decodeVarint function

Map<String, int> decodeVarint(List<int> buffer, int offset)

Decodes a varint (LEB128) from buffer starting at offset.

Returns a map with two entries:

• 'value': the decoded unsigned integer.
• 'bytesRead': the number of bytes consumed from the buffer.

Throws a FormatException if the varint exceeds 10 bytes (the maximum for a 64-bit value) or if the buffer ends before the varint is complete.

Implementation

Map<String, int> decodeVarint(List<int> buffer, int offset) {
  int result = 0;
  int shift = 0;
  int bytesRead = 0;

  while (true) {
    if (offset + bytesRead >= buffer.length) {
      throw FormatException(
        'Unexpected end of buffer while decoding varint at offset $offset',
      );
    }

    int byte = buffer[offset + bytesRead];
    bytesRead++;

    // Accumulate the 7 payload bits at the current shift position.
    result = result | ((byte & 0x7F) << shift);
    shift += 7;

    // If the continuation bit (MSB) is not set, we are done.
    if ((byte & 0x80) == 0) {
      break;
    }

    // Varints longer than 10 bytes cannot represent a 64-bit value.
    if (bytesRead >= 10) {
      throw FormatException(
        'Varint exceeds maximum length of 10 bytes at offset $offset',
      );
    }
  }

  return {'value': result, 'bytesRead': bytesRead};
}