async def read_msg(self) -> Tuple[protocol.Command, protocol.PayloadType]:
header_data = await self.read(HEADER_LEN + MAC_LEN)
header = self.decrypt_header(header_data)
frame_size = self.get_frame_size(header)
# The frame_size specified in the header does not include the padding to 16-byte boundary,
# so need to do this here to ensure we read all the frame's data.
read_size = roundup_16(frame_size)
frame_data = await self.read(read_size + MAC_LEN)
msg = self.decrypt_body(frame_data, frame_size)
cmd = self.get_protocol_command_for(msg)
# NOTE: This used to be a bottleneck but it doesn't seem to be so anymore. If we notice
# too much time is being spent on this again, we need to consider running this in a
# ProcessPoolExecutor(). Need to make sure we don't use all CPUs in the machine for that,
# though, otherwise asyncio's event loop can't run and we can't keep up with other peers.
try:
decoded_msg = cast(Dict[str, Any], cmd.decode(msg))
except MalformedMessage as err:
self.logger.debug(
"Malformed message from peer %s: CMD:%s Error: %r",
self,
type(cmd).__name__,
err,
)
raise
else:
self.logger.trace("Successfully decoded %s msg: %s", cmd,
decoded_msg)
self.received_msgs[cmd] += 1
return cmd, decoded_msg
def decrypt_body(self, data: bytes, body_size: int) -> bytes:
read_size = roundup_16(body_size)
if len(data) < read_size + MAC_LEN:
raise ValueError(
f"Insufficient body length; Got {len(data)}, wanted {read_size} + {MAC_LEN}"
)
frame_ciphertext = data[:read_size]
frame_mac = data[read_size:read_size + MAC_LEN]
self.ingress_mac.update(frame_ciphertext)
fmac_seed = self.ingress_mac.digest()[:MAC_LEN]
self.ingress_mac.update(sxor(self.mac_enc(fmac_seed), fmac_seed))
expected_frame_mac = self.ingress_mac.digest()[:MAC_LEN]
if not bytes_eq(expected_frame_mac, frame_mac):
raise DecryptionError(
f"Invalid frame mac: expected {expected_frame_mac}, got {frame_mac}"
)
return self.aes_dec.update(frame_ciphertext)[:body_size]
