Implement XID/SABM/SABME ack timers

Changes:

    * Implement patty_ax25_sock_timeR_ack_restart() to initialize the
      XID/SABM/SABME ack Timer T1

    * Implement patty_ax25_sock_timer_ack_cancel() to clear Timer T1

    * Implement patty_ax25_sock_timer_ack_sub() to subtract the value of
      a struct timeval from Timer T1

    * Implement patty_ax25_sock_timer_ack_expired() to indicate if the
      ack Timer T1 has expired

Other changes:

    * Rearrange patty_ax25_sock a bit

include/patty/ax25/sock.h

@@ -55,10 +55,6 @@ typedef struct _patty_ax25_sock {
     enum patty_ax25_sock_status status;
     enum patty_ax25_sock_mode   mode;
 
-    struct timeval timer_ack,
-                   timer_response,
-                   timer_keepalive;
-
     size_t n_maxlen_tx,
            n_maxlen_rx,
            n_window_tx,
@@ -66,12 +62,18 @@ typedef struct _patty_ax25_sock {
            n_ack,
            n_retry;
 
-    unsigned int seq_send,
+    struct timeval timer_ack,       /* Timer T1 */
-                 seq_recv;
+                   timer_response,
+                   timer_keepalive;
 
     uint32_t flags_classes,
              flags_hdlc;
 
+    unsigned int seq_send,
+                 seq_recv;
+
+    size_t retries;
+
     int fd;
     char pty[PATTY_AX25_SOCK_PATH_SIZE];
 
@@ -96,6 +98,15 @@ patty_ax25_sock *patty_ax25_sock_new(enum patty_ax25_proto proto,
 
 void patty_ax25_sock_destroy(patty_ax25_sock *sock);
 
+void patty_ax25_sock_timer_ack_restart(patty_ax25_sock *sock);
+
+void patty_ax25_sock_timer_ack_cancel(patty_ax25_sock *sock);
+
+void patty_ax25_sock_timer_ack_sub(patty_ax25_sock *sock,
+                                   struct timeval *elapsed);
+
+int patty_ax25_sock_timer_ack_expired(patty_ax25_sock *sock);
+
 int patty_ax25_sock_reset(patty_ax25_sock *sock);
 
 int patty_ax25_sock_upgrade(patty_ax25_sock *sock,

src/sock.c

@@ -179,12 +179,43 @@ void patty_ax25_sock_destroy(patty_ax25_sock *sock) {
     free(sock);
 }
 
+/*
+ * AX.25 v2.2 Specification, Section 6.3.1 "AX.25 Link Connection Establishment"
+ */
+void patty_ax25_sock_timer_ack_restart(patty_ax25_sock *sock) {
+    sock->timer_ack.tv_sec  =  sock->n_ack / 1000;
+    sock->timer_ack.tv_usec = (sock->n_ack % 1000) * 1000;
+}
+
+void patty_ax25_sock_timer_ack_cancel(patty_ax25_sock *sock) {
+    sock->timer_ack.tv_sec  = 0;
+    sock->timer_ack.tv_usec = 0;
+}
+
+void patty_ax25_sock_timer_ack_sub(patty_ax25_sock *sock,
+                                   struct timeval *elapsed) {
+    struct timeval res;
+
+    timersub(&sock->timer_ack, elapsed, &res);
+
+    memcpy(&sock->timer_ack, &res, sizeof(sock->timer_ack));
+}
+
+int patty_ax25_sock_timer_ack_expired(patty_ax25_sock *sock) {
+    return (sock->timer_ack.tv_sec <= 0 && sock->timer_ack.tv_usec == 0)? 1: 0;
+}
+
 /*
  * AX.25 v2.2 Specification, Section 6.5 "Resetting Procedure"
  */
 int patty_ax25_sock_reset(patty_ax25_sock *sock) {
     sock->seq_send = 0;
     sock->seq_recv = 0;
+    sock->retries  = sock->n_retry;
+
+    memset(&sock->timer_ack,       '\0', sizeof(sock->timer_ack));
+    memset(&sock->timer_response,  '\0', sizeof(sock->timer_response));
+    memset(&sock->timer_keepalive, '\0', sizeof(sock->timer_keepalive));
 
     return 0;
 }