MB-37100: Stop timeout timer before sending first response

view-engine uses same tcp connection to perform multiple
gather queries from other nodes. When it receives a request,
node will start the timer and after connection_timeout
milliseconds it will force close the connection.
In that case if there is any long running query
in receiving end will try to read from closed socket.
This patch will clear the timer before the successful
streaming of first response.

Change-Id: Ie0191484f718c1b34c0a5c9ee17bad8e5a174486
Reviewed-on: http://review.couchbase.org/118681
Reviewed-by: Suraj Naik <suraj.naik@couchbase.com>
Tested-by: Matt Carabine <matt.carabine@couchbase.com>
Tested-by: <ankit.prabhu@couchbase.com>

src/couch_index_merger/src/couch_httpd_view_merger.erl

@@ -121,6 +121,7 @@ http_sender({debug_info, From, Info}, SAcc) ->
     {ok, SAcc#sender_acc{debug_info_acc = DebugInfoAcc2}};
 
 http_sender(start, #sender_acc{req = Req} = SAcc) ->
+    maybe_stop_timer(),
     #httpd{mochi_req = MReq} = Req,
     ok = mochiweb_socket:setopts(MReq:get(socket), [{nodelay, true}]),
     {ok, Resp} = couch_httpd:start_json_response(Req, 200, []),
@@ -129,13 +130,7 @@ http_sender(start, #sender_acc{req = Req} = SAcc) ->
 http_sender({start, RowCount}, #sender_acc{req = Req} = SAcc) ->
     % The remote node is ready to start streaming the response
     % Call off the hit
-    case get(tref) of
-    nil ->
-        ok;
-    TRef ->
-        timer:cancel(TRef),
-        erase(tref)
-    end,
+    maybe_stop_timer(),
     #httpd{mochi_req = MReq} = Req,
     ok = mochiweb_socket:setopts(MReq:get(socket), [{nodelay, true}]),
     {ok, Resp} = couch_httpd:start_json_response(Req, 200, []),
@@ -260,3 +255,12 @@ log_bytes(Req, Size) ->
     catch
         _:_ -> ok
     end.
+
+maybe_stop_timer() ->
+    case get(tref) of
+    undefined ->
+        ok;
+    TRef ->
+        timer:cancel(TRef),
+        erase(tref)
+    end.