pySim/transport/modem_atcmd.py

# -*- coding: utf-8 -*-

# Copyright (C) 2020 Vadim Yanitskiy <axilirator@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#

import logging as log
import serial
import time
import re

from pySim.transport import LinkBase
from pySim.exceptions import *

# HACK: if somebody needs to debug this thing
# log.root.setLevel(log.DEBUG)

class ModemATCommandLink(LinkBase):
	"""Transport Link for 3GPP TS 27.007 compliant modems."""
	def __init__(self, device:str='/dev/ttyUSB0', baudrate:int=115200, **kwargs):
		super().__init__(**kwargs)
		self._sl = serial.Serial(device, baudrate, timeout=5)
		self._echo = False		# this will be auto-detected by _check_echo()
		self._device = device
		self._atr = None

		# Check the AT interface
		self._check_echo()

		# Trigger initial reset
		self.reset_card()

	def __del__(self):
		if hasattr(self, '_sl'):
			self._sl.close()

	def send_at_cmd(self, cmd, timeout=0.2, patience=0.002):
		# Convert from string to bytes, if needed
		bcmd = cmd if type(cmd) is bytes else cmd.encode()
		bcmd += b'\r'

		# Clean input buffer from previous/unexpected data
		self._sl.reset_input_buffer()

		# Send command to the modem
		log.debug('Sending AT command: %s', cmd)
		try:
			wlen = self._sl.write(bcmd)
			assert(wlen == len(bcmd))
		except:
			raise ReaderError('Failed to send AT command: %s' % cmd)

		rsp = b''
		its = 1
		t_start = time.time()
		while True:
			rsp = rsp + self._sl.read(self._sl.in_waiting)
			if rsp.endswith(b'OK\r\n'):
				log.debug('Command finished with result: OK')
				break
			if rsp.endswith(b'ERROR\r\n'):
				log.debug('Command finished with result: ERROR')
				break
			if time.time() - t_start >= timeout:
				log.debug('Command finished with timeout >= %ss', timeout)
				break
			time.sleep(patience)
			its += 1
		log.debug('Command took %0.6fs (%d cycles a %fs)', time.time() - t_start, its, patience)

		if self._echo:
			# Skip echo chars
			rsp = rsp[wlen:]
		rsp = rsp.strip()
		rsp = rsp.split(b'\r\n\r\n')

		log.debug('Got response from modem: %s', rsp)
		return rsp

	def _check_echo(self):
		"""Verify the correct response to 'AT' command
		and detect if inputs are echoed by the device

		Although echo of inputs can be enabled/disabled via
		ATE1/ATE0, respectively, we rather detect the current
		configuration of the modem without any change.
		"""
		# Next command shall not strip the echo from the response
		self._echo = False
		result = self.send_at_cmd('AT')

		# Verify the response
		if len(result) > 0:
			if result[-1] == b'OK':
				self._echo = False
				return
			elif result[-1] == b'AT\r\r\nOK':
				self._echo = True
				return
		raise ReaderError('Interface \'%s\' does not respond to \'AT\' command' % self._device)

	def reset_card(self):
		# Reset the modem, just to be sure
		if self.send_at_cmd('ATZ') != [b'OK']:
			raise ReaderError('Failed to reset the modem')

		# Make sure that generic SIM access is supported
		if self.send_at_cmd('AT+CSIM=?') != [b'OK']:
			raise ReaderError('The modem does not seem to support SIM access')

		log.info('Modem at \'%s\' is ready!' % self._device)

	def connect(self):
		pass # Nothing to do really ...

	def disconnect(self):
		pass # Nothing to do really ...

	def wait_for_card(self, timeout=None, newcardonly=False):
		pass # Nothing to do really ...

	def _send_apdu_raw(self, pdu):
		# Make sure pdu has upper case hex digits [A-F]
		pdu = pdu.upper()

		# Prepare the command as described in 8.17
		cmd = 'AT+CSIM=%d,\"%s\"' % (len(pdu), pdu)

		# Send AT+CSIM command to the modem
		# TODO: also handle +CME ERROR: <err>
		rsp = self.send_at_cmd(cmd)
		if len(rsp) != 2 or rsp[-1] != b'OK':
			raise ReaderError('APDU transfer failed: %s' % str(rsp))
		rsp = rsp[0] # Get rid of b'OK'

		# Make sure that the response has format: b'+CSIM: %d,\"%s\"'
		try:
			result = re.match(b'\+CSIM: (\d+),\"([0-9A-F]+)\"', rsp)
			(rsp_pdu_len, rsp_pdu) = result.groups()
		except:
			raise ReaderError('Failed to parse response from modem: %s' % rsp)

		# TODO: make sure we have at least SW
		data = rsp_pdu[:-4].decode()
		sw   = rsp_pdu[-4:].decode()
		return data, sw