+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)