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# -*- test-case-name: twisted.spread.test.test_banana -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Banana -- s-exp based protocol.
Future Plans: This module is almost entirely stable. The same caveat applies
to it as applies to L{twisted.spread.jelly}, however. Read its future plans
for more details.
@author: Glyph Lefkowitz
"""
import copy
import struct
from io import BytesIO
from twisted.internet import protocol
from twisted.persisted import styles
from twisted.python import log
from twisted.python.compat import iterbytes
from twisted.python.reflect import fullyQualifiedName
class BananaError(Exception):
pass
def int2b128(integer, stream):
if integer == 0:
stream(b"\0")
return
assert integer > 0, "can only encode positive integers"
while integer:
stream(bytes((integer & 0x7F,)))
integer = integer >> 7
def b1282int(st):
"""
Convert an integer represented as a base 128 string into an L{int}.
@param st: The integer encoded in a byte string.
@type st: L{bytes}
@return: The integer value extracted from the byte string.
@rtype: L{int}
"""
e = 1
i = 0
for char in iterbytes(st):
n = ord(char)
i += n * e
e <<= 7
return i
# delimiter characters.
LIST = b"\x80"
INT = b"\x81"
STRING = b"\x82"
NEG = b"\x83"
FLOAT = b"\x84"
# "optional" -- these might be refused by a low-level implementation.
LONGINT = b"\x85"
LONGNEG = b"\x86"
# really optional; this is part of the 'pb' vocabulary
VOCAB = b"\x87"
HIGH_BIT_SET = b"\x80"
def setPrefixLimit(limit):
"""
Set the limit on the prefix length for all Banana connections
established after this call.
The prefix length limit determines how many bytes of prefix a banana
decoder will allow before rejecting a potential object as too large.
@type limit: L{int}
@param limit: The number of bytes of prefix for banana to allow when
decoding.
"""
global _PREFIX_LIMIT
_PREFIX_LIMIT = limit
_PREFIX_LIMIT = None
setPrefixLimit(64)
SIZE_LIMIT = 640 * 1024 # 640k is all you'll ever need :-)
class Banana(protocol.Protocol, styles.Ephemeral):
"""
L{Banana} implements the I{Banana} s-expression protocol, client and
server.
@ivar knownDialects: These are the profiles supported by this Banana
implementation.
@type knownDialects: L{list} of L{bytes}
"""
# The specification calls these profiles but this implementation calls them
# dialects instead.
knownDialects = [b"pb", b"none"]
prefixLimit = None
sizeLimit = SIZE_LIMIT
def setPrefixLimit(self, limit):
"""
Set the prefix limit for decoding done by this protocol instance.
@see: L{setPrefixLimit}
"""
self.prefixLimit = limit
self._smallestLongInt = -(2 ** (limit * 7)) + 1
self._smallestInt = -(2**31)
self._largestInt = 2**31 - 1
self._largestLongInt = 2 ** (limit * 7) - 1
def connectionReady(self):
"""Surrogate for connectionMade
Called after protocol negotiation.
"""
def _selectDialect(self, dialect):
self.currentDialect = dialect
self.connectionReady()
def callExpressionReceived(self, obj):
if self.currentDialect:
self.expressionReceived(obj)
else:
# this is the first message we've received
if self.isClient:
# if I'm a client I have to respond
for serverVer in obj:
if serverVer in self.knownDialects:
self.sendEncoded(serverVer)
self._selectDialect(serverVer)
break
else:
# I can't speak any of those dialects.
log.msg(
"The client doesn't speak any of the protocols "
"offered by the server: disconnecting."
)
self.transport.loseConnection()
else:
if obj in self.knownDialects:
self._selectDialect(obj)
else:
# the client just selected a protocol that I did not suggest.
log.msg(
"The client selected a protocol the server didn't "
"suggest and doesn't know: disconnecting."
)
self.transport.loseConnection()
def connectionMade(self):
self.setPrefixLimit(_PREFIX_LIMIT)
self.currentDialect = None
if not self.isClient:
self.sendEncoded(self.knownDialects)
def gotItem(self, item):
l = self.listStack
if l:
l[-1][1].append(item)
else:
self.callExpressionReceived(item)
buffer = b""
def dataReceived(self, chunk):
buffer = self.buffer + chunk
listStack = self.listStack
gotItem = self.gotItem
while buffer:
assert self.buffer != buffer, "This ain't right: {} {}".format(
repr(self.buffer),
repr(buffer),
)
self.buffer = buffer
pos = 0
for ch in iterbytes(buffer):
if ch >= HIGH_BIT_SET:
break
pos = pos + 1
else:
if pos > self.prefixLimit:
raise BananaError(
"Security precaution: more than %d bytes of prefix"
% (self.prefixLimit,)
)
return
num = buffer[:pos]
typebyte = buffer[pos : pos + 1]
rest = buffer[pos + 1 :]
if len(num) > self.prefixLimit:
raise BananaError(
"Security precaution: longer than %d bytes worth of prefix"
% (self.prefixLimit,)
)
if typebyte == LIST:
num = b1282int(num)
if num > SIZE_LIMIT:
raise BananaError("Security precaution: List too long.")
listStack.append((num, []))
buffer = rest
elif typebyte == STRING:
num = b1282int(num)
if num > SIZE_LIMIT:
raise BananaError("Security precaution: String too long.")
if len(rest) >= num:
buffer = rest[num:]
gotItem(rest[:num])
else:
return
elif typebyte == INT:
buffer = rest
num = b1282int(num)
gotItem(num)
elif typebyte == LONGINT:
buffer = rest
num = b1282int(num)
gotItem(num)
elif typebyte == LONGNEG:
buffer = rest
num = b1282int(num)
gotItem(-num)
elif typebyte == NEG:
buffer = rest
num = -b1282int(num)
gotItem(num)
elif typebyte == VOCAB:
buffer = rest
num = b1282int(num)
item = self.incomingVocabulary[num]
if self.currentDialect == b"pb":
# the sender issues VOCAB only for dialect pb
gotItem(item)
else:
raise NotImplementedError(f"Invalid item for pb protocol {item!r}")
elif typebyte == FLOAT:
if len(rest) >= 8:
buffer = rest[8:]
gotItem(struct.unpack("!d", rest[:8])[0])
else:
return
else:
raise NotImplementedError(f"Invalid Type Byte {typebyte!r}")
while listStack and (len(listStack[-1][1]) == listStack[-1][0]):
item = listStack.pop()[1]
gotItem(item)
self.buffer = b""
def expressionReceived(self, lst):
"""Called when an expression (list, string, or int) is received."""
raise NotImplementedError()
outgoingVocabulary = {
# Jelly Data Types
b"None": 1,
b"class": 2,
b"dereference": 3,
b"reference": 4,
b"dictionary": 5,
b"function": 6,
b"instance": 7,
b"list": 8,
b"module": 9,
b"persistent": 10,
b"tuple": 11,
b"unpersistable": 12,
# PB Data Types
b"copy": 13,
b"cache": 14,
b"cached": 15,
b"remote": 16,
b"local": 17,
b"lcache": 18,
# PB Protocol Messages
b"version": 19,
b"login": 20,
b"password": 21,
b"challenge": 22,
b"logged_in": 23,
b"not_logged_in": 24,
b"cachemessage": 25,
b"message": 26,
b"answer": 27,
b"error": 28,
b"decref": 29,
b"decache": 30,
b"uncache": 31,
}
incomingVocabulary = {}
for k, v in outgoingVocabulary.items():
incomingVocabulary[v] = k
def __init__(self, isClient=1):
self.listStack = []
self.outgoingSymbols = copy.copy(self.outgoingVocabulary)
self.outgoingSymbolCount = 0
self.isClient = isClient
def sendEncoded(self, obj):
"""
Send the encoded representation of the given object:
@param obj: An object to encode and send.
@raise BananaError: If the given object is not an instance of one of
the types supported by Banana.
@return: L{None}
"""
encodeStream = BytesIO()
self._encode(obj, encodeStream.write)
value = encodeStream.getvalue()
self.transport.write(value)
def _encode(self, obj, write):
if isinstance(obj, (list, tuple)):
if len(obj) > SIZE_LIMIT:
raise BananaError("list/tuple is too long to send (%d)" % (len(obj),))
int2b128(len(obj), write)
write(LIST)
for elem in obj:
self._encode(elem, write)
elif isinstance(obj, int):
if obj < self._smallestLongInt or obj > self._largestLongInt:
raise BananaError("int is too large to send (%d)" % (obj,))
if obj < self._smallestInt:
int2b128(-obj, write)
write(LONGNEG)
elif obj < 0:
int2b128(-obj, write)
write(NEG)
elif obj <= self._largestInt:
int2b128(obj, write)
write(INT)
else:
int2b128(obj, write)
write(LONGINT)
elif isinstance(obj, float):
write(FLOAT)
write(struct.pack("!d", obj))
elif isinstance(obj, bytes):
# TODO: an API for extending banana...
if self.currentDialect == b"pb" and obj in self.outgoingSymbols:
symbolID = self.outgoingSymbols[obj]
int2b128(symbolID, write)
write(VOCAB)
else:
if len(obj) > SIZE_LIMIT:
raise BananaError(
"byte string is too long to send (%d)" % (len(obj),)
)
int2b128(len(obj), write)
write(STRING)
write(obj)
else:
raise BananaError(
"Banana cannot send {} objects: {!r}".format(
fullyQualifiedName(type(obj)), obj
)
)
# For use from the interactive interpreter
_i = Banana()
_i.connectionMade()
_i._selectDialect(b"none")
def encode(lst):
"""Encode a list s-expression."""
encodeStream = BytesIO()
_i.transport = encodeStream
_i.sendEncoded(lst)
return encodeStream.getvalue()
def decode(st):
"""
Decode a banana-encoded string.
"""
l = []
_i.expressionReceived = l.append
try:
_i.dataReceived(st)
finally:
_i.buffer = b""
del _i.expressionReceived
return l[0]