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007// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
008// *                                                                                                                         *
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012// ***************************************************************************************************************************
013package org.apache.juneau.http.header;
014
015import java.util.function.*;
016
017import org.apache.juneau.http.annotation.*;
018
019/**
020 * Represents a parsed <l>Warning</l> HTTP request/response header.
021 *
022 * <p>
023 * A general warning about possible problems with the entity body.
024 *
025 * <h5 class='figure'>Example</h5>
026 * <p class='bcode w800'>
027 *    Warning: 199 Miscellaneous warning
028 * </p>
029 *
030 * <h5 class='topic'>RFC2616 Specification</h5>
031 *
032 * The Warning general-header field is used to carry additional information about the status or transformation of a
033 * message which might not be reflected in the message.
034 * This information is typically used to warn about a possible lack of semantic transparency from caching operations
035 * or transformations applied to the entity body of the message.
036 *
037 * <p>
038 * Warning headers are sent with responses using:
039 * <p class='bcode w800'>
040 *    Warning    = "Warning" ":" 1#warning-value
041 *    warning-value = warn-code SP warn-agent SP warn-text
042 *                                          [SP warn-date]
043 *    warn-code  = 3DIGIT
044 *    warn-agent = ( host [ ":" port ] ) | pseudonym
045 *                    ; the name or pseudonym of the server adding
046 *                    ; the Warning header, for use in debugging
047 *    warn-text  = quoted-string
048 *    warn-date  = &lt;"&gt; HTTP-date &lt;"&gt;
049 * </p>
050 *
051 * <p>
052 * A response MAY carry more than one Warning header.
053 *
054 * <p>
055 * The warn-text SHOULD be in a natural language and character set that is most likely to be intelligible to the human
056 * user receiving the response.
057 * This decision MAY be based on any available knowledge, such as the location of the cache or user, the
058 * Accept-Language field in a request, the Content-Language field in a response, etc.
059 * The default language is English and the default character set is ISO-8859-1.
060 *
061 * <p>
062 * If a character set other than ISO-8859-1 is used, it MUST be encoded in the warn-text using the method described in
063 * RFC 2047.
064 *
065 * <p>
066 * Warning headers can in general be applied to any message, however some specific warn-codes are specific to caches
067 * and can only be applied to response messages.
068 * New Warning headers SHOULD be added after any existing Warning headers.
069 * A cache MUST NOT delete any Warning header that it received with a message.
070 * However, if a cache successfully validates a cache entry, it SHOULD remove any Warning headers previously attached
071 * to that entry except as specified for specific Warning codes.
072 * It MUST then add any Warning headers received in the validating response.
073 * In other words, Warning headers are those that would be attached to the most recent relevant response.
074 *
075 * <p>
076 * When multiple Warning headers are attached to a response, the user agent ought to inform the user of as many of them
077 * as possible, in the order that they appear in the response.
078 * If it is not possible to inform the user of all of the warnings, the user agent SHOULD follow these heuristics:
079 * <ul>
080 *    <li>Warnings that appear early in the response take priority over those appearing later in the response.
081 *    <li>Warnings in the user's preferred character set take priority over warnings in other character sets but with
082 * identical warn-codes and warn-agents.
083 * </ul>
084 *
085 * <p>
086 * Systems that generate multiple Warning headers SHOULD order them with this user agent behavior in mind.
087 *
088 * <p>
089 * Requirements for the behavior of caches with respect to Warnings are stated in section 13.1.2.
090 *
091 * <p>
092 * This is a list of the currently-defined warn-codes, each with a recommended warn-text in English, and a description
093 * of its meaning.
094 * <ul>
095 *    <li>110 Response is stale MUST be included whenever the returned response is stale.
096 *    <li>111 Revalidation failed MUST be included if a cache returns a stale response because an attempt to revalidate
097 *       the response failed, due to an inability to reach the server.
098 *    <li>112 Disconnected operation SHOULD be included if the cache is intentionally disconnected from the rest of the
099 *       network for a period of time.
100 *    <li>113 Heuristic expiration MUST be included if the cache heuristically chose a freshness lifetime greater than
101 *       24 hours and the response's age is greater than 24 hours.
102 *    <li>199 Miscellaneous warning The warning text MAY include arbitrary information to be presented to a human user,
103 *       or logged. A system receiving this warning MUST NOT take any automated action, besides presenting the warning
104 *       to the user.
105 *    <li>214 Transformation applied MUST be added by an intermediate cache or proxy if it applies any transformation
106 *       changing the content-coding (as specified in the Content-Encoding header) or media-type (as specified in the
107 *       Content-Type header) of the response, or the entity-body of the response, unless this Warning code already
108 *       appears in the response.
109 *    <li>299 Miscellaneous persistent warning The warning text MAY include arbitrary information to be presented to a
110 *       human user, or logged. A system receiving this warning MUST NOT take any automated action.
111 * </ul>
112 *
113 * <p>
114 * If an implementation sends a message with one or more Warning headers whose version is HTTP/1.0 or lower, then the
115 * sender MUST include in each warning-value a warn-date that matches the date in the response.
116 *
117 * <p>
118 * If an implementation receives a message with a warning-value that includes a warn-date, and that warn-date is
119 * different from the Date value in the response, then that warning-value MUST be deleted from the message before
120 * storing, forwarding, or using it.
121 * (This prevents bad consequences of naive caching of Warning header fields.)
122 * If all of the warning-values are deleted for this reason, the Warning header MUST be deleted as well.
123 *
124 * <ul class='seealso'>
125 *    <li class='extlink'>{@doc ExtRFC2616}
126 * </ul>
127 */
128@Header("Warning")
129public class Warning extends BasicStringHeader {
130
131   private static final long serialVersionUID = 1L;
132
133   /**
134    * Convenience creator.
135    *
136    * @param value
137    *    The header value.
138    *    <br>Can be any of the following:
139    *    <ul>
140    *       <li>{@link String}
141    *       <li>Anything else - Converted to <c>String</c> then parsed.
142    *    </ul>
143    * @return A new {@link Warning} object.
144    */
145   public static Warning of(Object value) {
146      if (value == null)
147         return null;
148      return new Warning(value);
149   }
150
151   /**
152    * Convenience creator using supplier.
153    *
154    * <p>
155    * Header value is re-evaluated on each call to {@link #getValue()}.
156    *
157    * @param value
158    *    The header value supplier.
159    *    <br>Can be any of the following:
160    *    <ul>
161    *       <li>{@link String}
162    *       <li>Anything else - Converted to <c>String</c> then parsed.
163    *    </ul>
164    * @return A new {@link Warning} object.
165    */
166   public static Warning of(Supplier<?> value) {
167      if (value == null)
168         return null;
169      return new Warning(value);
170   }
171
172   /**
173    * Constructor.
174    *
175    * @param value
176    *    The header value.
177    *    <br>Can be any of the following:
178    *    <ul>
179    *       <li>{@link String}
180    *       <li>Anything else - Converted to <c>String</c> then parsed.
181    *       <li>A {@link Supplier} of anything on this list.
182    *    </ul>
183    */
184   public Warning(Object value) {
185      super("Warning", value);
186   }
187
188   /**
189    * Constructor
190    *
191    * @param value
192    *    The header value.
193    */
194   public Warning(String value) {
195      this((Object)value);
196   }
197}