server.c

//
//    This file is part of Dire Wolf, an amateur radio packet TNC.
//
//    Copyright (C) 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2020  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
//    the Free Software Foundation, either version 2 of the License, or
//    (at your option) any later version.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU General Public License for more details.
//
//    You should have received a copy of the GNU General Public License
//    along with this program.  If not, see <http://www.gnu.org/licenses/>.
//


/*------------------------------------------------------------------
 *
 * Module:      server.c
 *
 * Purpose:   	Provide service to other applications via "AGW TCPIP Socket Interface".
 *		
 * Input:	
 *
 * Outputs:	  
 *
 * Description:	This provides a TCP socket for communication with a client application.
 *		It implements a subset of the AGW socket interface.
 *
 *		Commands from application recognized:
 *
 *			'R'	Request for version number.
 *				(See below for response.)
 *
 *			'G'	Ask about radio ports.
 *				(See below for response.)
 *
 *			'g'	Capabilities of a port.  (new in 0.8)
 *				(See below for response.)
 *
 *			'k'	Ask to start receiving RAW AX25 frames.
 *
 *			'm'	Ask to start receiving Monitor AX25 frames.
 *				Enables sending of U, I, S, and T messages to client app.
 *
 *			'V'	Transmit UI data frame.
 *
 *			'H'	Report recently heard stations.  Not implemented yet.
 *
 *			'K'	Transmit raw AX.25 frame.
 *		
 *			'X'	Register CallSign 
 *		
 *			'x'	Unregister CallSign 
 *		
 *			'y'	Ask Outstanding frames waiting on a Port   (new in 1.2)
 *
 *			'Y'	How many frames waiting for transmit for a particular station (new in 1.5)
 *
 *			'C'	Connect, Start an AX.25 Connection			(new in 1.4)
 *
 *			'v'	Connect VIA, Start an AX.25 circuit thru digipeaters	(new in 1.4)
 *
 *			'c'	Connection with non-standard PID			(new in 1.4)
 *
 *			'D'	Send Connected Data					(new in 1.4)
 *
 *			'd'	Disconnect, Terminate an AX.25 Connection		(new in 1.4)
 *
 *		
 *			A message is printed if any others are received.
 *
 *			TODO: Should others be implemented?
 *				
 *
 *		Messages sent to client application:
 *
 *			'R'	Reply to Request for version number.
 *				Currently responds with major 1, minor 0.
 *
 *			'G'	Reply to Ask about radio ports.
 *
 *			'g'	Reply to capabilities of a port.  (new in 0.8)
 *
 *			'K'	Received AX.25 frame in raw format.
 *				(Enabled with 'k' command.)
 *
 *			'U'	Received AX.25 "UI" frames in monitor format.
 *				(Enabled with 'm' command.)
 *
 *			'I'	Received AX.25 "I" frames in monitor format.	(new in 1.6)
 *				(Enabled with 'm' command.)
 *
 *			'S'	Received AX.25 "S" and "U" (other than UI) frames in monitor format.	(new in 1.6)
 *				(Enabled with 'm' command.)
 *
 *			'T'	Own Transmitted AX.25 frames in monitor format.	(new in 1.6)
 *				(Enabled with 'm' command.)
 *
 *			'y'	Outstanding frames waiting on a Port   (new in 1.2)
 *
 *			'Y'	How many frames waiting for transmit for a particular station (new in 1.5)
 *
 *			'C'	AX.25 Connection Received		(new in 1.4)
 *
 *			'D'	Connected AX.25 Data			(new in 1.4)
 *
 *			'd'	Disconnected				(new in 1.4)
 *
 *
 *
 * References:	AGWPE TCP/IP API Tutorial
 *		http://uz7ho.org.ua/includes/agwpeapi.htm
 *
 *		It has disappeared from the original location but you can find it here:
 *		https://web.archive.org/web/20130807113413/http:/uz7ho.org.ua/includes/agwpeapi.htm
 *		https://www.on7lds.net/42/sites/default/files/AGWPEAPI.HTM
 *
 * 		Getting Started with Winsock
 *		http://msdn.microsoft.com/en-us/library/windows/desktop/bb530742(v=vs.85).aspx
 *
 *
 * Major change in 1.1:
 *
 *		Formerly a single client was allowed.
 *		Now we can have multiple concurrent clients.
 *
 *---------------------------------------------------------------*/


/*
 * Native Windows:	Use the Winsock interface.
 * Linux:		Use the BSD socket interface.
 * Cygwin:		Can use either one.
 */

#include "direwolf.h"		// Sets _WIN32_WINNT for XP API level needed by ws2tcpip.h

#if __WIN32__
#include <winsock2.h>
#include <ws2tcpip.h>  		// _WIN32_WINNT must be set to 0x0501 before including this
#else 
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#endif

#include <unistd.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <time.h>
#include <ctype.h>
#include <stddef.h>

#include "tq.h"
#include "ax25_pad.h"
#include "textcolor.h"
#include "audio.h"
#include "server.h"
#include "dlq.h"



/*
 * Previously, we allowed only one network connection at a time to each port.
 * In version 1.1, we allow multiple concurrent client apps to attach with the AGW network protocol.
 * The default is a limit of 3 client applications at the same time.
 * You can increase the limit by changing the line below.
 * A larger number consumes more resources so don't go crazy by making it larger than needed.
 */
// FIXME:  Put in direwolf.h rather than in .c file. Change name to reflect AGW vs KISS. Update user guide 5.7.

#define MAX_NET_CLIENTS 3

static int client_sock[MAX_NET_CLIENTS];	
					/* File descriptor for socket for */
					/* communication with client application. */
					/* Set to -1 if not connected. */
					/* (Don't use SOCKET type because it is unsigned.) */

static int enable_send_raw_to_client[MAX_NET_CLIENTS];
					/* Should we send received packets to client app in raw form? */
					/* Note that it starts as false for a new connection. */
					/* the client app must send a command to enable this. */

static int enable_send_monitor_to_client[MAX_NET_CLIENTS];
					/* Should we send received packets to client app in monitor form? */
					/* Note that it starts as false for a new connection. */
					/* the client app must send a command to enable this. */


// TODO:  define in one place, use everywhere.
// TODO:  Macro to terminate thread when no point to go on.

#if __WIN32__
#define THREAD_F unsigned __stdcall
#else 
#define THREAD_F void *
#endif

static THREAD_F connect_listen_thread (void *arg);
static THREAD_F cmd_listen_thread (void *arg);

/*
 * Message header for AGW protocol.
 * Multibyte numeric values require rearranging for big endian cpu.
 */

/*
 * With MinGW version 4.6, obviously x86.
 * or Linux gcc version 4.9, Linux ARM.
 *
 *	$ gcc -E -dM - < /dev/null | grep END
 *	#define __ORDER_LITTLE_ENDIAN__ 1234
 *	#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
 *	#define __ORDER_PDP_ENDIAN__ 3412
 *	#define __ORDER_BIG_ENDIAN__ 4321
 *	#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 *
 * This is for standard OpenWRT on MIPS.
 *
 *	#define __ORDER_LITTLE_ENDIAN__ 1234
 *	#define __FLOAT_WORD_ORDER__ __ORDER_BIG_ENDIAN__
 *	#define __ORDER_PDP_ENDIAN__ 3412
 *	#define __ORDER_BIG_ENDIAN__ 4321
 *	#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
 *
 * This was reported for an old Mac with PowerPC processor.
 * (Newer versions have x86.)
 *
 *	$ gcc -E -dM - < /dev/null | grep END
 *	#define __BIG_ENDIAN__ 1
 *	#define _BIG_ENDIAN 1
 */


#if defined(__BIG_ENDIAN__) || (defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)

// gcc >= 4.2 has __builtin_swap32() but might not be compatible with older versions or other compilers.

#define host2netle(x) ( (((x)>>24)&0x000000ff) | (((x)>>8)&0x0000ff00) | (((x)<<8)&0x00ff0000) | (((x)<<24)&0xff000000) )
#define netle2host(x) ( (((x)>>24)&0x000000ff) | (((x)>>8)&0x0000ff00) | (((x)<<8)&0x00ff0000) | (((x)<<24)&0xff000000) )

#else

#define host2netle(x) (x)
#define netle2host(x) (x)

#endif


struct agwpe_s {	
  unsigned char portx;		/* 0 for first, 1 for second, etc. */
  unsigned char reserved1;
  unsigned char reserved2;
  unsigned char reserved3;

  unsigned char datakind;	/* message type, usually written as a letter. */
  unsigned char reserved4;
  unsigned char pid;
  unsigned char reserved5;

  char call_from[10];

  char call_to[10];

  int data_len_NETLE;		/* Number of data bytes following. */
				/* _NETLE suffix is reminder to convert for network byte order. */

  int user_reserved_NETLE;
};


static void send_to_client (int client, void *reply_p);


/*-------------------------------------------------------------------
 *
 * Name:        debug_print 
 *
 * Purpose:     Print message to/from client for debugging.
 *
 * Inputs:	fromto		- Direction of message.
 *		client		- client number, 0 .. MAX_NET_CLIENTS-1
 *		pmsg		- Address of the message block.
 *		msg_len		- Length of the message.
 *
 *--------------------------------------------------------------------*/

static int debug_client = 0;		/* Debug option: Print information flowing from and to client. */

void server_set_debug (int n) 
{	
	debug_client = n;
}

void hex_dump (unsigned char *p, int len) 
{
	int n, i, offset;

	offset = 0;
	while (len > 0) {
	  n = len < 16 ? len : 16; 
	  dw_printf ("  %03x: ", offset);
	  for (i=0; i<n; i++) {
	    dw_printf (" %02x", p[i]);
	  }
	  for (i=n; i<16; i++) {
	    dw_printf ("   ");
	  }
	  dw_printf ("  ");
	  for (i=0; i<n; i++) {
	    dw_printf ("%c", isprint(p[i]) ? p[i] : '.');
	  }
	  dw_printf ("\n");
	  p += 16;
	  offset += 16;
	  len -= 16;
	}
}

typedef enum fromto_e { FROM_CLIENT=0, TO_CLIENT=1 } fromto_t;

static void debug_print (fromto_t fromto, int client, struct agwpe_s *pmsg, int msg_len)
{
	char direction [10];
	char datakind[80];
	const char *prefix [2] = { "<<<", ">>>" };

	switch (fromto) {

	  case FROM_CLIENT:
	    strlcpy (direction, "from", sizeof(direction));		/* from the client application */

	    switch (pmsg->datakind) {
	      case 'P': strlcpy (datakind, "Application Login",				sizeof(datakind)); break;
	      case 'X': strlcpy (datakind, "Register CallSign",				sizeof(datakind)); break;
	      case 'x': strlcpy (datakind, "Unregister CallSign",			sizeof(datakind)); break;
	      case 'G': strlcpy (datakind, "Ask Port Information",			sizeof(datakind)); break;
	      case 'm': strlcpy (datakind, "Enable Reception of Monitoring Frames",	sizeof(datakind)); break;
	      case 'R': strlcpy (datakind, "AGWPE Version Info",			sizeof(datakind)); break;
	      case 'g': strlcpy (datakind, "Ask Port Capabilities",			sizeof(datakind)); break;
	      case 'H': strlcpy (datakind, "Callsign Heard on a Port",			sizeof(datakind)); break;
	      case 'y': strlcpy (datakind, "Ask Outstanding frames waiting on a Port",	sizeof(datakind)); break;
	      case 'Y': strlcpy (datakind, "Ask Outstanding frames waiting for a connection", sizeof(datakind)); break;
	      case 'M': strlcpy (datakind, "Send UNPROTO Information",			sizeof(datakind)); break;
	      case 'C': strlcpy (datakind, "Connect, Start an AX.25 Connection",	sizeof(datakind)); break;
	      case 'D': strlcpy (datakind, "Send Connected Data",			sizeof(datakind)); break;
	      case 'd': strlcpy (datakind, "Disconnect, Terminate an AX.25 Connection",	sizeof(datakind)); break;
	      case 'v': strlcpy (datakind, "Connect VIA, Start an AX.25 circuit thru digipeaters", sizeof(datakind)); break;
	      case 'V': strlcpy (datakind, "Send UNPROTO VIA",				sizeof(datakind)); break;
	      case 'c': strlcpy (datakind, "Non-Standard Connections, Connection with PID", sizeof(datakind)); break;
	      case 'K': strlcpy (datakind, "Send data in raw AX.25 format",		sizeof(datakind)); break;
	      case 'k': strlcpy (datakind, "Activate reception of Frames in raw format", sizeof(datakind)); break;
	      default:  strlcpy (datakind, "**INVALID**",				sizeof(datakind)); break;
	    }
	    break;

	  case TO_CLIENT:
	  default:
	    strlcpy (direction, "to", sizeof(direction));	/* sent to the client application. */

	    switch (pmsg->datakind) {
	      case 'R': strlcpy (datakind, "Version Number",				sizeof(datakind)); break;
	      case 'X': strlcpy (datakind, "Callsign Registration",			sizeof(datakind)); break;
	      case 'G': strlcpy (datakind, "Port Information",				sizeof(datakind)); break;
	      case 'g': strlcpy (datakind, "Capabilities of a Port",			sizeof(datakind)); break;
	      case 'y': strlcpy (datakind, "Frames Outstanding on a Port",		sizeof(datakind)); break;
	      case 'Y': strlcpy (datakind, "Frames Outstanding on a Connection",	sizeof(datakind)); break;
	      case 'H': strlcpy (datakind, "Heard Stations on a Port",			sizeof(datakind)); break;
	      case 'C': strlcpy (datakind, "AX.25 Connection Received",			sizeof(datakind)); break;
	      case 'D': strlcpy (datakind, "Connected AX.25 Data",			sizeof(datakind)); break;
	      case 'd': strlcpy (datakind, "Disconnected",				sizeof(datakind)); break;
	      case 'M': strlcpy (datakind, "Monitored Connected Information",		sizeof(datakind)); break;
	      case 'S': strlcpy (datakind, "Monitored Supervisory Information",		sizeof(datakind)); break;
	      case 'U': strlcpy (datakind, "Monitored Unproto Information",		sizeof(datakind)); break;
	      case 'T': strlcpy (datakind, "Monitoring Own Information",		sizeof(datakind)); break;
	      case 'K': strlcpy (datakind, "Monitored Information in Raw Format",	sizeof(datakind)); break;
	      default:  strlcpy (datakind, "**INVALID**",				sizeof(datakind)); break;
	    }
	}

	text_color_set(DW_COLOR_DEBUG);
	dw_printf ("\n");

	dw_printf ("%s %s %s AGWPE client application %d, total length = %d\n",
			prefix[(int)fromto], datakind, direction, client, msg_len);

	dw_printf ("\tportx = %d, datakind = '%c', pid = 0x%02x\n", pmsg->portx, pmsg->datakind, pmsg->pid);
	dw_printf ("\tcall_from = \"%s\", call_to = \"%s\"\n", pmsg->call_from, pmsg->call_to);
	dw_printf ("\tdata_len = %d, user_reserved = %d, data =\n", netle2host(pmsg->data_len_NETLE), netle2host(pmsg->user_reserved_NETLE));

	hex_dump ((unsigned char*)pmsg + sizeof(struct agwpe_s), netle2host(pmsg->data_len_NETLE));

	if (msg_len < 36) {
	  text_color_set (DW_COLOR_ERROR);
	  dw_printf ("AGWPE message length, %d, is shorter than minimum 36.\n", msg_len);
	}
	if (msg_len != netle2host(pmsg->data_len_NETLE) + 36) {
	  text_color_set (DW_COLOR_ERROR);
	  dw_printf ("AGWPE message length, %d, inconsistent with data length %d.\n", msg_len, netle2host(pmsg->data_len_NETLE));
	}

}

/*-------------------------------------------------------------------
 *
 * Name:        server_init
 *
 * Purpose:     Set up a server to listen for connection requests from
 *		an application such as Xastir.
 *
 * Inputs:	mc->agwpe_port	- TCP port for server.
 *				  Main program has default of 8000 but allows
 *				  an alternative to be specified on the command line
 *
 *				0 means disable.  New in version 1.2.
 *
 * Outputs:	
 *
 * Description:	This starts at least two threads:
 *		  *  one to listen for a connection from client app.
 *		  *  one or more to listen for commands from client app.
 *		so the main application doesn't block while we wait for these.
 *
 *--------------------------------------------------------------------*/

static struct audio_s *save_audio_config_p;


void server_init (struct audio_s *audio_config_p, struct misc_config_s *mc)
{
	int client;

#if __WIN32__
	HANDLE connect_listen_th;
	HANDLE cmd_listen_th[MAX_NET_CLIENTS];
#else
	pthread_t connect_listen_tid;
	pthread_t cmd_listen_tid[MAX_NET_CLIENTS];
	int e;
#endif
	int server_port = mc->agwpe_port;		/* Usually 8000 but can be changed. */


#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
	dw_printf ("server_init ( %d )\n", server_port);
	debug_a = 1;
#endif

	save_audio_config_p = audio_config_p;

	for (client=0; client<MAX_NET_CLIENTS; client++) {
	  client_sock[client] = -1;
	  enable_send_raw_to_client[client] = 0;
	  enable_send_monitor_to_client[client] = 0;
	}

	if (server_port == 0) {
	  text_color_set(DW_COLOR_INFO);
	  dw_printf ("Disabled AGW network client port.\n");
	  return;
	}


/*
 * This waits for a client to connect and sets an available client_sock[n].
 */
#if __WIN32__
	connect_listen_th = (HANDLE)_beginthreadex (NULL, 0, connect_listen_thread, (void *)(ptrdiff_t)server_port, 0, NULL);
	if (connect_listen_th == NULL) {
	  text_color_set(DW_COLOR_ERROR);
	  dw_printf ("Could not create AGW connect listening thread\n");
	  return;
	}
#else
	e = pthread_create (&connect_listen_tid, NULL, connect_listen_thread, (void *)(ptrdiff_t)server_port);
	if (e != 0) {
	  text_color_set(DW_COLOR_ERROR);
	  perror("Could not create AGW connect listening thread");
	  return;
	}
#endif

/*
 * These read messages from client when client_sock[n] is valid.
 * Currently we start up a separate thread for each potential connection.
 * Possible later refinement.  Start one now, others only as needed.
 */
	for (client = 0; client < MAX_NET_CLIENTS; client++) {

#if __WIN32__
	  cmd_listen_th[client] = (HANDLE)_beginthreadex (NULL, 0, cmd_listen_thread, (void*)(ptrdiff_t)client, 0, NULL);
	  if (cmd_listen_th[client] == NULL) {
	    text_color_set(DW_COLOR_ERROR);
	    dw_printf ("Could not create AGW command listening thread for client %d\n", client);
	    return;
	  }
#else
	  e = pthread_create (&cmd_listen_tid[client], NULL, cmd_listen_thread, (void *)(ptrdiff_t)client);
	  if (e != 0) {
	    text_color_set(DW_COLOR_ERROR);
	    dw_printf ("Could not create AGW command listening thread for client %d\n", client);
	    // Replace add perror with better message handling.
	    perror("");
	    return;
	  }
#endif
	}
}


/*-------------------------------------------------------------------
 *
 * Name:        connect_listen_thread
 *
 * Purpose:     Wait for a connection request from an application.
 *
 * Inputs:	arg		- TCP port for server.
 *				  Main program has default of 8000 but allows
 *				  an alternative to be specified on the command line
 *
 * Outputs:	client_sock	- File descriptor for communicating with client app.
 *
 * Description:	Wait for connection request from client and establish
 *		communication.
 *		Note that the client can go away and come back again and
 *		re-establish communication without restarting this application.
 *
 *--------------------------------------------------------------------*/

static THREAD_F connect_listen_thread (void *arg)
{
#if __WIN32__

	struct addrinfo hints;
	struct addrinfo *ai = NULL;
	int err;
	char server_port_str[12];

	SOCKET listen_sock;  
	WSADATA wsadata;

	snprintf (server_port_str, sizeof(server_port_str), "%d", (int)(ptrdiff_t)arg);
#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
        dw_printf ("DEBUG: serverport = %d = '%s'\n", (int)(ptrdiff_t)arg, server_port_str);
#endif
	err = WSAStartup (MAKEWORD(2,2), &wsadata);
	if (err != 0) {
	    text_color_set(DW_COLOR_ERROR);
	    dw_printf("WSAStartup failed: %d\n", err);
	    return (0);
	}

	if (LOBYTE(wsadata.wVersion) != 2 || HIBYTE(wsadata.wVersion) != 2) {
	  text_color_set(DW_COLOR_ERROR);
          dw_printf("Could not find a usable version of Winsock.dll\n");
          WSACleanup();
	  //sleep (1);
          return (0);
	}

	memset (&hints, 0, sizeof(hints));
	hints.ai_family = AF_INET;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_protocol = IPPROTO_TCP;
	hints.ai_flags = AI_PASSIVE;

	err = getaddrinfo(NULL, server_port_str, &hints, &ai);
	if (err != 0) {
	    text_color_set(DW_COLOR_ERROR);
	    dw_printf("getaddrinfo failed: %d\n", err);
	    //sleep (1);
	    WSACleanup();
	    return (0);
	}

	listen_sock= socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
	if (listen_sock == INVALID_SOCKET) {
	  text_color_set(DW_COLOR_ERROR);
	  dw_printf ("connect_listen_thread: Socket creation failed, err=%d", WSAGetLastError());
	  return (0);
	}

#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
    	dw_printf("Binding to port %s ... \n", server_port_str);
#endif

	err = bind( listen_sock, ai->ai_addr, (int)ai->ai_addrlen);
	if (err == SOCKET_ERROR) {
	  text_color_set(DW_COLOR_ERROR);
          dw_printf("Bind failed with error: %d\n", WSAGetLastError());		// TODO: translate number to text?
	  dw_printf("Some other application is probably already using port %s.\n", server_port_str);
	  dw_printf("Try using a different port number with AGWPORT in the configuration file.\n");
          freeaddrinfo(ai);
          closesocket(listen_sock);
          WSACleanup();
          return (0);
        }

	freeaddrinfo(ai);

#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
 	dw_printf("opened socket as fd (%d) on port (%s) for stream i/o\n", listen_sock, server_port_str );
#endif

 	while (1) {

	  int client;
	  int c;
	  
	  client = -1;
	  for (c = 0; c < MAX_NET_CLIENTS && client < 0; c++) {
	    if (client_sock[c] <= 0) {
	      client = c;
	    }
	  }

/*
 * Listen for connection if we have not reached maximum.
 */
	  if (client >= 0) {

	    if(listen(listen_sock, MAX_NET_CLIENTS) == SOCKET_ERROR)
	    {
	      text_color_set(DW_COLOR_ERROR);
              dw_printf("Listen failed with error: %d\n", WSAGetLastError());
	      return (0);
	    }
	
	    text_color_set(DW_COLOR_INFO);
            dw_printf("Ready to accept AGW client application %d on port %s ...\n", client, server_port_str);
         
            client_sock[client] = accept(listen_sock, NULL, NULL);

	    if (client_sock[client] == -1) {
	      text_color_set(DW_COLOR_ERROR);
              dw_printf("Accept failed with error: %d\n", WSAGetLastError());
              closesocket(listen_sock);
              WSACleanup();
              return (0);
            }

	    text_color_set(DW_COLOR_INFO);
	    dw_printf("\nAttached to AGW client application %d ...\n\n", client);

/*
 * The command to change this is actually a toggle, not explicit on or off.
 * Make sure it has proper state when we get a new connection.
 */ 
	    enable_send_raw_to_client[client] = 0;
	    enable_send_monitor_to_client[client] = 0;
	  }
	  else {
	    SLEEP_SEC(1);	/* wait then check again if more clients allowed. */
	  }
 	}

#else		/* End of Windows case, now Linux */


    	struct sockaddr_in sockaddr; /* Internet socket address struct */
    	socklen_t sockaddr_size = sizeof(struct sockaddr_in);
	int server_port = (int)(ptrdiff_t)arg;
	int listen_sock;  
	int bcopt = 1;

	listen_sock= socket(AF_INET,SOCK_STREAM,0);
	if (listen_sock == -1) {
	  text_color_set(DW_COLOR_ERROR);
	  perror ("connect_listen_thread: Socket creation failed");
	  return (NULL);
	}

	/* Version 1.3 - as suggested by G8BPQ. */
	/* Without this, if you kill the application then try to run it */
	/* again quickly the port number is unavailable for a while. */
	/* Don't try doing the same thing On Windows; It has a different meaning. */
	/* http://stackoverflow.com/questions/14388706/socket-options-so-reuseaddr-and-so-reuseport-how-do-they-differ-do-they-mean-t */

        setsockopt (listen_sock, SOL_SOCKET, SO_REUSEADDR, (const char *)&bcopt, 4);


    	sockaddr.sin_addr.s_addr = INADDR_ANY;
    	sockaddr.sin_port = htons(server_port);
    	sockaddr.sin_family = AF_INET;

#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
    	dw_printf("Binding to port %d ... \n", server_port);
#endif

        if (bind(listen_sock,(struct sockaddr*)&sockaddr,sizeof(sockaddr))  == -1) {
	  text_color_set(DW_COLOR_ERROR);
          dw_printf("Bind failed with error: %d\n", errno);
          dw_printf("%s\n", strerror(errno));
	  dw_printf("Some other application is probably already using port %d.\n", server_port);
	  dw_printf("Try using a different port number with AGWPORT in the configuration file.\n");
          return (NULL);
	}

	getsockname( listen_sock, (struct sockaddr *)(&sockaddr), &sockaddr_size);

#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
 	dw_printf("opened socket as fd (%d) on port (%d) for stream i/o\n", listen_sock, ntohs(sockaddr.sin_port) );
#endif

 	while (1) {

	  int client;
	  int c;
	  
	  client = -1;
	  for (c = 0; c < MAX_NET_CLIENTS && client < 0; c++) {
	    if (client_sock[c] <= 0) {
	      client = c;
	    }
	  }

	  if (client >= 0) {

	    if(listen(listen_sock,MAX_NET_CLIENTS) == -1)
	    {
	      text_color_set(DW_COLOR_ERROR);
	      perror ("connect_listen_thread: Listen failed");
	      return (NULL);
	    }
	
	    text_color_set(DW_COLOR_INFO);
            dw_printf("Ready to accept AGW client application %d on port %d ...\n", client, server_port);
         
            client_sock[client] = accept(listen_sock, (struct sockaddr*)(&sockaddr),&sockaddr_size);

	    text_color_set(DW_COLOR_INFO);
	    dw_printf("\nAttached to AGW client application %d...\n\n", client);

/*
 * The command to change this is actually a toggle, not explicit on or off.
 * Make sure it has proper state when we get a new connection.
 */ 
	    enable_send_raw_to_client[client] = 0;
	    enable_send_monitor_to_client[client] = 0;
	  }
	  else {
	    SLEEP_SEC(1);	/* wait then check again if more clients allowed. */
	  }
 	}
#endif
}


/*-------------------------------------------------------------------
 *
 * Name:        server_send_rec_packet
 *
 * Purpose:     Send a received packet to the client app.
 *
 * Inputs:	chan		- Channel number where packet was received.
 *				  0 = first, 1 = second if any.
 *
 *		pp		- Identifier for packet object.
 *
 *		fbuf		- Address of raw received frame buffer.
 *		flen		- Length of raw received frame.
 *		
 *
 * Description:	Send message to client if connected.
 *		Disconnect from client, and notify user, if any error.
 *
 *		There are two different formats:
 *			RAW - the original received frame.
 *			MONITOR - human readable monitoring format.
 *
 *--------------------------------------------------------------------*/

static void mon_addrs (int chan, packet_t pp, char *result, int result_size);
static char mon_desc (packet_t pp, char *result, int result_size);


void server_send_rec_packet (int chan, packet_t pp, unsigned char *fbuf,  int flen)
{
	struct {	
	  struct agwpe_s hdr;
	  char data[1+AX25_MAX_PACKET_LEN];		
	} agwpe_msg;

	int err;

/*
 * RAW format
 */
	for (int client=0; client<MAX_NET_CLIENTS; client++) {

	  if (enable_send_raw_to_client[client] && client_sock[client] > 0){

	    memset (&agwpe_msg.hdr, 0, sizeof(agwpe_msg.hdr));

	    agwpe_msg.hdr.portx = chan;

	    agwpe_msg.hdr.datakind = 'K';

	    ax25_get_addr_with_ssid (pp, AX25_SOURCE, agwpe_msg.hdr.call_from);

	    ax25_get_addr_with_ssid (pp, AX25_DESTINATION, agwpe_msg.hdr.call_to);

	    agwpe_msg.hdr.data_len_NETLE = host2netle(flen + 1);

	    /* Stick in extra byte for the "TNC" to use. */

	    agwpe_msg.data[0] = chan << 4;		// Was 0.  Fixed in 1.8.
	    memcpy (agwpe_msg.data + 1, fbuf, (size_t)flen);

	    if (debug_client) {
	      debug_print (TO_CLIENT, client, &agwpe_msg.hdr, sizeof(agwpe_msg.hdr) + netle2host(agwpe_msg.hdr.data_len_NETLE));
	    }

#if __WIN32__	
            err = SOCK_SEND (client_sock[client], (char*)(&agwpe_msg), sizeof(agwpe_msg.hdr) + netle2host(agwpe_msg.hdr.data_len_NETLE));
	    if (err == SOCKET_ERROR)
	    {
	      text_color_set(DW_COLOR_ERROR);
	      dw_printf ("\nError %d sending message to AGW client application.  Closing connection.\n\n", WSAGetLastError());
	      closesocket (client_sock[client]);
	      client_sock[client] = -1;
	      WSACleanup();
	      dlq_client_cleanup (client);
	    }
#else
            err = SOCK_SEND (client_sock[client], &agwpe_msg, sizeof(agwpe_msg.hdr) + netle2host(agwpe_msg.hdr.data_len_NETLE));
	    if (err <= 0)
	    {
	      text_color_set(DW_COLOR_ERROR);
	      dw_printf ("\nError sending message to AGW client application.  Closing connection.\n\n");
	      close (client_sock[client]);
	      client_sock[client] = -1;    
	      dlq_client_cleanup (client);
	    }
#endif
	  }
	}

	// Application might want more human readable format.

	server_send_monitored (chan, pp, 0);

} /* end server_send_rec_packet */



void server_send_monitored (int chan, packet_t pp, int own_xmit)
{
/*
 * MONITOR format - 	'I' for information frames.
 *			'U' for unnumbered information.
 *			'S' for supervisory and other unnumbered.
 */
	struct {
	  struct agwpe_s hdr;
	  char data[128+AX25_MAX_PACKET_LEN];	// Add plenty of room for header prefix.
	} agwpe_msg;

	int err;

	for (int client=0; client<MAX_NET_CLIENTS; client++) {

	  if (enable_send_monitor_to_client[client] && client_sock[client] > 0) {

	    memset (&agwpe_msg.hdr, 0, sizeof(agwpe_msg.hdr));

	    agwpe_msg.hdr.portx = chan;	// datakind is added later.
	    ax25_get_addr_with_ssid (pp, AX25_SOURCE, agwpe_msg.hdr.call_from);
	    ax25_get_addr_with_ssid (pp, AX25_DESTINATION, agwpe_msg.hdr.call_to);

	    /* http://uz7ho.org.ua/includes/agwpeapi.htm#_Toc500723812 */

	    /* Description mentions one CR character after timestamp but example has two. */
	    /* Actual observed cases have only one. */
	    /* Also need to add extra CR, CR, null at end. */
	    /* The documentation example includes these 3 extra in the Len= value */
	    /* but actual observed data uses only the packet info length. */

	    // Documentation doesn't mention anything about including the via path.
	    // In version 1.4, we add that to match observed behaviour.

	    // This inconsistency was reported:
	    // Direwolf:
	    // [AGWE-IN] 1:Fm ZL4FOX-8 To Q7P2U2 [08:25:07]`I1*l V>/"9<}[:Barts Tracker 3.83V X
	    // AGWPE:
	    // [AGWE-IN] 1:Fm ZL4FOX-8 To Q7P2U2 Via WIDE3-3 [08:32:14]`I0*l V>/"98}[:Barts Tracker 3.83V X

	    // Format the channel and addresses, with leading and trailing space.

	    mon_addrs (chan, pp, (char*)(agwpe_msg.data), sizeof(agwpe_msg.data));

	    // Add the description with <... >

	    char desc[120];
	    agwpe_msg.hdr.datakind = mon_desc (pp, desc, sizeof(desc));
	    if (own_xmit) {
	      agwpe_msg.hdr.datakind = 'T';
	    }
	    strlcat ((char*)(agwpe_msg.data), desc, sizeof(agwpe_msg.data));

	    // Timestamp with [...]\r

	    time_t clock = time(NULL);
	    struct tm *tm = localtime(&clock);		// TODO: use localtime_r ?
	    char ts[32];
	    snprintf (ts, sizeof(ts), "[%02d:%02d:%02d]\r", tm->tm_hour, tm->tm_min, tm->tm_sec);
	    strlcat ((char*)(agwpe_msg.data), ts, sizeof(agwpe_msg.data));

	    // Information if any with \r.

	    unsigned char *pinfo = NULL;
	    int info_len = ax25_get_info (pp, &pinfo);
	    int msg_data_len = strlen((char*)(agwpe_msg.data));	// result length so far

	    if (info_len > 0 && pinfo != NULL) {
	      // Issue 367: Use of strlcat truncated information part at any nul character.
	      // Use memcpy instead to preserve binary data, e.g. NET/ROM.
	      memcpy (agwpe_msg.data + msg_data_len, pinfo, info_len);
	      msg_data_len += info_len;
	      agwpe_msg.data[msg_data_len++] = '\r';
	    }

	    agwpe_msg.data[msg_data_len++] = '\0';	// add nul at end, included in length.
	    agwpe_msg.hdr.data_len_NETLE = host2netle(msg_data_len);

	    if (debug_client) {
	      debug_print (TO_CLIENT, client, &agwpe_msg.hdr, sizeof(agwpe_msg.hdr) + netle2host(agwpe_msg.hdr.data_len_NETLE));
	    }

#if __WIN32__
            err = SOCK_SEND (client_sock[client], (char*)(&agwpe_msg), sizeof(agwpe_msg.hdr) + netle2host(agwpe_msg.hdr.data_len_NETLE));
	    if (err == SOCKET_ERROR)
	    {
	      text_color_set(DW_COLOR_ERROR);
	      dw_printf ("\nError %d sending message to AGW client application %d.  Closing connection.\n\n", WSAGetLastError(), client);
	      closesocket (client_sock[client]);
	      client_sock[client] = -1;
	      WSACleanup();
	      dlq_client_cleanup (client);
	    }
#else
            err = SOCK_SEND (client_sock[client], &agwpe_msg, sizeof(agwpe_msg.hdr) + netle2host(agwpe_msg.hdr.data_len_NETLE));
	    if (err <= 0)
	    {
	      text_color_set(DW_COLOR_ERROR);
	      dw_printf ("\nError sending message to AGW client application %d.  Closing connection.\n\n", client);
	      close (client_sock[client]);
	      client_sock[client] = -1;
	      dlq_client_cleanup (client);
	    }
#endif
	  }
	}

} /* server_send_monitored */


// Next two are broken out in case they can be reused elsewhere.

// Format addresses in AGWPR monitoring format such as:
//	 1:Fm ZL4FOX-8 To Q7P2U2 Via WIDE3-3

static void mon_addrs (int chan, packet_t pp, char *result, int result_size)
{
	char src[AX25_MAX_ADDR_LEN];
	char dst[AX25_MAX_ADDR_LEN];

	ax25_get_addr_with_ssid (pp, AX25_SOURCE, src);
	ax25_get_addr_with_ssid (pp, AX25_DESTINATION, dst);
	int num_digi = ax25_get_num_repeaters(pp);

	if (num_digi > 0) {

	  char via[AX25_MAX_REPEATERS*(AX25_MAX_ADDR_LEN+1)];
	  char stemp[AX25_MAX_ADDR_LEN+1];
	  int j;

	  ax25_get_addr_with_ssid (pp, AX25_REPEATER_1, via);
	  for (j = 1; j < num_digi; j++) {
	    ax25_get_addr_with_ssid (pp, AX25_REPEATER_1 + j, stemp);
	    strlcat (via, ",", sizeof(via));
	    strlcat (via, stemp, sizeof(via));
	  }
	  snprintf (result, result_size, " %d:Fm %s To %s Via %s ",
		chan+1, src, dst, via);
	}
	else {
	  snprintf (result, result_size, " %d:Fm %s To %s ",
			chan+1, src, dst);
	}
}


// Generate frame description in AGWPE monitoring format such as
//	<UI pid=F0 Len=123 >
//	<I R1 S3 pid=F0 Len=123 >
//	<RR P1 R5 >
//
// Returns:
//	'I' for information frame.
//	'U' for unnumbered information frame.
//	'S' for supervisory and other unnumbered frames.

static char mon_desc (packet_t pp, char *result, int result_size)
{
	cmdres_t cr;		// command/response.
	char ignore[80];	// direwolf description.  not used here.
	int pf;			// poll/final bit.
	int ns;			// N(S) Send sequence number.
	int nr;			// N(R) Received sequence number.
	char pf_text[4];	// P or F depending on whether command or response.

	ax25_frame_type_t ftype = ax25_frame_type (pp, &cr, ignore, &pf, &nr, &ns);

	switch (cr) {
	  case cr_cmd:	strcpy(pf_text, "P"); break;	// P only: I, SABME, SABM, DISC
	  case cr_res:	strcpy(pf_text, "F"); break;	// F only: DM, UA, FRMR
							// Either: RR, RNR, REJ, SREJ, UI, XID, TEST

	  default:	strcpy(pf_text, "PF"); break;	// Not AX.25 version >= 2.0
							// APRS is often sloppy about this but it
							// is essential for connected mode.
	}

	unsigned char *pinfo = NULL;	// I, UI, XID, SREJ, TEST can have information part.
	int info_len = ax25_get_info (pp, &pinfo);

	switch (ftype) {

	  case frame_type_I:		snprintf (result, result_size, "<I S%d R%d pid=%02X Len=%d %s=%d >",  ns, nr, ax25_get_pid(pp), info_len, pf_text, pf); return ('I');

	  case frame_type_U_UI:		snprintf (result, result_size, "<UI pid=%02X Len=%d %s=%d >", 	ax25_get_pid(pp), info_len, pf_text, pf);  return ('U'); break;

	  case frame_type_S_RR:		snprintf (result, result_size, "<RR R%d %s=%d >",	nr, pf_text, pf);	return ('S'); break;
	  case frame_type_S_RNR:	snprintf (result, result_size, "<RNR R%d %s=%d >",	nr, pf_text, pf);	return ('S'); break;
	  case frame_type_S_REJ:	snprintf (result, result_size, "<REJ R%d %s=%d >",	nr, pf_text, pf);	return ('S'); break;
	  case frame_type_S_SREJ:	snprintf (result, result_size, "<SREJ R%d %s=%d Len=%d >", nr, pf_text, pf, info_len);	return ('S'); break;

	  case frame_type_U_SABME:	snprintf (result, result_size, "<SABME %s=%d >",	pf_text, pf);		return ('S'); break;
	  case frame_type_U_SABM:	snprintf (result, result_size, "<SABM %s=%d >", 	pf_text, pf);		return ('S'); break;
	  case frame_type_U_DISC:	snprintf (result, result_size, "<DISC %s=%d >", 	pf_text, pf);		return ('S'); break;
	  case frame_type_U_DM:		snprintf (result, result_size, "<DM %s=%d >", 		pf_text, pf);		return ('S'); break;
	  case frame_type_U_UA:		snprintf (result, result_size, "<UA %s=%d >", 		pf_text, pf);		return ('S'); break;
	  case frame_type_U_FRMR:	snprintf (result, result_size, "<FRMR %s=%d >", 	pf_text, pf);		return ('S'); break;
	  case frame_type_U_XID:	snprintf (result, result_size, "<XID %s=%d Len=%d >", 	pf_text, pf, info_len);	return ('S'); break;
	  case frame_type_U_TEST:	snprintf (result, result_size, "<TEST %s=%d Len=%d >", 	pf_text, pf, info_len);	return ('S'); break;
	  default:
	  case frame_type_U:		snprintf (result, result_size, "<U other??? >");				return ('S'); break;
	}
}


/*-------------------------------------------------------------------
 *
 * Name:        server_link_established
 *
 * Purpose:     Send notification to client app when a link has
 *		been established with another station.
 *
 *		DL-CONNECT Confirm or DL-CONNECT Indication in the protocol spec.
 *
 * Inputs:	chan		- Which radio channel.
 *
 * 		client		- Which one of potentially several clients.
 *
 *		remote_call	- Callsign[-ssid] of remote station.
 *
 *		own_call	- Callsign[-ssid] of my end.
 *
 *		incoming	- true if connection was initiated from other end.
 *				  false if this end started it.
 *
 *--------------------------------------------------------------------*/

void server_link_established (int chan, int client, char *remote_call, char *own_call, int incoming)
{

	struct {
	  struct agwpe_s hdr;
	  char info[100];
	} reply;


	memset (&reply, 0, sizeof(reply));
	reply.hdr.portx = chan;
	reply.hdr.datakind = 'C';

	strlcpy (reply.hdr.call_from, remote_call, sizeof(reply.hdr.call_from));
	strlcpy (reply.hdr.call_to,   own_call,    sizeof(reply.hdr.call_to));

	// Question:  Should the via path be provided too?

	if (incoming) {
	  // Other end initiated the connection.
	  snprintf (reply.info, sizeof(reply.info), "*** CONNECTED To Station %s\r", remote_call);
	}
	else {
	  // We started the connection.
	  snprintf (reply.info, sizeof(reply.info), "*** CONNECTED With Station %s\r", remote_call);
	}
	reply.hdr.data_len_NETLE = host2netle(strlen(reply.info) + 1);

	send_to_client (client, &reply);

} /* end server_link_established */



/*-------------------------------------------------------------------
 *
 * Name:        server_link_terminated
 *
 * Purpose:     Send notification to client app when a link with
 *		another station has been terminated or a connection
 *		attempt failed.
 *
 *		DL-DISCONNECT Confirm or DL-DISCONNECT Indication in the protocol spec.
 *
 * Inputs:	chan		- Which radio channel.
 *
 * 		client		- Which one of potentially several clients.
 *
 *		remote_call	- Callsign[-ssid] of remote station.
 *
 *		own_call	- Callsign[-ssid] of my end.
 *
 *		timeout		- true when no answer from other station.
 *				  How do we distinguish who asked for the
 *				  termination of an existing link?
 *
 *--------------------------------------------------------------------*/

void server_link_terminated (int chan, int client, char *remote_call, char *own_call, int timeout)
{

	struct {
	  struct agwpe_s hdr;
	  char info[100];
	} reply;


	memset (&reply, 0, sizeof(reply));
	reply.hdr.portx = chan;
	reply.hdr.datakind = 'd';
	strlcpy (reply.hdr.call_from, remote_call, sizeof(reply.hdr.call_from));  /* right order */
	strlcpy (reply.hdr.call_to,   own_call,    sizeof(reply.hdr.call_to));

	if (timeout) {
	  snprintf (reply.info, sizeof(reply.info), "*** DISCONNECTED RETRYOUT With %s\r", remote_call);
	}
	else {
	  snprintf (reply.info, sizeof(reply.info), "*** DISCONNECTED From Station %s\r", remote_call);
	}
	reply.hdr.data_len_NETLE = host2netle(strlen(reply.info) + 1);

	send_to_client (client, &reply);


} /* end server_link_terminated */


/*-------------------------------------------------------------------
 *
 * Name:        server_rec_conn_data
 *
 * Purpose:     Send received connected data to the application.
 *
 *		DL-DATA Indication in the protocol spec.
 *
 * Inputs:	chan		- Which radio channel.
 *
 * 		client		- Which one of potentially several clients.
 *
 *		remote_call	- Callsign[-ssid] of remote station.
 *
 *		own_call	- Callsign[-ssid] of my end.
 *
 *		pid		- Protocol ID from I frame.
 *
 *		data_ptr	- Pointer to a block of bytes.
 *
 *		data_len	- Number of bytes.  Could be zero.
 *
 *--------------------------------------------------------------------*/

void server_rec_conn_data (int chan, int client, char *remote_call, char *own_call, int pid, char *data_ptr, int data_len)
{

	struct {
	  struct agwpe_s hdr;
	  char info[AX25_MAX_INFO_LEN];		// I suppose there is potential for something larger.
						// We'll cross that bridge if we ever come to it.
	} reply;


	memset (&reply.hdr, 0, sizeof(reply.hdr));
	reply.hdr.portx = chan;
	reply.hdr.datakind = 'D';
	reply.hdr.pid = pid;

	strlcpy (reply.hdr.call_from, remote_call, sizeof(reply.hdr.call_from));
	strlcpy (reply.hdr.call_to,   own_call,    sizeof(reply.hdr.call_to));

	if (data_len < 0) {
	  text_color_set(DW_COLOR_ERROR);
	  dw_printf ("Invalid length %d for connected data to client %d.\n", data_len, client);
	  data_len = 0;
	}
	else if (data_len > AX25_MAX_INFO_LEN) {
	  text_color_set(DW_COLOR_ERROR);
	  dw_printf ("Invalid length %d for connected data to client %d.\n", data_len, client);
	  data_len = AX25_MAX_INFO_LEN;
	}

	memcpy (reply.info, data_ptr, data_len);
	reply.hdr.data_len_NETLE = host2netle(data_len);

	send_to_client (client, &reply);

} /* end server_rec_conn_data */


/*-------------------------------------------------------------------
 *
 * Name:        server_outstanding_frames_reply
 *
 * Purpose:     Send 'Y' Outstanding frames for connected data to the application.
 *
 * Inputs:	chan		- Which radio channel.
 *
 * 		client		- Which one of potentially several clients.
 *
 *		own_call	- Callsign[-ssid] of my end.
 *
 *		remote_call	- Callsign[-ssid] of remote station.
 *
 *		count		- Number of frames sent from the application but
 *				  not yet received by the other station.
 *
 *--------------------------------------------------------------------*/

void server_outstanding_frames_reply (int chan, int client, char *own_call, char *remote_call, int count)
{

	struct {
	  struct agwpe_s hdr;
	  int count_NETLE;
	} reply;


	memset (&reply.hdr, 0, sizeof(reply.hdr));

	reply.hdr.portx = chan;
	reply.hdr.datakind = 'Y';

	strlcpy (reply.hdr.call_from, own_call,    sizeof(reply.hdr.call_from));
	strlcpy (reply.hdr.call_to,   remote_call, sizeof(reply.hdr.call_to));

	reply.hdr.data_len_NETLE = host2netle(4);
	reply.count_NETLE = host2netle(count);

	send_to_client (client, &reply);

} /* end server_outstanding_frames_reply */


/*-------------------------------------------------------------------
 *
 * Name:        read_from_socket
 *
 * Purpose:     Read from socket until we have desired number of bytes.
 *
 * Inputs:	fd		- file descriptor.
 *		ptr		- address where data should be placed.
 *		len		- desired number of bytes.
 *
 * Description:	Just a wrapper for the "read" system call but it should
 *		never return fewer than the desired number of bytes.
 *
 *--------------------------------------------------------------------*/

static int read_from_socket (int fd, char *ptr, int len)
{
	int got_bytes = 0;

#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
	dw_printf ("read_from_socket (%d, %p, %d)\n", fd, ptr, len);
#endif
	while (got_bytes < len) {
	  int n;

	  n = SOCK_RECV (fd, ptr + got_bytes, len - got_bytes);

#if DEBUG
	  text_color_set(DW_COLOR_DEBUG);
	  dw_printf ("read_from_socket: n = %d\n", n);
#endif
	  if (n <= 0) {
	    return (n);
	  }

	  got_bytes += n;
	}
	assert (got_bytes >= 0 && got_bytes <= len);

#if DEBUG
	text_color_set(DW_COLOR_DEBUG);
	dw_printf ("read_from_socket: return %d\n", got_bytes);
#endif
	return (got_bytes);
}


/*-------------------------------------------------------------------
 *
 * Name:        cmd_listen_thread
 *
 * Purpose:     Wait for command messages from an application.
 *
 * Inputs:	arg		- client number, 0 .. MAX_NET_CLIENTS-1
 *
 * Outputs:	client_sock[n]	- File descriptor for communicating with client app.
 *
 * Description:	Process messages from the client application.
 *		Note that the client can go away and come back again and
 *		re-establish communication without restarting this application.
 *
 *--------------------------------------------------------------------*/


static void send_to_client (int client, void *reply_p)
{
	struct agwpe_s *ph;
	int len;
	int err;

	ph = (struct agwpe_s *) reply_p;	// Replies are often hdr + other stuff.

	len = sizeof(struct agwpe_s) + netle2host(ph->data_len_NETLE);

	/* Not sure what max data length might be. */

	if (netle2host(ph->data_len_NETLE) < 0 || netle2host(ph->data_len_NETLE) > 4096) {
	  text_color_set(DW_COLOR_ERROR);
	  dw_printf ("Invalid data length %d for AGW protocol message to client %d.\n", netle2host(ph->data_len_NETLE), client);
	  debug_print (TO_CLIENT, client, ph, len);
	}

	if (debug_client) {
	  debug_print (TO_CLIENT, client, ph, len);
	}

	err = SOCK_SEND (client_sock[client], (char*)(ph), len);
	(void)err;
}


static THREAD_F cmd_listen_thread (void *arg)
{
	int n;

	struct {
	  struct agwpe_s hdr;		/* Command header. */
	
	  char data[AX25_MAX_PACKET_LEN]; /* Additional data used by some commands. */
					/* Maximum for 'V': 1 + 8*10 + 256 */
					/* Maximum for 'D': Info part length + 1 */
	} cmd;

	int client = (int)(ptrdiff_t)arg;

	assert (client >= 0 && client < MAX_NET_CLIENTS);

	while (1) {

	  while (client_sock[client] <= 0) {
	    SLEEP_SEC(1);			/* Not connected.  Try again later. */
	  }

	  n = read_from_socket (client_sock[client], (char *)(&cmd.hdr), sizeof(cmd.hdr));
	  if (n != sizeof(cmd.hdr)) {
	    text_color_set(DW_COLOR_ERROR);
	    dw_printf ("\nError getting message header from AGW client application %d.\n", client);
	    dw_printf ("Tried to read %d bytes but got only %d.\n", (int)sizeof(cmd.hdr), n);
	    dw_printf ("Closing connection.\n\n");
#if __WIN32__
	    closesocket (client_sock[client]);
#else
	    close (client_sock[client]);
#endif
	    client_sock[client] = -1;
	    dlq_client_cleanup (client);
	    continue;
	  }

/*
 * Take some precautions to guard against bad data which could cause problems later.
 */
	if (cmd.hdr.portx < 0 || cmd.hdr.portx >= MAX_CHANS) {
	  text_color_set(DW_COLOR_ERROR);
	  dw_printf ("\nInvalid port number, %d, in command '%c', from AGW client application %d.\n",
			cmd.hdr.portx, cmd.hdr.datakind, client);
	  cmd.hdr.portx = 0;	// avoid subscript out of bounds, try to keep going.
	}

/*
 * Call to/from fields are 10 bytes but contents must not exceed 9 characters.
 * It's not guaranteed that unused bytes will contain 0 so we
 * don't issue error message in this case. 
 */
	  cmd.hdr.call_from[sizeof(cmd.hdr.call_from)-1] = '\0';
	  cmd.hdr.call_to[sizeof(cmd.hdr.call_to)-1] = '\0';

/*
 * Following data must fit in available buffer.
 * Leave room for an extra nul byte terminator at end later.
 */

	  int data_len = netle2host(cmd.hdr.data_len_NETLE);

	  if (data_len < 0 || data_len > (int)(sizeof(cmd.data) - 1)) {

	    text_color_set(DW_COLOR_ERROR);
	    dw_printf ("\nInvalid message from AGW client application %d.\n", client);
	    dw_printf ("Data Length of %d is out of range.\n", data_len);
	
	    /* This is a bad situation. */
	    /* If we tried to read again, the header probably won't be there. */
	    /* No point in trying to continue reading.  */

	    dw_printf ("Closing connection.\n\n");
#if __WIN32__
	    closesocket (client_sock[client]);
#else
	    close (client_sock[client]);
#endif
	    client_sock[client] = -1;
	    dlq_client_cleanup (client);
	    return (0);
	  }

	  cmd.data[0] = '\0';

	  if (data_len > 0) {
	    n = read_from_socket (client_sock[client], cmd.data, data_len);
	    if (n != data_len) {
	      text_color_set(DW_COLOR_ERROR);
	      dw_printf ("\nError getting message data from AGW client application %d.\n", client);
	      dw_printf ("Tried to read %d bytes but got only %d.\n", data_len, n);
	      dw_printf ("Closing connection.\n\n");
#if __WIN32__
	      closesocket (client_sock[client]);
#else
	      close (client_sock[client]);
#endif
	      client_sock[client] = -1;
	      dlq_client_cleanup (client);
	      return (0);
	    }
	    if (n >= 0) {
		cmd.data[n] = '\0';	// Tidy if we print for debug.
	    }
	  }

/*
 * print & process message from client.
 */

	  if (debug_client) {
	    debug_print (FROM_CLIENT, client, &cmd.hdr, sizeof(cmd.hdr) + data_len);
	  }

	  switch (cmd.hdr.datakind) {

	    case 'R':				/* Request for version number */
	      {
		struct {
		  struct agwpe_s hdr;
	          int major_version_NETLE;
	          int minor_version_NETLE;
		} reply;


	        memset (&reply, 0, sizeof(reply));
	        reply.hdr.datakind = 'R';
	        reply.hdr.data_len_NETLE = host2netle(sizeof(reply.major_version_NETLE) + sizeof(reply.minor_version_NETLE));
		assert (netle2host(reply.hdr.data_len_NETLE) == 8);

		// Xastir only prints this and doesn't care otherwise.
		// APRSIS32 doesn't seem to care.
		// UI-View32 wants on 2000.15 or later.

	        reply.major_version_NETLE = host2netle(2005);
	        reply.minor_version_NETLE = host2netle(127);

		assert (sizeof(reply) == 44);

	        send_to_client (client, &reply);

	      }
	      break;

	    case 'G':				/* Ask about radio ports */

	      {
		struct {
		  struct agwpe_s hdr;
	 	  char info[200];
		} reply;


		int j, count;


	        memset (&reply, 0, sizeof(reply));
	        reply.hdr.datakind = 'G';


		// Xastir only prints this and doesn't care otherwise.
		// YAAC uses this to identify available channels.

		// The interface manual wants the first to be "Port1" 
		// so channel 0 corresponds to "Port1."
		// We can have gaps in the numbering.
		// I wonder what applications will think about that.

		// No other place cares about total number.

		count = 0;
		for (j=0; j<MAX_CHANS; j++) {
	          if (save_audio_config_p->chan_medium[j] == MEDIUM_RADIO ||
	              save_audio_config_p->chan_medium[j] == MEDIUM_IGATE ||
	              save_audio_config_p->chan_medium[j] == MEDIUM_NETTNC) {
		    count++;
		  }
		}
		snprintf (reply.info, sizeof(reply.info), "%d;", count);

		for (j=0; j<MAX_CHANS; j++) {

	          switch (save_audio_config_p->chan_medium[j]) {

	            case MEDIUM_RADIO:
	              {
	                // Misleading if using stdin or udp.
		        char stemp[100];
		        int a = ACHAN2ADEV(j);
		        // If I was really ambitious, some description could be provided.
		        static const char *names[8] = { "first", "second", "third", "fourth", "fifth", "sixth", "seventh", "eighth" };

		        if (save_audio_config_p->adev[a].num_channels == 1) {
		          snprintf (stemp, sizeof(stemp), "Port%d %s soundcard mono;", j+1, names[a]);
		          strlcat (reply.info, stemp, sizeof(reply.info));
		        }
		        else {
		          snprintf (stemp, sizeof(stemp), "Port%d %s soundcard %s;", j+1, names[a], j&1 ? "right" : "left");
		          strlcat (reply.info, stemp, sizeof(reply.info));
		        }
	              }
	              break;

	            case MEDIUM_IGATE:
	              {
		        char stemp[100];
		        snprintf (stemp, sizeof(stemp), "Port%d Internet Gateway;", j+1);
		        strlcat (reply.info, stemp, sizeof(reply.info));
	              }
		      break;

	            case MEDIUM_NETTNC:
	              {
	                // could elaborate with hostname, etc.
		        char stemp[100];
		        snprintf (stemp, sizeof(stemp), "Port%d Network TNC;", j+1);
		        strlcat (reply.info, stemp, sizeof(reply.info));
	              }
	              break;

	            default:
	              ; // Only list valid channels.
	              break;

		  }  // switch
		}  // for each channel

	        reply.hdr.data_len_NETLE = host2netle(strlen(reply.info) + 1);

	        send_to_client (client, &reply);
	      }
	      break;


	    case 'g':				/* Ask about capabilities of a port. */

	      {
		struct {
		  struct agwpe_s hdr;
	 	  unsigned char on_air_baud_rate; 	/* 0=1200, 1=2400, 2=4800, 3=9600, ... */
		  unsigned char traffic_level;		/* 0xff if not in autoupdate mode */
		  unsigned char tx_delay;
		  unsigned char tx_tail;
		  unsigned char persist;
		  unsigned char slottime;
		  unsigned char maxframe;
		  unsigned char active_connections;
		  int how_many_bytes_NETLE;
		} reply;


	        memset (&reply, 0, sizeof(reply));

		reply.hdr.portx = cmd.hdr.portx;	/* Reply with same port number ! */
	        reply.hdr.datakind = 'g';
	        reply.hdr.data_len_NETLE = host2netle(12);

		// YAAC asks for this.
		// Fake it to keep application happy.
	        // TODO:  Supply real values instead of just faking it.

	        reply.on_air_baud_rate = 0;
		reply.traffic_level = 1;
		reply.tx_delay = 0x19;
		reply.tx_tail = 4;
		reply.persist = 0xc8;
		reply.slottime = 4;
		reply.maxframe = 7;
		reply.active_connections = 0;
		reply.how_many_bytes_NETLE = host2netle(1);

		assert (sizeof(reply) == 48);

	        send_to_client (client, &reply);

	      }
	      break;


	    case 'H':				/* Ask about recently heard stations on given port. */

		/* This should send back 20 'H' frames for the most recently heard stations. */
		/* If there are less available, empty frames are sent to make a total of 20. */
		/* Each contains the first and last heard times. */

	      {
#if 0						/* Currently, this information is not being collected. */
		struct {
		  struct agwpe_s hdr;
	 	  char info[100];
		} reply;


	        memset (&reply.hdr, 0, sizeof(reply.hdr));
	        reply.hdr.datakind = 'H';

		// TODO:  Implement properly.  

	        reply.hdr.portx = cmd.hdr.portx

	        strlcpy (reply.hdr.call_from, "WB2OSZ-15 Mon,01Jan2000 01:02:03  Tue,31Dec2099 23:45:56", sizeof(reply.hdr.call_from));
		// or                                                  00:00:00                00:00:00

	        strlcpy (agwpe_msg.data, ..., sizeof(agwpe_msg.data));

	        reply.hdr.data_len_NETLE = host2netle(strlen(reply.info));

	        send_to_client (client, &reply);
#endif
	      }
	      break;
	    



	    case 'k':				/* Ask to start receiving RAW AX25 frames */

	      // Actually it is a toggle so we must be sure to clear it for a new connection.

	      enable_send_raw_to_client[client] = ! enable_send_raw_to_client[client];
	      break;

	    case 'm':				/* Ask to start receiving Monitor frames */

	      // Actually it is a toggle so we must be sure to clear it for a new connection.

	      enable_send_monitor_to_client[client] = ! enable_send_monitor_to_client[client];
	      break;


	    case 'V':				/* Transmit UI data frame (with digipeater path) */
	      {
	      	// Data format is:
	      	//	1 byte for number of digipeaters.
	      	//	10 bytes for each digipeater.
	      	//	data part of message.

	      	char stemp[AX25_MAX_PACKET_LEN+2];
		char *p;
		int ndigi;
		int k;
	      
		packet_t pp;

	      	strlcpy (stemp, cmd.hdr.call_from, sizeof(stemp));
	      	strlcat (stemp, ">", sizeof(stemp));
	      	strlcat (stemp, cmd.hdr.call_to, sizeof(stemp));

		cmd.data[data_len] = '\0';
		ndigi = cmd.data[0];
		p = cmd.data + 1;

		for (k=0; k<ndigi; k++) {
		  strlcat (stemp, ",", sizeof(stemp));
		  strlcat (stemp, p, sizeof(stemp));
		  p += 10;
	        }
		strlcat (stemp, ":", sizeof(stemp));
		strlcat (stemp, p, sizeof(stemp));

	        //text_color_set(DW_COLOR_DEBUG);
		//dw_printf ("Transmit '%s'\n", stemp);

		pp = ax25_from_text (stemp, 1);


		if (pp == NULL) {
	          text_color_set(DW_COLOR_ERROR);
		  dw_printf ("Failed to create frame from AGW 'V' message.\n");
		}
		else {

		  /* This goes into the low priority queue because it is an original. */

		  /* Note that the protocol has no way to set the "has been used" */
		  /* bits in the digipeater fields. */

		  /* This explains why the digipeating option is grayed out in */
		  /* xastir when using the AGW interface.  */
		  /* The current version uses only the 'V' message, not 'K' for transmitting. */

		  tq_append (cmd.hdr.portx, TQ_PRIO_1_LO, pp);

		}
	      }
	      
	      break;

	    case 'K':				/* Transmit raw AX.25 frame */
	      {
	      	// Message contains:
	      	//	port number for transmission.
	      	//	data length
	      	//	data which is raw ax.25 frame.
		//		
	      
		packet_t pp;
		alevel_t alevel;

		// Bug fix in version 1.1:
		//
		// The first byte of data is described as:
		//
		// 		the "TNC" to use
		//		00=Port 1
		//		16=Port 2
		//
		// The seems to be redundant; we already a port number in the header.
		// Anyhow, the original code here added one to cmd.data to get the 
		// first byte of the frame.  Unfortunately, it did not subtract one from
		// cmd.hdr.data_len so we ended up sending an extra byte.

	        // TODO: Right now I just use the port (channel) number in the header.
		// What if the second one is inconsistent?  
		// - Continue to ignore port number at beginning of data?
		// - Use second one instead?
		// - Error message if a mismatch?

		memset (&alevel, 0xff, sizeof(alevel));
		pp = ax25_from_frame ((unsigned char *)cmd.data+1, data_len - 1, alevel);

		if (pp == NULL) {
	          text_color_set(DW_COLOR_ERROR);
		  dw_printf ("Failed to create frame from AGW 'K' message.\n");
		}
		else {

		  /* How can we determine if it is an original or repeated message? */
		  /* If there is at least one digipeater in the frame, AND */
		  /* that digipeater has been used, it should go out quickly thru */
		  /* the high priority queue. */
		  /* Otherwise, it is an original for the low priority queue. */

		  if (ax25_get_num_repeaters(pp) >= 1 &&
		      ax25_get_h(pp,AX25_REPEATER_1)) {
		    tq_append (cmd.hdr.portx, TQ_PRIO_0_HI, pp);
		  }
		  else {
		    tq_append (cmd.hdr.portx, TQ_PRIO_1_LO, pp);
		  }
		}
	      }
	      
	      break;

	    case 'P':				/* Application Login  */

	      // Silently ignore it.
	      break;

	    case 'X':				/* Register CallSign  */

	      {
		struct {
		  struct agwpe_s hdr;
		  char data;			/* 1 = success, 0 = failure */
		} reply;

		int ok = 1;

		// The protocol spec says it is an error to register the same one more than once.
	        // Too much trouble.  Report success if the channel is valid.


	        int chan = cmd.hdr.portx;

	        // Connected mode can only be used with internal modems.

		if (chan >= 0 && chan < MAX_CHANS && save_audio_config_p->chan_medium[chan] == MEDIUM_RADIO) {
		  ok = 1;
	          dlq_register_callsign (cmd.hdr.call_from, chan, client);
	        }
	        else {
	          text_color_set(DW_COLOR_ERROR);
	          dw_printf ("AGW protocol error.  Register callsign for invalid channel %d.\n", chan);
	          ok = 0;
	        }


	        memset (&reply, 0, sizeof(reply));
	        reply.hdr.datakind = 'X';
	        reply.hdr.portx = cmd.hdr.portx;
		memcpy (reply.hdr.call_from, cmd.hdr.call_from, sizeof(reply.hdr.call_from));
	        reply.hdr.data_len_NETLE = host2netle(1);
		reply.data = ok;
	        send_to_client (client, &reply);
	      }
	      break;

	    case 'x':				/* Unregister CallSign  */

	      {

	        int chan = cmd.hdr.portx;

	        // Connected mode can only be used with internal modems.

		if (chan >= 0 && chan < MAX_CHANS && save_audio_config_p->chan_medium[chan] == MEDIUM_RADIO) {
	          dlq_unregister_callsign (cmd.hdr.call_from, chan, client);
	        }
		else {
	          text_color_set(DW_COLOR_ERROR);
	          dw_printf ("AGW protocol error.  Unregister callsign for invalid channel %d.\n", chan);
	        }
	      }
	      /* No response is expected. */
	      break;

	    case 'C':				/* Connect, Start an AX.25 Connection  */
	    case 'v':	      			/* Connect VIA, Start an AX.25 circuit thru digipeaters */
	    case 'c':	      			/* Connection with non-standard PID */

	      {
	        struct via_info {
	          unsigned char num_digi;	/* Expect to be in range 1 to 7.  Why not up to 8? */
		  char dcall[7][10];
	        } 
#if 1
		// October 2017.  gcc ??? complained:
		//     warning: dereferencing pointer 'v' does break strict-aliasing rules
		// Try adding this attribute to get rid of the warning.
	        // If this upsets your compiler, take it out.
	        // Let me know.  Maybe we could put in a compiler version check here.

	           __attribute__((__may_alias__))
#endif
	                              *v = (struct via_info *)cmd.data;

	        char callsigns[AX25_MAX_ADDRS][AX25_MAX_ADDR_LEN];
	        int num_calls = 2;	/* 2 plus any digipeaters. */
	        int pid = 0xf0;		/* normal for AX.25 I frames. */
		int j;

	        strlcpy (callsigns[AX25_SOURCE], cmd.hdr.call_from, sizeof(callsigns[AX25_SOURCE]));
	        strlcpy (callsigns[AX25_DESTINATION], cmd.hdr.call_to, sizeof(callsigns[AX25_DESTINATION]));

	        if (cmd.hdr.datakind == 'c') {
	          pid = cmd.hdr.pid;		/* non standard for NETROM, TCP/IP, etc. */
	        }

	        if (cmd.hdr.datakind == 'v') {
	          if (v->num_digi >= 1 && v->num_digi <= 7) {

	            if (data_len != v->num_digi * 10 + 1 && data_len != v->num_digi * 10 + 2) {
	              // I'm getting 1 more than expected from AGWterminal.
	              text_color_set(DW_COLOR_ERROR);
	              dw_printf ("AGW client, connect via, has data len, %d when %d expected.\n", data_len, v->num_digi * 10 + 1);
	            }

	            for (j = 0; j < v->num_digi; j++) {
	              strlcpy (callsigns[AX25_REPEATER_1 + j], v->dcall[j], sizeof(callsigns[AX25_REPEATER_1 + j]));
	              num_calls++;
	            }
	          }
	          else {
	            text_color_set(DW_COLOR_ERROR);
	            dw_printf ("\n");
	            dw_printf ("AGW client, connect via, has invalid number of digipeaters = %d\n", v->num_digi);
	          }
	        }


	        dlq_connect_request (callsigns, num_calls, cmd.hdr.portx, client, pid);

	      }
	      break;


	    case 'D': 				/* Send Connected Data */

	      {
	        char callsigns[AX25_MAX_ADDRS][AX25_MAX_ADDR_LEN];
	        memset (callsigns, 0, sizeof(callsigns));
	        const int num_calls = 2;	// only first 2 used.  Digipeater path
						// must be remembered from connect request.

	        strlcpy (callsigns[AX25_SOURCE], cmd.hdr.call_from, sizeof(callsigns[AX25_SOURCE]));
	        strlcpy (callsigns[AX25_DESTINATION], cmd.hdr.call_to, sizeof(callsigns[AX25_SOURCE]));

	        dlq_xmit_data_request (callsigns, num_calls, cmd.hdr.portx, client, cmd.hdr.pid, cmd.data, netle2host(cmd.hdr.data_len_NETLE));

	      }
	      break;

	    case 'd': 				/* Disconnect, Terminate an AX.25 Connection */

	      {
	        char callsigns[AX25_MAX_ADDRS][AX25_MAX_ADDR_LEN];
	        memset (callsigns, 0, sizeof(callsigns));
	        const int num_calls = 2;	// only first 2 used.

	        strlcpy (callsigns[AX25_SOURCE], cmd.hdr.call_from, sizeof(callsigns[AX25_SOURCE]));
	        strlcpy (callsigns[AX25_DESTINATION], cmd.hdr.call_to, sizeof(callsigns[AX25_SOURCE]));

	        dlq_disconnect_request (callsigns, num_calls, cmd.hdr.portx, client);

	      }
	      break;


	    case 'M': 				/* Send UNPROTO Information (no digipeater path) */

		/* 
		Added in version 1.3.
		This is the same as 'V' except there is no provision for digipeaters.
		TODO: combine 'V' and 'M' into one case.
		AGWterminal sends this for beacon or ask QRA.

		<<< Send UNPROTO Information from AGWPE client application 0, total length = 253
		        portx = 0, datakind = 'M', pid = 0x00
		        call_from = "WB2OSZ-15", call_to = "BEACON"
		        data_len = 217, user_reserved = 556, data =
		  000:  54 68 69 73 20 76 65 72 73 69 6f 6e 20 75 73 65  This version use
		   ...

		<<< Send UNPROTO Information from AGWPE client application 0, total length = 37
		        portx = 0, datakind = 'M', pid = 0x00
		        call_from = "WB2OSZ-15", call_to = "QRA"
		        data_len = 1, user_reserved = 31759424, data =
		  000:  0d                                               .
                                          .

		There is also a report of it coming from UISS.

		<<< Send UNPROTO Information from AGWPE client application 0, total length = 50
			portx = 0, port_hi_reserved = 0
			datakind = 77 = 'M', kind_hi = 0
			call_from = "JH4XSY", call_to = "APRS"
			data_len = 14, user_reserved = 0, data =
		  000:  21 22 3c 43 2e 74 71 6c 48 72 71 21 21 5f        !"<C.tqlHrq!!_
		*/
	      {
	      
		int pid = cmd.hdr.pid;
		(void)(pid);
			/* The AGW protocol spec says, */
			/* "AX.25 PID 0x00 or 0xF0 for AX.25 0xCF NETROM and others" */

			/* BUG: In theory, the AX.25 PID octet should be set from this. */
			/* All examples seen (above) have 0. */
			/* The AX.25 protocol spec doesn't list 0 as a valid value. */
			/* We always send 0xf0, meaning no layer 3. */
			/* Maybe we should have an ax25_set_pid function for cases when */
			/* it is neither 0 nor 0xf0. */

	      	char stemp[AX25_MAX_PACKET_LEN];
		packet_t pp;

	      	strlcpy (stemp, cmd.hdr.call_from, sizeof(stemp));
	      	strlcat (stemp, ">", sizeof(stemp));
	      	strlcat (stemp, cmd.hdr.call_to, sizeof(stemp));

		cmd.data[data_len] = '\0';

		strlcat (stemp, ":", sizeof(stemp));
		strlcat (stemp, cmd.data, sizeof(stemp));

	        //text_color_set(DW_COLOR_DEBUG);
		//dw_printf ("Transmit '%s'\n", stemp);

		pp = ax25_from_text (stemp, 1);

		if (pp == NULL) {
	          text_color_set(DW_COLOR_ERROR);
		  dw_printf ("Failed to create frame from AGW 'M' message.\n");
		}
		else {
		  tq_append (cmd.hdr.portx, TQ_PRIO_1_LO, pp);
		}
	      }
	      break;


	    case 'y':				/* Ask Outstanding frames waiting on a Port  */

	      /* Number of frames sitting in transmit queue for specified channel. */
	      {
		struct {
		  struct agwpe_s hdr;
		  int data_NETLE;			// Little endian order.
		} reply;


	        memset (&reply, 0, sizeof(reply));
		reply.hdr.portx = cmd.hdr.portx;	/* Reply with same port number */
	        reply.hdr.datakind = 'y';
	        reply.hdr.data_len_NETLE = host2netle(4);

	        int n = 0;
	        if (cmd.hdr.portx >= 0 && cmd.hdr.portx < MAX_CHANS) {
	          // Count both normal and expedited in transmit queue for given channel.
		  n = tq_count (cmd.hdr.portx, -1, "", "", 0);
		}
		reply.data_NETLE = host2netle(n);

	        send_to_client (client, &reply);
	      }
	      break;

	    case 'Y':				/* How Many Outstanding frames wait for tx for a particular station  */

	      // This is different than the above 'y' because this refers to a specific
	      // link in connected mode.

	      // This would be useful for a couple different purposes.

	      // When sending bulk data, we want to keep a fair amount queued up to take
	      // advantage of large window sizes (MAXFRAME, EMAXFRAME).  On the other
	      // hand we don't want to get TOO far ahead when transferring a large file.

	      // Before disconnecting from another station, it would be good to know
	      // that it actually received the last message we sent.  For this reason,
	      // I think it would be good for this to include information frames that were 
	      // transmitted but not yet acknowledged.
	      // You could say that a particular frame is still waiting to be sent even
	      // if was already sent because it could be sent again if lost previously.

	      // The documentation is inconsistent about the address order.
	      // One place says "callfrom" is my callsign and "callto" is the other guy.
	      // That would make sense.  We are asking about frames going to the other guy.

	      // But another place says it depends on who initiated the connection.
	      //
	      //	"If we started the connection CallFrom=US and CallTo=THEM
	      //	If the other end started the connection CallFrom=THEM and CallTo=US"
	      //
	      // The response description says nothing about the order; it just mentions two addresses.
	      // If you are writing a client or server application, the order would
	      // be clear but right here it could be either case.
	      //
	      // Another version of the documentation mentioned the source address being optional.
	      //

	      // The only way to get this information is from inside the data link state machine.
	      // We will send a request to it and the result coming out will be used to
	      // send the reply back to the client application.

	      {

	        char callsigns[AX25_MAX_ADDRS][AX25_MAX_ADDR_LEN];
	        memset (callsigns, 0, sizeof(callsigns));
	        const int num_calls = 2;	// only first 2 used.

	        strlcpy (callsigns[AX25_SOURCE], cmd.hdr.call_from, sizeof(callsigns[AX25_SOURCE]));
	        strlcpy (callsigns[AX25_DESTINATION], cmd.hdr.call_to, sizeof(callsigns[AX25_SOURCE]));

	        dlq_outstanding_frames_request (callsigns, num_calls, cmd.hdr.portx, client);
	      }
	      break;

	    default:

	      text_color_set(DW_COLOR_ERROR);
	      dw_printf ("--- Unexpected Command from application %d using AGW protocol:\n", client);
	      debug_print (FROM_CLIENT, client, &cmd.hdr, sizeof(cmd.hdr) + data_len);

	      break;
	  }
	}

} /* end send_to_client */


/* end server.c */