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012// ***************************************************************************************************************************
013package org.apache.juneau.http.header;
014
015import java.util.*;
016import java.util.function.*;
017
018import org.apache.juneau.http.annotation.*;
019
020/**
021 * Represents a parsed <l>Upgrade</l> HTTP request header.
022 *
023 * <p>
024 * Ask the client to upgrade to another protocol.
025 *
026 * <h5 class='figure'>Example</h5>
027 * <p class='bcode w800'>
028 *    Upgrade: HTTP/2.0, HTTPS/1.3, IRC/6.9, RTA/x11, websocket
029 * </p>
030 *
031 * <h5 class='topic'>RFC2616 Specification</h5>
032 *
033 * The Upgrade general-header allows the client to specify what additional communication protocols it supports and
034 * would like to use if the server finds it appropriate to switch protocols.
035 * The server MUST use the Upgrade header field within a 101 (Switching Protocols) response to indicate which
036 * protocol(s) are being switched.
037 *
038 * <p class='bcode w800'>
039 *    Upgrade        = "Upgrade" ":" 1#product
040 * </p>
041 *
042 * <p>
043 * For example,
044 * <p class='bcode w800'>
045 *    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
046 * </p>
047 *
048 * <p>
049 * The Upgrade header field is intended to provide a simple mechanism for transition from HTTP/1.1 to some other,
050 * incompatible protocol.
051 * It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP
052 * with a higher major version number, even though the current request has been made using HTTP/1.1.
053 * This eases the difficult transition between incompatible protocols by allowing the client to initiate a request in
054 * the more commonly supported protocol while indicating to the server that it would like to use a "better" protocol if
055 * available (where "better" is determined by the server, possibly according to the nature of the method and/or resource
056 * being requested).
057 *
058 * <p>
059 * The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer
060 * connection.
061 * Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional.
062 * The capabilities and nature of the application-layer communication after the protocol change is entirely dependent
063 * upon the new protocol chosen, although the first action after changing the protocol MUST be a response to the initial
064 * HTTP request containing the Upgrade header field.
065 *
066 * <p>
067 * The Upgrade header field only applies to the immediate connection.
068 * Therefore, the upgrade keyword MUST be supplied within a Connection header field (section 14.10) whenever Upgrade is
069 * present in an HTTP/1.1 message.
070 *
071 * <p>
072 * The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection.
073 * For that purpose, it is more appropriate to use a 301, 302, 303, or 305 redirection response.
074 *
075 * <p>
076 * This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as
077 * defined by the HTTP version rules of section 3.1 and future updates to this specification.
078 * Any token can be used as a protocol name; however, it will only be useful if both the client and server associate
079 * the name with the same protocol.
080 *
081 * <ul class='seealso'>
082 *    <li class='extlink'>{@doc ExtRFC2616}
083 * </ul>
084 */
085@Header("Upgrade")
086public class Upgrade extends BasicCsvArrayHeader {
087
088   private static final long serialVersionUID = 1L;
089
090   /**
091    * Convenience creator.
092    *
093    * @param value
094    *    The header value.
095    *    <br>Can be any of the following:
096    *    <ul>
097    *       <li><c>String</c> - A comma-delimited string.
098    *       <li><c>String[]</c> - A pre-parsed value.
099    *       <li>Any other array type - Converted to <c>String[]</c>.
100    *       <li>Any {@link Collection} - Converted to <c>String[]</c>.
101    *       <li>Anything else - Converted to <c>String</c>.
102    *    </ul>
103    * @return The parsed <c>Upgrade</c> header, or <jk>null</jk> if the value was null.
104    */
105   public static Upgrade of(Object value) {
106      if (value == null)
107         return null;
108      return new Upgrade(value);
109   }
110
111   /**
112    * Convenience creator using supplier.
113    *
114    * <p>
115    * Header value is re-evaluated on each call to {@link #getValue()}.
116    *
117    * @param value
118    *    The header value supplier.
119    *    <br>Can be any of the following:
120    *    <ul>
121    *       <li><c>String</c> - A comma-delimited string.
122    *       <li><c>String[]</c> - A pre-parsed value.
123    *       <li>Any other array type - Converted to <c>String[]</c>.
124    *       <li>Any {@link Collection} - Converted to <c>String[]</c>.
125    *       <li>Anything else - Converted to <c>String</c>.
126    *    </ul>
127    * @return The parsed <c>Upgrade</c> header, or <jk>null</jk> if the value was null.
128    */
129   public static Upgrade of(Supplier<?> value) {
130      if (value == null)
131         return null;
132      return new Upgrade(value);
133   }
134
135   /**
136    * Constructor.
137    *
138    * @param value
139    *    The header value.
140    *    <br>Can be any of the following:
141    *    <ul>
142    *       <li><c>String</c> - A comma-delimited string.
143    *       <li><c>String[]</c> - A pre-parsed value.
144    *       <li>Any other array type - Converted to <c>String[]</c>.
145    *       <li>Any {@link Collection} - Converted to <c>String[]</c>.
146    *       <li>Anything else - Converted to <c>String</c>.
147    *       <li>A {@link Supplier} of anything on this list.
148    *    </ul>
149    */
150   public Upgrade(Object value) {
151      super("Upgrade", value);
152   }
153
154   /**
155    * Constructor
156    *
157    * @param value
158    *    The header value.
159    */
160   public Upgrade(String value) {
161      this((Object)value);
162   }
163}