Support SASL PLAIN by xmpp_stream_out

Also, SASL mechanisms chaining is now supported:
if several mechanisms are supported and authentication
fails, next mechanism in the list is picked, until the
list is exhausted. In the case of a failure, the latest
SASL failure reason is returned within handle_auth_failure/3
callback.

src/xmpp_stream_out.erl

@@ -91,6 +91,7 @@
 -callback tls_verify(state()) -> boolean().
 -callback tls_enabled(state()) -> boolean().
 -callback resolve(string(), state()) -> [host_port()].
+-callback sasl_mechanisms(state()) -> [binary()].
 -callback dns_timeout(state()) -> timeout().
 -callback dns_retries(state()) -> non_neg_integer().
 -callback default_port(state()) -> inet:port_number().
@@ -124,6 +125,7 @@
 		     tls_verify/1,
 		     tls_enabled/1,
 		     resolve/2,
+		     sasl_mechanisms/1,
 		     dns_timeout/1,
 		     dns_retries/1,
 		     default_port/1,
@@ -260,6 +262,7 @@ init([Mod, From, To, Opts]) ->
 	      server => From,
 	      user => <<"">>,
 	      resource => <<"">>,
+	      password => <<"">>,
 	      lang => <<"">>,
 	      remote_server => To,
 	      xmlns => ?NS_SERVER,
@@ -317,16 +320,8 @@ handle_cast(connect, #{remote_server := RemoteServer,
 	      end
       end);
 handle_cast(connect, #{stream_state := disconnected} = State) ->
-    State1 = State#{stream_id => new_id(),
+    State1 = reset_state(State),
-		    stream_encrypted => false,
+    handle_cast(connect, State1);
-		    stream_verified => false,
-		    stream_authenticated => false,
-		    stream_restarted => false,
-		    stream_state => connecting},
-    State2 = maps:remove(ip, State1),
-    State3 = maps:remove(socket, State2),
-    State4 = maps:remove(socket_monitor, State3),
-    handle_cast(connect, State4);
 handle_cast(connect, State) ->
     %% Ignoring connection attempts in other states
     noreply(State);
@@ -559,8 +554,7 @@ process_features(StreamFeatures,
     catch _:{?MODULE, undef} -> process_bind(StreamFeatures, State)
     end;
 process_features(StreamFeatures,
-		 #{stream_encrypted := Encrypted,
+		 #{stream_encrypted := Encrypted, lang := Lang} = State) ->
-		   lang := Lang, xmlns := NS} = State) ->
     State1 = try callback(handle_unauthenticated_features, StreamFeatures, State)
 	     catch _:{?MODULE, undef} -> State
 	     end,
@@ -573,39 +567,21 @@ process_features(StreamFeatures,
 		false when TLSRequired and not Encrypted ->
 		    Txt = <<"Use of STARTTLS required">>,
 		    send_pkt(State1, xmpp:serr_policy_violation(Txt, Lang));
-		false when NS == ?NS_SERVER andalso not Encrypted ->
-		    process_sasl_failure(
-		      <<"Peer doesn't support STARTTLS">>, State1);
 		#starttls{required = true} when not TLSAvailable and not Encrypted ->
 		    Txt = <<"Use of STARTTLS forbidden">>,
 		    send_pkt(State1, xmpp:serr_unsupported_feature(Txt, Lang));
 		#starttls{} when TLSAvailable and not Encrypted ->
 		    State2 = State1#{stream_state => wait_for_starttls_response},
 		    send_pkt(State2, #starttls{});
-		#starttls{} when NS == ?NS_SERVER andalso not Encrypted ->
-		    process_sasl_failure(
-		      <<"STARTTLS is disabled in local configuration">>, State1);
 		_ ->
 		    State2 = process_cert_verification(State1),
 		    case is_disconnected(State2) of
 			true -> State2;
-			false ->
+			false -> process_sasl_mechanisms(StreamFeatures, State2)
-			    try xmpp:try_subtag(StreamFeatures, #sasl_mechanisms{}) of
-				#sasl_mechanisms{list = Mechs} ->
-				    process_sasl_mechanisms(Mechs, State2);
-				false ->
-				    Txt = <<"Peer provided no SASL mechanisms; "
-					    "most likely it doesn't accept "
-					    "our certificate">>,
-				    process_sasl_failure(Txt, State2)
-			    catch _:{xmpp_codec, Why} ->
-				    Txt = xmpp:io_format_error(Why),
-				    process_sasl_failure(Txt, State1)
-			    end
 		    end
 	    catch _:{xmpp_codec, Why} ->
 		    Txt = xmpp:io_format_error(Why),
-		    process_sasl_failure(Txt, State1)
+		    send_pkt(State1, xmpp:serr_invalid_xml(Txt, Lang))
 	    end
     end.
 
@@ -621,18 +597,56 @@ process_stream_established(State) ->
     catch _:{?MODULE, undef} -> State1
     end.
 
--spec process_sasl_mechanisms([binary()], state()) -> state().
+-spec process_sasl_mechanisms(stream_features(), state()) -> state().
-process_sasl_mechanisms(Mechs, #{user := User, server := Server} = State) ->
+process_sasl_mechanisms(StreamFeatures, State) ->
-    %% TODO: support other mechanisms
+    AvailMechs = sasl_mechanisms(State),
-    Mech = <<"EXTERNAL">>,
+    State1 = State#{sasl_mechs_available => AvailMechs},
-    case lists:member(<<"EXTERNAL">>, Mechs) of
+    try xmpp:try_subtag(StreamFeatures, #sasl_mechanisms{}) of
-	true ->
+	#sasl_mechanisms{list = ProvidedMechs} ->
-	    State1 = State#{stream_state => wait_for_sasl_response},
+	    process_sasl_auth(State1#{sasl_mechs_provided => ProvidedMechs});
-	    Authzid = jid:encode(jid:make(User, Server)),
-	    send_pkt(State1, #sasl_auth{mechanism = Mech, text = Authzid});
 	false ->
-	    process_sasl_failure(
+	    process_sasl_auth(State1#{sasl_mechs_provided => []})
-	      <<"Peer doesn't support EXTERNAL authentication">>, State)
+    catch _:{xmpp_codec, Why} ->
+	    Txt = xmpp:io_format_error(Why),
+	    Lang = maps:get(lang, State),
+	    send_pkt(State, xmpp:serr_invalid_xml(Txt, Lang))
+    end.
+
+process_sasl_auth(#{stream_encrypted := false, xmlns := ?NS_SERVER} = State) ->
+    State1 = State#{sasl_mechs_available => []},
+    Txt = case is_starttls_available(State) of
+	      true -> <<"Peer doesn't support STARTTLS">>;
+	      false -> <<"STARTTLS is disabled in local configuration">>
+	  end,
+    process_sasl_failure(Txt, State1);
+process_sasl_auth(#{sasl_mechs_provided := [],
+		    stream_encrypted := Encrypted} = State) ->
+    State1 = State#{sasl_mechs_available => []},
+    Hint = case Encrypted of
+	       true -> <<"; most likely it doesn't accept our certificate">>;
+	       false -> <<"">>
+	   end,
+    Txt = <<"Peer provided no SASL mechanisms", Hint/binary>>,
+    process_sasl_failure(Txt, State1);
+process_sasl_auth(#{sasl_mechs_available := []} = State) ->
+    Err = maps:get(sasl_error, State,
+		   <<"No mutually supported SASL mechanisms found">>),
+    process_sasl_failure(Err, State);
+process_sasl_auth(#{sasl_mechs_available := [Mech|AvailMechs],
+		    sasl_mechs_provided := ProvidedMechs} = State) ->
+    State1 = State#{sasl_mechs_available => AvailMechs},
+    if Mech == <<"EXTERNAL">> orelse Mech == <<"PLAIN">> ->
+	    case lists:member(Mech, ProvidedMechs) of
+		true ->
+		    Text = make_sasl_authzid(Mech, State1),
+		    State2 = State1#{sasl_mech => Mech,
+				     stream_state => wait_for_sasl_response},
+		    send(State2, #sasl_auth{mechanism = Mech, text = Text});
+		false ->
+		    process_sasl_auth(State1)
+	    end;
+       true ->
+	    process_sasl_auth(State1)
     end.
 
 -spec process_starttls(state()) -> state().
@@ -685,30 +699,42 @@ process_cert_verification(State) ->
     State.
 
 -spec process_sasl_success(state()) -> state().
-process_sasl_success(#{socket := Socket} = State) ->
+process_sasl_success(#{socket := Socket, sasl_mech := Mech} = State) ->
     Socket1 = xmpp_socket:reset_stream(Socket),
-    State0 = State#{socket => Socket1},
+    State1 = State#{socket => Socket1},
-    State1 = State0#{stream_id => new_id(),
+    State2 = State1#{stream_id => new_id(),
 		     stream_restarted => true,
 		     stream_state => wait_for_stream,
 		     stream_authenticated => true},
-    State2 = send_header(State1),
+    State3 = reset_sasl_state(State2),
-    case is_disconnected(State2) of
+    State4 = send_header(State3),
-	true -> State2;
+    case is_disconnected(State4) of
+	true -> State4;
 	false ->
-	    try callback(handle_auth_success, <<"EXTERNAL">>, State2)
+	    try callback(handle_auth_success, Mech, State4)
-	    catch _:{?MODULE, undef} -> State2
+	    catch _:{?MODULE, undef} -> State4
 	    end
     end.
 
 -spec process_sasl_failure(sasl_failure() | binary(), state()) -> state().
+process_sasl_failure(Failure, #{sasl_mechs_available := [_|_]} = State) ->
+    process_sasl_auth(State#{sasl_failure => Failure});
 process_sasl_failure(#sasl_failure{} = Failure, State) ->
     Reason = format("Peer responded with error: ~s",
 		    [xmpp:format_sasl_error(Failure)]),
     process_sasl_failure(Reason, State);
 process_sasl_failure(Reason, State) ->
-    try callback(handle_auth_failure, <<"EXTERNAL">>, {auth, Reason}, State)
+    Mech = case maps:get(sasl_mech, State, undefined) of
-    catch _:{?MODULE, undef} -> process_stream_end({auth, Reason}, State)
+	       undefined ->
+		   case sasl_mechanisms(State) of
+		       [] -> <<"EXTERNAL">>;
+		       [M|_] -> M
+		   end;
+	       M -> M
+	   end,
+    State1 = reset_sasl_state(State),
+    try callback(handle_auth_failure, Mech, {auth, Reason}, State1)
+    catch _:{?MODULE, undef} -> process_stream_end({auth, Reason}, State1)
     end.
 
 -spec process_bind(stream_features(), state()) -> state().
@@ -736,7 +762,7 @@ process_bind(_, State) ->
 -spec process_bind_response(xmpp_element(), state()) -> state().
 process_bind_response(#iq{type = result, id = ID} = IQ,
 		      #{lang := Lang, bind_id := ID} = State) ->
-    State1 = maps:remove(bind_id, State),
+    State1 = reset_bind_state(State),
     try xmpp:try_subtag(IQ, #bind{}) of
 	#bind{jid = #jid{user = U, server = S, resource = R}} ->
 	    State2 = State1#{user => U, server => S, resource => R},
@@ -757,7 +783,7 @@ process_bind_response(#iq{type = result, id = ID} = IQ,
 process_bind_response(#iq{type = error, id = ID} = IQ,
 		      #{bind_id := ID} = State) ->
     Err = xmpp:get_error(IQ),
-    State1 = maps:remove(bind_id, State),
+    State1 = reset_bind_state(State),
     try callback(handle_bind_failure, Err, State1)
     catch _:{?MODULE, undef} -> process_stream_end({bind, Err}, State1)
     end;
@@ -782,6 +808,17 @@ is_starttls_available(State) ->
     catch _:{?MODULE, undef} -> true
     end.
 
+-spec sasl_mechanisms(state()) -> [binary()].
+sasl_mechanisms(#{stream_encrypted := Encrypted} = State) ->
+    try callback(sasl_mechanisms, State) of
+	Ms when Encrypted -> Ms;
+	Ms -> lists:delete(<<"EXTERNAL">>, Ms)
+    catch _:{?MODULE, undef} ->
+	    if Encrypted -> [<<"EXTERNAL">>];
+	       true -> []
+	    end
+    end.
+
 -spec send_header(state()) -> state().
 send_header(#{remote_server := RemoteServer,
 	      stream_encrypted := Encrypted,
@@ -912,6 +949,54 @@ format_tls_error(Reason) ->
 format(Fmt, Args) ->
     iolist_to_binary(io_lib:format(Fmt, Args)).
 
+-spec make_sasl_authzid(binary(), state()) -> binary().
+make_sasl_authzid(Mech, #{user := User, server := Server,
+			  password := Password}) ->
+    case Mech of
+	<<"EXTERNAL">> ->
+	    jid:encode(jid:make(User, Server));
+	<<"PLAIN">> ->
+	    JID = jid:encode(jid:make(User, Server)),
+	    <<JID/binary, 0, User/binary, 0, Password/binary>>
+    end.
+
+%%%===================================================================
+%%% State resets
+%%%===================================================================
+-spec reset_sasl_state(state()) -> state().
+reset_sasl_state(State) ->
+    State1 = maps:remove(sasl_mech, State),
+    State2 = maps:remove(sasl_failure, State1),
+    State3 = maps:remove(sasl_mechs_provided, State2),
+    maps:remove(sasl_mechs_available, State3).
+
+-spec reset_connection_state(state()) -> state().
+reset_connection_state(State) ->
+    State1 = maps:remove(ip, State),
+    State2 = maps:remove(socket, State1),
+    maps:remove(socket_monitor, State2).
+
+-spec reset_stream_state(state()) -> state().
+reset_stream_state(State) ->
+    State1 = State#{stream_id => new_id(),
+		    stream_encrypted => false,
+		    stream_verified => false,
+		    stream_authenticated => false,
+		    stream_restarted => false,
+		    stream_state => connecting},
+    maps:remove(stream_remote_id, State1).
+
+-spec reset_bind_state(state()) -> state().
+reset_bind_state(State) ->
+    maps:remove(bind_id, State).
+
+-spec reset_state(state()) -> state().
+reset_state(State) ->
+    State1 = reset_bind_state(State),
+    State2 = reset_sasl_state(State1),
+    State3 = reset_connection_state(State2),
+    reset_stream_state(State3).
+
 %%%===================================================================
 %%% Connection stuff
 %%%===================================================================