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# -*- test-case-name: twisted.conch.test.test_channel -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
The parent class for all the SSH Channels. Currently implemented channels
are session, direct-tcp, and forwarded-tcp.
Maintainer: Paul Swartz
"""
from zope.interface import implementer
from twisted.internet import interfaces
from twisted.logger import Logger
from twisted.python import log
@implementer(interfaces.ITransport)
class SSHChannel(log.Logger):
"""
A class that represents a multiplexed channel over an SSH connection.
The channel has a local window which is the maximum amount of data it will
receive, and a remote which is the maximum amount of data the remote side
will accept. There is also a maximum packet size for any individual data
packet going each way.
@ivar name: the name of the channel.
@type name: L{bytes}
@ivar localWindowSize: the maximum size of the local window in bytes.
@type localWindowSize: L{int}
@ivar localWindowLeft: how many bytes are left in the local window.
@type localWindowLeft: L{int}
@ivar localMaxPacket: the maximum size of packet we will accept in bytes.
@type localMaxPacket: L{int}
@ivar remoteWindowLeft: how many bytes are left in the remote window.
@type remoteWindowLeft: L{int}
@ivar remoteMaxPacket: the maximum size of a packet the remote side will
accept in bytes.
@type remoteMaxPacket: L{int}
@ivar conn: the connection this channel is multiplexed through.
@type conn: L{SSHConnection}
@ivar data: any data to send to the other side when the channel is
requested.
@type data: L{bytes}
@ivar avatar: an avatar for the logged-in user (if a server channel)
@ivar localClosed: True if we aren't accepting more data.
@type localClosed: L{bool}
@ivar remoteClosed: True if the other side isn't accepting more data.
@type remoteClosed: L{bool}
"""
_log = Logger()
name: bytes = None # type: ignore[assignment] # only needed for client channels
def __init__(
self,
localWindow=0,
localMaxPacket=0,
remoteWindow=0,
remoteMaxPacket=0,
conn=None,
data=None,
avatar=None,
):
self.localWindowSize = localWindow or 131072
self.localWindowLeft = self.localWindowSize
self.localMaxPacket = localMaxPacket or 32768
self.remoteWindowLeft = remoteWindow
self.remoteMaxPacket = remoteMaxPacket
self.areWriting = 1
self.conn = conn
self.data = data
self.avatar = avatar
self.specificData = b""
self.buf = b""
self.extBuf = []
self.closing = 0
self.localClosed = 0
self.remoteClosed = 0
self.id = None # gets set later by SSHConnection
def __str__(self) -> str:
return self.__bytes__().decode("ascii")
def __bytes__(self) -> bytes:
"""
Return a byte string representation of the channel
"""
name = self.name
if not name:
name = b"None"
return b"<SSHChannel %b (lw %d rw %d)>" % (
name,
self.localWindowLeft,
self.remoteWindowLeft,
)
def logPrefix(self):
id = (self.id is not None and str(self.id)) or "unknown"
if self.name:
name = self.name.decode("ascii")
else:
name = "None"
return f"SSHChannel {name} ({id}) on {self.conn.logPrefix()}"
def channelOpen(self, specificData):
"""
Called when the channel is opened. specificData is any data that the
other side sent us when opening the channel.
@type specificData: L{bytes}
"""
self._log.info("channel open")
def openFailed(self, reason):
"""
Called when the open failed for some reason.
reason.desc is a string descrption, reason.code the SSH error code.
@type reason: L{error.ConchError}
"""
self._log.error("other side refused open\nreason: {reason}", reason=reason)
def addWindowBytes(self, data):
"""
Called when bytes are added to the remote window. By default it clears
the data buffers.
@type data: L{bytes}
"""
self.remoteWindowLeft = self.remoteWindowLeft + data
if not self.areWriting and not self.closing:
self.areWriting = True
self.startWriting()
if self.buf:
b = self.buf
self.buf = b""
self.write(b)
if self.extBuf:
b = self.extBuf
self.extBuf = []
for type, data in b:
self.writeExtended(type, data)
def requestReceived(self, requestType, data):
"""
Called when a request is sent to this channel. By default it delegates
to self.request_<requestType>.
If this function returns true, the request succeeded, otherwise it
failed.
@type requestType: L{bytes}
@type data: L{bytes}
@rtype: L{bool}
"""
foo = requestType.replace(b"-", b"_").decode("ascii")
f = getattr(self, "request_" + foo, None)
if f:
return f(data)
self._log.info("unhandled request for {requestType}", requestType=requestType)
return 0
def dataReceived(self, data):
"""
Called when we receive data.
@type data: L{bytes}
"""
self._log.debug("got data {data}", data=data)
def extReceived(self, dataType, data):
"""
Called when we receive extended data (usually standard error).
@type dataType: L{int}
@type data: L{str}
"""
self._log.debug(
"got extended data {dataType} {data!r}", dataType=dataType, data=data
)
def eofReceived(self):
"""
Called when the other side will send no more data.
"""
self._log.info("remote eof")
def closeReceived(self):
"""
Called when the other side has closed the channel.
"""
self._log.info("remote close")
self.loseConnection()
def closed(self):
"""
Called when the channel is closed. This means that both our side and
the remote side have closed the channel.
"""
self._log.info("closed")
def write(self, data):
"""
Write some data to the channel. If there is not enough remote window
available, buffer until it is. Otherwise, split the data into
packets of length remoteMaxPacket and send them.
@type data: L{bytes}
"""
if self.buf:
self.buf += data
return
top = len(data)
if top > self.remoteWindowLeft:
data, self.buf = (
data[: self.remoteWindowLeft],
data[self.remoteWindowLeft :],
)
self.areWriting = 0
self.stopWriting()
top = self.remoteWindowLeft
rmp = self.remoteMaxPacket
write = self.conn.sendData
r = range(0, top, rmp)
for offset in r:
write(self, data[offset : offset + rmp])
self.remoteWindowLeft -= top
if self.closing and not self.buf:
self.loseConnection() # try again
def writeExtended(self, dataType, data):
"""
Send extended data to this channel. If there is not enough remote
window available, buffer until there is. Otherwise, split the data
into packets of length remoteMaxPacket and send them.
@type dataType: L{int}
@type data: L{bytes}
"""
if self.extBuf:
if self.extBuf[-1][0] == dataType:
self.extBuf[-1][1] += data
else:
self.extBuf.append([dataType, data])
return
if len(data) > self.remoteWindowLeft:
data, self.extBuf = (
data[: self.remoteWindowLeft],
[[dataType, data[self.remoteWindowLeft :]]],
)
self.areWriting = 0
self.stopWriting()
while len(data) > self.remoteMaxPacket:
self.conn.sendExtendedData(self, dataType, data[: self.remoteMaxPacket])
data = data[self.remoteMaxPacket :]
self.remoteWindowLeft -= self.remoteMaxPacket
if data:
self.conn.sendExtendedData(self, dataType, data)
self.remoteWindowLeft -= len(data)
if self.closing:
self.loseConnection() # try again
def writeSequence(self, data):
"""
Part of the Transport interface. Write a list of strings to the
channel.
@type data: C{list} of L{str}
"""
self.write(b"".join(data))
def loseConnection(self):
"""
Close the channel if there is no buferred data. Otherwise, note the
request and return.
"""
self.closing = 1
if not self.buf and not self.extBuf:
self.conn.sendClose(self)
def getPeer(self):
"""
See: L{ITransport.getPeer}
@return: The remote address of this connection.
@rtype: L{SSHTransportAddress}.
"""
return self.conn.transport.getPeer()
def getHost(self):
"""
See: L{ITransport.getHost}
@return: An address describing this side of the connection.
@rtype: L{SSHTransportAddress}.
"""
return self.conn.transport.getHost()
def stopWriting(self):
"""
Called when the remote buffer is full, as a hint to stop writing.
This can be ignored, but it can be helpful.
"""
def startWriting(self):
"""
Called when the remote buffer has more room, as a hint to continue
writing.
"""