Add documentation to ALPN functionality in dart:io

sdk/lib/io/secure_server_socket.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 /**
  * The [SecureServerSocket] is a server socket, providing a stream of high-level
  * [Socket]s.
  *
@@ skipping 35 matching lines @@
    * [address] must be given as a numeric address, not a host name.
    *
    * To request or require that clients authenticate by providing an SSL (TLS)
    * client certificate, set the optional parameter [requestClientCertificate]
    * or [requireClientCertificate] to true.  Requiring a certificate implies
    * requesting a certificate, so setting both is redundant.
    * To check whether a client certificate was received, check
    * SecureSocket.peerCertificate after connecting.  If no certificate
    * was received, the result will be null.
    *
+   * [supportedProtocols] is an optional list of protocols (in decreasing
+   * order of preference) to use during the ALPN protocol negogiation with
+   * clients.  Example values are "http/1.1" or "h2".  The selected protocol
+   * can be obtained via [SecureSocket.selectedProtocol].
+   *
    * The optional argument [shared] specifies whether additional
    * SecureServerSocket objects can bind to the same combination of `address`,
    * `port` and `v6Only`.  If `shared` is `true` and more `SecureServerSocket`s
    * from this isolate or other isolates are bound to the port, then the
    * incoming connections will be distributed among all the bound
    * `SecureServerSocket`s. Connections can be distributed over multiple
    * isolates this way.
    */
   static Future<SecureServerSocket> bind(
       address, int port, SecurityContext context,
@@ skipping 104 matching lines @@
    *
    * [address] must be given as a numeric address, not a host name.
    *
    * To request or require that clients authenticate by providing an SSL (TLS)
    * client certificate, set the optional parameters requestClientCertificate or
    * requireClientCertificate to true.  Require implies request, so one doesn't
    * need to specify both.  To check whether a client certificate was received,
    * check SecureSocket.peerCertificate after connecting.  If no certificate
    * was received, the result will be null.
    *
+   * [supportedProtocols] is an optional list of protocols (in decreasing
+   * order of preference) to use during the ALPN protocol negogiation with
+   * clients.  Example values are "http/1.1" or "h2".  The selected protocol
+   * can be obtained via [RawSecureSocket.selectedProtocol].
+   *
    * The optional argument [shared] specifies whether additional
    * RawSecureServerSocket objects can bind to the same combination of
    * `address`, `port` and `v6Only`.  If `shared` is `true` and more
    * `RawSecureServerSocket`s from this isolate or other isolates are bound to
    * the port, then the incoming connections will be distributed among all the
    * bound `RawSecureServerSocket`s. Connections can be distributed over
    * multiple isolates this way.
    */
   static Future<RawSecureServerSocket> bind(
       address, int port, SecurityContext context,
@@ skipping 82 matching lines @@
           onError: _controller.addError, onDone: _controller.close);
     } else {
       close();
     }
   }
 
   void set _owner(owner) {
     (_socket as dynamic)._owner = owner;
   }
 }