''' =============================== XMODEM file transfer protocol =============================== .. $Id: __init__.py,v 696ce0cd218b 2010/04/22 16:58:05 maze $ 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' __url__ = 'http://maze.io/' __version__ = '0.1' import time import sys # Protocol bytes SOH = chr(0x01) STX = chr(0x02) EOT = chr(0x04) ACK = chr(0x06) NAK = chr(0x15) CAN = chr(0x18) CRC = chr(0x43) 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 ... >>> x = XMODEM(getc, putc) ''' # 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): self.getc = getc self.putc = putc def abort(self, count=2, timeout=60): ''' Send an abort sequence using CAN bytes. ''' for counter in xrange(0, count): self.putc(CAN, timeout) def send(self, stream, retry=16, timeout=60, quiet=0): ''' Send a stream via the XMODEM protocol. >>> stream = file('/etc/issue', 'rb') >>> print x.send(stream) True Returns ``True`` upon succesful transmission or ``False`` in case of failure. ''' # initialize protocol 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 >> sys.stderr, 'received CAN' if cancel: return False else: cancel = 1 else: if not quiet: print >> sys.stderr, \ 'send ERROR expected NAK/CRC, got', ord(char) error_count += 1 if error_count >= retry: self.abort(timeout=timeout) return False # send data error_count = 0 packet_size = 128 sequence = 1 while True: data = stream.read(packet_size) if not data: if not quiet: print >> sys.stderr, 'send EOS' # end of stream break data = data.ljust(packet_size, '\xff') if crc_mode: crc = self.calc_crc(data) else: crc = self.calc_checksum(data) # emit packet while True: self.putc(SOH) self.putc(chr(sequence)) self.putc(chr(0xff - sequence)) self.putc(data) if crc_mode: self.putc(chr(crc >> 8)) self.putc(chr(crc & 0xff)) else: self.putc(chr(crc)) char = self.getc(1, timeout) if char == ACK: break if char == NAK: error_count += 1 if error_count >= retry: # excessive amounts of retransmissions requested, # abort transfer self.abort(timeout=timeout) return False # protocol error self.abort(timeout=timeout) return False # keep track of sequence sequence = (sequence + 1 ) % 0xff # end of transmission self.putc(EOT) 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 x.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 in [STX, CAN]: 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: return income_size elif char == CAN: # cancel at two consecutive cancels if cancel: return None else: cancel = 1 else: if not quiet: print >> sys.stderr, \ 'recv ERROR expected SOH/EOT, got', ord(char) 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) if crc_mode: csum = (ord(data[-2]) << 8) + ord(data[-1]) data = data[:-2] if not quiet: print >> sys.stderr, 'CRC(%04x <> %04x)' % (csum, self.calc_crc(data)), valid = csum == self.calc_crc(data) else: csum = data[-1] data = data[:-1] if not quiet: print >> sys.stderr, '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) % 0xff char = self.getc(1, timeout) continue else: # consume data self.getc(packet_size + 1 + crc_mode) if not quiet: print >> sys.stderr, 'expected 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 = xmodem.calc_checksum('hello') >>> csum = xmodem.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 = xmodem.calc_crc('hello') >>> crc = xmodem.calc_crc('world', crc) >>> hex(54755) '0xd5e3' ''' for char in data: crc = (crc << 8) ^ self.crctable[((crc >> 8) ^ ord(char)) & 0xff] return crc & 0xffff