BUG: http: re-enable TCP quick-ack upon incomplete HTTP requests

By default we disable TCP quick-acking on HTTP requests so that we
avoid sending a pure ACK immediately followed by the HTTP response.
However, if the client sends an incomplete request in a short packet,
its TCP stack might wait for this packet to be ACKed before sending
the rest of the request, delaying incoming requests by up to 40-200ms.

We can detect this undesirable situation when parsing the request :
  - if an incomplete request is received
  - if a full request is received and uses chunked encoding or advertises
    a content-length larger than the data available in the buffer

In these situations, we re-enable TCP quick-ack if we had previously
disabled it.

diff --git a/src/proto_http.c b/src/proto_http.c
index 87115d22161bfe2324169c5218e6aa53de8de085..14dc24be06fce3d002a48308ea95ac2ea795957d 100644 (file)
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -19,6 +19,8 @@
 #include <syslog.h>
 #include <time.h>
 
+#include <netinet/tcp.h>
+
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -2582,6 +2584,15 @@ int http_wait_for_request(struct session *s, struct buffer *req, int an_bit)
                buffer_dont_connect(req);
                req->flags |= BF_READ_DONTWAIT; /* try to get back here ASAP */
                s->rep->flags &= ~BF_EXPECT_MORE; /* speed up sending a previous response */
+#ifdef TCP_QUICKACK
+               if (s->listener->options & LI_O_NOQUICKACK) {
+                       /* We need more data, we have to re-enable quick-ack in case we
+                        * previously disabled it, otherwise we might cause the client
+                        * to delay next data.
+                        */
+                       setsockopt(s->si[0].fd, IPPROTO_TCP, TCP_QUICKACK, &one, sizeof(one));
+               }
+#endif
 
                if ((msg->msg_state != HTTP_MSG_RQBEFORE) && (txn->flags & TX_WAIT_NEXT_RQ)) {
                        /* If the client starts to talk, let's fall back to
@@ -3692,8 +3703,20 @@ int http_process_request(struct session *s, struct buffer *req, int an_bit)
                req->analysers |= AN_REQ_HTTP_BODY;
        }
 
-       if (txn->flags & TX_REQ_XFER_LEN)
+       if (txn->flags & TX_REQ_XFER_LEN) {
                req->analysers |= AN_REQ_HTTP_XFER_BODY;
+#ifdef TCP_QUICKACK
+               /* We expect some data from the client. Unless we know for sure
+                * we already have a full request, we have to re-enable quick-ack
+                * in case we previously disabled it, otherwise we might cause
+                * the client to delay further data.
+                */
+               if ((s->listener->options & LI_O_NOQUICKACK) &&
+                   ((txn->flags & TX_REQ_TE_CHNK) ||
+                    (msg->body_len > req->l - txn->req.eoh - 2)))
+                       setsockopt(s->si[0].fd, IPPROTO_TCP, TCP_QUICKACK, &one, sizeof(one));
+#endif
+       }
 
        /*************************************************************
         * OK, that's finished for the headers. We have done what we *