Clean up AGWPE connection data upon termination

Per-connection data for an AGWPE connection was being cleaned up only
when the client itself went away, rather than when each connection
was terminated. This led to reuse of stale state machine instances,
which in turn led to incorrect connection attempts and statistics.

The following changes have been made to address this:

* Per-connection cleanup code from dl_client_cleanup has been moved
  to a new function, dl_connection_cleanup. dl_client_cleanup now
  calls this new function from within its existing loop, walking
  though all connections for the client being cleaned up.

* A new function, dl_connection_terminated, encapsulates the removal
  of a single state machine instance from the list and the cleanup of
  that connection instance, calling dl_connection_cleanup for the
  latter.

* Everywhere that server_link_terminated is being called, a new call
  to dl_connection_terminated has been added nearby, to ensure the
  connection is cleaned up. The call is "nearby" because invocations
  of server_link_terminated differ in their surrounding calls to
  other timer and state functions, and the order of those calls, so
  simply wrapping server_link_terminated is not appropriate.

  Many, but not all, existing calls to server_link_terminated have
  nearby calls to set the state machine state to disconnected. While
  this is also done in dl_connection_cleanup, the existing calls have
  been left to minimize disruption. (There is no real cost associated
  with changing state from disconnected to disconnected.)

These changes have been tested in as many situations as possible, with
Direwolf started using '-d ac' to watch debug output for both AGWPE
and connection / state machine related activity.

Fixes #534, Fixes #535

Author: mfncooper

src/ax25_link.c

@@ -1,7 +1,7 @@
 //
 //    This file is part of Dire Wolf, an amateur radio packet TNC.
 //
-//    Copyright (C) 2016, 2017, 2018, 2023, 2024  John Langner, WB2OSZ
+//    Copyright (C) 2016, 2017, 2018, 2023, 2024, 2025  John Langner, WB2OSZ
 //
 //    This program is free software: you can redistribute it and/or modify
 //    it under the terms of the GNU General Public License as published by
@@ -599,6 +599,8 @@ static int AX25MODULO(int n, int m, const char *file, const char *func, int line
 // TODO: add SELECT_T1_VALUE	for debugging.
 
 
+static void dl_connection_cleanup (ax25_dlsm_t *S);
+static void dl_connection_terminated (ax25_dlsm_t *S);
 static void dl_data_indication (ax25_dlsm_t *S, int pid, char *data, int len);
 
 static void i_frame (ax25_dlsm_t *S, cmdres_t cr, int p, int nr, int ns, int pid, char *info_ptr, int info_len);
@@ -1101,6 +1103,7 @@ void dl_disconnect_request (dlq_item_t *E)
 	    text_color_set(DW_COLOR_INFO);
 	    dw_printf ("Stream %d: Disconnected from %s.\n", S->stream_id, S->addrs[PEERCALL]);
 	    server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 0);
+	    dl_connection_terminated (S);
 	    break;
 
 	  case 	state_1_awaiting_connection:
@@ -1129,6 +1132,7 @@ void dl_disconnect_request (dlq_item_t *E)
 	    STOP_T3;	// probably don't need.
 	    enter_new_state (S, state_0_disconnected, __func__, __LINE__);
 	    server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 0);
+	    dl_connection_terminated (S);
 	    break;
 
 	  case 	state_2_awaiting_release:
@@ -1159,6 +1163,7 @@ void dl_disconnect_request (dlq_item_t *E)
 
 	      STOP_T1;
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    break;
 
@@ -1742,6 +1747,133 @@ void dl_outstanding_frames_request (dlq_item_t *E)
 
 
 
+/*------------------------------------------------------------------------------
+ *
+ * Name:	dl_connection_cleanup
+ *
+ * Purpose:	Clean out a specific state machine and its references, freeing
+ *              associated memory.
+ *
+ * Inputs:	S	- Data Link State Machine.
+ *
+ * Description:	Clean out a specific state machine and anything related to it.
+ *              Free the associated memory.
+ *
+ *------------------------------------------------------------------------------*/
+
+static void dl_connection_cleanup (ax25_dlsm_t *S)
+{
+	int n;
+
+	if (s_debug_stats) {
+	  text_color_set(DW_COLOR_INFO);
+	  dw_printf ("%d  I frames received\n",    S->count_recv_frame_type[frame_type_I]);
+
+	  dw_printf ("%d  RR frames received\n",   S->count_recv_frame_type[frame_type_S_RR]);
+	  dw_printf ("%d  RNR frames received\n",  S->count_recv_frame_type[frame_type_S_RNR]);
+	  dw_printf ("%d  REJ frames received\n",  S->count_recv_frame_type[frame_type_S_REJ]);
+	  dw_printf ("%d  SREJ frames received\n", S->count_recv_frame_type[frame_type_S_SREJ]);
+
+	  dw_printf ("%d  SABME frames received\n", S->count_recv_frame_type[frame_type_U_SABME]);
+	  dw_printf ("%d  SABM frames received\n",  S->count_recv_frame_type[frame_type_U_SABM]);
+	  dw_printf ("%d  DISC frames received\n",  S->count_recv_frame_type[frame_type_U_DISC]);
+	  dw_printf ("%d  DM frames received\n",    S->count_recv_frame_type[frame_type_U_DM]);
+	  dw_printf ("%d  UA frames received\n",    S->count_recv_frame_type[frame_type_U_UA]);
+	  dw_printf ("%d  FRMR frames received\n",  S->count_recv_frame_type[frame_type_U_FRMR]);
+	  dw_printf ("%d  UI frames received\n",    S->count_recv_frame_type[frame_type_U_UI]);
+	  dw_printf ("%d  XID frames received\n",   S->count_recv_frame_type[frame_type_U_XID]);
+	  dw_printf ("%d  TEST frames received\n",  S->count_recv_frame_type[frame_type_U_TEST]);
+
+	  dw_printf ("%d  peak retry count\n",      S->peak_rc_value);
+	}
+
+	if (s_debug_client_app) {
+	  text_color_set(DW_COLOR_DEBUG);
+	  dw_printf ("dl_connection_cleanup: remove %s>%s\n", S->addrs[AX25_SOURCE], S->addrs[AX25_DESTINATION]);
+	}
+
+	discard_i_queue (S);
+
+	for (n = 0; n < 128; n++) {
+	  if (S->txdata_by_ns[n] != NULL) {
+	    cdata_delete (S->txdata_by_ns[n]);
+	    S->txdata_by_ns[n] = NULL;
+	  }
+	}
+
+	for (n = 0; n < 128; n++) {
+	  if (S->rxdata_by_ns[n] != NULL) {
+	    cdata_delete (S->rxdata_by_ns[n]);
+	    S->rxdata_by_ns[n] = NULL;
+	  }
+	}
+
+	if (S->ra_buff != NULL) {
+	  cdata_delete (S->ra_buff);
+	  S->ra_buff = NULL;
+	}
+
+	// Put into disconnected state.
+	// If "connected" indicator (e.g. LED) was on, this will turn it off.
+
+	enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+
+	S->magic1 = 0;
+	S->magic2 = 0;
+	S->magic3 = 0;
+
+	free (S);
+
+} /* end dl_connection_cleanup */
+
+
+
+/*------------------------------------------------------------------------------
+ *
+ * Name:	dl_connection_terminated
+ *
+ * Purpose:	Connection has gone away.  Clean up any data associated with it.
+ *
+ * Inputs:	S	- Data Link State Machine.
+ *
+ * Description:	Clean out anything related to the specified connection, and
+ *              remove the associated state machine from the list.
+ *
+ *------------------------------------------------------------------------------*/
+
+static void dl_connection_terminated (ax25_dlsm_t *S)
+{
+	ax25_dlsm_t *dlentry;
+	ax25_dlsm_t *dlprev;
+
+	// Look for corruption or double freeing.
+
+	assert (S->magic1 == MAGIC1);
+	assert (S->magic2 == MAGIC2);
+	assert (S->magic3 == MAGIC3);
+
+	// Remove from the list.
+
+	dlprev = NULL;
+	dlentry = list_head;
+	while (dlentry != S) {
+	  dlprev = dlentry;
+	  dlentry = dlentry->next;
+	}
+	if (!dlprev) {
+	  list_head = dlentry->next;
+	} else {
+	  dlprev->next = dlentry->next;
+	}
+
+	// Clean up the connection.
+
+	dl_connection_cleanup(S);
+
+} /* end dl_connection_terminated */
+
+
+
 /*------------------------------------------------------------------------------
  *
  * Name:	dl_client_cleanup
@@ -1785,76 +1917,15 @@ void dl_client_cleanup (dlq_item_t *E)
 
 	  if (S->client == E->client ) {
 
-	    int n;
-
-	    if (s_debug_stats) {
-	      text_color_set(DW_COLOR_INFO);
-	      dw_printf ("%d  I frames received\n",    S->count_recv_frame_type[frame_type_I]);
-
-	      dw_printf ("%d  RR frames received\n",   S->count_recv_frame_type[frame_type_S_RR]);
-	      dw_printf ("%d  RNR frames received\n",  S->count_recv_frame_type[frame_type_S_RNR]);
-	      dw_printf ("%d  REJ frames received\n",  S->count_recv_frame_type[frame_type_S_REJ]);
-	      dw_printf ("%d  SREJ frames received\n", S->count_recv_frame_type[frame_type_S_SREJ]);
-
-	      dw_printf ("%d  SABME frames received\n", S->count_recv_frame_type[frame_type_U_SABME]);
-	      dw_printf ("%d  SABM frames received\n",  S->count_recv_frame_type[frame_type_U_SABM]);
-	      dw_printf ("%d  DISC frames received\n",  S->count_recv_frame_type[frame_type_U_DISC]);
-	      dw_printf ("%d  DM frames received\n",    S->count_recv_frame_type[frame_type_U_DM]);
-	      dw_printf ("%d  UA frames received\n",    S->count_recv_frame_type[frame_type_U_UA]);
-	      dw_printf ("%d  FRMR frames received\n",  S->count_recv_frame_type[frame_type_U_FRMR]);
-	      dw_printf ("%d  UI frames received\n",    S->count_recv_frame_type[frame_type_U_UI]);
-	      dw_printf ("%d  XID frames received\n",   S->count_recv_frame_type[frame_type_U_XID]);
-	      dw_printf ("%d  TEST frames received\n",  S->count_recv_frame_type[frame_type_U_TEST]);
-
-	      dw_printf ("%d  peak retry count\n",      S->peak_rc_value);
-	    }
-
-	    if (s_debug_client_app) {
-	      text_color_set(DW_COLOR_DEBUG);
-	      dw_printf ("dl_client_cleanup: remove %s>%s\n", S->addrs[AX25_SOURCE], S->addrs[AX25_DESTINATION]);
-	    }
-
-	    discard_i_queue (S);
-
-	    for (n = 0; n < 128; n++) {
-	      if (S->txdata_by_ns[n] != NULL) {
-	        cdata_delete (S->txdata_by_ns[n]);
-	        S->txdata_by_ns[n] = NULL;
-	      }
-	    }
-
-	    for (n = 0; n < 128; n++) {
-	      if (S->rxdata_by_ns[n] != NULL) {
-	        cdata_delete (S->rxdata_by_ns[n]);
-	        S->rxdata_by_ns[n] = NULL;
-	      }
-	    }
-
-	    if (S->ra_buff != NULL) {
-	      cdata_delete (S->ra_buff);
-	      S->ra_buff = NULL;
-	    }
-
-	    // Put into disconnected state.
-	    // If "connected" indicator (e.g. LED) was on, this will turn it off.
-
-	    enter_new_state (S, state_0_disconnected, __func__, __LINE__);
-
-	    // Take S out of list.
-
-	    S->magic1 = 0;
-	    S->magic2 = 0;
-	    S->magic3 = 0;
-
 	    if (S == list_head) {		// first one on list.
 
 	      list_head = S->next;
-	      free (S);
+	      dl_connection_cleanup (S);
 	      S = list_head;
 	    }
 	    else {				// not the first one.
 	      dlprev->next = S->next;
-	      free (S);
+	      dl_connection_cleanup (S);
 	      S = dlprev->next;
 	    }
 	  }
@@ -4504,6 +4575,7 @@ static void disc_frame (ax25_dlsm_t *S, int p)
 	      STOP_T1;
 	      STOP_T3;
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    break;
 	}
@@ -4591,6 +4663,7 @@ static void dm_frame (ax25_dlsm_t *S, int f)
 	      server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 0);
 	      STOP_T1;
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    else {
 	      // keep current state.
@@ -4613,6 +4686,7 @@ static void dm_frame (ax25_dlsm_t *S, int f)
 	      server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 0);
 	      STOP_T1;
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    else {
 	      // keep current state.
@@ -4634,6 +4708,7 @@ static void dm_frame (ax25_dlsm_t *S, int f)
 	    STOP_T1;
 	    STOP_T3;
 	    enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	    dl_connection_terminated (S);
 	    break;
 
 	  case 	state_5_awaiting_v22_connection:
@@ -4651,6 +4726,7 @@ static void dm_frame (ax25_dlsm_t *S, int f)
 	      server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 0);
 	      STOP_T1;
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    else {
 	      // keep current state.
@@ -4858,6 +4934,7 @@ static void ua_frame (ax25_dlsm_t *S, int f)
 	      server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 0);
 	      STOP_T1;
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    else {
 	      if (s_debug_protocol_errors) {
@@ -5374,6 +5451,7 @@ static void t1_expiry (ax25_dlsm_t *S)
 	      dw_printf ("Failed to connect to %s after %d tries.\n", S->addrs[PEERCALL], S->n2_retry);
 	      server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 1);
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    else {
 	      cmdres_t cmd = cr_cmd;
@@ -5400,6 +5478,7 @@ static void t1_expiry (ax25_dlsm_t *S)
 	      dw_printf ("Stream %d: Disconnected from %s.\n", S->stream_id, S->addrs[PEERCALL]);
 	      server_link_terminated (S->chan, S->client, S->addrs[PEERCALL], S->addrs[OWNCALL], 0);
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    else {
 	      cmdres_t cmd = cr_cmd;
@@ -5473,6 +5552,7 @@ static void t1_expiry (ax25_dlsm_t *S)
 	      lm_data_request (S->chan, TQ_PRIO_1_LO, pp);
 
 	      enter_new_state (S, state_0_disconnected, __func__, __LINE__);
+	      dl_connection_terminated (S);
 	    }
 	    else {
 	      SET_RC(S->rc+1);