TFO: better detection of client fast-open connections

3 files changed, 25 insertions, 43 deletions

diff --git a/src/OS/os.h-Linux b/src/OS/os.h-Linux
index f6d35772b..cc1f3cab2 100644
--- a/src/OS/os.h-Linux
+++ b/src/OS/os.h-Linux
@@ -79,7 +79,6 @@ then change the 0 to 1 in the next block. */
 #if defined(TCP_FASTOPEN) && !defined(MSG_FASTOPEN)
 # define MSG_FASTOPEN 0x20000000
 #endif
-#define EXIM_HAVE_TCPI_UNACKED
 
 
 /* End */
diff --git a/src/src/ip.c b/src/src/ip.c
index 872745144..258ab5c23 100644
--- a/src/src/ip.c
+++ b/src/src/ip.c
@@ -229,27 +229,37 @@ if (timeout > 0) alarm(timeout);
 /* TCP Fast Open, if the system has a cookie from a previous call to
 this peer, can send data in the SYN packet.  The peer can send data
 before it gets our ACK of its SYN,ACK - the latter is useful for
-the SMTP banner.  Is there any usage where the former might be?
-We might extend the ip_connect() args for data if so.  For now,
-connect in FASTOPEN mode but with zero data.
-*/
+the SMTP banner.  Other (than SMTP) cases of TCP connections can
+possibly use the data-on-syn, so support that too.  */
 
 if (fastopen)
   {
   if ((rc = sendto(sock, fastopen->data, fastopen->len,
-		    MSG_FASTOPEN | MSG_DONTWAIT, s_ptr, s_len)) < 0)
-    if (errno == EINPROGRESS)		/* expected for nonready peer */
-      {					/* queue the data */
-      if (  (rc = send(sock, fastopen->data, fastopen->len, 0)) < 0
-	 && errno == EINPROGRESS)	/* expected for nonready peer */
-	rc = 0;
-      }
-    else if(errno == EOPNOTSUPP)
+		    MSG_FASTOPEN | MSG_DONTWAIT, s_ptr, s_len)) >= 0)
+    {
+    DEBUG(D_transport|D_v)
+      debug_printf("TCP_FASTOPEN mode connection, with data\n");
+    tcp_out_fastopen = TRUE;
+    }
+  else if (errno == EINPROGRESS)	/* expected for nonready peer */
+    {
+    if (!fastopen->data)
       {
-      DEBUG(D_transport)
-	debug_printf("Tried TCP Fast Open but apparently not enabled by sysctl\n");
-      goto legacy_connect;
+      DEBUG(D_transport|D_v)
+	debug_printf("TCP_FASTOPEN mode connection, no data\n");
+      tcp_out_fastopen = TRUE;
+      rc = 0;
       }
+    else if (  (rc = send(sock, fastopen->data, fastopen->len, 0)) < 0
+	    && errno == EINPROGRESS)	/* expected for nonready peer */
+      rc = 0;
+    }
+  else if(errno == EOPNOTSUPP)
+    {
+    DEBUG(D_transport)
+      debug_printf("Tried TCP Fast Open but apparently not enabled by sysctl\n");
+    goto legacy_connect;
+    }
   }
 else
 #endif
diff --git a/src/src/smtp_out.c b/src/src/smtp_out.c
index 9221aa868..db33ac66e 100644
--- a/src/src/smtp_out.c
+++ b/src/src/smtp_out.c
@@ -140,30 +140,6 @@ return TRUE;
 
 
 
-#ifdef TCP_FASTOPEN
-static void
-tfo_out_check(int sock)
-{
-# if defined(TCP_INFO) && defined(EXIM_HAVE_TCPI_UNACKED)
-struct tcp_info tinfo;
-socklen_t len = sizeof(tinfo);
-
-if (getsockopt(sock, IPPROTO_TCP, TCP_INFO, &tinfo, &len) == 0)
-  {
-  /* This is a somewhat dubious detection method; totally undocumented so likely
-  to fail in future kernels.  There seems to be no documented way. */
-
-  if (tinfo.tcpi_unacked > 1)
-    {
-    DEBUG(D_transport|D_v) debug_printf("TCP_FASTOPEN mode connection\n");
-    tcp_out_fastopen = TRUE;
-    }
-  }
-# endif
-}
-#endif
-
-
 /* Arguments as for smtp_connect(), plus
   early_data	if non-NULL, data to be sent - preferably in the TCP SYN segment
 
@@ -278,9 +254,6 @@ else
     return -1;
     }
   if (ob->keepalive) ip_keepalive(sock, host->address, TRUE);
-#ifdef TCP_FASTOPEN
-  tfo_out_check(sock);
-#endif
   return sock;
   }
 }