From cc892ddc01e28a682ad63734918b50c67c39d711 Mon Sep 17 00:00:00 2001
From: Evgeny Khramtsov <ekhramtsov@process-one.net>
Date: Tue, 23 Apr 2019 16:19:26 +0300
Subject: [PATCH] Improve request_handlers validator

---
 src/ejabberd_http.erl | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/src/ejabberd_http.erl b/src/ejabberd_http.erl
index 9588e6cd1..e37269659 100644
--- a/src/ejabberd_http.erl
+++ b/src/ejabberd_http.erl
@@ -397,10 +397,11 @@ process(Handlers, Request) ->
             %% requested path is "/test/foo/bar", the local path is
             %% ["foo", "bar"]
             LocalPath = lists:nthtail(length(HandlerPathPrefix), Request#request.path),
-	    R = try
-		    HandlerModule:socket_handoff(
-		      LocalPath, Request, HandlerOpts)
-		catch error:undef ->
+	    R = case erlang:function_exported(HandlerModule, socket_handoff, 3) of
+		    true ->
+			HandlerModule:socket_handoff(
+			  LocalPath, Request, HandlerOpts);
+		    false ->
 			HandlerModule:process(LocalPath, Request)
 		end,
             ejabberd_hooks:run(http_request_debug, [{LocalPath, Request}]),
@@ -962,6 +963,23 @@ transform_listen_option({request_handlers, Hs}, Opts) ->
 transform_listen_option(Opt, Opts) ->
     [Opt|Opts].
 
+prepare_request_module(mod_http_bind) ->
+    mod_bosh;
+prepare_request_module(Mod) when is_atom(Mod) ->
+    case code:ensure_loaded(Mod) of
+	{module, Mod} ->
+	    Mod;
+	Err ->
+	    ?ERROR_MSG(
+	       "Failed to load request handler ~s: "
+	       "make sure there is no typo and file ~s.beam "
+	       "exists inside either ~s or ~s directory",
+	       [Mod, Mod,
+		filename:dirname(code:which(?MODULE)),
+		ext_mod:modules_dir()]),
+	    erlang:error(Err)
+    end.
+
 -spec opt_type(atom()) -> fun((any()) -> any()) | [atom()].
 opt_type(trusted_proxies) ->
     fun (all) -> all;
@@ -1003,11 +1021,7 @@ listen_opt_type(request_handlers) ->
 	    Hs2 = [{str:tokens(
 		      iolist_to_binary(Path), <<"/">>),
 		    Mod} || {Path, Mod} <- Hs1],
-	    [{Path,
-	      case Mod of
-		  mod_http_bind -> mod_bosh;
-		  _ -> Mod
-	      end} || {Path, Mod} <- Hs2]
+	    [{Path, prepare_request_module(Mod)} || {Path, Mod} <- Hs2]
     end;
 listen_opt_type(default_host) ->
     fun iolist_to_binary/1;