Fix up syslog protocol options to set ip to localhost if unset

Author: lukebakken

src/rabbit_lager.erl

@@ -196,7 +196,7 @@ configure_lager() ->
     %% Set rabbit.log config variable based on environment.
     prepare_rabbit_log_config(),
     %% Configure syslog library.
-    ok = configure_syslog(),
+    ok = configure_syslog_error_logger(),
     %% At this point we should have rabbit.log application variable
     %% configured to generate RabbitMQ log handlers.
     GeneratedHandlers = generate_lager_handlers(),
@@ -266,14 +266,44 @@ configure_lager() ->
     end,
     ok.
 
-configure_syslog() ->
+configure_syslog_error_logger() ->
     %% Disable error_logger forwarding to syslog if it's not configured
     case application:get_env(syslog, syslog_error_logger) of
         undefined ->
-            ok = application:set_env(syslog, syslog_error_logger, false);
+            application:set_env(syslog, syslog_error_logger, false);
         _ -> ok
     end.
 
+-define(SYSLOG_LOCAL_IP, {ip,{127,0,0,1}}).
+configure_syslog() ->
+    ok = app_utils:load_applications([syslog]),
+    %% https://github.com/schlagert/syslog#configuration
+    Protocol = case application:get_env(syslog, protocol) of
+                   undefined ->
+                       {rfc3164, udp, [{ip,{127,0,0,1}}]};
+                   %% {protocol,
+                   %%     rfc3164 |
+                   %%     rfc5424 |
+                   %%     {rfc3164 | rfc5424, tcp | udp} |
+                   %%     {rfc3164 | rfc5424, udp, [gen_udp:option()]} |
+                   %%     {rfc3164 | rfc5424, tcp, [gen_tcp:option()]} |
+                   %%     {rfc5424, tls, [ssl:connect_option()]}
+                   %% }
+                   {ok, Rfc} when Rfc =:= rfc3164; Rfc =:= rfc5424 ->
+                       {Rfc, udp, [?SYSLOG_LOCAL_IP]};
+                   {ok, {Rfc, Transport}} when Rfc =:= rfc3164; Rfc =:= rfc5424 ->
+                       {Rfc, Transport, [?SYSLOG_LOCAL_IP]};
+                   {ok, {Rfc, Transport, Opts}} when Rfc =:= rfc3164; Rfc =:= rfc5424 ->
+                       case proplists:lookup(ip, Opts) of
+                           none ->
+                               {Rfc, Transport, [?SYSLOG_LOCAL_IP|Opts]};
+                           _ ->
+                               {Rfc, Transport, Opts}
+                        end
+               end,
+    ok = application:unset_env(syslog, protocol),
+    ok = application:set_env(syslog, protocol, Protocol).
+
 remove_rabbit_handlers(Handlers, FormerHandlers) ->
     lists:filter(fun(Handler) ->
         not lists:member(Handler, FormerHandlers)
@@ -317,6 +347,7 @@ lager_backend(exchange) -> lager_exchange_backend.
 generate_handler(syslog_lager_backend, HandlerConfig) ->
     DefaultConfigVal = default_config_value(level),
     Level = proplists:get_value(level, HandlerConfig, DefaultConfigVal),
+    ok = configure_syslog(),
     ok = app_utils:start_applications([syslog]),
     [{syslog_lager_backend,
      [Level,