Function decompressResponse

src/cmap/wire_protocol/compression.ts:185–215

(message: Uint8Array)

 * This method does not parse the response's BSON.
 */
export async function decompressResponse(message: Uint8Array): Promise<OpMsgResponse | OpReply> {
  const messageHeader: MessageHeader = {
    length: readInt32LE(message, 0),
    requestId: readInt32LE(message, 4),
    responseTo: readInt32LE(message, 8),
    opCode: readInt32LE(message, 12)
  };

  if (messageHeader.opCode !== OP_COMPRESSED) {
    const ResponseType = messageHeader.opCode === OP_MSG ? OpMsgResponse : OpReply;
    const messageBody = message.subarray(MESSAGE_HEADER_SIZE);
    return new ResponseType(message, messageHeader, messageBody);
  }

  const header: MessageHeader = {
    ...messageHeader,
    fromCompressed: true,
    opCode: readInt32LE(message, MESSAGE_HEADER_SIZE),
    length: readInt32LE(message, MESSAGE_HEADER_SIZE + 4)
  };
  const compressorID = message[MESSAGE_HEADER_SIZE + 8];
  const compressedBuffer = message.slice(MESSAGE_HEADER_SIZE + 9);

  // recalculate based on wrapped opcode
  const ResponseType = header.opCode === OP_MSG ? OpMsgResponse : OpReply;
  const messageBody = await decompress(compressorID, compressedBuffer);
  if (messageBody.length !== header.length) {
    throw new MongoDecompressionError('Message body and message header must be the same length');
  }
  return new ResponseType(message, header, messageBody);
}