+
+#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. 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)
+ /* seen for with-data, experimental TFO option, with-cookie case */
+ /* seen for with-data, proper TFO opt, with-cookie case */
+ {
+ DEBUG(D_transport|D_v) debug_printf("TFO mode connection attempt, %s data\n",
+ fastopen->len > 0 ? "with" : "no");
+ tcp_out_fastopen = fastopen->len > 0 ? 2 : 1;
+ }
+ else if (errno == EINPROGRESS) /* expected if we had no cookie for peer */
+ /* seen for no-data, proper TFO option, both cookie-request and with-cookie cases */
+ /* apparently no visibility of the diffference at this point */
+ /* seen for with-data, proper TFO opt, cookie-req */
+ /* with netwk delay, post-conn tcp_info sees unacked 1 for R, 2 for C; code in smtp_out.c */
+ /* ? older Experimental TFO option behaviour ? */
+ { /* queue unsent data */
+ DEBUG(D_transport|D_v) debug_printf("TFO mode sendto, %s data: EINPROGRESS\n",
+ fastopen->len > 0 ? "with" : "no");
+ if (!fastopen->data)
+ {
+ tcp_out_fastopen = 1; /* we tried; unknown if useful yet */
+ rc = 0;
+ }
+ else
+ rc = send(sock, fastopen->data, fastopen->len, 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;
+ }
+