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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011// * specific language governing permissions and limitations under the License.                                              *
012// ***************************************************************************************************************************
013package org.apache.juneau.http;
014
015import org.apache.juneau.http.annotation.*;
016
017/**
018 * Represents a parsed <l>Expect</l> HTTP request header.
019 *
020 * <p>
021 * Indicates that particular server behaviors are required by the client.
022 *
023 * <h5 class='figure'>Example</h5>
024 * <p class='bcode w800'>
025 *    Expect: 100-continue
026 * </p>
027 *
028 * <h5 class='topic'>RFC2616 Specification</h5>
029 *
030 * The Expect request-header field is used to indicate that particular server behaviors are required by the client.
031 * <p class='bcode w800'>
032 *    Expect       =  "Expect" ":" 1#expectation
033 *    expectation  =  "100-continue" | expectation-extension
034 *    expectation-extension =  token [ "=" ( token | quoted-string )
035 *                             *expect-params ]
036 *    expect-params =  ";" token [ "=" ( token | quoted-string ) ]
037 * </p>
038 *
039 * <p>
040 * A server that does not understand or is unable to comply with any of the expectation values in the Expect field of a
041 * request MUST respond with appropriate error status.
042 * The server MUST respond with a 417 (Expectation Failed) status if any of the expectations cannot be met or, if there
043 * are other problems with the request, some other 4xx status.
044 *
045 * <p>
046 * This header field is defined with extensible syntax to allow for future extensions.
047 * If a server receives a request containing an Expect field that includes an expectation-extension that it does not
048 * support, it MUST respond with a 417 (Expectation Failed) status.
049 *
050 * <p>
051 * Comparison of expectation values is case-insensitive for unquoted tokens (including the 100-continue token), and is
052 * case-sensitive for quoted-string expectation-extensions.
053 *
054 * <p>
055 * The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST return a 417 (Expectation Failed) status if it
056 * receives a request with an expectation that it cannot meet.
057 * However, the Expect request-header itself is end-to-end; it MUST be forwarded if the request is forwarded.
058 *
059 * <p>
060 * Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect header.
061 *
062 * <p>
063 * See section 8.2.3 for the use of the 100 (continue) status.
064 *
065 * <ul class='seealso'>
066 *    <li class='extlink'>{@doc RFC2616}
067 * </ul>
068 */
069@Header("Expect")
070public final class Expect extends HeaderString {
071
072   /**
073    * Returns a parsed <c>Expect</c> header.
074    *
075    * @param value The <c>Expect</c> header string.
076    * @return The parsed <c>Expect</c> header, or <jk>null</jk> if the string was null.
077    */
078   public static Expect forString(String value) {
079      if (value == null)
080         return null;
081      return new Expect(value);
082   }
083
084   private Expect(String value) {
085      super(value);
086   }
087}