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khepri-tftpy/tftpy/TftpPacketTypes.py

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2010-07-11 23:27:49 +00:00
"""This module implements the packet types of TFTP itself, and the
corresponding encode and decode methods for them."""
import struct
from TftpShared import *
class TftpSession(object):
"""This class is the base class for the tftp client and server. Any shared
code should be in this class."""
# FIXME: do we need this anymore?
pass
class TftpPacketWithOptions(object):
"""This class exists to permit some TftpPacket subclasses to share code
regarding options handling. It does not inherit from TftpPacket, as the
goal is just to share code here, and not cause diamond inheritance."""
def __init__(self):
self.options = {}
def setoptions(self, options):
log.debug("in TftpPacketWithOptions.setoptions")
log.debug("options: " + str(options))
myoptions = {}
for key in options:
newkey = str(key)
myoptions[newkey] = str(options[key])
log.debug("populated myoptions with %s = %s"
% (newkey, myoptions[newkey]))
log.debug("setting options hash to: " + str(myoptions))
self._options = myoptions
def getoptions(self):
log.debug("in TftpPacketWithOptions.getoptions")
return self._options
# Set up getter and setter on options to ensure that they are the proper
# type. They should always be strings, but we don't need to force the
# client to necessarily enter strings if we can avoid it.
options = property(getoptions, setoptions)
def decode_options(self, buffer):
"""This method decodes the section of the buffer that contains an
unknown number of options. It returns a dictionary of option names and
values."""
format = "!"
options = {}
log.debug("decode_options: buffer is: " + repr(buffer))
log.debug("size of buffer is %d bytes" % len(buffer))
if len(buffer) == 0:
log.debug("size of buffer is zero, returning empty hash")
return {}
# Count the nulls in the buffer. Each one terminates a string.
log.debug("about to iterate options buffer counting nulls")
length = 0
for c in buffer:
#log.debug("iterating this byte: " + repr(c))
if ord(c) == 0:
log.debug("found a null at length %d" % length)
if length > 0:
format += "%dsx" % length
length = -1
else:
raise TftpException, "Invalid options in buffer"
length += 1
log.debug("about to unpack, format is: %s" % format)
mystruct = struct.unpack(format, buffer)
tftpassert(len(mystruct) % 2 == 0,
"packet with odd number of option/value pairs")
for i in range(0, len(mystruct), 2):
log.debug("setting option %s to %s" % (mystruct[i], mystruct[i+1]))
options[mystruct[i]] = mystruct[i+1]
return options
class TftpPacket(object):
"""This class is the parent class of all tftp packet classes. It is an
abstract class, providing an interface, and should not be instantiated
directly."""
def __init__(self):
self.opcode = 0
self.buffer = None
def encode(self):
"""The encode method of a TftpPacket takes keyword arguments specific
to the type of packet, and packs an appropriate buffer in network-byte
order suitable for sending over the wire.
This is an abstract method."""
raise NotImplementedError, "Abstract method"
def decode(self):
"""The decode method of a TftpPacket takes a buffer off of the wire in
network-byte order, and decodes it, populating internal properties as
appropriate. This can only be done once the first 2-byte opcode has
already been decoded, but the data section does include the entire
datagram.
This is an abstract method."""
raise NotImplementedError, "Abstract method"
class TftpPacketInitial(TftpPacket, TftpPacketWithOptions):
"""This class is a common parent class for the RRQ and WRQ packets, as
they share quite a bit of code."""
def __init__(self):
TftpPacket.__init__(self)
TftpPacketWithOptions.__init__(self)
self.filename = None
self.mode = None
def encode(self):
"""Encode the packet's buffer from the instance variables."""
tftpassert(self.filename, "filename required in initial packet")
tftpassert(self.mode, "mode required in initial packet")
ptype = None
if self.opcode == 1: ptype = "RRQ"
else: ptype = "WRQ"
log.debug("Encoding %s packet, filename = %s, mode = %s"
% (ptype, self.filename, self.mode))
for key in self.options:
log.debug(" Option %s = %s" % (key, self.options[key]))
format = "!H"
format += "%dsx" % len(self.filename)
if self.mode == "octet":
format += "5sx"
else:
raise AssertionError, "Unsupported mode: %s" % mode
# Add options.
options_list = []
if self.options.keys() > 0:
log.debug("there are options to encode")
for key in self.options:
# Populate the option name
format += "%dsx" % len(key)
options_list.append(key)
# Populate the option value
format += "%dsx" % len(str(self.options[key]))
options_list.append(str(self.options[key]))
log.debug("format is %s" % format)
log.debug("options_list is %s" % options_list)
log.debug("size of struct is %d" % struct.calcsize(format))
self.buffer = struct.pack(format,
self.opcode,
self.filename,
self.mode,
*options_list)
log.debug("buffer is " + repr(self.buffer))
return self
def decode(self):
tftpassert(self.buffer, "Can't decode, buffer is empty")
# FIXME - this shares a lot of code with decode_options
nulls = 0
format = ""
nulls = length = tlength = 0
log.debug("in decode: about to iterate buffer counting nulls")
subbuf = self.buffer[2:]
for c in subbuf:
log.debug("iterating this byte: " + repr(c))
if ord(c) == 0:
nulls += 1
log.debug("found a null at length %d, now have %d"
% (length, nulls))
format += "%dsx" % length
length = -1
# At 2 nulls, we want to mark that position for decoding.
if nulls == 2:
break
length += 1
tlength += 1
log.debug("hopefully found end of mode at length %d" % tlength)
# length should now be the end of the mode.
tftpassert(nulls == 2, "malformed packet")
shortbuf = subbuf[:tlength+1]
log.debug("about to unpack buffer with format: %s" % format)
log.debug("unpacking buffer: " + repr(shortbuf))
mystruct = struct.unpack(format, shortbuf)
tftpassert(len(mystruct) == 2, "malformed packet")
self.filename = mystruct[0]
self.mode = mystruct[1].lower() # force lc - bug 17
log.debug("set filename to %s" % self.filename)
log.debug("set mode to %s" % self.mode)
self.options = self.decode_options(subbuf[tlength+1:])
return self
class TftpPacketRRQ(TftpPacketInitial):
"""
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::
2 bytes string 1 byte string 1 byte
-----------------------------------------------
RRQ/ | 01/02 | Filename | 0 | Mode | 0 |
WRQ -----------------------------------------------
"""
def __init__(self):
TftpPacketInitial.__init__(self)
self.opcode = 1
def __str__(self):
s = 'RRQ packet: filename = %s' % self.filename
s += ' mode = %s' % self.mode
if self.options:
s += '\n options = %s' % self.options
return s
class TftpPacketWRQ(TftpPacketInitial):
"""
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::
2 bytes string 1 byte string 1 byte
-----------------------------------------------
RRQ/ | 01/02 | Filename | 0 | Mode | 0 |
WRQ -----------------------------------------------
"""
def __init__(self):
TftpPacketInitial.__init__(self)
self.opcode = 2
def __str__(self):
s = 'WRQ packet: filename = %s' % self.filename
s += ' mode = %s' % self.mode
if self.options:
s += '\n options = %s' % self.options
return s
class TftpPacketDAT(TftpPacket):
"""
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::
2 bytes 2 bytes n bytes
---------------------------------
DATA | 03 | Block # | Data |
---------------------------------
"""
def __init__(self):
TftpPacket.__init__(self)
self.opcode = 3
self.blocknumber = 0
self.data = None
def __str__(self):
s = 'DAT packet: block %s' % self.blocknumber
if self.data:
s += '\n data: %d bytes' % len(self.data)
return s
def encode(self):
"""Encode the DAT packet. This method populates self.buffer, and
returns self for easy method chaining."""
if len(self.data) == 0:
log.debug("Encoding an empty DAT packet")
format = "!HH%ds" % len(self.data)
self.buffer = struct.pack(format,
self.opcode,
self.blocknumber,
self.data)
return self
def decode(self):
"""Decode self.buffer into instance variables. It returns self for
easy method chaining."""
# We know the first 2 bytes are the opcode. The second two are the
# block number.
(self.blocknumber,) = struct.unpack("!H", self.buffer[2:4])
log.debug("decoding DAT packet, block number %d" % self.blocknumber)
log.debug("should be %d bytes in the packet total"
% len(self.buffer))
# Everything else is data.
self.data = self.buffer[4:]
log.debug("found %d bytes of data"
% len(self.data))
return self
class TftpPacketACK(TftpPacket):
"""
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::
2 bytes 2 bytes
-------------------
ACK | 04 | Block # |
--------------------
"""
def __init__(self):
TftpPacket.__init__(self)
self.opcode = 4
self.blocknumber = 0
def __str__(self):
return 'ACK packet: block %d' % self.blocknumber
def encode(self):
log.debug("encoding ACK: opcode = %d, block = %d"
% (self.opcode, self.blocknumber))
self.buffer = struct.pack("!HH", self.opcode, self.blocknumber)
return self
def decode(self):
self.opcode, self.blocknumber = struct.unpack("!HH", self.buffer)
log.debug("decoded ACK packet: opcode = %d, block = %d"
% (self.opcode, self.blocknumber))
return self
class TftpPacketERR(TftpPacket):
"""
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::
2 bytes 2 bytes string 1 byte
----------------------------------------
ERROR | 05 | ErrorCode | ErrMsg | 0 |
----------------------------------------
Error Codes
Value Meaning
0 Not defined, see error message (if any).
1 File not found.
2 Access violation.
3 Disk full or allocation exceeded.
4 Illegal TFTP operation.
5 Unknown transfer ID.
6 File already exists.
7 No such user.
8 Failed to negotiate options
"""
def __init__(self):
TftpPacket.__init__(self)
self.opcode = 5
self.errorcode = 0
# FIXME: We don't encode the errmsg...
self.errmsg = None
# FIXME - integrate in TftpErrors references?
self.errmsgs = {
1: "File not found",
2: "Access violation",
3: "Disk full or allocation exceeded",
4: "Illegal TFTP operation",
5: "Unknown transfer ID",
6: "File already exists",
7: "No such user",
8: "Failed to negotiate options"
}
def __str__(self):
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s = 'ERR packet: errorcode = %d' % self.errorcode
s += '\n msg = %s' % self.errmsgs.get(self.errorcode, '')
return s
def encode(self):
"""Encode the DAT packet based on instance variables, populating
self.buffer, returning self."""
format = "!HH%dsx" % len(self.errmsgs[self.errorcode])
log.debug("encoding ERR packet with format %s" % format)
self.buffer = struct.pack(format,
self.opcode,
self.errorcode,
self.errmsgs[self.errorcode])
return self
def decode(self):
"Decode self.buffer, populating instance variables and return self."
buflen = len(self.buffer)
tftpassert(buflen >= 4, "malformed ERR packet, too short")
log.debug("Decoding ERR packet, length %s bytes" % buflen)
if buflen == 4:
log.debug("Allowing this affront to the RFC of a 4-byte packet")
format = "!HH"
log.debug("Decoding ERR packet with format: %s" % format)
self.opcode, self.errorcode = struct.unpack(format,
self.buffer)
else:
log.debug("Good ERR packet > 4 bytes")
format = "!HH%dsx" % (len(self.buffer) - 5)
log.debug("Decoding ERR packet with format: %s" % format)
self.opcode, self.errorcode, self.errmsg = struct.unpack(format,
self.buffer)
log.error("ERR packet - errorcode: %d, message: %s"
% (self.errorcode, self.errmsg))
return self
class TftpPacketOACK(TftpPacket, TftpPacketWithOptions):
"""
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::
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
| opc | opt1 | 0 | value1 | 0 | optN | 0 | valueN | 0 |
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
"""
def __init__(self):
TftpPacket.__init__(self)
TftpPacketWithOptions.__init__(self)
self.opcode = 6
def __str__(self):
return 'OACK packet:\n options = %s' % self.options
def encode(self):
format = "!H" # opcode
options_list = []
log.debug("in TftpPacketOACK.encode")
for key in self.options:
log.debug("looping on option key %s" % key)
log.debug("value is %s" % self.options[key])
format += "%dsx" % len(key)
format += "%dsx" % len(self.options[key])
options_list.append(key)
options_list.append(self.options[key])
self.buffer = struct.pack(format, self.opcode, *options_list)
return self
def decode(self):
self.options = self.decode_options(self.buffer[2:])
return self
def match_options(self, options):
"""This method takes a set of options, and tries to match them with
its own. It can accept some changes in those options from the server as
part of a negotiation. Changed or unchanged, it will return a dict of
the options so that the session can update itself to the negotiated
options."""
for name in self.options:
if options.has_key(name):
if name == 'blksize':
# We can accept anything between the min and max values.
size = self.options[name]
if size >= MIN_BLKSIZE and size <= MAX_BLKSIZE:
log.debug("negotiated blksize of %d bytes" % size)
options[blksize] = size
else:
raise TftpException, "Unsupported option: %s" % name
return True