fix(compression): recalculate opcode after determine OP_COMPRESSED

Author: mbroadst

lib/core/cmap/message_stream.js

@@ -131,7 +131,7 @@ function processMessage(stream, message, callback) {
     opCode: message.readInt32LE(12)
   };
 
-  const ResponseType = messageHeader.opCode === OP_MSG ? BinMsg : Response;
+  let ResponseType = messageHeader.opCode === OP_MSG ? BinMsg : Response;
   const responseOptions = stream.responseOptions;
   if (messageHeader.opCode !== OP_COMPRESSED) {
     const messageBody = message.slice(MESSAGE_HEADER_SIZE);
@@ -150,6 +150,8 @@ function processMessage(stream, message, callback) {
   const compressorID = message[MESSAGE_HEADER_SIZE + 8];
   const compressedBuffer = message.slice(MESSAGE_HEADER_SIZE + 9);
 
+  // recalculate based on wrapped opcode
+  ResponseType = messageHeader.opCode === OP_MSG ? BinMsg : Response;
   decompress(compressorID, compressedBuffer, (err, messageBody) => {
     if (err) {
       callback(err);