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See the License for the * 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>Upgrade</l> HTTP request header. 019 * 020 * <p> 021 * Ask the client to upgrade to another protocol. 022 * 023 * <h5 class='figure'>Example</h5> 024 * <p class='bcode w800'> 025 * Upgrade: HTTP/2.0, HTTPS/1.3, IRC/6.9, RTA/x11, websocket 026 * </p> 027 * 028 * <h5 class='topic'>RFC2616 Specification</h5> 029 * 030 * The Upgrade general-header allows the client to specify what additional communication protocols it supports and 031 * would like to use if the server finds it appropriate to switch protocols. 032 * The server MUST use the Upgrade header field within a 101 (Switching Protocols) response to indicate which 033 * protocol(s) are being switched. 034 * 035 * <p class='bcode w800'> 036 * Upgrade = "Upgrade" ":" 1#product 037 * </p> 038 * 039 * <p> 040 * For example, 041 * <p class='bcode w800'> 042 * Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11 043 * </p> 044 * 045 * <p> 046 * The Upgrade header field is intended to provide a simple mechanism for transition from HTTP/1.1 to some other, 047 * incompatible protocol. 048 * It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP 049 * with a higher major version number, even though the current request has been made using HTTP/1.1. 050 * This eases the difficult transition between incompatible protocols by allowing the client to initiate a request in 051 * the more commonly supported protocol while indicating to the server that it would like to use a "better" protocol if 052 * available (where "better" is determined by the server, possibly according to the nature of the method and/or resource 053 * being requested). 054 * 055 * <p> 056 * The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer 057 * connection. 058 * Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. 059 * The capabilities and nature of the application-layer communication after the protocol change is entirely dependent 060 * upon the new protocol chosen, although the first action after changing the protocol MUST be a response to the initial 061 * HTTP request containing the Upgrade header field. 062 * 063 * <p> 064 * The Upgrade header field only applies to the immediate connection. 065 * Therefore, the upgrade keyword MUST be supplied within a Connection header field (section 14.10) whenever Upgrade is 066 * present in an HTTP/1.1 message. 067 * 068 * <p> 069 * The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. 070 * For that purpose, it is more appropriate to use a 301, 302, 303, or 305 redirection response. 071 * 072 * <p> 073 * This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as 074 * defined by the HTTP version rules of section 3.1 and future updates to this specification. 075 * Any token can be used as a protocol name; however, it will only be useful if both the client and server associate 076 * the name with the same protocol. 077 * 078 * <ul class='seealso'> 079 * <li class='extlink'>{@doc RFC2616} 080 * </ul> 081 */ 082@Header("Upgrade") 083public final class Upgrade extends HeaderStringArray { 084 085 /** 086 * Constructor. 087 * 088 * @param value The value for this header. 089 */ 090 public Upgrade(String[] value) { 091 super(value); 092 } 093 094 /** 095 * Returns a parsed <c>Upgrade</c> header. 096 * 097 * @param value The <c>Upgrade</c> header string. 098 * @return The parsed <c>Upgrade</c> header, or <jk>null</jk> if the string was null. 099 */ 100 public static Upgrade forString(String value) { 101 if (value == null) 102 return null; 103 return new Upgrade(value); 104 } 105 106 private Upgrade(String value) { 107 super(value); 108 } 109}