Make the handling of the tcp window explicit for the SYN_SENT case

in tcp_outout().  This is currently not strictly necessary but paves
the way to simplify the entire SYN options handling quite a bit.
Clarify comment.  No change in effective behavour with this commit.

RFC1323 requires the window field in a SYN (i.e., a <SYN> or
<SYN,ACK>) segment itself never be scaled.

1 files changed, 10 insertions, 4 deletions

diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index d8adff3..da30813 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -906,9 +906,6 @@ send:
 	/*
 	 * Calculate receive window.  Don't shrink window,
 	 * but avoid silly window syndrome.
-	 *
-	 * XXX: RFC1323:  The Window field in a SYN (i.e., a <SYN> or
-	 * <SYN,ACK>) segment itself is never scaled.
 	 */
 	if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
 	    recwin < (long)tp->t_maxseg)
@@ -917,8 +914,17 @@ send:
 		recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
 	if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
 		recwin = (long)TCP_MAXWIN << tp->rcv_scale;
-	th->th_win = htons((u_short) (recwin >> tp->rcv_scale));
 
+	/*
+	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
+	 * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
+	 * case is handled in syncache.
+	 */
+	if (flags & TH_SYN)
+		th->th_win = htons((u_short)
+				(min(sbspace(&so->so_rcv), TCP_MAXWIN)));
+	else
+		th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
 
 	/*
 	 * Adjust the RXWIN0SENT flag - indicate that we have advertised