allow discarding body while a long response transfer

src/http/ngx_http_request.c

diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index bad89a4..7533806 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -2145,7 +2145,9 @@
 
     r->http_state = NGX_HTTP_WRITING_REQUEST_STATE;
 
-    r->read_event_handler = ngx_http_test_reading;
+    r->read_event_handler = r->discard_body ?
+                                ngx_http_discarded_request_body_handler:
+                                ngx_http_test_reading;
     r->write_event_handler = ngx_http_writer;
 
     wev = r->connection->write;