NSS: move the first protocol to the end of the ALPN extension.

net/third_party/nss/ssl/ssl.h

 /*
  * This file contains prototypes for the public SSL functions.
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef __ssl_h_
 #define __ssl_h_
 
@@ skipping 190 matching lines @@
  * SSL_SetNextProtoCallback. It also causes a client to advertise NPN and
  * installs a default callback function which selects the first supported
  * protocol in server-preference order. If no matching protocol is found it
  * selects the first supported protocol.
  *
  * Using this function also allows the client to transparently support ALPN.
  * The same set of protocols will be advertised via ALPN and, if the server
  * uses ALPN to select a protocol, SSL_GetNextProto will return
  * SSL_NEXT_PROTO_SELECTED as the state.
  *
+ * Since NPN uses the first protocol as the fallback protocol, when sending an
+ * ALPN extension, the first protocol is moved to the end of the list. This
+ * indicates that the fallback protocol is the least preferred. The other
+ * protocols should be in preference order.
+ *
  * The supported protocols are specified in |data| in wire-format (8-bit
  * length-prefixed). For example: "\010http/1.1\006spdy/2". */
 SSL_IMPORT SECStatus SSL_SetNextProtoNego(PRFileDesc *fd,
                                           const unsigned char *data,
                                           unsigned int length);
 
 typedef enum SSLNextProtoState { 
   SSL_NEXT_PROTO_NO_SUPPORT = 0, /* No peer support                */
   SSL_NEXT_PROTO_NEGOTIATED = 1, /* Mutual agreement               */
   SSL_NEXT_PROTO_NO_OVERLAP = 2, /* No protocol overlap found      */
@@ skipping 875 matching lines @@
  * should continue using the connection. If the application passes a non-zero
  * value for second argument (error), or if SSL_AuthCertificateComplete returns
  * anything other than SECSuccess, then the application should close the
  * connection.
  */
 SSL_IMPORT SECStatus SSL_AuthCertificateComplete(PRFileDesc *fd,
                                                  PRErrorCode error);
 SEC_END_PROTOS
 
 #endif /* __ssl_h_ */