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

@@ -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];

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;
@@ -1628,11 +1636,15 @@ static int handle_sock(uint32_t key,
 
     ssize_t len;
 
-    if (sock->status == PATTY_AX25_SOCK_PENDING_CONNECT) {
+    switch (sock->status) {
+        case PATTY_AX25_SOCK_PENDING_CONNECT:
+            patty_timer_tick(&sock->timer_t1, &server->elapsed);
+
             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;
@@ -1641,11 +1653,23 @@ static int handle_sock(uint32_t key,
 
                     return sock_close(server, sock);
                 }
-        } else {
-            patty_timer_tick(&sock->timer_t1, &server->elapsed);
             }
 
             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)) {

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);