finalizing with rc == 0 in unbuffered proxy mode caused nginx to wait
for another send_timeout before actually closing client's connection
if client timed out while still talking to upstream server

patch by Maxim Dounin

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index ad5b449..42b351c 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2317,7 +2317,7 @@
     if (wev->timedout) {
         c->timedout = 1;
         ngx_connection_error(c, NGX_ETIMEDOUT, "client timed out");
-        ngx_http_upstream_finalize_request(r, u, 0);
+        ngx_http_upstream_finalize_request(r, u, NGX_HTTP_REQUEST_TIME_OUT);
         return;
     }
 
@@ -3013,6 +3013,7 @@
 #endif
 
     if (u->header_sent
+        && rc != NGX_HTTP_REQUEST_TIME_OUT
         && (rc == NGX_ERROR || rc >= NGX_HTTP_SPECIAL_RESPONSE))
     {
         rc = 0;