def decode_frame(raw_data):
"""
Try to create a frame instance from the raw data.
It's assumed that raw_data is a buffer and can still be incomplete to
create a valid frame or it has multiple frames packed into it.
Arguments:
raw_data - byte() with the raw data of the buffer
Returns (bytes consumed, frame instance) or
(0, None) if no complete frame is in the buffer
Raises FrameException if an invalid frame was detected.
"""
log.debug("RAW DATA: %r" % raw_data)
try:
msg_type, payload_size = struct.unpack(FRAME_HEADER_STRUCT,
raw_data[:FRAME_HEADER_SIZE])
except struct.error:
log.debug("Invalid frame - couldn't unpack headers")
return 0, None
frame_end = FRAME_HEADER_SIZE + payload_size + FRAME_END_SIZE
if len(raw_data) < frame_end:
log.debug("Invalid frame - incomplete frame (%d, %d)" % \
(len(raw_data), frame_end))
return 0, None
if raw_data[frame_end - FRAME_END_SIZE] != FRAME_END:
raise FrameException(
"Frame doesn't end with the expected FRAME_END marker")
payload = raw_data[FRAME_HEADER_SIZE:frame_end-FRAME_END_SIZE]
log.debug("PAYLOAD: %r" % payload)
if msg_type not in MessageType.values():
raise FrameException("Frame has invalid message type")
return frame_end, Frame(msg_type, payload)
