/* vi: set sw=4 ts=4: */
/*
 * Copyright:     Copyright (C) 2001, Hewlett-Packard Company
 * Author:        Christopher Hoover <ch@hpl.hp.com>
 * Description:   xmodem functionality for uploading of kernels
 *                and the like
 * Created at:    Thu Dec 20 01:58:08 PST 2001
 *
 * xmodem functionality for uploading of kernels and the like
 *
 * Copyright (C) 2001 Hewlett-Packard Laboratories
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 *
 * This was originally written for blob and then adapted for busybox.
 */

#include "libbb.h"

#define SOH 0x01
#define STX 0x02
#define EOT 0x04
#define ACK 0x06
#define NAK 0x15
#define BS  0x08
#define PAD 0x1A

/*
Cf:
  http://www.textfiles.com/apple/xmodem
  http://www.phys.washington.edu/~belonis/xmodem/docxmodem.txt
  http://www.phys.washington.edu/~belonis/xmodem/docymodem.txt
  http://www.phys.washington.edu/~belonis/xmodem/modmprot.col
*/

#define TIMEOUT 1
#define TIMEOUT_LONG 10
#define MAXERRORS 10

#define read_fd  STDIN_FILENO
#define write_fd STDOUT_FILENO

static int read_byte(unsigned timeout)
{
        unsigned char buf;
        int n;

        alarm(timeout);
        /* NOT safe_read! We want ALRM to interrupt us */
        n = read(read_fd, &buf, 1);
        alarm(0);
        if (n == 1)
                return buf;
        return -1;
}

static int receive(/*int read_fd, */int file_fd)
{
        unsigned char blockBuf[1024];
        unsigned blockLength = 0;
        unsigned errors = 0;
        unsigned wantBlockNo = 1;
        unsigned length = 0;
        int do_crc = 1;
        char reply_char;
        unsigned timeout = TIMEOUT_LONG;

        /* Flush pending input */
        tcflush(read_fd, TCIFLUSH);

        /* Ask for CRC; if we get errors, we will go with checksum */
        reply_char = 'C';
        full_write(write_fd, &reply_char, 1);

        for (;;) {
                int blockBegin;
                int blockNo, blockNoOnesCompl;
                int cksum_or_crc;
                int expected;
                int i, j;

                blockBegin = read_byte(timeout);
                if (blockBegin < 0)
                        goto timeout;

                /* If last block, remove padding */
                if (blockBegin == EOT) {
                        /* Data blocks can be padded with ^Z characters */
                        /* This code tries to detect and remove them */
                        if (blockLength >= 3
                         && blockBuf[blockLength - 1] == PAD
                         && blockBuf[blockLength - 2] == PAD
                         && blockBuf[blockLength - 3] == PAD
                        ) {
                                while (blockLength
                                   && blockBuf[blockLength - 1] == PAD
                                ) {
                                        blockLength--;
                                }
                        }
                }
                /* Write previously received block */
                if (blockLength) {
                        errno = 0;
                        if (full_write(file_fd, blockBuf, blockLength) != blockLength) {
                                bb_perror_msg("can't write to file");
                                goto fatal;
                        }
                }

                timeout = TIMEOUT;
                reply_char = NAK;

                switch (blockBegin) {
                case SOH:
                case STX:
                        break;
                case EOT:
                        reply_char = ACK;
                        full_write(write_fd, &reply_char, 1);
                        return length;
                default:
                        goto error;
                }

                /* Block no */
                blockNo = read_byte(TIMEOUT);
                if (blockNo < 0)
                        goto timeout;

                /* Block no, in one's complement form */
                blockNoOnesCompl = read_byte(TIMEOUT);
                if (blockNoOnesCompl < 0)
                        goto timeout;

                if (blockNo != (255 - blockNoOnesCompl)) {
                        bb_error_msg("bad block ones compl");
                        goto error;
                }

                blockLength = (blockBegin == SOH) ? 128 : 1024;

                for (i = 0; i < blockLength; i++) {
                        int cc = read_byte(TIMEOUT);
                        if (cc < 0)
                                goto timeout;
                        blockBuf[i] = cc;
                }

                if (do_crc) {
                        cksum_or_crc = read_byte(TIMEOUT);
                        if (cksum_or_crc < 0)
                                goto timeout;
                        cksum_or_crc = (cksum_or_crc << 8) | read_byte(TIMEOUT);
                        if (cksum_or_crc < 0)
                                goto timeout;
                } else {
                        cksum_or_crc = read_byte(TIMEOUT);
                        if (cksum_or_crc < 0)
                                goto timeout;
                }

                if (blockNo == ((wantBlockNo - 1) & 0xff)) {
                        /* a repeat of the last block is ok, just ignore it. */
                        /* this also ignores the initial block 0 which is */
                        /* meta data. */
                        goto next;
                }
                if (blockNo != (wantBlockNo & 0xff)) {
                        bb_error_msg("unexpected block no, 0x%08x, expecting 0x%08x", blockNo, wantBlockNo);
                        goto error;
                }

                expected = 0;
                if (do_crc) {
                        for (i = 0; i < blockLength; i++) {
                                expected = expected ^ blockBuf[i] << 8;
                                for (j = 0; j < 8; j++) {
                                        if (expected & 0x8000)
                                                expected = (expected << 1) ^ 0x1021;
                                        else
                                                expected = (expected << 1);
                                }
                        }
                        expected &= 0xffff;
                } else {
                        for (i = 0; i < blockLength; i++)
                                expected += blockBuf[i];
                        expected &= 0xff;
                }
                if (cksum_or_crc != expected) {
                        bb_error_msg(do_crc ? "crc error, expected 0x%04x, got 0x%04x"
                                           : "checksum error, expected 0x%02x, got 0x%02x",
                                        expected, cksum_or_crc);
                        goto error;
                }

                wantBlockNo++;
                length += blockLength;
 next:
                errors = 0;
                reply_char = ACK;
                full_write(write_fd, &reply_char, 1);
                continue;
 error:
 timeout:
                errors++;
                if (errors == MAXERRORS) {
                        /* Abort */

                        /* If were asking for crc, try again w/o crc */
                        if (reply_char == 'C') {
                                reply_char = NAK;
                                errors = 0;
                                do_crc = 0;
                                goto timeout;
                        }
                        bb_error_msg("too many errors; giving up");
 fatal:
                        /* 5 CAN followed by 5 BS. Don't try too hard... */
                        safe_write(write_fd, "\030\030\030\030\030\010\010\010\010\010", 10);
                        return -1;
                }

                /* Flush pending input */
                tcflush(read_fd, TCIFLUSH);

                full_write(write_fd, &reply_char, 1);
        } /* for (;;) */
}

static void sigalrm_handler(int UNUSED_PARAM signum)
{
}

int rx_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int rx_main(int argc UNUSED_PARAM, char **argv)
{
        struct termios tty, orig_tty;
        int termios_err;
        int file_fd;
        int n;

        /* Disabled by vda:
         * why we can't receive from stdin? Why we *require*
         * controlling tty?? */
        /*read_fd = xopen(CURRENT_TTY, O_RDWR);*/
        file_fd = xopen(single_argv(argv), O_RDWR|O_CREAT|O_TRUNC);

        termios_err = tcgetattr(read_fd, &tty);
        if (termios_err == 0) {
                orig_tty = tty;
                cfmakeraw(&tty);
                tcsetattr(read_fd, TCSAFLUSH, &tty);
        }

        /* No SA_RESTART: we want ALRM to interrupt read() */
        signal_no_SA_RESTART_empty_mask(SIGALRM, sigalrm_handler);

        n = receive(file_fd);

        if (termios_err == 0)
                tcsetattr(read_fd, TCSAFLUSH, &orig_tty);
        if (ENABLE_FEATURE_CLEAN_UP)
                close(file_fd);
        fflush_stdout_and_exit(n >= 0);
}