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rfc2217.py
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#! python # # This module implements a RFC2217 compatible client. RF2217 descibes a # protocol to access serial ports over TCP/IP and allows setting the baud rate, # modem control lines etc. # # This file is part of pySerial. https://github.com/pyserial/pyserial # (C) 2001-2015 Chris Liechti <cliechti@gmx.net> # # SPDX-License-Identifier: BSD-3-Clause # TODO: # - setting control line -> answer is not checked (had problems with one of the # severs). consider implementing a compatibility mode flag to make check # conditional # - write timeout not implemented at all # ########################################################################### # observations and issues with servers # =========================================================================== # sredird V2.2.1 # - http://www.ibiblio.org/pub/Linux/system/serial/ sredird-2.2.2.tar.gz # - does not acknowledge SET_CONTROL (RTS/DTR) correctly, always responding # [105 1] instead of the actual value. # - SET_BAUDRATE answer contains 4 extra null bytes -> probably for larger # numbers than 2**32? # - To get the signature [COM_PORT_OPTION 0] has to be sent. # - run a server: while true; do nc -l -p 7000 -c "sredird debug /dev/ttyUSB0 /var/lock/sredir"; done # =========================================================================== # telnetcpcd (untested) # - http://ftp.wayne.edu/kermit/sredird/telnetcpcd-1.09.tar.gz # - To get the signature [COM_PORT_OPTION] w/o data has to be sent. # =========================================================================== # ser2net # - does not negotiate BINARY or COM_PORT_OPTION for his side but at least # acknowledges that the client activates these options # - The configuration may be that the server prints a banner. As this client # implementation does a flushInput on connect, this banner is hidden from # the user application. # - NOTIFY_MODEMSTATE: the poll interval of the server seems to be one # second. # - To get the signature [COM_PORT_OPTION 0] has to be sent. # - run a server: run ser2net daemon, in /etc/ser2net.conf: # 2000:telnet:0:/dev/ttyS0:9600 remctl banner # ########################################################################### # How to identify ports? pySerial might want to support other protocols in the # future, so lets use an URL scheme. # for RFC2217 compliant servers we will use this: # rfc2217://<host>:<port>[?option[&option...]] # # options: # - "logging" set log level print diagnostic messages (e.g. "logging=debug") # - "ign_set_control": do not look at the answers to SET_CONTROL # - "poll_modem": issue NOTIFY_MODEMSTATE requests when CTS/DTR/RI/CD is read. # Without this option it expects that the server sends notifications # automatically on change (which most servers do and is according to the # RFC). # the order of the options is not relevant from __future__ import absolute_import import logging import socket import struct import threading import time try: import urlparse except ImportError: import urllib.parse as urlparse try: import Queue except ImportError: import queue as Queue import serial from serial.serialutil import SerialBase, SerialException, to_bytes, \ iterbytes, PortNotOpenError, Timeout # port string is expected to be something like this: # rfc2217://host:port # host may be an IP or including domain, whatever. # port is 0...65535 # map log level names to constants. used in from_url() LOGGER_LEVELS = { 'debug': logging.DEBUG, 'info': logging.INFO, 'warning': logging.WARNING, 'error': logging.ERROR, } # telnet protocol characters SE = b'\xf0' # Subnegotiation End NOP = b'\xf1' # No Operation DM = b'\xf2' # Data Mark BRK = b'\xf3' # Break IP = b'\xf4' # Interrupt process AO = b'\xf5' # Abort output AYT = b'\xf6' # Are You There EC = b'\xf7' # Erase Character EL = b'\xf8' # Erase Line GA = b'\xf9' # Go Ahead SB = b'\xfa' # Subnegotiation Begin WILL = b'\xfb' WONT = b'\xfc' DO = b'\xfd' DONT = b'\xfe' IAC = b'\xff' # Interpret As Command IAC_DOUBLED = b'\xff\xff' # selected telnet options BINARY = b'\x00' # 8-bit data path ECHO = b'\x01' # echo SGA = b'\x03' # suppress go ahead # RFC2217 COM_PORT_OPTION = b'\x2c' # Client to Access Server SET_BAUDRATE = b'\x01' SET_DATASIZE = b'\x02' SET_PARITY = b'\x03' SET_STOPSIZE = b'\x04' SET_CONTROL = b'\x05' NOTIFY_LINESTATE = b'\x06' NOTIFY_MODEMSTATE = b'\x07' FLOWCONTROL_SUSPEND = b'\x08' FLOWCONTROL_RESUME = b'\x09' SET_LINESTATE_MASK = b'\x0a' SET_MODEMSTATE_MASK = b'\x0b' PURGE_DATA = b'\x0c' SERVER_SET_BAUDRATE = b'\x65' SERVER_SET_DATASIZE = b'\x66' SERVER_SET_PARITY = b'\x67' SERVER_SET_STOPSIZE = b'\x68' SERVER_SET_CONTROL = b'\x69' SERVER_NOTIFY_LINESTATE = b'\x6a' SERVER_NOTIFY_MODEMSTATE = b'\x6b' SERVER_FLOWCONTROL_SUSPEND = b'\x6c' SERVER_FLOWCONTROL_RESUME = b'\x6d' SERVER_SET_LINESTATE_MASK = b'\x6e' SERVER_SET_MODEMSTATE_MASK = b'\x6f' SERVER_PURGE_DATA = b'\x70' RFC2217_ANSWER_MAP = { SET_BAUDRATE: SERVER_SET_BAUDRATE, SET_DATASIZE: SERVER_SET_DATASIZE, SET_PARITY: SERVER_SET_PARITY, SET_STOPSIZE: SERVER_SET_STOPSIZE, SET_CONTROL: SERVER_SET_CONTROL, NOTIFY_LINESTATE: SERVER_NOTIFY_LINESTATE, NOTIFY_MODEMSTATE: SERVER_NOTIFY_MODEMSTATE, FLOWCONTROL_SUSPEND: SERVER_FLOWCONTROL_SUSPEND, FLOWCONTROL_RESUME: SERVER_FLOWCONTROL_RESUME, SET_LINESTATE_MASK: SERVER_SET_LINESTATE_MASK, SET_MODEMSTATE_MASK: SERVER_SET_MODEMSTATE_MASK, PURGE_DATA: SERVER_PURGE_DATA, } SET_CONTROL_REQ_FLOW_SETTING = b'\x00' # Request Com Port Flow Control Setting (outbound/both) SET_CONTROL_USE_NO_FLOW_CONTROL = b'\x01' # Use No Flow Control (outbound/both) SET_CONTROL_USE_SW_FLOW_CONTROL = b'\x02' # Use XON/XOFF Flow Control (outbound/both) SET_CONTROL_USE_HW_FLOW_CONTROL = b'\x03' # Use HARDWARE Flow Control (outbound/both) SET_CONTROL_REQ_BREAK_STATE = b'\x04' # Request BREAK State SET_CONTROL_BREAK_ON = b'\x05' # Set BREAK State ON SET_CONTROL_BREAK_OFF = b'\x06' # Set BREAK State OFF SET_CONTROL_REQ_DTR = b'\x07' # Request DTR Signal State SET_CONTROL_DTR_ON = b'\x08' # Set DTR Signal State ON SET_CONTROL_DTR_OFF = b'\x09' # Set DTR Signal State OFF SET_CONTROL_REQ_RTS = b'\x0a' # Request RTS Signal State SET_CONTROL_RTS_ON = b'\x0b' # Set RTS Signal State ON SET_CONTROL_RTS_OFF = b'\x0c' # Set RTS Signal State OFF SET_CONTROL_REQ_FLOW_SETTING_IN = b'\x0d' # Request Com Port Flow Control Setting (inbound) SET_CONTROL_USE_NO_FLOW_CONTROL_IN = b'\x0e' # Use No Flow Control (inbound) SET_CONTROL_USE_SW_FLOW_CONTOL_IN = b'\x0f' # Use XON/XOFF Flow Control (inbound) SET_CONTROL_USE_HW_FLOW_CONTOL_IN = b'\x10' # Use HARDWARE Flow Control (inbound) SET_CONTROL_USE_DCD_FLOW_CONTROL = b'\x11' # Use DCD Flow Control (outbound/both) SET_CONTROL_USE_DTR_FLOW_CONTROL = b'\x12' # Use DTR Flow Control (inbound) SET_CONTROL_USE_DSR_FLOW_CONTROL = b'\x13' # Use DSR Flow Control (outbound/both) LINESTATE_MASK_TIMEOUT = 128 # Time-out Error LINESTATE_MASK_SHIFTREG_EMPTY = 64 # Transfer Shift Register Empty LINESTATE_MASK_TRANSREG_EMPTY = 32 # Transfer Holding Register Empty LINESTATE_MASK_BREAK_DETECT = 16 # Break-detect Error LINESTATE_MASK_FRAMING_ERROR = 8 # Framing Error LINESTATE_MASK_PARTIY_ERROR = 4 # Parity Error LINESTATE_MASK_OVERRUN_ERROR = 2 # Overrun Error LINESTATE_MASK_DATA_READY = 1 # Data Ready MODEMSTATE_MASK_CD = 128 # Receive Line Signal Detect (also known as Carrier Detect) MODEMSTATE_MASK_RI = 64 # Ring Indicator MODEMSTATE_MASK_DSR = 32 # Data-Set-Ready Signal State MODEMSTATE_MASK_CTS = 16 # Clear-To-Send Signal State MODEMSTATE_MASK_CD_CHANGE = 8 # Delta Receive Line Signal Detect MODEMSTATE_MASK_RI_CHANGE = 4 # Trailing-edge Ring Detector MODEMSTATE_MASK_DSR_CHANGE = 2 # Delta Data-Set-Ready MODEMSTATE_MASK_CTS_CHANGE = 1 # Delta Clear-To-Send PURGE_RECEIVE_BUFFER = b'\x01' # Purge access server receive data buffer PURGE_TRANSMIT_BUFFER = b'\x02' # Purge access server transmit data buffer PURGE_BOTH_BUFFERS = b'\x03' # Purge both the access server receive data # buffer and the access server transmit data buffer RFC2217_PARITY_MAP = { serial.PARITY_NONE: 1, serial.PARITY_ODD: 2, serial.PARITY_EVEN: 3, serial.PARITY_MARK: 4, serial.PARITY_SPACE: 5, } RFC2217_REVERSE_PARITY_MAP = dict((v, k) for k, v in RFC2217_PARITY_MAP.items()) RFC2217_STOPBIT_MAP = { serial.STOPBITS_ONE: 1, serial.STOPBITS_ONE_POINT_FIVE: 3, serial.STOPBITS_TWO: 2, } RFC2217_REVERSE_STOPBIT_MAP = dict((v, k) for k, v in RFC2217_STOPBIT_MAP.items()) # Telnet filter states M_NORMAL = 0 M_IAC_SEEN = 1 M_NEGOTIATE = 2 # TelnetOption and TelnetSubnegotiation states REQUESTED = 'REQUESTED' ACTIVE = 'ACTIVE' INACTIVE = 'INACTIVE' REALLY_INACTIVE = 'REALLY_INACTIVE' class TelnetOption(object): """Manage a single telnet option, keeps track of DO/DONT WILL/WONT.""" def __init__(self, connection, name, option, send_yes, send_no, ack_yes, ack_no, initial_state, activation_callback=None): """\ Initialize option. :param connection: connection used to transmit answers :param name: a readable name for debug outputs :param send_yes: what to send when option is to be enabled. :param send_no: what to send when option is to be disabled. :param ack_yes: what to expect when remote agrees on option. :param ack_no: what to expect when remote disagrees on option. :param initial_state: options initialized with REQUESTED are tried to be enabled on startup. use INACTIVE for all others. """ self.connection = connection self.name = name self.option = option self.send_yes = send_yes self.send_no = send_no self.ack_yes = ack_yes self.ack_no = ack_no self.state = initial_state self.active = False self.activation_callback = activation_callback def __repr__(self): """String for debug outputs""" return "{o.name}:{o.active}({o.state})".format(o=self) def process_incoming(self, command): """\ A DO/DONT/WILL/WONT was received for this option, update state and answer when needed. """ if command == self.ack_yes: if self.state is REQUESTED: self.state = ACTIVE self.active = True if self.activation_callback is not None: self.activation_callback() elif self.state is ACTIVE: pass elif self.state is INACTIVE: self.state = ACTIVE self.connection.telnet_send_option(self.send_yes, self.option) self.active = True if self.activation_callback is not None: self.activation_callback() elif self.state is REALLY_INACTIVE: self.connection.telnet_send_option(self.send_no, self.option) else: raise ValueError('option in illegal state {!r}'.format(self)) elif command == self.ack_no: if self.state is REQUESTED: self.state = INACTIVE self.active = False elif self.state is ACTIVE: self.state = INACTIVE self.connection.telnet_send_option(self.send_no, self.option) self.active = False elif self.state is INACTIVE: pass elif self.state is REALLY_INACTIVE: pass else: raise ValueError('option in illegal state {!r}'.format(self)) class TelnetSubnegotiation(object): """\ A object to handle subnegotiation of options. In this case actually sub-sub options for RFC 2217. It is used to track com port options. """ def __init__(self, connection, name, option, ack_option=None): if ack_option is None: ack_option = option self.connection = connection self.name = name self.option = option self.value = None self.ack_option = ack_option self.state = INACTIVE def __repr__(self): """String for debug outputs.""" return "{sn.name}:{sn.state}".format(sn=self) def set(self, value): """\ Request a change of the value. a request is sent to the server. if the client needs to know if the change is performed he has to check the state of this object. """ self.value = value self.state = REQUESTED self.connection.rfc2217_send_subnegotiation(self.option, self.value) if self.connection.logger: self.connection.logger.debug("SB Requesting {} -> {!r}".format(self.name, self.value)) def is_ready(self): """\ Check if answer from server has been received. when server rejects the change, raise a ValueError. """ if self.state == REALLY_INACTIVE: raise ValueError("remote rejected value for option {!r}".format(self.name)) return self.state == ACTIVE # add property to have a similar interface as TelnetOption active = property(is_ready) def wait(self, timeout=3): """\ Wait until the subnegotiation has been acknowledged or timeout. It can also throw a value error when the answer from the server does not match the value sent. """ timeout_timer = Timeout(timeout) while not timeout_timer.expired(): time.sleep(0.05) # prevent 100% CPU load if self.is_ready(): break else: raise SerialException("timeout while waiting for option {!r}".format(self.name)) def check_answer(self, suboption): """\ Check an incoming subnegotiation block. The parameter already has cut off the header like sub option number and com port option value. """ if self.value == suboption[:len(self.value)]: self.state = ACTIVE else: # error propagation done in is_ready self.state = REALLY_INACTIVE if self.connection.logger: self.connection.logger.debug("SB Answer {} -> {!r} -> {}".format(self.name, suboption, self.state)) class Serial(SerialBase): """Serial port implementation for RFC 2217 remote serial ports.""" BAUDRATES = (50, 75, 110, 134, 150, 200, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200, 38400, 57600, 115200) def __init__(self, *args, **kwargs): self._thread = None self._socket = None self._linestate = 0 self._modemstate = None self._modemstate_timeout = Timeout(-1) self._remote_suspend_flow = False self._write_lock = None self.logger = None self._ignore_set_control_answer = False self._poll_modem_state = False self._network_timeout = 3 self._telnet_options = None self._rfc2217_port_settings = None self._rfc2217_options = None self._read_buffer = None super(Serial, self).__init__(*args, **kwargs) # must be last call in case of auto-open def open(self): """\ Open port with current settings. This may throw a SerialException if the port cannot be opened. """ self.logger = None self._ignore_set_control_answer = False self._poll_modem_state = False self._network_timeout = 3 if self._port is None: raise SerialException("Port must be configured before it can be used.") if self.is_open: raise SerialException("Port is already open.") try: self._socket = socket.create_connection(self.from_url(self.portstr), timeout=5) # XXX good value? self._socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1) except Exception as msg: self._socket = None raise SerialException("Could not open port {}: {}".format(self.portstr, msg)) # use a thread save queue as buffer. it also simplifies implementing # the read timeout self._read_buffer = Queue.Queue() # to ensure that user writes does not interfere with internal # telnet/rfc2217 options establish a lock self._write_lock = threading.Lock() # name the following separately so that, below, a check can be easily done mandadory_options = [ TelnetOption(self, 'we-BINARY', BINARY, WILL, WONT, DO, DONT, INACTIVE), TelnetOption(self, 'we-RFC2217', COM_PORT_OPTION, WILL, WONT, DO, DONT, REQUESTED), ] # all supported telnet options self._telnet_options = [ TelnetOption(self, 'ECHO', ECHO, DO, DONT, WILL, WONT, REQUESTED), TelnetOption(self, 'we-SGA', SGA, WILL, WONT, DO, DONT, REQUESTED), TelnetOption(self, 'they-SGA', SGA, DO, DONT, WILL, WONT, REQUESTED), TelnetOption(self, 'they-BINARY', BINARY, DO, DONT, WILL, WONT, INACTIVE), TelnetOption(self, 'they-RFC2217', COM_PORT_OPTION, DO, DONT, WILL, WONT, REQUESTED), ] + mandadory_options # RFC 2217 specific states # COM port settings self._rfc2217_port_settings = { 'baudrate': TelnetSubnegotiation(self, 'baudrate', SET_BAUDRATE, SERVER_SET_BAUDRATE), 'datasize': TelnetSubnegotiation(self, 'datasize', SET_DATASIZE, SERVER_SET_DATASIZE), 'parity': TelnetSubnegotiation(self, 'parity', SET_PARITY, SERVER_SET_PARITY), 'stopsize': TelnetSubnegotiation(self, 'stopsize', SET_STOPSIZE, SERVER_SET_STOPSIZE), } # There are more subnegotiation objects, combine all in one dictionary # for easy access self._rfc2217_options = { 'purge': TelnetSubnegotiation(self, 'purge', PURGE_DATA, SERVER_PURGE_DATA), 'control': TelnetSubnegotiation(self, 'control', SET_CONTROL, SERVER_SET_CONTROL), } self._rfc2217_options.update(self._rfc2217_port_settings) # cache for line and modem states that the server sends to us self._linestate = 0 self._modemstate = None self._modemstate_timeout = Timeout(-1) # RFC 2217 flow control between server and client self._remote_suspend_flow = False self.is_open = True self._thread = threading.Thread(target=self._telnet_read_loop) self._thread.setDaemon(True) self._thread.setName('pySerial RFC 2217 reader thread for {}'.format(self._port)) self._thread.start() try: # must clean-up if open fails # negotiate Telnet/RFC 2217 -> send initial requests for option in self._telnet_options: if option.state is REQUESTED: self.telnet_send_option(option.send_yes, option.option) # now wait until important options are negotiated timeout = Timeout(self._network_timeout) while not timeout.expired(): time.sleep(0.05) # prevent 100% CPU load if sum(o.active for o in mandadory_options) == sum(o.state != INACTIVE for o in mandadory_options): break else: raise SerialException( "Remote does not seem to support RFC2217 or BINARY mode {!r}".format(mandadory_options)) if self.logger: self.logger.info("Negotiated options: {}".format(self._telnet_options)) # fine, go on, set RFC 2217 specific things self._reconfigure_port() # all things set up get, now a clean start if not self._dsrdtr: self._update_dtr_state() if not self._rtscts: self._update_rts_state() self.reset_input_buffer() self.reset_output_buffer() except: self.close() raise def _reconfigure_port(self): """Set communication parameters on opened port.""" if self._socket is None: raise SerialException("Can only operate on open ports") # if self._timeout != 0 and self._interCharTimeout is not None: # XXX if self._write_timeout is not None: raise NotImplementedError('write_timeout is currently not supported') # XXX # Setup the connection # to get good performance, all parameter changes are sent first... if not 0 < self._baudrate < 2 ** 32: raise ValueError("invalid baudrate: {!r}".format(self._baudrate)) self._rfc2217_port_settings['baudrate'].set(struct.pack(b'!I', self._baudrate)) self._rfc2217_port_settings['datasize'].set(struct.pack(b'!B', self._bytesize)) self._rfc2217_port_settings['parity'].set(struct.pack(b'!B', RFC2217_PARITY_MAP[self._parity])) self._rfc2217_port_settings['stopsize'].set(struct.pack(b'!B', RFC2217_STOPBIT_MAP[self._stopbits])) # and now wait until parameters are active items = self._rfc2217_port_settings.values() if self.logger: self.logger.debug("Negotiating settings: {}".format(items)) timeout = Timeout(self._network_timeout) while not timeout.expired(): time.sleep(0.05) # prevent 100% CPU load if sum(o.active for o in items) == len(items): break else: raise SerialException("Remote does not accept parameter change (RFC2217): {!r}".format(items)) if self.logger: self.logger.info("Negotiated settings: {}".format(items)) if self._rtscts and self._xonxoff: raise ValueError('xonxoff and rtscts together are not supported') elif self._rtscts: self.rfc2217_set_control(SET_CONTROL_USE_HW_FLOW_CONTROL) elif self._xonxoff: self.rfc2217_set_control(SET_CONTROL_USE_SW_FLOW_CONTROL) else: self.rfc2217_set_control(SET_CONTROL_USE_NO_FLOW_CONTROL) def close(self): """Close port""" self.is_open = False if self._socket: try: self._socket.shutdown(socket.SHUT_RDWR) self._socket.close() except: # ignore errors. pass if self._thread: self._thread.join(7) # XXX more than socket timeout self._thread = None # in case of quick reconnects, give the server some time time.sleep(0.3) self._socket = None def from_url(self, url): """\ extract host and port from an URL string, other settings are extracted an stored in instance """ parts = urlparse.urlsplit(url) if parts.scheme != "rfc2217": raise SerialException( 'expected a string in the form ' '"rfc2217://<host>:<port>[?option[&option...]]": ' 'not starting with rfc2217:// ({!r})'.format(parts.scheme)) try: # process options now, directly altering self for option, values in urlparse.parse_qs(parts.query, True).items(): if option == 'logging': logging.basicConfig() # XXX is that good to call it here? self.logger = logging.getLogger('pySerial.rfc2217') self.logger.setLevel(LOGGER_LEVELS[values[0]]) self.logger.debug('enabled logging') elif option == 'ign_set_control': self._ignore_set_control_answer = True elif option == 'poll_modem': self._poll_modem_state = True elif option == 'timeout': self._network_timeout = float(values[0]) else: raise ValueError('unknown option: {!r}'.format(option)) if not 0 <= parts.port < 65536: raise ValueError("port not in range 0...65535") except ValueError as e: raise SerialException( 'expected a string in the form ' '"rfc2217://<host>:<port>[?option[&option...]]": {}'.format(e)) return (parts.hostname, parts.port) # - - - - - - - - - - - - - - - - - - - - - - - - @property def in_waiting(self): """Return the number of bytes currently in the input buffer.""" if not self.is_open: raise PortNotOpenError() return self._read_buffer.qsize() def read(self, size=1): """\ Read size bytes from the serial port. If a timeout is set it may return less characters as requested. With no timeout it will block until the requested number of bytes is read. """ if not self.is_open: raise PortNotOpenError() data = bytearray() try: timeout = Timeout(self._timeout) while len(data) < size: if self._thread is None or not self._thread.is_alive(): raise SerialException('connection failed (reader thread died)') buf = self._read_buffer.get(True, timeout.time_left()) if buf is None: return bytes(data) data += buf if timeout.expired(): break except Queue.Empty: # -> timeout pass return bytes(data) def write(self, data): """\ Output the given byte string over the serial port. Can block if the connection is blocked. May raise SerialException if the connection is closed. """ if not self.is_open: raise PortNotOpenError() with self._write_lock: try: self._socket.sendall(to_bytes(data).replace(IAC, IAC_DOUBLED)) except socket.error as e: raise SerialException("connection failed (socket error): {}".format(e)) return len(data) def reset_input_buffer(self): """Clear input buffer, discarding all that is in the buffer.""" if not self.is_open: raise PortNotOpenError() self.rfc2217_send_purge(PURGE_RECEIVE_BUFFER) # empty read buffer while self._read_buffer.qsize(): self._read_buffer.get(False) def reset_output_buffer(self): """\ Clear output buffer, aborting the current output and discarding all that is in the buffer. """ if not self.is_open: raise PortNotOpenError() self.rfc2217_send_purge(PURGE_TRANSMIT_BUFFER) def _update_break_state(self): """\ Set break: Controls TXD. When active, to transmitting is possible. """ if not self.is_open: raise PortNotOpenError() if self.logger: self.logger.info('set BREAK to {}'.format('active' if self._break_state else 'inactive')) if self._break_state: self.rfc2217_set_control(SET_CONTROL_BREAK_ON) else: self.rfc2217_set_control(SET_CONTROL_BREAK_OFF) def _update_rts_state(self): """Set terminal status line: Request To Send.""" if not self.is_open: raise PortNotOpenError() if self.logger: self.logger.info('set RTS to {}'.format('active' if self._rts_state else 'inactive')) if self._rts_state: self.rfc2217_set_control(SET_CONTROL_RTS_ON) else: self.rfc2217_set_control(SET_CONTROL_RTS_OFF) def _update_dtr_state(self): """Set terminal status line: Data Terminal Ready.""" if not self.is_open: raise PortNotOpenError() if self.logger: self.logger.info('set DTR to {}'.format('active' if self._dtr_state else 'inactive')) if self._dtr_state: self.rfc2217_set_control(SET_CONTROL_DTR_ON) else: self.rfc2217_set_control(SET_CONTROL_DTR_OFF) @property def cts(self): """Read terminal status line: Clear To Send.""" if not self.is_open: raise PortNotOpenError() return bool(self.get_modem_state() & MODEMSTATE_MASK_CTS) @property def dsr(self): """Read terminal status line: Data Set Ready.""" if not self.is_open: raise PortNotOpenError() return bool(self.get_modem_state() & MODEMSTATE_MASK_DSR) @property def ri(self): """Read terminal status line: Ring Indicator.""" if not self.is_open: raise PortNotOpenError() return bool(self.get_modem_state() & MODEMSTATE_MASK_RI) @property def cd(self): """Read terminal status line: Carrier Detect.""" if not self.is_open: raise PortNotOpenError() return bool(self.get_modem_state() & MODEMSTATE_MASK_CD) @property def timeout(self): """Get the current timeout setting.""" return self._timeout @timeout.setter def timeout(self, timeout): """Change timeout setting.""" if timeout is not None: try: timeout + 1 # test if it's a number, will throw a TypeError if not... except TypeError: raise ValueError("Not a valid timeout: {!r}".format(timeout)) if timeout < 0: raise ValueError("Not a valid timeout: {!r}".format(timeout)) self._timeout = timeout # - - - platform specific - - - # None so far # - - - RFC2217 specific - - - def _telnet_read_loop(self): """Read loop for the socket.""" mode = M_NORMAL suboption = None try: while self.is_open: try: data = self._socket.recv(1024) except socket.timeout: # just need to get out of recv form time to time to check if # still alive continue except socket.error as e: # connection fails -> terminate loop if self.logger: self.logger.debug("socket error in reader thread: {}".format(e)) self._read_buffer.put(None) break if not data: self._read_buffer.put(None) break # lost connection for byte in iterbytes(data): if mode == M_NORMAL: # interpret as command or as data if byte == IAC: mode = M_IAC_SEEN else: # store data in read buffer or sub option buffer # depending on state if suboption is not None: suboption += byte else: self._read_buffer.put(byte) elif mode == M_IAC_SEEN: if byte == IAC: # interpret as command doubled -> insert character # itself if suboption is not None: suboption += IAC else: self._read_buffer.put(IAC) mode = M_NORMAL elif byte == SB: # sub option start suboption = bytearray() mode = M_NORMAL elif byte == SE: # sub option end -> process it now self._telnet_process_subnegotiation(bytes(suboption)) suboption = None mode = M_NORMAL elif byte in (DO, DONT, WILL, WONT): # negotiation telnet_command = byte mode = M_NEGOTIATE else: # other telnet commands self._telnet_process_command(byte) mode = M_NORMAL elif mode == M_NEGOTIATE: # DO, DONT, WILL, WONT was received, option now following self._telnet_negotiate_option(telnet_command, byte) mode = M_NORMAL finally: if self.logger: self.logger.debug("read thread terminated") # - incoming telnet commands and options def _telnet_process_command(self, command): """Process commands other than DO, DONT, WILL, WONT.""" # Currently none. RFC2217 only uses negotiation and subnegotiation. if self.logger: self.logger.warning("ignoring Telnet command: {!r}".format(command)) def _telnet_negotiate_option(self, command, option): """Process incoming DO, DONT, WILL, WONT.""" # check our registered telnet options and forward command to them # they know themselves if they have to answer or not known = False for item in self._telnet_options: # can have more than one match! as some options are duplicated for # 'us' and 'them' if item.option == option: item.process_incoming(command) known = True if not known: # handle unknown options # only answer to positive requests and deny them if command == WILL or command == DO: self.telnet_send_option((DONT if command == WILL else WONT), option) if self.logger: self.logger.warning("rejected Telnet option: {!r}".format(option)) def _telnet_process_subnegotiation(self, suboption): """Process subnegotiation, the data between IAC SB and IAC SE.""" if suboption[0:1] == COM_PORT_OPTION: if suboption[1:2] == SERVER_NOTIFY_LINESTATE and len(suboption) >= 3: self._linestate = ord(suboption[2:3]) # ensure it is a number if self.logger: self.logger.info("NOTIFY_LINESTATE: {}".format(self._linestate)) elif suboption[1:2] == SERVER_NOTIFY_MODEMSTATE and len(suboption) >= 3: self._modemstate = ord(suboption[2:3]) # ensure it is a number if self.logger: self.logger.info("NOTIFY_MODEMSTATE: {}".format(self._modemstate)) # update time when we think that a poll would make sense self._modemstate_timeout.restart(0.3) elif suboption[1:2] == FLOWCONTROL_SUSPEND: self._remote_suspend_flow = True elif suboption[1:2] == FLOWCONTROL_RESUME: self._remote_suspend_flow = False else: for item in self._rfc2217_options.values(): if item.ack_option == suboption[1:2]: #~ print "processing COM_PORT_OPTION: %r" % list(suboption[1:]) item.check_answer(bytes(suboption[2:])) break else: if self.logger: self.logger.warning("ignoring COM_PORT_OPTION: {!r}".format(suboption)) else: if self.logger: self.logger.warning("ignoring subnegotiation: {!r}".format(suboption)) # - outgoing telnet commands and options def _internal_raw_write(self, data): """internal socket write with no data escaping. used to send telnet stuff.""" with self._write_lock: self._socket.sendall(data) def telnet_send_option(self, action, option): """Send DO, DONT, WILL, WONT.""" self._internal_raw_write(IAC + action + option) def rfc2217_send_subnegotiation(self, option, value=b''): """Subnegotiation of RFC2217 parameters.""" value = value.replace(IAC, IAC_DOUBLED) self._internal_raw_write(IAC + SB + COM_PORT_OPTION + option + value + IAC + SE) def rfc2217_send_purge(self, value): """\ Send purge request to the remote. (PURGE_RECEIVE_BUFFER / PURGE_TRANSMIT_BUFFER / PURGE_BOTH_BUFFERS) """ item = self._rfc2217_options['purge'] item.set(value) # transmit desired purge type item.wait(self._network_timeout) # wait for acknowledge from the server def rfc2217_set_control(self, value): """transmit change of control line to remote""" item = self._rfc2217_options['control'] item.set(value) # transmit desired control type if self._ignore_set_control_answer: # answers are ignored when option is set. compatibility mode for # servers that answer, but not the expected one... (or no answer # at all) i.e. sredird time.sleep(0.1) # this helps getting the unit tests passed else: item.wait(self._network_timeout) # wait for acknowledge from the server def rfc2217_flow_server_ready(self): """\ check if server is ready to receive data. block for some time when not. """ #~ if self._remote_suspend_flow: #~ wait--- def get_modem_state(self): """\ get last modem state (cached value. If value is "old", request a new one. This cache helps that we don't issue to many requests when e.g. all status lines, one after the other is queried by the user (CTS, DSR etc.) """ # active modem state polling enabled? is the value fresh enough? if self._poll_modem_state and self._modemstate_timeout.expired(): if self.logger: self.logger.debug('polling modem state') # when it is older, request an update self.rfc2217_send_subnegotiation(NOTIFY_MODEMSTATE) timeout = Timeout(self._network_timeout) while not timeout.expired(): time.sleep(0.05) # prevent 100% CPU load # when expiration time is updated, it means that there is a new # value if not self._modemstate_timeout.expired(): break else: if self.logger: self.logger.warning('poll for modem state failed') # even when there is a timeout, do not generate an error just # return the last known value. this way we can support buggy # servers that do not respond to polls, but send automatic # updates. if self._modemstate is not None: if self.logger: self.logger.debug('using cached modem state') return self._modemstate else: # never received a notification from the server raise SerialException("remote sends no NOTIFY_MODEMSTATE") ############################################################################# # The following is code that helps implementing an RFC 2217 server. class PortManager(object): """\ This class manages the state of Telnet and RFC 2217. It needs a serial instance and a connection to work with. Connection is expected to implement a (thread safe) write function, that writes the string to the network. """ def __init__(self, serial_port, connection, logger=None): self.serial = serial_port self.connection = connection self.logger = logger self._client_is_rfc2217 = False # filter state machine self.mode = M_NORMAL self.suboption = None self.telnet_command = None # states for modem/line control events self.modemstate_mask = 255 self.last_modemstate = None self.linstate_mask = 0 # all supported telnet options self._telnet_options = [ TelnetOption(self, 'ECHO', ECHO, WILL, WONT, DO, DONT, REQUESTED), TelnetOption(self, 'we-SGA', SGA, WILL, WONT, DO, DONT, REQUESTED), TelnetOption(self, 'they-SGA', SGA, DO, DONT, WILL, WONT, INACTIVE), TelnetOption(self, 'we-BINARY', BINARY, WILL, WONT, DO, DONT, INACTIVE), TelnetOption(self, 'they-BINARY', BINARY, DO, DONT, WILL, WONT, REQUESTED), TelnetOption(self, 'we-RFC2217', COM_PORT_OPTION, WILL, WONT, DO, DONT, REQUESTED, self._client_ok), TelnetOption(self, 'they-RFC2217', COM_PORT_OPTION, DO, DONT, WILL, WONT, INACTIVE, self._client_ok), ] # negotiate Telnet/RFC2217 -> send initial requests if self.logger: self.logger.debug("requesting initial Telnet/RFC 2217 options") for option in self._telnet_options: if option.state is REQUESTED: self.telnet_send_option(option.send_yes, option.option) # issue 1st modem state notification def _client_ok(self): """\ callback of telnet option. It gets called when option is activated. This one here is used to detect when the client agrees on RFC 2217. A flag is set so that other functions like check_modem_lines know if the client is OK. """ # The callback is used for we and they so if one party agrees, we're # already happy. it seems not all servers do the negotiation correctly # and i guess there are incorrect clients too.. so be happy if client # answers one or the other positively. self._client_is_rfc2217 = True if self.logger: self.logger.info("client accepts RFC 2217") # this is to ensure that the client gets a notification, even if there # was no change self.check_modem_lines(force_notification=True) # - outgoing telnet commands and options def telnet_send_option(self, action, option): """Send DO, DONT, WILL, WONT.""" self.connection.write(IAC + action + option) def rfc2217_send_subnegotiation(self, option, value=b''): """Subnegotiation of RFC 2217 parameters.""" value = value.replace(IAC, IAC_DOUBLED) self.connection.write(IAC + SB + COM_PORT_OPTION + option + value + IAC + SE) # - check modem lines, needs to be called periodically from user to # establish polling def check_modem_lines(self, force_notification=False): """\ read control lines from serial port and compare the last value sent to remote. send updates on changes. """ modemstate = ( (self.serial.cts and MODEMSTATE_MASK_CTS) | (self.serial.dsr and MODEMSTATE_MASK_DSR) | (self.serial.ri and MODEMSTATE_MASK_RI) | (self.serial.cd and MODEMSTATE_MASK_CD)) # check what has changed deltas = modemstate ^ (self.last_modemstate or 0) # when last is None -> 0 if deltas & MODEMSTATE_MASK_CTS: modemstate |= MODEMSTATE_MASK_CTS_CHANGE if deltas & MODEMSTATE_MASK_DSR: modemstate |= MODEMSTATE_MASK_DSR_CHANGE if deltas & MODEMSTATE_MASK_RI: modemstate |= MODEMSTATE_MASK_RI_CHANGE if deltas & MODEMSTATE_MASK_CD: modemstate |= MODEMSTATE_MASK_CD_CHANGE # if new state is different and the mask allows this change, send # notification. suppress notifications when client is not rfc2217 if modemstate != self.last_modemstate or force_notification: if (self._client_is_rfc2217 and (modemstate & self.modemstate_mask)) or force_notification: self.rfc2217_send_subnegotiation( SERVER_NOTIFY_MODEMSTATE, to_bytes([modemstate & self.modemstate_mask])) if self.logger: self.logger.info("NOTIFY_MODEMSTATE: {}".format(modemstate)) # save last state, but forget about deltas. # otherwise it would also notify about changing deltas which is # probably not very useful self.last_modemstate = modemstate & 0xf0 # - outgoing data escaping def escape(self, data): """\ This generator function is for the user. All outgoing data has to be properly escaped, so that no IAC character in the data stream messes up the Telnet state machine in the server. socket.sendall(escape(data)) """ for byte in iterbytes(data): if byte == IAC: yield IAC yield IAC else: yield byte # - incoming data filter def filter(self, data): """\ Handle a bunch of incoming bytes. This is a generator. It will yield all characters not of interest for Telnet/RFC 2217. The idea is that the reader thread pushes data from the socket through this filter: for byte in filter(socket.recv(1024)): # do things like CR/LF conversion/whatever # and write data to the serial port serial.write(byte) (socket error handling code left as exercise for the reader) """ for byte in iterbytes(data): if self.mode == M_NORMAL: # interpret as command or as data if byte == IAC: self.mode = M_IAC_SEEN else: # store data in sub option buffer or pass it to our # consumer depending on state if self.suboption is not None: self.suboption += byte else: yield byte elif self.mode == M_IAC_SEEN: if byte == IAC: # interpret as command doubled -> insert character # itself if self.suboption is not None: self.suboption += byte else: yield byte self.mode = M_NORMAL elif byte == SB: # sub option start self.suboption = bytearray() self.mode = M_NORMAL elif byte == SE: # sub option end -> process it now self._telnet_process_subnegotiation(bytes(self.suboption)) self.suboption = None self.mode = M_NORMAL elif byte in (DO, DONT, WILL, WONT): # negotiation self.telnet_command = byte self.mode = M_NEGOTIATE else: # other telnet commands self._telnet_process_command(byte) self.mode = M_NORMAL elif self.mode == M_NEGOTIATE: # DO, DONT, WILL, WONT was received, option now following self._telnet_negotiate_option(self.telnet_command, byte) self.mode = M_NORMAL # - incoming telnet commands and options def _telnet_process_command(self, command): """Process commands other than DO, DONT, WILL, WONT.""" # Currently none. RFC2217 only uses negotiation and subnegotiation. if self.logger: self.logger.warning("ignoring Telnet command: {!r}".format(command)) def _telnet_negotiate_option(self, command, option): """Process incoming DO, DONT, WILL, WONT.""" # check our registered telnet options and forward command to them # they know themselves if they have to answer or not known = False for item in self._telnet_options: # can have more than one match! as some options are duplicated for # 'us' and 'them' if item.option == option: item.process_incoming(command) known = True if not known: # handle unknown options # only answer to positive requests and deny them if command == WILL or command == DO: self.telnet_send_option((DONT if command == WILL else WONT), option) if self.logger: self.logger.warning("rejected Telnet option: {!r}".format(option)) def _telnet_process_subnegotiation(self, suboption): """Process subnegotiation, the data between IAC SB and IAC SE.""" if suboption[0:1] == COM_PORT_OPTION: if self.logger: self.logger.debug('received COM_PORT_OPTION: {!r}'.format(suboption)) if suboption[1:2] == SET_BAUDRATE: backup = self.serial.baudrate try: (baudrate,) = struct.unpack(b"!I", suboption[2:6]) if baudrate != 0: self.serial.baudrate = baudrate except ValueError as e: if self.logger: self.logger.error("failed to set baud rate: {}".format(e)) self.serial.baudrate = backup else: if self.logger: self.logger.info("{} baud rate: {}".format('set' if baudrate else 'get', self.serial.baudrate)) self.rfc2217_send_subnegotiation(SERVER_SET_BAUDRATE, struct.pack(b"!I", self.serial.baudrate)) elif suboption[1:2] == SET_DATASIZE: backup = self.serial.bytesize try: (datasize,) = struct.unpack(b"!B", suboption[2:3]) if datasize != 0: self.serial.bytesize = datasize except ValueError as e: if self.logger: self.logger.error("failed to set data size: {}".format(e)) self.serial.bytesize = backup else: if self.logger: self.logger.info("{} data size: {}".format('set' if datasize else 'get', self.serial.bytesize)) self.rfc2217_send_subnegotiation(SERVER_SET_DATASIZE, struct.pack(b"!B", self.serial.bytesize)) elif suboption[1:2] == SET_PARITY: backup = self.serial.parity try: parity = struct.unpack(b"!B", suboption[2:3])[0] if parity != 0: self.serial.parity = RFC2217_REVERSE_PARITY_MAP[parity] except ValueError as e: if self.logger: self.logger.error("failed to set parity: {}".format(e)) self.serial.parity = backup else: if self.logger: self.logger.info("{} parity: {}".format('set' if parity else 'get', self.serial.parity)) self.rfc2217_send_subnegotiation( SERVER_SET_PARITY, struct.pack(b"!B", RFC2217_PARITY_MAP[self.serial.parity])) elif suboption[1:2] == SET_STOPSIZE: backup = self.serial.stopbits try: stopbits = struct.unpack(b"!B", suboption[2:3])[0] if stopbits != 0: self.serial.stopbits = RFC2217_REVERSE_STOPBIT_MAP[stopbits] except ValueError as e: if self.logger: self.logger.error("failed to set stop bits: {}".format(e)) self.serial.stopbits = backup else: if self.logger: self.logger.info("{} stop bits: {}".format('set' if stopbits else 'get', self.serial.stopbits)) self.rfc2217_send_subnegotiation( SERVER_SET_STOPSIZE, struct.pack(b"!B", RFC2217_STOPBIT_MAP[self.serial.stopbits])) elif suboption[1:2] == SET_CONTROL: if suboption[2:3] == SET_CONTROL_REQ_FLOW_SETTING: if self.serial.xonxoff: self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_USE_SW_FLOW_CONTROL) elif self.serial.rtscts: self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_USE_HW_FLOW_CONTROL) else: self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_USE_NO_FLOW_CONTROL) elif suboption[2:3] == SET_CONTROL_USE_NO_FLOW_CONTROL: self.serial.xonxoff = False self.serial.rtscts = False if self.logger: self.logger.info("changed flow control to None") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_USE_NO_FLOW_CONTROL) elif suboption[2:3] == SET_CONTROL_USE_SW_FLOW_CONTROL: self.serial.xonxoff = True if self.logger: self.logger.info("changed flow control to XON/XOFF") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_USE_SW_FLOW_CONTROL) elif suboption[2:3] == SET_CONTROL_USE_HW_FLOW_CONTROL: self.serial.rtscts = True if self.logger: self.logger.info("changed flow control to RTS/CTS") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_USE_HW_FLOW_CONTROL) elif suboption[2:3] == SET_CONTROL_REQ_BREAK_STATE: if self.logger: self.logger.warning("requested break state - not implemented") pass # XXX needs cached value elif suboption[2:3] == SET_CONTROL_BREAK_ON: self.serial.break_condition = True if self.logger: self.logger.info("changed BREAK to active") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_BREAK_ON) elif suboption[2:3] == SET_CONTROL_BREAK_OFF: self.serial.break_condition = False if self.logger: self.logger.info("changed BREAK to inactive") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_BREAK_OFF) elif suboption[2:3] == SET_CONTROL_REQ_DTR: if self.logger: self.logger.warning("requested DTR state - not implemented") pass # XXX needs cached value elif suboption[2:3] == SET_CONTROL_DTR_ON: self.serial.dtr = True if self.logger: self.logger.info("changed DTR to active") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_DTR_ON) elif suboption[2:3] == SET_CONTROL_DTR_OFF: self.serial.dtr = False if self.logger: self.logger.info("changed DTR to inactive") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_DTR_OFF) elif suboption[2:3] == SET_CONTROL_REQ_RTS: if self.logger: self.logger.warning("requested RTS state - not implemented") pass # XXX needs cached value #~ self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_RTS_ON) elif suboption[2:3] == SET_CONTROL_RTS_ON: self.serial.rts = True if self.logger: self.logger.info("changed RTS to active") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_RTS_ON) elif suboption[2:3] == SET_CONTROL_RTS_OFF: self.serial.rts = False if self.logger: self.logger.info("changed RTS to inactive") self.rfc2217_send_subnegotiation(SERVER_SET_CONTROL, SET_CONTROL_RTS_OFF) #~ elif suboption[2:3] == SET_CONTROL_REQ_FLOW_SETTING_IN: #~ elif suboption[2:3] == SET_CONTROL_USE_NO_FLOW_CONTROL_IN: #~ elif suboption[2:3] == SET_CONTROL_USE_SW_FLOW_CONTOL_IN: #~ elif suboption[2:3] == SET_CONTROL_USE_HW_FLOW_CONTOL_IN: #~ elif suboption[2:3] == SET_CONTROL_USE_DCD_FLOW_CONTROL: #~ elif suboption[2:3] == SET_CONTROL_USE_DTR_FLOW_CONTROL: #~ elif suboption[2:3] == SET_CONTROL_USE_DSR_FLOW_CONTROL: elif suboption[1:2] == NOTIFY_LINESTATE: # client polls for current state self.rfc2217_send_subnegotiation( SERVER_NOTIFY_LINESTATE, to_bytes([0])) # sorry, nothing like that implemented elif suboption[1:2] == NOTIFY_MODEMSTATE: if self.logger: self.logger.info("request for modem state") # client polls for current state self.check_modem_lines(force_notification=True) elif suboption[1:2] == FLOWCONTROL_SUSPEND: if self.logger: self.logger.info("suspend") self._remote_suspend_flow = True elif suboption[1:2] == FLOWCONTROL_RESUME: if self.logger: self.logger.info("resume") self._remote_suspend_flow = False elif suboption[1:2] == SET_LINESTATE_MASK: self.linstate_mask = ord(suboption[2:3]) # ensure it is a number if self.logger: self.logger.info("line state mask: 0x{:02x}".format(self.linstate_mask)) elif suboption[1:2] == SET_MODEMSTATE_MASK: self.modemstate_mask = ord(suboption[2:3]) # ensure it is a number if self.logger: self.logger.info("modem state mask: 0x{:02x}".format(self.modemstate_mask)) elif suboption[1:2] == PURGE_DATA: if suboption[2:3] == PURGE_RECEIVE_BUFFER: self.serial.reset_input_buffer() if self.logger: self.logger.info("purge in") self.rfc2217_send_subnegotiation(SERVER_PURGE_DATA, PURGE_RECEIVE_BUFFER) elif suboption[2:3] == PURGE_TRANSMIT_BUFFER: self.serial.reset_output_buffer() if self.logger: self.logger.info("purge out") self.rfc2217_send_subnegotiation(SERVER_PURGE_DATA, PURGE_TRANSMIT_BUFFER) elif suboption[2:3] == PURGE_BOTH_BUFFERS: self.serial.reset_input_buffer() self.serial.reset_output_buffer() if self.logger: self.logger.info("purge both") self.rfc2217_send_subnegotiation(SERVER_PURGE_DATA, PURGE_BOTH_BUFFERS) else: if self.logger: self.logger.error("undefined PURGE_DATA: {!r}".format(list(suboption[2:]))) else: if self.logger: self.logger.error("undefined COM_PORT_OPTION: {!r}".format(list(suboption[1:]))) else: if self.logger: self.logger.warning("unknown subnegotiation: {!r}".format(suboption)) # simple client test if __name__ == '__main__': import sys s = Serial('rfc2217://localhost:7000', 115200) sys.stdout.write('{}\n'.format(s)) sys.stdout.write("write...\n") s.write(b"hello\n") s.flush() sys.stdout.write("read: {}\n".format(s.read(5))) s.close()