splitCoalescedPackets function

List<Uint8List> splitCoalescedPackets(Uint8List buf)

Implementation

List<Uint8List> splitCoalescedPackets(Uint8List buf) {
  final out = <Uint8List>[];
  int i = 0;

  while (i < buf.length) {
    // Need at least 5 bytes for long header
    if (i + 5 > buf.length) break;

    final flags = buf[i];
    final isLong = (flags & 0x80) != 0;

    if (isLong) {
      int p = i + 1;

      // ---- Version (4 bytes) ----
      if (p + 4 > buf.length) break;
      p += 4;

      // ---- DCID ----
      if (p >= buf.length) break;
      final dcidLen = buf[p++];
      if (p + dcidLen > buf.length) break;
      p += dcidLen;

      // ---- SCID ----
      if (p >= buf.length) break;
      final scidLen = buf[p++];
      if (p + scidLen > buf.length) break;
      p += scidLen;

      // ---- Token Length (ONLY Initial packets) ----
      final packetType = (flags >> 4) & 0x03;

      if (packetType == 0x00) {
        // Initial packet → token field present
        final token = readVarInt(buf, p);
        if (token == null) break;

        p += token.byteLength;

        if (p + token.value > buf.length) break;
        p += token.value;
      }

      // ---- Length field (varint) ----
      final lengthField = readVarInt(buf, p);
      if (lengthField == null) break;

      final payloadLen = lengthField.value;
      p += lengthField.byteLength;

      // ---- Bounds check to avoid RangeError ----
      final pktEnd = p + payloadLen;
      if (pktEnd > buf.length) {
        throw RangeError(
          "QUIC long header claims payload length $payloadLen but only "
          "${buf.length - p} bytes remain",
        );
      }

      // ---- Extract packet ----
      out.add(buf.sublist(i, pktEnd));

      // Move to next packet
      i = pktEnd;
      continue;
    }

    // ------------------------------
    // Short header → runs to end of UDP datagram
    // ------------------------------
    out.add(buf.sublist(i));
    break;
  }

  return out;
}