X-Git-Url: http://www.average.org/gitweb/?a=blobdiff_plain;f=gps303%2Fgps303proto.py;h=baa9a6cf64ac7af7b6fcb5605de3783f02b35955;hb=7bf96d53196eb6caf035335260a2dc25cec72e57;hp=0a222d05634930679995e6e4807d939d35104346;hpb=18eda7307e92eeee6a9e2fdd2e810f98d25df654;p=loctrkd.git diff --git a/gps303/gps303proto.py b/gps303/gps303proto.py index 0a222d0..baa9a6c 100755 --- a/gps303/gps303proto.py +++ b/gps303/gps303proto.py @@ -18,6 +18,7 @@ from datetime import datetime, timezone from enum import Enum from inspect import isclass from struct import error, pack, unpack +from time import time from typing import ( Any, Callable, @@ -31,6 +32,7 @@ from typing import ( ) __all__ = ( + "GPS303Conn", "class_by_prefix", "inline_response", "parse_message", @@ -77,6 +79,75 @@ __all__ = ( "UNKNOWN_B3", ) +### Deframer ### + +MAXBUFFER: int = 4096 + + +class GPS303Conn: + def __init__(self) -> None: + self.buffer = b"" + + @staticmethod + def enframe(buffer: bytes) -> bytes: + return b"xx" + buffer + b"\r\n" + + def recv(self, segment: bytes) -> List[Union[bytes, str]]: + """ + Process next segment of the stream. Return successfully deframed + packets as `bytes` and error messages as `str`. + """ + when = time() + self.buffer += segment + if len(self.buffer) > MAXBUFFER: + # We are receiving junk. Let's drop it or we run out of memory. + self.buffer = b"" + return [f"More than {MAXBUFFER} unparseable data, dropping"] + msgs: List[Union[bytes, str]] = [] + while True: + framestart = self.buffer.find(b"xx") + if framestart == -1: # No frames, return whatever we have + break + if framestart > 0: # Should not happen, report + msgs.append( + f'Undecodable data ({framestart}) "{self.buffer[:framestart][:64].hex()}"' + ) + self.buffer = self.buffer[framestart:] + # At this point, buffer starts with a packet + if len(self.buffer) < 6: # no len and proto - cannot proceed + break + exp_end = self.buffer[2] + 3 # Expect '\r\n' here + frameend = 0 + # Length field can legitimeely be much less than the + # length of the packet (e.g. WiFi positioning), but + # it _should not_ be greater. Still sometimes it is. + # Luckily, not by too much: by maybe two or three bytes? + # Do this embarrassing hack to avoid accidental match + # of some binary data in the packet against '\r\n'. + while True: + frameend = self.buffer.find(b"\r\n", frameend + 1) + if frameend == -1 or frameend >= ( + exp_end - 3 + ): # Found realistic match or none + break + if frameend == -1: # Incomplete frame, return what we have + break + packet = self.buffer[2:frameend] + self.buffer = self.buffer[frameend + 2 :] + if len(packet) < 2: # frameend comes too early + msgs.append(f"Packet too short: {packet.hex()}") + else: + msgs.append(packet) + return msgs + + def close(self) -> bytes: + ret = self.buffer + self.buffer = b"" + return ret + + +### Parser/Constructor ### + class DecodeError(Exception): def __init__(self, e: Exception, **kwargs: Any) -> None: