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224 | class AsynctelnetTransport(AsyncTransport):
def __init__(
self, base_transport_args: BaseTransportArgs, plugin_transport_args: PluginTransportArgs
) -> None:
super().__init__(base_transport_args=base_transport_args)
self.plugin_transport_args = plugin_transport_args
self.stdout: Optional[asyncio.StreamReader] = None
self.stdin: Optional[asyncio.StreamWriter] = None
self._eof = False
self._raw_buf = b""
self._cooked_buf = b""
self._control_char_sent_counter = 0
self._control_char_sent_limit = 10
def _handle_control_chars_response(self, control_buf: bytes, c: bytes) -> bytes:
"""
Handle the actual response to control characters
Broken up to be easier to test as well as to appease mr. mccabe
Args:
control_buf: current control_buf to work with
c: currently read control char to process
Returns:
bytes: updated control_buf
Raises:
ScrapliConnectionNotOpened: if connection is not opened for some reason
"""
if not self.stdin:
raise ScrapliConnectionNotOpened
# control_buf is empty, lets see if we got a control character
if not control_buf:
if c != IAC:
# add whatever character we read to the "normal" output buf so it gets sent off
# to the auth method later (username/show prompts may show up here)
self._cooked_buf += c
else:
# we got a control character, put it into the control_buf
control_buf += c
elif len(control_buf) == 1 and c in (DO, DONT, WILL, WONT):
# control buf already has the IAC byte loaded, if the next char is DO/DONT/WILL/WONT
# add that into the control buffer and move on
control_buf += c
elif len(control_buf) == 2:
# control buffer is already loaded with IAC and directive, we now have an option to
# deal with, create teh base command out of the existing buffer then reset the buf
# for the next go around
cmd = control_buf[1:2]
control_buf = b""
if (cmd == DO) and (c == SUPPRESS_GO_AHEAD):
# if server says do suppress go ahead we say will for that option
self.stdin.write(IAC + WILL + c)
elif cmd in (DO, DONT):
# if server says do/dont we always say wont for that option
self.stdin.write(IAC + WONT + c)
elif cmd == WILL:
# if server says will we always say do for that option
self.stdin.write(IAC + DO + c)
elif cmd == WONT:
# if server says wont we always say dont for that option
self.stdin.write(IAC + DONT + c)
return control_buf
def _handle_control_chars(self) -> None:
"""
Handle control characters -- nearly identical to CPython telnetlib
Basically we want to read and "decline" any and all control options that the server proposes
to us -- so if they say "DO" XYZ directive, we say "DONT", if they say "WILL" we say "WONT".
Args:
N/A
Returns:
None
Raises:
ScrapliConnectionNotOpened: if connection is not opened for some reason
ScrapliConnectionNotOpened: if we read an empty byte string from the reader -- this
indicates the server sent an EOF -- see #142
"""
if not self.stdout:
raise ScrapliConnectionNotOpened
# control_buf is the buffer for control characters, we reset this after being "done" with
# responding to a control sequence, so it always represents the "current" control sequence
# we are working on responding to
control_buf = b""
while self._raw_buf:
c, self._raw_buf = self._raw_buf[:1], self._raw_buf[1:]
if not c:
raise ScrapliConnectionNotOpened("server returned EOF, connection not opened")
control_buf = self._handle_control_chars_response(control_buf=control_buf, c=c)
async def open(self) -> None:
self._pre_open_closing_log(closing=False)
try:
fut = asyncio.open_connection(
host=self._base_transport_args.host, port=self._base_transport_args.port
)
self.stdout, self.stdin = await asyncio.wait_for(
fut, timeout=self._base_transport_args.timeout_socket
)
except ConnectionError as exc:
msg = f"Failed to open telnet session to host {self._base_transport_args.host}"
if "connection refused" in str(exc).lower():
msg = (
f"Failed to open telnet session to host {self._base_transport_args.host}, "
"connection refused"
)
raise ScrapliConnectionError(msg) from exc
except asyncio.TimeoutError as exc:
msg = "timed out opening connection to device"
self.logger.critical(msg)
raise ScrapliAuthenticationFailed(msg) from exc
except (OSError, socket.gaierror) as exc:
msg = (
f"Failed to open telnet session to host {self._base_transport_args.host} -- "
"do you have a bad host/port?"
)
raise ScrapliConnectionError(msg) from exc
self._post_open_closing_log(closing=False)
def close(self) -> None:
self._pre_open_closing_log(closing=True)
if self.stdin:
self.stdin.close()
with suppress(AttributeError):
# wait closed only in 3.7+... unclear if we should be doing something else for 3.6?
# it doesnt seem to hurt anything... note 9/2022 probably can remove this but...
# it still doesnt seem to hurt anything :)
self.stdin.close()
self.stdin = None
self.stdout = None
self._post_open_closing_log(closing=True)
def isalive(self) -> bool:
if not self.stdin or not self.stdout:
return False
return not self.stdout.at_eof()
async def _read(self, n: int = 65535) -> None:
if not self.stdout:
raise ScrapliConnectionNotOpened
if not self._raw_buf:
try:
buf = await self.stdout.read(n)
self._eof = not buf
if self._control_char_sent_counter < self._control_char_sent_limit:
self._raw_buf += buf
else:
self._cooked_buf += buf
except EOFError as exc:
raise ScrapliConnectionError(
"encountered EOF reading from transport; typically means the device closed the "
"connection"
) from exc
@timeout_wrapper
async def read(self) -> bytes:
if not self.stdout:
raise ScrapliConnectionNotOpened
if self._control_char_sent_counter < self._control_char_sent_limit:
self._handle_control_chars()
while not self._cooked_buf and not self._eof:
await self._read()
if self._control_char_sent_counter < self._control_char_sent_limit:
self._handle_control_chars()
buf = self._cooked_buf
self._cooked_buf = b""
# possible to still have null bytes in the buf, replace them with nothing
return buf.replace(NULL, b"")
def write(self, channel_input: bytes) -> None:
if not self.stdin:
raise ScrapliConnectionNotOpened
self.stdin.write(channel_input)
|