001// ***************************************************************************************************************************
002// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
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006// *                                                                                                                         *
007// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
008// *                                                                                                                         *
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012// ***************************************************************************************************************************
013package org.apache.juneau.http;
014
015/**
016 * Represents a parsed <l>Trailer</l> HTTP response header.
017 * 
018 * <p>
019 * The Trailer general field value indicates that the given set of header fields is present in the trailer of a message
020 * encoded with chunked transfer coding.
021 * 
022 * <h5 class='figure'>Example</h5>
023 * <p class='bcode'>
024 *    Trailer: Max-Forwards
025 * </p>
026 * 
027 * <h5 class='topic'>RFC2616 Specification</h5>
028 * 
029 * The Trailer general field value indicates that the given set of header fields is present in the trailer of a message
030 * encoded with chunked transfer-coding.
031 * 
032 * <p class='bcode'>
033 *    Trailer  = "Trailer" ":" 1#field-name
034 * </p>
035 * 
036 * <p>
037 * An HTTP/1.1 message SHOULD include a Trailer header field in a message using chunked transfer-coding with a non-empty
038 * trailer.
039 * Doing so allows the recipient to know which header fields to expect in the trailer.
040 * 
041 * <p>
042 * If no Trailer header field is present, the trailer SHOULD NOT include any header fields.
043 * See section 3.6.1 for restrictions on the use of trailer fields in a "chunked" transfer-coding.
044 * 
045 * <p>
046 * Message header fields listed in the Trailer header field MUST NOT include the following header fields:
047 * <ul>
048 *    <li>Transfer-Encoding
049 *    <li>Content-Length
050 *    <li>Trailer
051 * </ul>
052 * 
053 * <h5 class='section'>See Also:</h5>
054 * <ul class='doctree'>
055 *    <li class='extlink'><a class='doclink' href='https://www.w3.org/Protocols/rfc2616/rfc2616.html'>Hypertext Transfer Protocol -- HTTP/1.1</a>
056 * </ul>
057 */
058public final class Trailer extends HeaderString {
059
060   /**
061    * Returns a parsed <code>Trailer</code> header.
062    * 
063    * @param value The <code>Trailer</code> header string.
064    * @return The parsed <code>Trailer</code> header, or <jk>null</jk> if the string was null.
065    */
066   public static Trailer forString(String value) {
067      if (value == null)
068         return null;
069      return new Trailer(value);
070   }
071
072   private Trailer(String value) {
073      super(value);
074   }
075}