def parse_ais_messages(self, raw, bits, source='internal'):
"Generator code - read forever from source stream, parsing AIS messages."
values = {}
values['length'] = bits.bitlen
# Without the following magic, we'd have a subtle problem near
# certain variable-length messages: DSV reports would
# sometimes have fewer fields than expected, because the
# unpacker would never generate cooked tuples for the omitted
# part of the message. Presently a known issue for types 15
# and 16 only. (Would never affect variable-length messages in
# which the last field type is 'string' or 'raw').
bits.extend_to(168)
# Magic recursive unpacking operation
try:
cooked = ais.aivdm_unpack(0, bits, 0, values, ais.aivdm_decode)
# We now have a list of tuples containing unpacked fields
# Collect some field groups into ISO8601 format
for (offset, template, label, legend,
formatter) in ais.field_groups:
segment = cooked[offset:offset + len(template)]
if map(lambda x: x[0], segment) == template:
group = ais.formatter(*map(lambda x: x[1], segment))
group = (label, group, 'string', legend, None)
cooked = cooked[:offset] + [group] + cooked[offset +
len(template):]
# Apply the postprocessor stage
cooked = ais.postprocess(cooked)
expected = ais.lengths.get(values['msgtype'], None)
# Check length; has to be done after so we have the type field
bogon = False
if expected is not None:
if type(expected) == type(0):
expected_range = (expected, expected)
else:
expected_range = expected
actual = values['length']
if not (actual >= expected_range[0]
and actual <= expected_range[1]):
raise Exception(
"invalid length %d(%d..%d)" %
(actual, expected_range[0], expected_range[1]))
# We're done, hand back a decoding
#AVNLog.ld('decoded AIS data',cooked)
self.storeAISdata(cooked, source=source)
return True
except:
(exc_type, exc_value, exc_traceback) = sys.exc_info()
AVNLog.debug("exception %s while decoding AIS data %s", exc_value,
raw.strip())
return False
def parse_ais_messages(self,raw,bits):
"Generator code - read forever from source stream, parsing AIS messages."
values = {}
values['length'] = bits.bitlen
# Without the following magic, we'd have a subtle problem near
# certain variable-length messages: DSV reports would
# sometimes have fewer fields than expected, because the
# unpacker would never generate cooked tuples for the omitted
# part of the message. Presently a known issue for types 15
# and 16 only. (Would never affect variable-length messages in
# which the last field type is 'string' or 'raw').
bits.extend_to(168)
# Magic recursive unpacking operation
try:
cooked = ais.aivdm_unpack(0, bits, 0, values, ais.aivdm_decode)
# We now have a list of tuples containing unpacked fields
# Collect some field groups into ISO8601 format
for (offset, template, label, legend, formatter) in ais.field_groups:
segment = cooked[offset:offset+len(template)]
if map(lambda x: x[0], segment) == template:
group = ais.formatter(*map(lambda x: x[1], segment))
group = (label, group, 'string', legend, None)
cooked = cooked[:offset]+[group]+cooked[offset+len(template):]
# Apply the postprocessor stage
cooked = ais.postprocess(cooked)
expected = ais.lengths.get(values['msgtype'], None)
# Check length; has to be done after so we have the type field
bogon = False
if expected is not None:
if type(expected) == type(0):
expected_range = (expected, expected)
else:
expected_range = expected
actual = values['length']
if not (actual >= expected_range[0] and actual <= expected_range[1]):
raise AISUnpackingException(0, "length", actual)
# We're done, hand back a decoding
#AVNLog.ld('decoded AIS data',cooked)
self.storeAISdata(cooked)
return True
except:
(exc_type, exc_value, exc_traceback) = sys.exc_info()
AVNLog.debug("exception %s while decoding AIS data %s",exc_value,raw.strip())
return False