Ensure no more than one response per requestprevent-multiple-responses-rebased

Due to a retry loop in erlfb:transactional couchdb might try to send
multiple http responses for a single request which is clearly an
error.

This PR ensures the second attempt is prevented, closing the TCP
socket instead.

3 files changed, 29 insertions, 0 deletions

diff --git a/src/chttpd/src/chttpd.erl b/src/chttpd/src/chttpd.erl
index 53fdf989a..ba26b2b68 100644
--- a/src/chttpd/src/chttpd.erl
+++ b/src/chttpd/src/chttpd.erl
@@ -160,6 +160,7 @@ stop() ->
     mochiweb_http:stop(?MODULE).
 
 handle_request(MochiReq0) ->
+    couch_httpd:response_not_started(),
     MochiReq = couch_httpd_vhost:dispatch_host(MochiReq0),
     handle_request_int(MochiReq).
 
@@ -1330,8 +1331,10 @@ handle_response(Req0, Code0, Headers0, Args0, Type) ->
     respond_(Req1, Code1, Headers1, Args1, Type).
 
 respond_(#httpd{mochi_req = MochiReq}, Code, Headers, _Args, start_response) ->
+    couch_httpd:abort_if_response_already_started(),
     MochiReq:start_response({Code, Headers});
 respond_(#httpd{mochi_req = MochiReq}, Code, Headers, Args, Type) ->
+    couch_httpd:abort_if_response_already_started(),
     MochiReq:Type({Code, Headers, Args}).
 
 get_user(#httpd{user_ctx = #user_ctx{name = null}}) ->
diff --git a/src/chttpd/test/eunit/chttpd_handlers_tests.erl b/src/chttpd/test/eunit/chttpd_handlers_tests.erl
index 649d82e86..489ff6761 100644
--- a/src/chttpd/test/eunit/chttpd_handlers_tests.erl
+++ b/src/chttpd/test/eunit/chttpd_handlers_tests.erl
@@ -63,6 +63,15 @@ should_escape_dbname_on_replicate(Url) ->
         end).
 
 
+prevent_multiple_http_response_test() ->
+    ?assertEqual(undefined, couch_httpd:abort_if_response_already_started()),
+    ?assertEqual(true, couch_httpd:response_not_started()),
+    ?assertEqual(undefined, couch_httpd:abort_if_response_already_started()),
+    Err = multiple_responses_attempted,
+    ?assertThrow({http_abort, {mochiweb_response, _}, Err},
+        couch_httpd:abort_if_response_already_started()).
+
+
 json_value(JSON, Keys) ->
     couch_util:get_nested_json_value(JSON, Keys).
 
diff --git a/src/couch/src/couch_httpd.erl b/src/couch/src/couch_httpd.erl
index fd83c258a..b90d6dae8 100644
--- a/src/couch/src/couch_httpd.erl
+++ b/src/couch/src/couch_httpd.erl
@@ -36,6 +36,7 @@
 -export([validate_bind_address/1]).
 -export([check_max_request_length/1]).
 -export([maybe_decompress/2]).
+-export([response_not_started/0, abort_if_response_already_started/0]).
 
 -define(HANDLER_NAME_IN_MODULE_POS, 6).
 -define(MAX_DRAIN_BYTES, 1048576).
@@ -871,6 +872,7 @@ respond_(#httpd{mochi_req = MochiReq} = Req, Code, Headers, Args, Type) ->
     end.
 
 http_respond_(#httpd{mochi_req = MochiReq}, Code, Headers, _Args, start_response) ->
+    abort_if_response_already_started(),
     MochiReq:start_response({Code, Headers});
 http_respond_(#httpd{mochi_req = MochiReq}, 413, Headers, Args, Type) ->
     % Special handling for the 413 response. Make sure the socket is closed as
@@ -885,9 +887,24 @@ http_respond_(#httpd{mochi_req = MochiReq}, 413, Headers, Args, Type) ->
     mochiweb_socket:recv(Socket, ?MAX_DRAIN_BYTES, ?MAX_DRAIN_TIME_MSEC),
     Result;
 http_respond_(#httpd{mochi_req = MochiReq}, Code, Headers, Args, Type) ->
+    abort_if_response_already_started(),
     MochiReq:Type({Code, Headers, Args}).
 
 
+response_not_started() ->
+    erase(http_response_started).
+
+
+abort_if_response_already_started() ->
+    case get(http_response_started) of
+        undefined ->
+            put(http_response_started, true);
+        true ->
+            ErrResp = mochiweb:new_response({nil, 500, []}),
+            throw({http_abort, ErrResp, multiple_responses_attempted})
+    end.
+
+
 %%%%%%%% module tests below %%%%%%%%
 
 -ifdef(TEST).