def __try_read_record(self):
"""Try reading a record.
Returns:
(data, record_type) tuple.
Raises:
EOFError: when end of file was reached.
InvalidRecordError: when valid record could not be read.
"""
block_remaining = _BLOCK_SIZE - self.__reader.tell() % _BLOCK_SIZE
if block_remaining < _HEADER_LENGTH:
return ('', _RECORD_TYPE_NONE)
header = self.__reader.read(_HEADER_LENGTH)
if len(header) != _HEADER_LENGTH:
raise EOFError('Read %s bytes instead of %s' %
(len(header), _HEADER_LENGTH))
(masked_crc, length,
record_type) = struct.unpack(_HEADER_FORMAT, header)
crc = _unmask_crc(masked_crc)
if length + _HEADER_LENGTH > block_remaining:
raise errors.InvalidRecordError('Length is too big')
data = self.__reader.read(length)
if len(data) != length:
raise EOFError('Not enough data read. Expected: %s but got %s' %
(length, len(data)))
if record_type == _RECORD_TYPE_NONE:
return ('', record_type)
actual_crc = crc32c.crc_update(crc32c.CRC_INIT, [record_type])
actual_crc = crc32c.crc_update(actual_crc, data)
actual_crc = crc32c.crc_finalize(actual_crc)
if actual_crc != crc:
raise errors.InvalidRecordError('Data crc does not match')
return (data, record_type)
def read(self):
"""Reads record from current position in reader.
Returns:
original bytes stored in a single record.
"""
data = None
while True:
last_offset = self.tell()
try:
(chunk, record_type) = self.__try_read_record()
if record_type == _RECORD_TYPE_NONE:
self.__sync()
elif record_type == _RECORD_TYPE_FULL:
if data is not None:
logging.warning(
"Ordering corruption: Got FULL record while already "
"in a chunk at offset %d", last_offset)
return chunk
elif record_type == _RECORD_TYPE_FIRST:
if data is not None:
logging.warning(
"Ordering corruption: Got FIRST record while already "
"in a chunk at offset %d", last_offset)
data = chunk
elif record_type == _RECORD_TYPE_MIDDLE:
if data is None:
logging.warning(
"Ordering corruption: Got MIDDLE record before FIRST "
"record at offset %d", last_offset)
else:
data += chunk
elif record_type == _RECORD_TYPE_LAST:
if data is None:
logging.warning(
"Ordering corruption: Got LAST record but no chunk is in "
"progress at offset %d", last_offset)
else:
result = data + chunk
data = None
return result
else:
raise errors.InvalidRecordError(
"Unsupported record type: %s" % record_type)
except errors.InvalidRecordError, e:
logging.warning(
"Invalid record encountered at %s (%s). Syncing to "
"the next block", last_offset, e)
data = None
self.__sync()
