From aa2fd9b06d1a5014c27dde7aa7bc6191d4b71360 Mon Sep 17 00:00:00 2001
From: XANTRONIX Development <dev@xantronix.com>
Date: Fri, 31 Jul 2020 01:14:11 -0400
Subject: [PATCH] Implement Response Delay Timer T2

Implement AX.25 v2.2 Section 6.7.1.2 "Response Delay Timer T2" as per
specification; do not acknowledge several sequential I frames until a
certain period of time has passed since the receipt of the most recent I
frame
---
 include/patty/ax25/sock.h |  3 +-
 src/server.c              | 60 +++++++++++++++++++++++++++------------
 src/sock.c                |  1 +
 3 files changed, 45 insertions(+), 19 deletions(-)

diff --git a/include/patty/ax25/sock.h b/include/patty/ax25/sock.h
index d22d37d..6acb477 100644
--- a/include/patty/ax25/sock.h
+++ b/include/patty/ax25/sock.h
@@ -72,7 +72,8 @@ typedef struct _patty_ax25_sock {
     unsigned int seq_send,
                  seq_recv;
 
-    size_t retries;
+    size_t retries,
+           pending;
 
     int fd;
     char pty[PATTY_AX25_SOCK_PATH_SIZE];
diff --git a/src/server.c b/src/server.c
index 2908b03..977766c 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1314,8 +1314,16 @@ static int handle_i(patty_ax25_server *server,
         goto error_write;
     }
 
-    return frame->pf?
-        patty_ax25_sock_send_rr(sock, PATTY_AX25_FRAME_RESPONSE, 0): 0;
+    if (++sock->pending == sock->n_window_rx / 2) {
+        sock->pending = 0;
+        patty_timer_cancel(&sock->timer_t2);
+
+        return patty_ax25_sock_send_rr(sock, PATTY_AX25_FRAME_RESPONSE, 0);
+    } else {
+        patty_timer_start(&sock->timer_t2, &server->timer, 3000);
+    }
+
+    return 0;
 
 error_write:
     return -1;
@@ -1628,24 +1636,40 @@ static int handle_sock(uint32_t key,
 
     ssize_t len;
 
-    if (sock->status == PATTY_AX25_SOCK_PENDING_CONNECT) {
-        if (patty_timer_expired(&sock->timer_t1)) {
-            if (sock->retries) {
-                int ret = patty_ax25_sock_send_sabm(sock, PATTY_AX25_FRAME_POLL);
-
-                patty_timer_start(&sock->timer_t1, &server->timer, sock->n_ack);
-
-                return ret;
-            } else {
-                (void)sock_shutdown(server, sock);
-
-                return sock_close(server, sock);
-            }
-        } else {
+    switch (sock->status) {
+        case PATTY_AX25_SOCK_PENDING_CONNECT:
             patty_timer_tick(&sock->timer_t1, &server->elapsed);
-        }
 
-        goto done;
+            if (patty_timer_expired(&sock->timer_t1)) {
+                if (sock->retries) {
+                    int ret = patty_ax25_sock_send_sabm(sock, PATTY_AX25_FRAME_POLL);
+
+                    sock->retries--;
+                    patty_timer_start(&sock->timer_t1, &server->timer, sock->n_ack);
+
+                    return ret;
+                } else {
+                    (void)sock_shutdown(server, sock);
+
+                    return sock_close(server, sock);
+                }
+            }
+
+            goto done;
+
+        case PATTY_AX25_SOCK_ESTABLISHED:
+            patty_timer_tick(&sock->timer_t2, &server->elapsed);
+
+            if (patty_timer_expired(&sock->timer_t2)) {
+                if (sock->pending) {
+                    sock->pending = 0;
+
+                    return patty_ax25_sock_send_rr(sock, PATTY_AX25_FRAME_RESPONSE, 0);
+                }
+            }
+
+        default:
+            break;
     }
 
     if (!FD_ISSET(sock->fd, &server->fds_r)) {
diff --git a/src/sock.c b/src/sock.c
index 869885b..72c9282 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -180,6 +180,7 @@ int patty_ax25_sock_reset(patty_ax25_sock *sock) {
     sock->seq_send = 0;
     sock->seq_recv = 0;
     sock->retries  = sock->n_retry;
+    sock->pending  = 0;
 
     timerclear(&sock->timer_t1);
     timerclear(&sock->timer_t2);