Skip to content

transport

scrapli.transport.plugins.telnet.transport

TelnetTransport

Bases: Transport

Source code in transport/plugins/telnet/transport.py
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
class TelnetTransport(Transport):
    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.socket: Optional[Socket] = 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 _set_socket_timeout(self, timeout: float) -> None:
        """
        Set underlying socket timeout

        Mostly this exists just to assert that socket and socket.sock are not None to appease mypy!

        Args:
            timeout: float value to set as the timeout

        Returns:
            N/A

        Raises:
            ScrapliConnectionNotOpened: if either socket or socket.sock are None
        """
        if self.socket is None:
            raise ScrapliConnectionNotOpened
        if self.socket.sock is None:
            raise ScrapliConnectionNotOpened
        self.socket.sock.settimeout(timeout)

    def _handle_control_chars_socket_timeout_update(self) -> None:
        """
        Handle updating (if necessary) the socket timeout

        Args:
            N/A

        Returns:
            None

        Raises:
            N/A

        """
        self._control_char_sent_counter += 1

        if self._control_char_sent_counter > self._control_char_sent_limit:
            # connection is opened, effectively ignore socket timeout at this point as we want
            # the timeout socket to be "just" for opening the connection basically
            # the number 8 is fairly arbitrary -- it looks like *most* platforms send around
            # 8 - 12 control char/instructions on session opening, so we'll go with 8!
            self._set_socket_timeout(600)

    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

        NOTE: see the asynctelnet transport for additional comments inline about what is going on
        here.

        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.socket:
            raise ScrapliConnectionNotOpened

        if not control_buf:
            if c != IAC:
                self._cooked_buf += c
            else:
                control_buf += c

        elif len(control_buf) == 1 and c in (DO, DONT, WILL, WONT):
            control_buf += c

        elif len(control_buf) == 2:
            cmd = control_buf[1:2]
            control_buf = b""

            if (cmd == DO) and (c == SUPPRESS_GO_AHEAD):
                self.write(IAC + WILL + c)
            elif cmd in (DO, DONT):
                self.write(IAC + WONT + c)
            elif cmd == WILL:
                self.write(IAC + DO + c)
            elif cmd == WONT:
                self.write(IAC + DONT + c)

            self._handle_control_chars_socket_timeout_update()

        return control_buf

    def _handle_control_chars(self) -> None:
        """
        Handle control characters -- nearly identical to CPython (removed in 3.11) 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".

        NOTE: see the asynctelnet transport for additional comments inline about what is going on
        here.

        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.socket:
            raise ScrapliConnectionNotOpened

        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)

    def open(self) -> None:
        self._pre_open_closing_log(closing=False)

        if not self.socket:
            self.socket = Socket(
                host=self._base_transport_args.host,
                port=self._base_transport_args.port,
                timeout=self._base_transport_args.timeout_socket,
            )

        if not self.socket.isalive():
            self.socket.open()

        self._post_open_closing_log(closing=False)

    def close(self) -> None:
        self._pre_open_closing_log(closing=True)

        if self.socket:
            self.socket.close()

        self.socket = None

        self._post_open_closing_log(closing=True)

    def isalive(self) -> bool:
        if not self.socket:
            return False
        if not self.socket.isalive():
            return False
        return True

    def _read(self, n: int = 65535) -> None:
        """
        Read n bytes from the socket and fill raw buffer

        Mostly this exists just to assert that socket and socket.sock are not None to appease mypy!

        Args:
            n: optional amount of bytes to try to recv from the underlying socket

        Returns:
            N/A

        Raises:
            ScrapliConnectionNotOpened: if either socket or socket.sock are None
            ScrapliConnectionError: if we fail to recv from the underlying socket

        """
        if self.socket is None:
            raise ScrapliConnectionNotOpened
        if self.socket.sock is None:
            raise ScrapliConnectionNotOpened
        if not self._raw_buf:
            try:
                buf = self.socket.sock.recv(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 Exception as exc:
                raise ScrapliConnectionError(
                    "encountered EOF reading from transport; typically means the device closed the "
                    "connection"
                ) from exc

    @timeout_wrapper
    def read(self) -> bytes:
        if not self.socket:
            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:
            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 self.socket is None:
            raise ScrapliConnectionNotOpened
        if self.socket.sock is None:
            raise ScrapliConnectionNotOpened
        self.socket.sock.send(channel_input)