+#ifdef TCP_FASTOPEN
+/* Try to record if TFO was attmepted and if it was successfully used. */
+
+static void
+tfo_out_check(int sock)
+{
+static BOOL done_once = FALSE;
+
+if (done_once) return;
+done_once = TRUE;
+
+# ifdef __FreeBSD__
+struct tcp_info tinfo;
+socklen_t len = sizeof(tinfo);
+
+/* A getsockopt TCP_FASTOPEN unfortunately returns "was-used" for a TFO/R as
+well as a TFO/C. Use what we can of the Linux hack below; reliability issues ditto. */
+switch (tcp_out_fastopen)
+ {
+ case TFO_ATTEMPTED_NODATA:
+ if ( getsockopt(sock, IPPROTO_TCP, TCP_INFO, &tinfo, &len) == 0
+ && tinfo.tcpi_state == TCPS_SYN_SENT
+ && tinfo.__tcpi_unacked > 0
+ )
+ {
+ DEBUG(D_transport|D_v)
+ debug_printf("TCP_FASTOPEN tcpi_unacked %d\n", tinfo.__tcpi_unacked);
+ tcp_out_fastopen = TFO_USED_NODATA;
+ }
+ break;
+ /*
+ case TFO_ATTEMPTED_DATA:
+ case TFO_ATTEMPTED_DATA:
+ if (tinfo.tcpi_options & TCPI_OPT_SYN_DATA) XXX no equvalent as of 12.2
+ */
+ }
+
+switch (tcp_out_fastopen)
+ {
+ case TFO_ATTEMPTED_DATA: tcp_out_fastopen = TFO_USED_DATA; break;
+ default: break; /* compiler quietening */
+ }
+
+# else /* Linux & Apple */
+# if defined(TCP_INFO) && defined(EXIM_HAVE_TCPI_UNACKED)
+struct tcp_info tinfo;
+socklen_t len = sizeof(tinfo);
+
+switch (tcp_out_fastopen)
+ {
+ /* This is a somewhat dubious detection method; totally undocumented so likely
+ to fail in future kernels. There seems to be no documented way. What we really
+ want to know is if the server sent smtp-banner data before our ACK of his SYN,ACK
+ hit him. What this (possibly?) detects is whether we sent a TFO cookie with our
+ SYN, as distinct from a TFO request. This gets a false-positive when the server
+ key is rotated; we send the old one (which this test sees) but the server returns
+ the new one and does not send its SMTP banner before we ACK his SYN,ACK.
+ To force that rotation case:
+ '# echo -n "00000000-00000000-00000000-0000000" >/proc/sys/net/ipv4/tcp_fastopen_key'
+ The kernel seems to be counting unack'd packets. */
+
+ case TFO_ATTEMPTED_NODATA:
+ if ( getsockopt(sock, IPPROTO_TCP, TCP_INFO, &tinfo, &len) == 0
+ && tinfo.tcpi_state == TCP_SYN_SENT
+ && tinfo.tcpi_unacked > 1
+ )
+ {
+ DEBUG(D_transport|D_v)
+ debug_printf("TCP_FASTOPEN tcpi_unacked %d\n", tinfo.tcpi_unacked);
+ tcp_out_fastopen = TFO_USED_NODATA;
+ }
+ break;
+
+ /* When called after waiting for received data we should be able
+ to tell if data we sent was accepted. */
+
+ case TFO_ATTEMPTED_DATA:
+ if ( getsockopt(sock, IPPROTO_TCP, TCP_INFO, &tinfo, &len) == 0
+ && tinfo.tcpi_state == TCP_ESTABLISHED
+ )
+ if (tinfo.tcpi_options & TCPI_OPT_SYN_DATA)
+ {
+ DEBUG(D_transport|D_v) debug_printf("TFO: data was acked\n");
+ tcp_out_fastopen = TFO_USED_DATA;
+ }
+ else
+ {
+ DEBUG(D_transport|D_v) debug_printf("TFO: had to retransmit\n");
+ tcp_out_fastopen = TFO_NOT_USED;
+ }
+ break;
+
+ default: break; /* compiler quietening */
+ }
+# endif
+# endif /* Linux & Apple */
+}
+#endif
+
+
+/* Create and bind a socket, given the connect-args.
+Update those with the state. Return the fd, or -1 with errno set.
+*/
+