// xmodem.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "crc16.h"

#define SOH  0x01
#define STX  0x02
#define EOT  0x04
#define ACK  0x06
#define NAK  0x15
#define CAN  0x18
#define CTRLZ 0x1A

#define DLY_1S 1000
#define MAXRETRANS 25

int xmodemReceive(FILE *fp);
int xmodemTransmit(FILE *fp);
static int check(int crc, const unsigned char *buf, int sz);
static int get_byte(DWORD delay);
unsigned short crc16_ccitt(const unsigned char *buf, int len);


/********************************************************************/

int _tmain(int argc, _TCHAR* argv[])
{
	char filename[80];
	FILE *fp;
	int err;
	
	printf("\nXmodem program...");
	
	// No arguments?
	if((argc == 1 || argc > 3))
	{
		printf("\nUsage: xmodem [filename] /r /s");
		exit(1);
	}
 
	// Get the filename
	strcpy(filename, argv[1]);

	if(argv[2][0] == '/')
	{
		switch(argv[2][1])
		{
		case 'r':	// Receive
			if((fp = fopen(filename, "wb")) == NULL)
			{
				puts("\nError: cannot open receive file.");
				exit(1);
			}
			err = xmodemReceive(fp);
			if(err)
			{
				printf("\nError %d in xmodemreceive()", err);
			}
			fclose(fp);
			break;

		case 's':	// Send
			if((fp = fopen(filename, "rb")) == NULL)
			{
				puts("\nError: cannot open transmit file.");
				exit(1);
			}
			if(err = xmodemTransmit(fp))
			{
				printf("\nError %d in xmodemtransmit()", err);
			}
			fclose(fp);
			break;
		default:
			printf("\nUnrecognized argument");
		}
	}
	else printf("\nUnrecognized argument");

	return 0;
}

/********************************************************************************/

static int get_byte(DWORD delay)
{
	DWORD dwStart = GetTickCount();

	while(1)
	{
		// Stop if this has taken too long
		if( GetTickCount() - dwStart >= delay ) return 0;
		// Handle rollover (quick and dirty)
		if( GetTickCount() - dwStart <= 0 ) return 0;
		// If there's a character, return it
		if( _kbhit()) return _getch();
	}
}

/*******************************************************************************/
/*
	Copyright 2001, 2002 Georges Menie (www.menie.org)

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU Lesser 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 Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/


static int check(int crc, const unsigned char *buf, int sz)
{
	if (crc) {
		unsigned short crc = crc16_ccitt(buf, sz);
		unsigned short tcrc = (buf[sz]<<8)+buf[sz+1];
		if (crc == tcrc)
			return 1;
	}
	else {
		int i;
		unsigned char cks = 0;
		for (i = 0; i < sz; ++i) {
			cks += buf[i];
		}
		if (cks == buf[sz])
		return 1;
	}

	return 0;
}

/********************************************************************/

static void flushinput(void)
{
	while (get_byte(((DLY_1S)*3)>>1) >= 0)
		;
}

/**********************************************************************/

int xmodemReceive(FILE *fp)
{
	unsigned char xbuff[1030]; /* 1024 for XModem 1k + 3 head chars + 2 crc + nul */
	unsigned char *p;
	int bufsz, crc = 0;
	unsigned char trychar = 'C';
	unsigned char packetno = 1;
	int i, c;
	int retry, retrans = MAXRETRANS;

	for(;;) {
		for( retry = 0; retry < 16; ++retry) {
			if (trychar) putchar(trychar);
			if ((c = get_byte((DLY_1S)<<1)) >= 0) {
				switch (c) {
				case SOH:
					bufsz = 128;
					goto start_recv;
				case STX:
					bufsz = 1024;
					goto start_recv;
				case EOT:
					flushinput();
					putchar(ACK);
					return 0; /* normal end */
				case CAN:
					if ((c = get_byte(DLY_1S)) == CAN) {
						flushinput();
						putchar(ACK);
						return -1; /* canceled by remote */
					}
					break;
				default:
					break;
				}
			}
		}
		if (trychar == 'C') { trychar = NAK; continue; }
		flushinput();
		putchar(CAN);
		putchar(CAN);
		putchar(CAN);
		return -2; /* sync error */

	start_recv:
		if (trychar == 'C') crc = 1;
		trychar = 0;
		p = xbuff;
		*p++ = c;
		for (i = 0;  i < (bufsz+(crc?1:0)+3); ++i)
		{
			if ((c = get_byte(DLY_1S)) < 0) goto reject;
			*p++ = c;
		}

		if (xbuff[1] == (unsigned char)(~xbuff[2]) && 
			(xbuff[1] == packetno || xbuff[1] == (unsigned char)packetno-1) &&
			check(crc, &xbuff[3], bufsz))
		{
			if (xbuff[1] == packetno)
			{
				fwrite(&xbuff[3], sizeof(unsigned char), bufsz, fp);
				++packetno;
				retrans = MAXRETRANS+1;
			}
			if (--retrans <= 0) {
				flushinput();
				putchar(CAN);
				putchar(CAN);
				putchar(CAN);
				return -3; /* too many retry error */
			}
			putchar(ACK);
			continue;
		}
	reject:
		flushinput();
		putchar(NAK);
	}
}

int xmodemTransmit(FILE *fp)
{
	unsigned char xbuff[1030]; /* 1024 for XModem 1k + 3 head chars + 2 crc + nul */
	int bufsz, crc = -1;
	unsigned char packetno = 1;
	int i, c, count = 1024;
	int retry;

	for(;;) {
		for( retry = 0; retry < 16; ++retry) {
			if ((c = get_byte((DLY_1S)<<1)) >= 0) {
				switch (c) {
				case 'C':
					crc = 1;
					goto start_trans;
				case NAK:
					crc = 0;
					goto start_trans;
				case CAN:
					if ((c = get_byte(DLY_1S)) == CAN) {
						putchar(ACK);
						flushinput();
						return -1; /* canceled by remote */
					}
					break;
				default:
					break;
				}
			}
		}
		putchar(CAN);
		putchar(CAN);
		putchar(CAN);
		flushinput();
		return -2; /* no sync */

		for(;;) {
		start_trans:
			xbuff[0] = STX; bufsz = 1024;
			xbuff[1] = packetno;
			xbuff[2] = ~packetno;
			if (count >= 0) {
				memset (&xbuff[3], 0, bufsz);
				if (count == 0) {
					xbuff[3] = CTRLZ;
				}
				else {
					count = (int)fread(&xbuff[3], sizeof(unsigned char), bufsz, fp);
					if (count < bufsz) xbuff[3+count] = CTRLZ;
				}
				if (crc) {
					unsigned short ccrc = crc16_ccitt(&xbuff[3], bufsz);
					xbuff[bufsz+3] = (ccrc>>8) & 0xFF;
					xbuff[bufsz+4] = ccrc & 0xFF;
				}
				else {
					unsigned char ccks = 0;
					for (i = 3; i < bufsz+3; ++i) {
						ccks += xbuff[i];
					}
					xbuff[bufsz+3] = ccks;
				}
				for (retry = 0; retry < MAXRETRANS; ++retry) {
					for (i = 0; i < bufsz+4+(crc?1:0); ++i) {
						putchar(xbuff[i]);
					}
					if ((c = get_byte(DLY_1S)) >= 0 ) {
						switch (c) {
						case ACK:
							++packetno;
							goto start_trans;
						case CAN:
							if ((c = get_byte(DLY_1S)) == CAN) {
								putchar(ACK);
								flushinput();
								return -1; /* canceled by remote */
							}
							break;
						case NAK:
						default:
							break;
						}
					}
				}
				putchar(CAN);
				putchar(CAN);
				putchar(CAN);
				flushinput();
				return -4; /* xmit error */
			}
			else {
				for (retry = 0; retry < 10; ++retry) {
					putchar(EOT);
					if ((c = get_byte((DLY_1S)<<1)) == ACK) break;
				}
				flushinput();
				return 0;
			}
		}
	}
}

/**************************************************************************/

static const unsigned short crc16tab[256]= {
	0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
	0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
	0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,
	0x9339,0x8318,0xb37b,0xa35a,0xd3bd,0xc39c,0xf3ff,0xe3de,
	0x2462,0x3443,0x0420,0x1401,0x64e6,0x74c7,0x44a4,0x5485,
	0xa56a,0xb54b,0x8528,0x9509,0xe5ee,0xf5cf,0xc5ac,0xd58d,
	0x3653,0x2672,0x1611,0x0630,0x76d7,0x66f6,0x5695,0x46b4,
	0xb75b,0xa77a,0x9719,0x8738,0xf7df,0xe7fe,0xd79d,0xc7bc,
	0x48c4,0x58e5,0x6886,0x78a7,0x0840,0x1861,0x2802,0x3823,
	0xc9cc,0xd9ed,0xe98e,0xf9af,0x8948,0x9969,0xa90a,0xb92b,
	0x5af5,0x4ad4,0x7ab7,0x6a96,0x1a71,0x0a50,0x3a33,0x2a12,
	0xdbfd,0xcbdc,0xfbbf,0xeb9e,0x9b79,0x8b58,0xbb3b,0xab1a,
	0x6ca6,0x7c87,0x4ce4,0x5cc5,0x2c22,0x3c03,0x0c60,0x1c41,
	0xedae,0xfd8f,0xcdec,0xddcd,0xad2a,0xbd0b,0x8d68,0x9d49,
	0x7e97,0x6eb6,0x5ed5,0x4ef4,0x3e13,0x2e32,0x1e51,0x0e70,
	0xff9f,0xefbe,0xdfdd,0xcffc,0xbf1b,0xaf3a,0x9f59,0x8f78,
	0x9188,0x81a9,0xb1ca,0xa1eb,0xd10c,0xc12d,0xf14e,0xe16f,
	0x1080,0x00a1,0x30c2,0x20e3,0x5004,0x4025,0x7046,0x6067,
	0x83b9,0x9398,0xa3fb,0xb3da,0xc33d,0xd31c,0xe37f,0xf35e,
	0x02b1,0x1290,0x22f3,0x32d2,0x4235,0x5214,0x6277,0x7256,
	0xb5ea,0xa5cb,0x95a8,0x8589,0xf56e,0xe54f,0xd52c,0xc50d,
	0x34e2,0x24c3,0x14a0,0x0481,0x7466,0x6447,0x5424,0x4405,
	0xa7db,0xb7fa,0x8799,0x97b8,0xe75f,0xf77e,0xc71d,0xd73c,
	0x26d3,0x36f2,0x0691,0x16b0,0x6657,0x7676,0x4615,0x5634,
	0xd94c,0xc96d,0xf90e,0xe92f,0x99c8,0x89e9,0xb98a,0xa9ab,
	0x5844,0x4865,0x7806,0x6827,0x18c0,0x08e1,0x3882,0x28a3,
	0xcb7d,0xdb5c,0xeb3f,0xfb1e,0x8bf9,0x9bd8,0xabbb,0xbb9a,
	0x4a75,0x5a54,0x6a37,0x7a16,0x0af1,0x1ad0,0x2ab3,0x3a92,
	0xfd2e,0xed0f,0xdd6c,0xcd4d,0xbdaa,0xad8b,0x9de8,0x8dc9,
	0x7c26,0x6c07,0x5c64,0x4c45,0x3ca2,0x2c83,0x1ce0,0x0cc1,
	0xef1f,0xff3e,0xcf5d,0xdf7c,0xaf9b,0xbfba,0x8fd9,0x9ff8,
	0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0
};
  
unsigned short crc16_ccitt(const unsigned char *buf, int len)
{
	register int counter;
	register unsigned short crc = 0;
	for( counter = 0; counter < len; counter++)
		crc = (crc<<8) ^ crc16tab[((crc>>8) ^ *buf++)&0x00FF];
	return crc;
}