Implement additional socket flow control

Implement the SOCK_WAIT and SOCK_READY socket flow control states to
indicate a Receive Ready or Receive Not Ready state on the remote end

Other changes:

    * Fix issue wherein flow control was never halted when the remote
      end has received k (window) number of frames without the sending
      station asking for acknowledgment

include/patty/ax25/sock.h

@@ -58,6 +58,11 @@ enum patty_ax25_sock_mode {
     PATTY_AX25_SOCK_SABME
 };
 
+enum patty_ax25_sock_flow {
+    PATTY_AX25_SOCK_WAIT,
+    PATTY_AX25_SOCK_READY
+};
+
 enum patty_ax25_sock_opt {
     PATTY_AX25_SOCK_IF
 };
@@ -68,6 +73,7 @@ typedef struct _patty_ax25_sock {
     enum patty_ax25_version     version;
     enum patty_ax25_sock_status status;
     enum patty_ax25_sock_mode   mode;
+    enum patty_ax25_sock_flow   flow;
 
     size_t n_maxlen_tx,
            n_maxlen_rx,

src/server.c

@@ -1416,6 +1416,7 @@ static int handle_rr(patty_ax25_server *server,
 
         case PATTY_AX25_FRAME_RESPONSE:
             sock->vs = frame->nr;
+
             fd_watch(server, sock->fd);
 
             patty_timer_start(&sock->timer_t3, PATTY_AX25_SOCK_DEFAULT_KEEPALIVE);
@@ -1447,7 +1448,9 @@ static int handle_rnr(patty_ax25_server *server,
                 patty_ax25_sock_send_rnr(sock, PATTY_AX25_FRAME_RESPONSE, 1);
 
         case PATTY_AX25_FRAME_RESPONSE:
-            sock->vs = frame->nr;
+            sock->flow = PATTY_AX25_SOCK_WAIT;
+            sock->vs   = frame->nr;
+
             fd_clear(server, sock->fd);
 
             patty_timer_start(&sock->timer_t3, PATTY_AX25_SOCK_DEFAULT_KEEPALIVE);
@@ -1833,7 +1836,7 @@ static int handle_sock(uint32_t key,
 
             if (patty_timer_expired(&sock->timer_t3)) {
                 /*
-                 * AX.25 v.2.2 Section 6.7.1.3 "Inactive Link Timer T3"
+                 * AX.25 v.2.2 Section 6.7.1.3, "Inactive Link Timer T3"
                  */
                 int ret = FD_ISSET(sock->fd, &server->fds_watch)?
                     patty_ax25_sock_send_rr(sock, PATTY_AX25_FRAME_COMMAND, 1):
@@ -1854,13 +1857,21 @@ static int handle_sock(uint32_t key,
     }
 
     /*
-     * NOTE: See AX.25 2.2, Section 6.4.1, "Sending I Frames"
+     * AX.25 v2.2, Section 6.4.1, "Sending I Frames"
      */
-    if (sock->vs + sock->n_window_tx == sock->vs) {
+    if (sock->flow == PATTY_AX25_SOCK_READY) {
-        fd_clear(server, sock->fd);
+        if (sock->vs % sock->n_window_tx == sock->n_window_tx - 1) {
+            sock->flow = PATTY_AX25_SOCK_WAIT;
 
-        return patty_ax25_sock_send_rnr(sock, PATTY_AX25_FRAME_COMMAND, 1);
+            fd_clear(server, sock->fd);
-        goto done;
+
+            patty_timer_start(&sock->timer_t1, sock->n_ack);
+            patty_timer_stop(&sock->timer_t3);
+
+            return patty_ax25_sock_send_rr(sock, PATTY_AX25_FRAME_COMMAND, 1);
+        }
+    } else if (sock->flow == PATTY_AX25_SOCK_WAIT) {
+        sock->flow = PATTY_AX25_SOCK_READY;
     }
 
     if ((len = read(sock->fd, sock->rx_buf, sock->n_maxlen_rx)) < 0) {
@@ -1882,7 +1893,7 @@ static int handle_sock(uint32_t key,
     }
 
     /*
-     * AX.25 v2.2, Section 6.4.1 "Sending I Frames"
+     * AX.25 v2.2, Section 6.4.1, "Sending I Frames"
      */
     patty_timer_start(&sock->timer_t1, sock->n_ack);
 

src/sock.c

@@ -200,6 +200,7 @@ void patty_ax25_sock_destroy(patty_ax25_sock *sock) {
 void patty_ax25_sock_init(patty_ax25_sock *sock) {
     sock->status      = PATTY_AX25_SOCK_CLOSED;
     sock->mode        = PATTY_AX25_SOCK_DM;
+    sock->flow        = PATTY_AX25_SOCK_WAIT;
     sock->n_maxlen_tx = PATTY_AX25_SOCK_DEFAULT_I_LEN;
     sock->n_maxlen_rx = PATTY_AX25_SOCK_DEFAULT_I_LEN;
     sock->n_window_tx = PATTY_AX25_SOCK_DEFAULT_WINDOW;
@@ -211,9 +212,10 @@ void patty_ax25_sock_init(patty_ax25_sock *sock) {
 }
 
 /*
- * AX.25 v2.2 Specification, Section 6.5 "Resetting Procedure"
+ * AX.25 v2.2, Section 6.5 "Resetting Procedure"
  */
 void patty_ax25_sock_reset(patty_ax25_sock *sock) {
+    sock->flow    = PATTY_AX25_SOCK_READY;
     sock->vs      = 0;
     sock->vr      = 0;
     sock->va      = 0;