""" =============================== XMODEM file transfer protocol =============================== .. $Id$ This is a literal implementation of XMODEM.TXT_, XMODEM1K.TXT_ and XMODMCRC.TXT_, support for YMODEM and ZMODEM is pending. YMODEM should be fairly easy to implement as it is a hack on top of the XMODEM protocol using sequence bytes ``0x00`` for sending file names (and some meta data). .. _XMODEM.TXT: doc/XMODEM.TXT .. _XMODEM1K.TXT: doc/XMODEM1K.TXT .. _XMODMCRC.TXT: doc/XMODMCRC.TXT Data flow example including error recovery ========================================== Here is a sample of the data flow, sending a 3-block message. It includes the two most common line hits - a garbaged block, and an ``ACK`` reply getting garbaged. ``CRC`` or ``CSUM`` represents the checksum bytes. XMODEM 128 byte blocks ---------------------- :: SENDER RECEIVER <-- NAK SOH 01 FE Data[128] CSUM --> <-- ACK SOH 02 FD Data[128] CSUM --> <-- ACK SOH 03 FC Data[128] CSUM --> <-- ACK SOH 04 FB Data[128] CSUM --> <-- ACK SOH 05 FA Data[100] CPMEOF[28] CSUM --> <-- ACK EOT --> <-- ACK XMODEM-1k blocks, CRC mode -------------------------- :: SENDER RECEIVER <-- C STX 01 FE Data[1024] CRC CRC --> <-- ACK STX 02 FD Data[1024] CRC CRC --> <-- ACK STX 03 FC Data[1000] CPMEOF[24] CRC CRC --> <-- ACK EOT --> <-- ACK Mixed 1024 and 128 byte Blocks ------------------------------ :: SENDER RECEIVER <-- C STX 01 FE Data[1024] CRC CRC --> <-- ACK STX 02 FD Data[1024] CRC CRC --> <-- ACK SOH 03 FC Data[128] CRC CRC --> <-- ACK SOH 04 FB Data[100] CPMEOF[28] CRC CRC --> <-- ACK EOT --> <-- ACK YMODEM Batch Transmission Session (1 file) ------------------------------------------ :: SENDER RECEIVER <-- C (command:rb) SOH 00 FF foo.c NUL[123] CRC CRC --> <-- ACK <-- C SOH 01 FE Data[128] CRC CRC --> <-- ACK SOH 02 FC Data[128] CRC CRC --> <-- ACK SOH 03 FB Data[100] CPMEOF[28] CRC CRC --> <-- ACK EOT --> <-- NAK EOT --> <-- ACK <-- C SOH 00 FF NUL[128] CRC CRC --> <-- ACK """ __author__ = "Wijnand Modderman " __copyright__ = ["Copyright (c) 2010 Wijnand Modderman", "Copyright (c) 1981 Chuck Forsberg"] __license__ = "MIT" __version__ = "0.3.2" import logging import time import sys from functools import partial import collections # Loggerr log = logging.getLogger("xmodem") # Protocol bytes SOH = bytes([0x01]) STX = bytes([0x02]) EOT = bytes([0x04]) ACK = bytes([0x06]) DLE = bytes([0x10]) NAK = bytes([0x15]) CAN = bytes([0x18]) CRC = bytes([0x43]) # C class XMODEM(object): """ XMODEM Protocol handler, expects an object to read from and an object to write to. >>> def getc(size, timeout=1): ... return data or None ... >>> def putc(data, timeout=1): ... return size or None ... >>> modem = XMODEM(getc, putc) :param getc: Function to retreive bytes from a stream :type getc: callable :param putc: Function to transmit bytes to a stream :type putc: callable :param mode: XMODEM protocol mode :type mode: string :param pad: Padding character to make the packets match the packet size :type pad: char """ # crctab calculated by Mark G. Mendel, Network Systems Corporation crctable = [ 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, ] def __init__(self, getc, putc, mode="xmodem", pad=b"\x1a"): self.getc = getc self.putc = putc self.mode = mode self.pad = pad def abort(self, count=2, timeout=60): """ Send an abort sequence using CAN bytes. """ for counter in range(0, count): self.putc(CAN, timeout) def send(self, stream, retry=32, timeout=360, quiet=0, callback=None): """ Send a stream via the XMODEM protocol. >>> stream = file('/etc/issue', 'rb') >>> print modem.send(stream) True Returns ``True`` upon succesful transmission or ``False`` in case of failure. :param stream: The stream object to send data from. :type stream: stream (file, etc.) :param retry: The maximum number of times to try to resend a failed packet before failing. :type retry: int :param timeout: The number of seconds to wait for a response before timing out. :type timeout: int :param quiet: If 0, it prints info to stderr. If 1, it does not print any info. :type quiet: int :param callback: Reference to a callback function that has the following signature. This is useful for getting status updates while a xmodem transfer is underway. Expected callback signature: def callback(total_packets, success_count, error_count) :type callback: callable """ # initialize protocol try: packet_size = dict(xmodem=128, xmodem1k=1024)[self.mode] except AttributeError: raise ValueError("An invalid mode was supplied") error_count = 0 crc_mode = 0 cancel = 0 while True: char = self.getc(1) if char: if char == NAK: crc_mode = 0 break elif char == CRC: crc_mode = 1 break elif char == CAN: if not quiet: print("received CAN", file=sys.stderr) if cancel: return False else: cancel = 1 else: log.error("send ERROR expected NAK/CRC, got %s" % (ord(char),)) error_count += 1 if error_count >= retry: self.abort(timeout=timeout) return False # send data error_count = 0 success_count = 0 total_packets = 0 sequence = 1 while True: data = stream.read(packet_size) if not data: log.info("sending EOT") # end of stream break total_packets += 1 data = data.ljust(packet_size, self.pad) if crc_mode: crc = self.calc_crc(data) else: crc = self.calc_checksum(data) # emit packet while True: if packet_size == 128: self.putc(SOH) else: # packet_size == 1024 self.putc(STX) self.putc(bytes([sequence])) self.putc(bytes([0xFF - sequence])) self.putc(data) if crc_mode: self.putc(bytes([crc >> 8])) self.putc(bytes([crc & 0xFF])) else: self.putc(bytes([crc])) char = self.getc(1, timeout) if char == ACK: success_count += 1 if isinstance(callback, collections.Callable): callback(total_packets, success_count, error_count) break if char == NAK: error_count += 1 if isinstance(callback, collections.Callable): callback(total_packets, success_count, error_count) if error_count >= retry: # excessive amounts of retransmissions requested, # abort transfer self.abort(timeout=timeout) log.warning("excessive NAKs, transfer aborted") return False # return to loop and resend continue else: log.error("Not ACK, Not NAK") error_count += 1 if isinstance(callback, collections.Callable): callback(total_packets, success_count, error_count) if error_count >= retry: # excessive amounts of retransmissions requested, # abort transfer self.abort(timeout=timeout) log.warning("excessive protocol errors, transfer aborted") return False # return to loop and resend continue # protocol error self.abort(timeout=timeout) log.error("protocol error") return False # keep track of sequence sequence = (sequence + 1) % 0x100 while True: # end of transmission self.putc(EOT) # An ACK should be returned char = self.getc(1, timeout) if char == ACK: break else: error_count += 1 if error_count >= retry: self.abort(timeout=timeout) log.warning("EOT was not ACKd, transfer aborted") return False return True def recv(self, stream, crc_mode=1, retry=16, timeout=60, delay=1, quiet=0): """ Receive a stream via the XMODEM protocol. >>> stream = file('/etc/issue', 'wb') >>> print modem.recv(stream) 2342 Returns the number of bytes received on success or ``None`` in case of failure. """ # initiate protocol error_count = 0 char = 0 cancel = 0 while True: # first try CRC mode, if this fails, # fall back to checksum mode if error_count >= retry: self.abort(timeout=timeout) return None elif crc_mode and error_count < (retry / 2): if not self.putc(CRC): time.sleep(delay) error_count += 1 else: crc_mode = 0 if not self.putc(NAK): time.sleep(delay) error_count += 1 char = self.getc(1, timeout) if not char: error_count += 1 continue elif char == SOH: # crc_mode = 0 break elif char == STX: break elif char == CAN: if cancel: return None else: cancel = 1 else: error_count += 1 # read data error_count = 0 income_size = 0 packet_size = 128 sequence = 1 cancel = 0 while True: while True: if char == SOH: packet_size = 128 break elif char == STX: packet_size = 1024 break elif char == EOT: # We received an EOT, so send an ACK and return the received # data length self.putc(ACK) return income_size elif char == CAN: # cancel at two consecutive cancels if cancel: return None else: cancel = 1 else: if not quiet: print("recv ERROR expected SOH/EOT, got", ord(char), file=sys.stderr) error_count += 1 if error_count >= retry: self.abort() return None # read sequence error_count = 0 cancel = 0 seq1 = ord(self.getc(1)) seq2 = 0xFF - ord(self.getc(1)) if seq1 == sequence and seq2 == sequence: # sequence is ok, read packet # packet_size + checksum data = self.getc(packet_size + 1 + crc_mode, timeout) if crc_mode: csum = (ord(data[-2]) << 8) + ord(data[-1]) data = data[:-2] log.debug("CRC (%04x <> %04x)" % (csum, self.calc_crc(data))) valid = csum == self.calc_crc(data) else: csum = data[-1] data = data[:-1] log.debug( "checksum (checksum(%02x <> %02x)" % (ord(csum), self.calc_checksum(data)) ) valid = ord(csum) == self.calc_checksum(data) # valid data, append chunk if valid: income_size += len(data) stream.write(data) self.putc(ACK) sequence = (sequence + 1) % 0x100 char = self.getc(1, timeout) continue else: # consume data self.getc(packet_size + 1 + crc_mode) self.debug("expecting sequence %d, got %d/%d" % (sequence, seq1, seq2)) # something went wrong, request retransmission self.putc(NAK) def calc_checksum(self, data, checksum=0): """ Calculate the checksum for a given block of data, can also be used to update a checksum. >>> csum = modem.calc_checksum('hello') >>> csum = modem.calc_checksum('world', csum) >>> hex(csum) '0x3c' """ return (sum(map(ord, data)) + checksum) % 256 def calc_crc(self, data, crc=0): """ Calculate the Cyclic Redundancy Check for a given block of data, can also be used to update a CRC. >>> crc = modem.calc_crc('hello') >>> crc = modem.calc_crc('world', crc) >>> hex(crc) '0xd5e3' """ for char in data: crc = (crc << 8) ^ self.crctable[((crc >> 8) ^ int(char)) & 0xFF] return crc & 0xFFFF XMODEM1k = partial(XMODEM, mode="xmodem1k") def run(): import optparse import subprocess parser = optparse.OptionParser(usage="%prog [] filename filename") parser.add_option("-m", "--mode", default="xmodem", help="XMODEM mode (xmodem, xmodem1k)") options, args = parser.parse_args() if len(args) != 3: parser.error("invalid arguments") return 1 elif args[0] not in ("send", "recv"): parser.error("invalid mode") return 1 def _func(so, si): import select import subprocess print("si", si) print("so", so) def getc(size, timeout=3): w, t, f = select.select([so], [], [], timeout) if w: data = so.read(size) else: data = None print("getc(", repr(data), ")") return data def putc(data, timeout=3): w, t, f = select.select([], [si], [], timeout) if t: si.write(data) si.flush() size = len(data) else: size = None print("putc(", repr(data), repr(size), ")") return size return getc, putc def _pipe(*command): pipe = subprocess.Popen(command, stdout=subprocess.PIPE, stdin=subprocess.PIPE) return pipe.stdout, pipe.stdin if args[0] == "recv": import io getc, putc = _func(*_pipe("sz", "--xmodem", args[2])) stream = open(args[1], "wb") xmodem = XMODEM(getc, putc, mode=options.mode) status = xmodem.recv(stream, retry=8) stream.close() elif args[0] == "send": getc, putc = _func(*_pipe("rz", "--xmodem", args[2])) stream = open(args[1], "rb") xmodem = XMODEM(getc, putc, mode=options.mode) status = xmodem.send(stream, retry=8) stream.close() if __name__ == "__main__": sys.exit(run())