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012// ***************************************************************************************************************************
013package org.apache.juneau.http;
014
015import org.apache.juneau.http.annotation.*;
016
017/**
018 * Represents a parsed <l>Host</l> HTTP request header.
019 *
020 * <p>
021 * The domain name of the server (for virtual hosting), and the TCP port number on which the server is listening.
022 * The port number may be omitted if the port is the standard port for the service requested.
023 * Mandatory since HTTP/1.1.
024 *
025 * <h5 class='figure'>Example</h5>
026 * <p class='bcode w800'>
027 *    Host: en.wikipedia.org:8080
028 *    Host: en.wikipedia.org
029 * </p>
030 *
031 * <h5 class='topic'>RFC2616 Specification</h5>
032 *
033 * The Host request-header field specifies the Internet host and port number of the resource being requested, as
034 * obtained from the original URI given by the user or referring resource (generally an HTTP URL, as described in
035 * section 3.2.2).
036 * The Host field value MUST represent the naming authority of the origin server or gateway given by the original URL.
037 * This allows the origin server or gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL
038 * of a server for multiple host names on a single IP address.
039 *
040 * <p class='bcode w800'>
041 *    Host = "Host" ":" host [ ":" port ] ; Section 3.2.2
042 * </p>
043 *
044 * <p>
045 * A "host" without any trailing port information implies the default port for the service requested (e.g., "80" for an
046 * HTTP URL).
047 * For example, a request on the origin server for &lt;http://www.w3.org/pub/WWW/&gt; would properly include:
048 * <p class='bcode w800'>
049 *    GET /pub/WWW/ HTTP/1.1
050 *    Host: www.w3.org
051 * </p>
052 *
053 * <p>
054 * A client MUST include a Host header field in all HTTP/1.1 request messages.
055 * If the requested URI does not include an Internet host name for the service being requested, then the Host header
056 * field MUST be given with an empty value.
057 * An HTTP/1.1 proxy MUST ensure that any request message it forwards does contain an appropriate Host header field that
058 * identifies the service being requested by the proxy.
059 * All Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request) status code to any HTTP/1.1 request
060 * message which lacks a Host header field.
061 *
062 * <p>
063 * See sections 5.2 and 19.6.1.1 for other requirements relating to Host.
064 *
065 * <h5 class='section'>See Also:</h5>
066 * <ul class='doctree'>
067 *    <li class='extlink'>{@doc RFC2616}
068 * </ul>
069 */
070@Header("Host")
071public final class Host extends HeaderString {
072
073   /**
074    * Returns a parsed <code>Host</code> header.
075    *
076    * @param value The <code>Host</code> header string.
077    * @return The parsed <code>Host</code> header, or <jk>null</jk> if the string was null.
078    */
079   public static Host forString(String value) {
080      if (value == null)
081         return null;
082      return new Host(value);
083   }
084
085   private Host(String value) {
086      super(value);
087   }
088}