302 lines
8.3 KiB
Python
302 lines
8.3 KiB
Python
# Copyright (C) 2011 Jeff Forcier <jeff@bitprophet.org>
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#
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# This file is part of ssh.
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#
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# 'ssh' is free software; you can redistribute it and/or modify it under the
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# terms of the GNU Lesser General Public License as published by the Free
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# Software Foundation; either version 2.1 of the License, or (at your option)
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# any later version.
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#
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# 'ssh' is distrubuted in the hope that it will be useful, but WITHOUT ANY
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# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
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# A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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# details.
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#
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# You should have received a copy of the GNU Lesser General Public License
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# along with 'ssh'; if not, write to the Free Software Foundation, Inc.,
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# 51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA.
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"""
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Implementation of an SSH2 "message".
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"""
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import struct
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import cStringIO
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from ssh import util
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class Message (object):
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"""
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An SSH2 I{Message} is a stream of bytes that encodes some combination of
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strings, integers, bools, and infinite-precision integers (known in python
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as I{long}s). This class builds or breaks down such a byte stream.
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Normally you don't need to deal with anything this low-level, but it's
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exposed for people implementing custom extensions, or features that
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ssh doesn't support yet.
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"""
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def __init__(self, content=None):
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"""
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Create a new SSH2 Message.
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@param content: the byte stream to use as the Message content (passed
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in only when decomposing a Message).
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@type content: string
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"""
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if content != None:
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self.packet = cStringIO.StringIO(content)
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else:
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self.packet = cStringIO.StringIO()
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def __str__(self):
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"""
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Return the byte stream content of this Message, as a string.
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@return: the contents of this Message.
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@rtype: string
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"""
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return self.packet.getvalue()
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def __repr__(self):
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"""
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Returns a string representation of this object, for debugging.
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@rtype: string
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"""
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return 'ssh.Message(' + repr(self.packet.getvalue()) + ')'
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def rewind(self):
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"""
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Rewind the message to the beginning as if no items had been parsed
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out of it yet.
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"""
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self.packet.seek(0)
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def get_remainder(self):
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"""
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Return the bytes of this Message that haven't already been parsed and
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returned.
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@return: a string of the bytes not parsed yet.
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@rtype: string
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"""
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position = self.packet.tell()
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remainder = self.packet.read()
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self.packet.seek(position)
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return remainder
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def get_so_far(self):
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"""
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Returns the bytes of this Message that have been parsed and returned.
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The string passed into a Message's constructor can be regenerated by
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concatenating C{get_so_far} and L{get_remainder}.
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@return: a string of the bytes parsed so far.
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@rtype: string
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"""
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position = self.packet.tell()
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self.rewind()
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return self.packet.read(position)
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def get_bytes(self, n):
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"""
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Return the next C{n} bytes of the Message, without decomposing into
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an int, string, etc. Just the raw bytes are returned.
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@return: a string of the next C{n} bytes of the Message, or a string
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of C{n} zero bytes, if there aren't C{n} bytes remaining.
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@rtype: string
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"""
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b = self.packet.read(n)
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if len(b) < n:
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return b + '\x00' * (n - len(b))
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return b
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def get_byte(self):
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"""
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Return the next byte of the Message, without decomposing it. This
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is equivalent to L{get_bytes(1)<get_bytes>}.
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@return: the next byte of the Message, or C{'\000'} if there aren't
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any bytes remaining.
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@rtype: string
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"""
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return self.get_bytes(1)
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def get_boolean(self):
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"""
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Fetch a boolean from the stream.
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@return: C{True} or C{False} (from the Message).
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@rtype: bool
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"""
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b = self.get_bytes(1)
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return b != '\x00'
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def get_int(self):
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"""
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Fetch an int from the stream.
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@return: a 32-bit unsigned integer.
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@rtype: int
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"""
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return struct.unpack('>I', self.get_bytes(4))[0]
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def get_int64(self):
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"""
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Fetch a 64-bit int from the stream.
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@return: a 64-bit unsigned integer.
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@rtype: long
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"""
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return struct.unpack('>Q', self.get_bytes(8))[0]
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def get_mpint(self):
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"""
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Fetch a long int (mpint) from the stream.
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@return: an arbitrary-length integer.
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@rtype: long
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"""
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return util.inflate_long(self.get_string())
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def get_string(self):
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"""
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Fetch a string from the stream. This could be a byte string and may
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contain unprintable characters. (It's not unheard of for a string to
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contain another byte-stream Message.)
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@return: a string.
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@rtype: string
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"""
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return self.get_bytes(self.get_int())
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def get_list(self):
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"""
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Fetch a list of strings from the stream. These are trivially encoded
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as comma-separated values in a string.
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@return: a list of strings.
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@rtype: list of strings
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"""
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return self.get_string().split(',')
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def add_bytes(self, b):
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"""
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Write bytes to the stream, without any formatting.
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@param b: bytes to add
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@type b: str
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"""
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self.packet.write(b)
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return self
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def add_byte(self, b):
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"""
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Write a single byte to the stream, without any formatting.
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@param b: byte to add
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@type b: str
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"""
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self.packet.write(b)
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return self
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def add_boolean(self, b):
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"""
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Add a boolean value to the stream.
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@param b: boolean value to add
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@type b: bool
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"""
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if b:
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self.add_byte('\x01')
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else:
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self.add_byte('\x00')
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return self
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def add_int(self, n):
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"""
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Add an integer to the stream.
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@param n: integer to add
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@type n: int
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"""
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self.packet.write(struct.pack('>I', n))
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return self
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def add_int64(self, n):
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"""
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Add a 64-bit int to the stream.
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@param n: long int to add
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@type n: long
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"""
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self.packet.write(struct.pack('>Q', n))
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return self
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def add_mpint(self, z):
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"""
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Add a long int to the stream, encoded as an infinite-precision
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integer. This method only works on positive numbers.
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@param z: long int to add
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@type z: long
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"""
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self.add_string(util.deflate_long(z))
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return self
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def add_string(self, s):
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"""
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Add a string to the stream.
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@param s: string to add
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@type s: str
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"""
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self.add_int(len(s))
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self.packet.write(s)
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return self
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def add_list(self, l):
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"""
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Add a list of strings to the stream. They are encoded identically to
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a single string of values separated by commas. (Yes, really, that's
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how SSH2 does it.)
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@param l: list of strings to add
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@type l: list(str)
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"""
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self.add_string(','.join(l))
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return self
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def _add(self, i):
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if type(i) is str:
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return self.add_string(i)
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elif type(i) is int:
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return self.add_int(i)
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elif type(i) is long:
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if i > 0xffffffffL:
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return self.add_mpint(i)
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else:
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return self.add_int(i)
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elif type(i) is bool:
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return self.add_boolean(i)
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elif type(i) is list:
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return self.add_list(i)
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else:
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raise Exception('Unknown type')
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def add(self, *seq):
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"""
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Add a sequence of items to the stream. The values are encoded based
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on their type: str, int, bool, list, or long.
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@param seq: the sequence of items
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@type seq: sequence
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@bug: longs are encoded non-deterministically. Don't use this method.
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"""
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for item in seq:
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self._add(item)
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