added telegram CRC verification

dsmr_parser/exceptions.py

@@ -1,2 +1,6 @@
 class ParseError(Exception):
     pass
+
+
+class InvalidChecksumError(ParseError):
+    pass

dsmr_parser/parsers.py

@@ -1,8 +1,10 @@
 import logging
 import re
 
+from PyCRC.CRC16 import CRC16
+
 from .objects import MBusObject, MBusObjectV2_2, CosemObject
-from .exceptions import ParseError
+from .exceptions import ParseError, InvalidChecksumError
 from .obis_references import GAS_METER_READING
 
 logger = logging.getLogger(__name__)
@@ -18,7 +20,6 @@ class TelegramParser(object):
         self.telegram_specification = telegram_specification
 
     def _find_line_parser(self, line_value):
-
         for obis_reference, parser in self.telegram_specification.items():
             if re.search(obis_reference, line_value):
                 return obis_reference, parser
@@ -29,7 +30,10 @@ class TelegramParser(object):
         telegram = {}
 
         for line_value in line_values:
-            obis_reference, dsmr_object = self.parse_line(line_value.strip())
+            # TODO temporarily strip newline characters.
+            line_value = line_value.strip()
+
+            obis_reference, dsmr_object = self.parse_line(line_value)
 
             telegram[obis_reference] = dsmr_object
 
@@ -47,7 +51,51 @@ class TelegramParser(object):
         return obis_reference, parser.parse(line_value)
 
 
+class TelegramParserV4(TelegramParser):
+
+    @staticmethod
+    def validate_telegram_checksum(line_values):
+        """
+        :type line_values: list
+        :raises ParseError:
+        :raises InvalidChecksumError:
+        """
+
+        full_telegram = ''.join(line_values)
+
+        # Extract the bytes that count towards the checksum.
+        checksum_contents = re.search(r'\/.+\!', full_telegram, re.DOTALL)
+
+        # Extract the hexadecimal checksum value itself.
+        checksum_hex = re.search(r'((?<=\!)[0-9A-Z]{4}(?=\r\n))+', full_telegram)
+
+        if not checksum_contents or not checksum_hex:
+            raise ParseError(
+                'Failed to perform CRC validation because the telegram is '
+                'incomplete. The checksum and/or content values are missing.'
+            )
+
+        calculated_crc = CRC16().calculate(checksum_contents.group(0))
+        expected_crc = checksum_hex.group(0)
+        expected_crc = int(expected_crc, base=16)
+
+        if calculated_crc != expected_crc:
+            raise InvalidChecksumError(
+                "Invalid telegram. The CRC checksum '{}' does not match the "
+                "expected '{}'".format(
+                    calculated_crc,
+                    expected_crc
+                )
+            )
+
+    def parse(self, line_values):
+        self.validate_telegram_checksum(line_values)
+
+        return super(self, TelegramParserV4).parse(line_values)
+
+
 class TelegramParserV2_2(TelegramParser):
+
     def parse(self, line_values):
         """Join lines for gas meter."""
 

dsmr_parser/serial.py

@@ -1,11 +1,11 @@
 import asyncio
 import logging
-
 import serial
-
 import serial_asyncio
+
 from dsmr_parser.exceptions import ParseError
-from dsmr_parser.parsers import TelegramParser, TelegramParserV2_2
+from dsmr_parser.parsers import TelegramParser, TelegramParserV2_2, \
+    TelegramParserV4
 
 logger = logging.getLogger(__name__)
 
@@ -32,15 +32,20 @@ SERIAL_SETTINGS_V4 = {
 
 
 def is_start_of_telegram(line):
+    """
+    :type line: line
+    """
     return line.startswith('/')
 
 
 def is_end_of_telegram(line):
+    """
+    :type line: line
+    """
     return line.startswith('!')
 
 
 class SerialReader(object):
-
     PORT_KEY = 'port'
 
     def __init__(self, device, serial_settings, telegram_specification):
@@ -49,8 +54,11 @@ class SerialReader(object):
 
         if serial_settings is SERIAL_SETTINGS_V2_2:
             telegram_parser = TelegramParserV2_2
+        elif serial_settings is SERIAL_SETTINGS_V4:
+            telegram_parser = TelegramParserV4
         else:
             telegram_parser = TelegramParser
+
         self.telegram_parser = telegram_parser(telegram_specification)
 
     def read(self):
@@ -65,7 +73,7 @@ class SerialReader(object):
 
             while True:
                 line = serial_handle.readline()
-                line = line.decode('ascii')
+                line = line.decode('ascii')  # TODO move this to the parser?
 
                 # Telegrams need to be complete because the values belong to a
                 # particular reading and can also be related to eachother.
@@ -75,7 +83,12 @@ class SerialReader(object):
                 telegram.append(line)
 
                 if is_end_of_telegram(line):
-                    yield self.telegram_parser.parse(telegram)
+
+                    try:
+                        yield self.telegram_parser.parse(telegram)
+                    except ParseError as e:
+                        logger.error('Failed to parse telegram: %s', e)
+
                     telegram = []
 
 
@@ -119,7 +132,7 @@ class AsyncSerialReader(SerialReader):
                     parsed_telegram = self.telegram_parser.parse(telegram)
                     # push new parsed telegram onto queue
                     queue.put_nowait(parsed_telegram)
-                except ParseError:
-                    logger.exception("failed to parse telegram")
+                except ParseError as e:
+                    logger.warning('Failed to parse telegram: %s', e)
 
                 telegram = []

dsmr_parser/value_types.py

@@ -4,8 +4,9 @@ import pytz
 
 
 def timestamp(value):
-
     naive_datetime = datetime.datetime.strptime(value[:-1], '%y%m%d%H%M%S')
+
+    # TODO comment on this exception
     if len(value) == 13:
         is_dst = value[12] == 'S'  # assume format 160322150000W
     else: