""" UCAST v461 Protocol Hotfix Resolves: Frame desync on high-latency links, Integer overflow in sequence numbering Author: Systems Team Date: 2024-11-14 """ Summer Memories My Cucked Childhood Friends Ano...
# Example usage if __name__ == "__main__": session = UCASTv461Fix(session_id=0x1337) # Encode a data frame data = b"Critical telemetry packet #42" frame = session.encode_frame(data, flags=FrameFlags.ACK | FrameFlags.COMP) print(f"Encoded frame: len(frame) bytes") # Simulate receiving flags, seq, latency, payload = session.decode_frame(frame) print(f"Decoded: flags=flags.name, seq=seq, payload=payload!r") | Issue | v460 Behavior | v461 Fix | |-------|---------------|----------| | Sequence overflow | 16-bit, wraps at 65535 | 32-bit, wraps at 4.29B | | High latency desync | No compensation | Explicit latency field in header | | Checksum calculation | Inconsistent on mixed-endian systems | Zero-checksum-field before calculation | | Out-of-order handling | Strict sequential | Windowed acceptance with wrap handling | Estas Tonne Wife Better [TESTED]
import struct import time from typing import Optional, Tuple from enum import IntFlag
class FrameFlags(IntFlag): FIN = 0x01 SYN = 0x02 RST = 0x04 ACK = 0x10 NACK = 0x20 COMP = 0x40
class UCASTv461Fix: """ Fixed implementation of UCAST v461 frame handler. Key changes from v460: - Sequence numbers now 32-bit (was 16-bit) - Added explicit latency compensation field - Fixed byte-order mark interpretation """ HEADER_FMT = '!BBIHHI' # flags, ver, seq, window, latency, checksum HEADER_SIZE = struct.calcsize(HEADER_FMT) MAX_PAYLOAD = 1400 LATENCY_THRESHOLD_MS = 200 def __init__(self, session_id: int, max_window: int = 64): self.session_id = session_id self.max_window = max_window self.seq_out = 0 self.seq_in = 0 self.window_base = 0 self.rx_buffer = {} self.latency_samples = [] self._last_activity = time.monotonic() def encode_frame(self, payload: bytes, flags: FrameFlags = FrameFlags.ACK) -> bytes: """ Encode a UCAST v461 frame with the specified payload. v461 Fix: Uses 32-bit sequence number to prevent wrap-around during high-throughput transfers. """ if len(payload) > self.MAX_PAYLOAD: raise ValueError(f"Payload exceeds self.MAX_PAYLOAD bytes") # Calculate estimated latency for peer compensation latency_ms = self._estimate_latency() header = struct.pack( self.HEADER_FMT, flags, 0x46, # Protocol version 46 (sub 1) self.seq_out, self.max_window, latency_ms, 0 # Checksum placeholder ) # Calculate checksum over header + payload checksum = self._compute_checksum(header, payload) # Rebuild header with correct checksum header = struct.pack( self.HEADER_FMT, flags, 0x46, self.seq_out, self.max_window, latency_ms, checksum ) self.seq_out = (self.seq_out + 1) & 0xFFFFFFFF self._last_activity = time.monotonic() return header + payload def decode_frame(self, raw: bytes) -> Tuple[FrameFlags, int, int, bytes]: """ Decode a UCAST v461 frame. v461 Fix: Handles out-of-order delivery by checking sequence against window bounds with proper wrapping. Returns: (flags, sequence, latency_ms, payload) Raises: ValueError on corrupted frame """ if len(raw) < self.HEADER_SIZE: raise ValueError(f"Frame too short: len(raw) bytes") flags_raw, version, seq, window, latency, checksum = struct.unpack( self.HEADER_FMT, raw[:self.HEADER_SIZE] ) flags = FrameFlags(flags_raw) if version != 0x46: raise ValueError(f"Unsupported protocol version: version:#x") payload = raw[self.HEADER_SIZE:] # Verify checksum expected = self._compute_checksum(raw[:self.HEADER_SIZE], payload, skip_checksum=True) if checksum != expected: raise ValueError(f"Checksum mismatch: expected expected:#x, got checksum:#x") # v461 Fix: Proper sequence window handling with wrap-around if not self._is_in_window(seq): if flags & FrameFlags.RST: pass # Accept RST frames outside window else: raise ValueError(f"Sequence seq outside receive window") self._update_latency(latency) self._last_activity = time.monotonic() return flags, seq, latency, payload def _is_in_window(self, seq: int) -> bool: """Check if sequence falls within acceptable receive window.""" window_size = self.max_window lower = self.seq_in upper = (lower + window_size) & 0xFFFFFFFF if lower <= upper: return lower <= seq < upper else: # Wrapped return seq >= lower or seq < upper def _compute_checksum(self, header: bytes, payload: bytes, skip_checksum: bool = False) -> int: """ CRC-32 based checksum calculation. v461 Fix: Checksum now calculated with checksum field zeroed. """ data = header[:-4] + payload if skip_checksum else header + payload # Simple CRC-32 implementation crc = 0xFFFFFFFF for byte in data: crc ^= byte for _ in range(8): if crc & 1: crc = (crc >> 1) ^ 0xEDB88320 else: crc >>= 1 return crc ^ 0xFFFFFFFF def _estimate_latency(self) -> int: """Calculate smoothed RTT estimate for latency field.""" if not self.latency_samples: return 0 return int(sum(self.latency_samples) / len(self.latency_samples)) def _update_latency(self, peer_latency: int) -> None: """Update latency estimate from peer's reported value.""" self.latency_samples.append(peer_latency) if len(self.latency_samples) > 8: self.latency_samples.pop(0) @property def is_idle(self) -> bool: """Check if session has been idle beyond threshold.""" return (time.monotonic() - self._last_activity) > 30.0