Reply with 400 on header parsing crash

This is a first step to improve the HTTP status codes returned
by Cowboy on crashes. We will tweak it over time.

Also fixes a small bug where two replies may have been sent
when using loop handlers under rare conditions.

test/handlers/input_crash_h.erl

@@ -0,0 +1,10 @@
+%% This module crashes on request input data
+%% depending on the given option.
+
+-module(input_crash_h).
+
+-export([init/3]).
+
+init(_, Req, content_length) ->
+	cowboy_error_h:ignore(cow_http_hd, number, 2),
+	cowboy_req:parse_header(<<"content-length">>, Req).

test/http_SUITE.erl

@@ -193,6 +193,7 @@ init_dispatch(Config) ->
 			{"/multipart/large", http_multipart_stream, []},
 			{"/echo/body", http_echo_body, []},
 			{"/echo/body_qs", http_body_qs, []},
+			{"/crash/content-length", input_crash_h, content_length},
 			{"/param_all", rest_param_all, []},
 			{"/bad_accept", rest_simple_resource, []},
 			{"/bad_content_type", rest_patch_resource, []},
@@ -274,6 +275,7 @@ The document has moved
 		{400, "GET / HTTP/1.1\r\nHost: ninenines.eu\r\n\r\n"},
 		{400, "GET http://proxy/ HTTP/1.1\r\n\r\n"},
 		{400, "GET / HTTP/1.1\r\nHost: localhost:bad_port\r\n\r\n"},
+		{400, ["POST /crash/content-length HTTP/1.1\r\nHost: localhost\r\nContent-Length: 5000,5000\r\n\r\n", Huge]},
 		{505, ResponsePacket},
 		{408, "GET / HTTP/1.1\r\n"},
 		{408, "GET / HTTP/1.1\r\nHost: localhost"},