Return {error, badarg} if start_listener got a bad transport module

src/ranch.erl

@@ -47,13 +47,21 @@
 %% of connections.
 %%
 %% <em>Ref</em> can be used to stop the listener later on.
+%%
+%% This function will return `{error, badarg}` if and only if the transport
+%% module given doesn't appear to be correct.
 -spec start_listener(any(), non_neg_integer(), module(), any(), module(), any())
-	-> {ok, pid()}.
+	-> {ok, pid()} | {error, badarg}.
 start_listener(Ref, NbAcceptors, Transport, TransOpts, Protocol, ProtoOpts)
 		when is_integer(NbAcceptors) andalso is_atom(Transport)
 		andalso is_atom(Protocol) ->
-	supervisor:start_child(ranch_sup, child_spec(Ref, NbAcceptors,
-		Transport, TransOpts, Protocol, ProtoOpts)).
+	case erlang:function_exported(Transport, name, 0) of
+		false ->
+			{error, badarg};
+		true ->
+			supervisor:start_child(ranch_sup, child_spec(Ref, NbAcceptors,
+				Transport, TransOpts, Protocol, ProtoOpts))
+	end.
 
 %% @doc Stop a listener identified by <em>Ref</em>.
 %%

test/acceptor_SUITE.erl

@@ -24,6 +24,9 @@
 -export([init_per_group/2]).
 -export([end_per_group/2]).
 
+%% misc.
+-export([misc_bad_transport/1]).
+
 %% ssl.
 -export([ssl_accept_error/1]).
 -export([ssl_active_echo/1]).
@@ -39,7 +42,7 @@
 %% ct.
 
 all() ->
-	[{group, tcp}, {group, ssl}].
+	[{group, tcp}, {group, ssl}, {group, misc}].
 
 groups() ->
 	[{tcp, [
@@ -52,6 +55,8 @@ groups() ->
 		ssl_accept_error,
 		ssl_active_echo,
 		ssl_echo
+	]}, {misc, [
+		misc_bad_transport
 	]}].
 
 init_per_suite(Config) ->
@@ -78,6 +83,14 @@ end_per_group(ssl, _) ->
 end_per_group(_, _) ->
 	ok.
 
+%% misc.
+
+misc_bad_transport(_) ->
+	{error, badarg} = ranch:start_listener(misc_bad_transport, 1,
+		bad_transport, [{port, 0}],
+		echo_protocol, []),
+	ok.
+
 %% ssl.
 
 ssl_accept_error(Config) ->