+
+#if defined(TCP_FASTOPEN) && defined(MSG_FASTOPEN)
+/* 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.
+*/
+
+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)
+ {
+ DEBUG(D_transport)
+ debug_printf("Tried TCP Fast Open but apparently not enabled by sysctl\n");
+ goto legacy_connect;
+ }
+ }
+else
+#endif
+ {
+legacy_connect:
+ if ((rc = connect(sock, s_ptr, s_len)) >= 0)
+ if ( fastopen && fastopen->data && fastopen->len
+ && send(sock, fastopen->data, fastopen->len, 0) < 0)
+ rc = -1;
+ }
+