From 1ba57a8df2254b1088e0a5233378fa4efb5b3b9b Mon Sep 17 00:00:00 2001
From: XANTRONIX Development <dev@xantronix.com>
Date: Sun, 26 Jul 2020 01:48:08 -0400
Subject: [PATCH] Prevent I frame TX overflow

As per the AX.25 v2.2 Specification, Section 6.4.1, "Sending I Frames",
do not send an I frame if V(R) + x (TX window) equals V(S)
---
 src/server.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/server.c b/src/server.c
index bc45229..33fadf1 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1618,6 +1618,13 @@ static int handle_sock(uint32_t key,
         goto done;
     }
 
+    /*
+     * NOTE: See AX.25 2.2, Section 6.4.1, "Sending I Frames"
+     */
+    if (sock->seq_recv + sock->n_window_tx == sock->seq_send) {
+        goto done;
+    }
+
     if ((len = read(sock->fd, sock->rx_buf, sock->n_maxlen_rx)) < 0) {
         if (errno == EIO) {
             (void)sock_shutdown(server, sock);