Improve version selection

Use the list of versions that the server allows and among those choose
the highest version that is not higher than the client's version.

Note that this chosen version might be lower than the client's version,
but is used to improve interoperability.

Patch suggested by Dimitry Borisov refering to RFC 5246 appendix E.1.

1 files changed, 35 insertions, 3 deletions

diff --git a/lib/ssl/src/ssl_handshake.erl b/lib/ssl/src/ssl_handshake.erl
index 235d6efbb6..43b0c42f8d 100644
--- a/lib/ssl/src/ssl_handshake.erl
+++ b/lib/ssl/src/ssl_handshake.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2013-2015. All Rights Reserved.
+%% Copyright Ericsson AB 2013-2016. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -1258,8 +1258,40 @@ handle_server_hello_extensions(RecordCB, Random, CipherSuite, Compression,
     end.
 
 select_version(RecordCB, ClientVersion, Versions) ->
-    ServerVersion = RecordCB:highest_protocol_version(Versions),
-    RecordCB:lowest_protocol_version(ClientVersion, ServerVersion).
+    do_select_version(RecordCB, ClientVersion, Versions).
+
+do_select_version(_, ClientVersion, []) ->
+    ClientVersion;
+do_select_version(RecordCB, ClientVersion, [Version | Versions]) ->
+    case RecordCB:is_higher(Version, ClientVersion) of
+	true ->
+	    %% Version too high for client - keep looking
+	    do_select_version(RecordCB, ClientVersion, Versions);
+	false ->
+	    %% Version ok for client - look for a higher
+	    do_select_version(RecordCB, ClientVersion, Versions, Version)
+    end.
+%%
+do_select_version(_, _, [], GoodVersion) ->
+    GoodVersion;
+do_select_version(
+  RecordCB, ClientVersion, [Version | Versions], GoodVersion) ->
+    BetterVersion =
+	case RecordCB:is_higher(Version, ClientVersion) of
+	    true ->
+		%% Version too high for client
+		GoodVersion;
+	    false ->
+		%% Version ok for client
+		case RecordCB:is_higher(Version, GoodVersion) of
+		    true ->
+			%% Use higher version
+			Version;
+		    false ->
+			GoodVersion
+		end
+	end,
+    do_select_version(RecordCB, ClientVersion, Versions, BetterVersion).
 
 renegotiation_info(_, client, _, false) ->
     #renegotiation_info{renegotiated_connection = undefined};