:isbn:096139210x}</td></tr>

 * </table></blockquote>

 *

 * <p> A <i>hierarchical</i> URI is either an absolute URI whose

 * scheme-specific part begins with a slash character, or a relative URI, that

 * is, a URI that does not specify a scheme.  Some examples of hierarchical

 * URIs are:

 *

 * <blockquote>

 * {@code http://java.sun.com/j2se/1.3/}<br>

 * {@code docs/guide/collections/designfaq.html#28}<br>

 * {@code ../../../demo/jfc/SwingSet2/src/SwingSet2.java}<br>

 * {@code file:///~/calendar}

 * </blockquote>

 *

 * <p> A hierarchical URI is subject to further parsing according to the syntax

 *

 * <blockquote>

 * [<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>]

 * </blockquote>

 *

 * where the characters <b>{@code :}</b>, <b>{@code /}</b>,

 * <b>{@code ?}</b>, and <b>{@code #}</b> stand for themselves.  The

 * scheme-specific part of a hierarchical URI consists of the characters

 * between the scheme and fragment components.

 *

 * <p> The authority component of a hierarchical URI is, if specified, either

 * <i>server-based</i> or <i>registry-based</i>.  A server-based authority

 * parses according to the familiar syntax

 *

 * <blockquote>

 * [<i>user-info</i><b>{@code @}</b>]<i>host</i>[<b>{@code :}</b><i>port</i>]

 * </blockquote>

 *

 * where the characters <b>{@code @}</b> and <b>{@code :}</b> stand for

 * themselves.  Nearly all URI schemes currently in use are server-based.  An

 * authority component that does not parse in this way is considered to be

 * registry-based.

 *

 * <p> The path component of a hierarchical URI is itself said to be absolute

 * if it begins with a slash character ({@code '/'}); otherwise it is

 * relative.  The path of a hierarchical URI that is either absolute or

 * specifies an authority is always absolute.

 *

 * <p> All told, then, a URI instance has the following nine components:

 *

 * <blockquote><table summary="Describes the components of a URI:scheme,scheme-specific-part,authority,user-info,host,port,path,query,fragment">

 * <tr><th><i>Component</i></th><th><i>Type</i></th></tr>

 * <tr><td>scheme</td><td>{@code String}</td></tr>

 * <tr><td>scheme-specific-part&nbsp;&nbsp;&nbsp;&nbsp;</td><td>{@code String}</td></tr>

 * <tr><td>authority</td><td>{@code String}</td></tr>

 * <tr><td>user-info</td><td>{@code String}</td></tr>

 * <tr><td>host</td><td>{@code String}</td></tr>

 * <tr><td>port</td><td>{@code int}</td></tr>

 * <tr><td>path</td><td>{@code String}</td></tr>

 * <tr><td>query</td><td>{@code String}</td></tr>

 * <tr><td>fragment</td><td>{@code String}</td></tr>

 * </table></blockquote>

 *

 * In a given instance any particular component is either <i>undefined</i> or

 * <i>defined</i> with a distinct value.  Undefined string components are

 * represented by {@code null}, while undefined integer components are

 * represented by {@code -1}.  A string component may be defined to have the

 * empty string as its value; this is not equivalent to that component being

 * undefined.

 *

 * <p> Whether a particular component is or is not defined in an instance

 * depends upon the type of the URI being represented.  An absolute URI has a

 * scheme component.  An opaque URI has a scheme, a scheme-specific part, and

 * possibly a fragment, but has no other components.  A hierarchical URI always

 * has a path (though it may be empty) and a scheme-specific-part (which at

 * least contains the path), and may have any of the other components.  If the

 * authority component is present and is server-based then the host component

 * will be defined and the user-information and port components may be defined.

 *

 *

 * <h4> Operations on URI instances </h4>

 *

 * The key operations supported by this class are those of

 * <i>normalization</i>, <i>resolution</i>, and <i>relativization</i>.

 *

 * <p> <i>Normalization</i> is the process of removing unnecessary {@code "."}

 * and {@code ".."} segments from the path component of a hierarchical URI.

 * Each {@code "."} segment is simply removed.  A {@code ".."} segment is

 * removed only if it is preceded by a non-{@code ".."} segment.

 * Normalization has no effect upon opaque URIs.

 *

 * <p> <i>Resolution</i> is the process of resolving one URI against another,

 * <i>base</i> URI.  The resulting URI is constructed from components of both

 * URIs in the manner specified by RFC 2396, taking components from the

 * base URI for those not specified in the original.  For hierarchical URIs,

 * the path of the original is resolved against the path of the base and then

 * normalized.  The result, for example, of resolving

 *

 * <blockquote>

 * {@code docs/guide/collections/designfaq.html#28}

 *             

 *     (1)

 * </blockquote>

 *

 * against the base URI {@code http://java.sun.com/j2se/1.3/} is the result

 * URI

 *

 * <blockquote>

 * {@code http://docs.oracle.com/javase/1.3/docs/guide/collections/designfaq.html#28}

 * </blockquote>

 *

 * Resolving the relative URI

 *

 * <blockquote>

 * {@code ../../../demo/jfc/SwingSet2/src/SwingSet2.java}    (2)

 * </blockquote>

 *

 * against this result yields, in turn,

 *

 * <blockquote>

 * {@code http://java.sun.com/j2se/1.3/demo/jfc/SwingSet2/src/SwingSet2.java}

 * </blockquote>

 *

 * Resolution of both absolute and relative URIs, and of both absolute and

 * relative paths in the case of hierarchical URIs, is supported.  Resolving

 * the URI {@code file:///~calendar} against any other URI simply yields the

 * original URI, since it is absolute.  Resolving the relative URI (2) above

 * against the relative base URI (1) yields the normalized, but still relative,

 * URI

 *

 * <blockquote>

 * {@code demo/jfc/SwingSet2/src/SwingSet2.java}

 * </blockquote>

 *

 * <p> <i>Relativization</i>, finally, is the inverse of resolution: For any

 * two normalized URIs <i>u</i> and&nbsp;<i>v</i>,

 *

 * <blockquote>

 *   <i>u</i>{@code .relativize(}<i>u</i>{@code .resolve(}<i>v</i>{@code )).equals(}<i>v</i>{@code )}&nbsp;&nbsp;and<br>

 *   <i>u</i>{@code .resolve(}<i>u</i>{@code .relativize(}<i>v</i>{@code )).equals(}<i>v</i>{@code )}&nbsp;&nbsp;.<br>

 * </blockquote>

 *

 * This operation is often useful when constructing a document containing URIs

 * that must be made relative to the base URI of the document wherever

 * possible.  For example, relativizing the URI

 *

 * <blockquote>

 * {@code http://docs.oracle.com/javase/1.3/docs/guide/index.html}

 * </blockquote>

 *

 * against the base URI

 *

 * <blockquote>

 * {@code http://java.sun.com/j2se/1.3}

 * </blockquote>

 *

 * yields the relative URI {@code docs/guide/index.html}.

 *

 *

 * <h4> Character categories </h4>

 *

 * RFC 2396 specifies precisely which characters are permitted in the

 * various components of a URI reference.  The following categories, most of

 * which are taken from that specification, are used below to describe these

 * constraints:

 *

 * <blockquote><table cellspacing=2 summary="Describes categories alpha,digit,alphanum,unreserved,punct,reserved,escaped,and other">

 *   <tr><th valign=top><i>alpha</i></th>

 *       <td>The US-ASCII alphabetic characters,

 *        {@code 'A'} through {@code 'Z'}

 *        and {@code 'a'}&nbsp;through&nbsp;{@code 'z'}</td></tr>

 *   <tr><th valign=top><i>digit</i></th>

 *       <td>The US-ASCII decimal digit characters,

 *       {@code '0'}&nbsp;through&nbsp;{@code '9'}</td></tr>

 *   <tr><th valign=top><i>alphanum</i></th>

 *       <td>All <i>alpha</i> and <i>digit</i> characters</td></tr>

 *   <tr><th valign=top><i>unreserved</i>&nbsp;&nbsp;&nbsp;&nbsp;</th>

 *       <td>All <i>alphanum</i> characters together with those in the string

 *        {@code "_-!.~'()*"}</td></tr>

 *   <tr><th valign=top><i>punct</i></th>

 *       <td>The characters in the string {@code ",;:$&+="}</td></tr>

 *   <tr><th valign=top><i>reserved</i></th>

 *       <td>All <i>punct</i> characters together with those in the string

 *        {@code "?/[]@"}</td></tr>

 *   <tr><th valign=top><i>escaped</i></th>

 *       <td>Escaped octets, that is, triplets consisting of the percent

 *           character ({@code '%'}) followed by two hexadecimal digits

 *           ({@code '0'}-{@code '9'}, {@code 'A'}-{@code 'F'}, and

 *           {@code 'a'}-{@code 'f'})</td></tr>

 *   <tr><th valign=top><i>other</i></th>

 *       <td>The Unicode characters that are not in the US-ASCII character set,

 *           are not control characters (according to the {@link

 *           java.lang.Character#isISOControl(char) Character.isISOControl}

 *           method), and are not space characters (according to the {@link

 *           java.lang.Character#isSpaceChar(char) Character.isSpaceChar}

 *           method)&nbsp;&nbsp;<i>(<b>Deviation from RFC 2396</b>, which is

 *           limited to US-ASCII)</i></td></tr>

 * </table></blockquote>

 *

 * <p><a name="legal-chars"></a> The set of all legal URI characters consists of

 * the <i>unreserved</i>, <i>reserved</i>, <i>escaped</i>, and <i>other</i>

 * characters.

 *

 *

 * <h4> Escaped octets, quotation, encoding, and decoding </h4>

 *

 * RFC 2396 allows escaped octets to appear in the user-info, path, query, and

 * fragment components.  Escaping serves two purposes in URIs:

 *

 * <ul>

 *

 *   <li><p> To <i>encode</i> non-US-ASCII characters when a URI is required to

 *   conform strictly to RFC&nbsp;2396 by not containing any <i>other</i>

 *   characters.  </p></li>

 *

 *   <li><p> To <i>quote</i> characters that are otherwise illegal in a

 *   component.  The user-info, path, query, and fragment components differ

 *   slightly in terms of which characters are considered legal and illegal.

 *   </p></li>

 *

 * </ul>

 *

 * These purposes are served in this class by three related operations:

 *

 * <ul>

 *

 *   <li><p><a name="encode"></a> A character is <i>encoded</i> by replacing it

 *   with the sequence of escaped octets that represent that character in the

 *   UTF-8 character set.  The Euro currency symbol ({@code '\u005Cu20AC'}),

 *   for example, is encoded as {@code "%E2%82%AC"}.  <i>(<b>Deviation from

 *   RFC&nbsp;2396</b>, which does not specify any particular character

 *   set.)</i> </p></li>

 *

 *   <li><p><a name="quote"></a> An illegal character is <i>quoted</i> simply by

 *   encoding it.  The space character, for example, is quoted by replacing it

 *   with {@code "%20"}.  UTF-8 contains US-ASCII, hence for US-ASCII

 *   characters this transformation has exactly the effect required by

 *   RFC&nbsp;2396. </p></li>

 *

 *   <li><p><a name="decode"></a>

 *   A sequence of escaped octets is <i>decoded</i> by

 *   replacing it with the sequence of characters that it represents in the

 *   UTF-8 character set.  UTF-8 contains US-ASCII, hence decoding has the

 *   effect of de-quoting any quoted US-ASCII characters as well as that of

 *   decoding any encoded non-US-ASCII characters.  If a <a

 *   href="../nio/charset/CharsetDecoder.html#ce">decoding error</a> occurs

 *   when decoding the escaped octets then the erroneous octets are replaced by

 *   {@code '\u005CuFFFD'}, the Unicode replacement character.  </p></li>

 *

 * </ul>

 *

 * These operations are exposed in the constructors and methods of this class

 * as follows:

 *

 * <ul>

 *

 *   <li><p> The {@linkplain #URI(java.lang.String) single-argument

 *   constructor} requires any illegal characters in its argument to be

 *   quoted and preserves any escaped octets and <i>other</i> characters that

 *   are present.  </p></li>

 *

 *   <li><p> The {@linkplain

 *   #URI(java.lang.String,java.lang.String,java.lang.String,int,java.lang.String,java.lang.String,java.lang.String)

 *   multi-argument constructors} quote illegal characters as

 *   required by the components in which they appear.  The percent character

 *   ({@code '%'}) is always quoted by these constructors.  Any <i>other</i>

 *   characters are preserved.  </p></li>

 *

 *   <li><p> The {@link #getRawUserInfo() getRawUserInfo}, {@link #getRawPath()

 *   getRawPath}, {@link #getRawQuery() getRawQuery}, {@link #getRawFragment()

 *   getRawFragment}, {@link #getRawAuthority() getRawAuthority}, and {@link

 *   #getRawSchemeSpecificPart() getRawSchemeSpecificPart} methods return the

 *   values of their corresponding components in raw form, without interpreting

 *   any escaped octets.  The strings returned by these methods may contain

 *   both escaped octets and <i>other</i> characters, and will not contain any

 *   illegal characters.  </p></li>

 *

 *   <li><p> The {@link #getUserInfo() getUserInfo}, {@link #getPath()

 *   getPath}, {@link #getQuery() getQuery}, {@link #getFragment()

 *   getFragment}, {@link #getAuthority() getAuthority}, and {@link

 *   #getSchemeSpecificPart() getSchemeSpecificPart} methods decode any escaped

 *   octets in their corresponding components.  The strings returned by these

 *   methods may contain both <i>other</i> characters and illegal characters,

 *   and will not contain any escaped octets.  </p></li>

 *

 *   <li><p> The {@link #toString() toString} method returns a URI string with

 *   all necessary quotation but which may contain <i>other</i> characters.

 *   </p></li>

 *

 *   <li><p> The {@link #toASCIIString() toASCIIString} method returns a fully

 *   quoted and encoded URI string that does not contain any <i>other</i>

 *   characters.  </p></li>

 *

 * </ul>

 *

 *

 * <h4> Identities </h4>

 *

 * For any URI <i>u</i>, it is always the case that

 *

 * <blockquote>

 * {@code new URI(}<i>u</i>{@code .toString()).equals(}<i>u</i>{@code )}&nbsp;.

 * </blockquote>

 *

 * For any URI <i>u</i> that does not contain redundant syntax such as two

 * slashes before an empty authority (as in {@code file:///tmp/} ) or a

 * colon following a host name but no port (as in

 * {@code http://java.sun.com:} ), and that does not encode characters

 * except those that must be quoted, the following identities also hold:

 * <pre>

 *     new URI(<i>u</i>.getScheme(),

 *             <i>u</i>.getSchemeSpecificPart(),

 *             <i>u</i>.getFragment())

 *     .equals(<i>u</i>)</pre>

 * in all cases,

 * <pre>

 *     new URI(<i>u</i>.getScheme(),

 *             <i>u</i>.getAuthority(),

 *             <i>u</i>.getPath(), <i>u</i>.getQuery(),

 *             <i>u</i>.getFragment())

 *     .equals(<i>u</i>)</pre>

 * if <i>u</i> is hierarchical, and

 * <pre>

 *     new URI(<i>u</i>.getScheme(),

 *             <i>u</i>.getUserInfo(), <i>u</i>.getHost(), <i>u</i>.getPort(),

 *             <i>u</i>.getPath(), <i>u</i>.getQuery(),

 *             <i>u</i>.getFragment())

 *     .equals(<i>u</i>)</pre>

 * if <i>u</i> is hierarchical and has either no authority or a server-based

 * authority.

 *

 *

 * <h4> URIs, URLs, and URNs </h4>

 *

 * A URI is a uniform resource <i>identifier</i> while a URL is a uniform

 * resource <i>locator</i>.  Hence every URL is a URI, abstractly speaking, but

 * not every URI is a URL.  This is because there is another subcategory of

 * URIs, uniform resource <i>names</i> (URNs), which name resources but do not

 * specify how to locate them.  The {@code mailto}, {@code news}, and

 * {@code isbn} URIs shown above are examples of URNs.

 *

 * <p> The conceptual distinction between URIs and URLs is reflected in the

 * differences between this class and the {@link URL} class.

 *

 * <p> An instance of this class represents a URI reference in the syntactic

 * sense defined by RFC 2396.  A URI may be either absolute or relative.

 * A URI string is parsed according to the generic syntax without regard to the

 * scheme, if any, that it specifies.  No lookup of the host, if any, is

 * performed, and no scheme-dependent stream handler is constructed.  Equality,

 * hashing, and comparison are defined strictly in terms of the character

 * content of the instance.  In other words, a URI instance is little more than

 * a structured string that supports the syntactic, scheme-independent

 * operations of comparison, normalization, resolution, and relativization.

 *

 * <p> An instance of the {@link URL} class, by contrast, represents the

 * syntactic components of a URL together with some of the information required

 * to access the resource that it describes.  A URL must be absolute, that is,

 * it must always specify a scheme.  A URL string is parsed according to its

 * scheme.  A stream handler is always established for a URL, and in fact it is

 * impossible to create a URL instance for a scheme for which no handler is

 * available.  Equality and hashing depend upon both the scheme and the

 * Internet address of the host, if any; comparison is not defined.  In other

 * words, a URL is a structured string that supports the syntactic operation of

 * resolution as well as the network I/O operations of looking up the host and

 * opening a connection to the specified resource.

 *

 *

 * @author Mark Reinhold

 * @since 1.4

 *

 * @see <a href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC&nbsp;2279: UTF-8, a

 * transformation format of ISO 10646</i></a>, <br><a

 * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IPv6 Addressing

 * Architecture</i></a>, <br><a

 * href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform

 * Resource Identifiers (URI): Generic Syntax</i></a>, <br><a

 * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for

 * Literal IPv6 Addresses in URLs</i></a>, <br><a

 * href="URISyntaxException.html">URISyntaxException</a>

 */

public final class URI

    implements Comparable<URI>, Serializable

{

    // Note: Comments containing the word "ASSERT" indicate places where a

    // throw of an InternalError should be replaced by an appropriate assertion

    // statement once asserts are enabled in the build.

    static final long serialVersionUID = -6052424284110960213L;

    // -- Properties and components of this instance --

    // Components of all URIs: [<scheme>:]<scheme-specific-part>[#<fragment>]

    private transient String scheme;            // null ==> relative URI

    private transient String fragment;

    // Hierarchical URI components: [//<authority>]<path>[?<query>]

    private transient String authority;         // Registry or server

    // Server-based authority: [<userInfo>@]<host>[:<port>]

    private transient String userInfo;

    private transient String host;              // null ==> registry-based

    private transient int port = -1;            // -1 ==> undefined

    // Remaining components of hierarchical URIs

    private transient String path;              // null ==> opaque

    private transient String query;

    // The remaining fields may be computed on demand

    /**

     * The string form of this URI.

     *

     * @serial

     */

    private volatile String string;             // The only serializable field

    // -- Constructors and factories --