feat(OP_MSG): adding class for translating OP_MSG from binary

This will be used for parsing OP_MSG replies from the server

lib/connection/msg.js

@@ -169,9 +169,86 @@ Msg.getRequestId = function() {
   return ++_requestId;
 };
 
+class BinMsg {
+  constructor(bson, message, msgHeader, msgBody, opts) {
+    opts = opts || { promoteLongs: true, promoteValues: true, promoteBuffers: false };
+    this.parsed = false;
+    this.raw = message;
+    this.data = msgBody;
+    this.bson = bson;
+    this.opts = opts;
+
+    // Read the message header
+    this.length = msgHeader.length;
+    this.requestId = msgHeader.requestId;
+    this.responseTo = msgHeader.responseTo;
+    this.opCode = msgHeader.opCode;
+
+    // Read response flags
+    this.responseFlags = msgBody.readInt32LE(0);
+    this.checksumPresent = (this.responseFlags & Msg.flags.CHECKSUM_PRESENT) !== 0;
+    this.moreToCome = (this.responseFlags & Msg.flags.MORE_TO_COME) !== 0;
+    this.exhaustAllowed = (this.responseFlags & Msg.flags.EXHAUST_ALLOWED) !== 0;
+    this.promoteLongs = typeof opts.promoteLongs === 'boolean' ? opts.promoteLongs : true;
+    this.promoteValues = typeof opts.promoteValues === 'boolean' ? opts.promoteValues : true;
+    this.promoteBuffers = typeof opts.promoteBuffers === 'boolean' ? opts.promoteBuffers : false;
+
+    this.documents = [];
+  }
+
+  isParsed() {
+    return this.parsed;
+  }
+
+  parse(options) {
+    // Don't parse again if not needed
+    if (this.parsed) return;
+    options = options || {};
+
+    this.index = 4;
+    // Allow the return of raw documents instead of parsing
+    const raw = options.raw || false;
+    const promoteLongs =
+      typeof options.promoteLongs === 'boolean' ? options.promoteLongs : this.opts.promoteLongs;
+    const promoteValues =
+      typeof options.promoteValues === 'boolean' ? options.promoteValues : this.opts.promoteValues;
+    const promoteBuffers =
+      typeof options.promoteBuffers === 'boolean'
+        ? options.promoteBuffers
+        : this.opts.promoteBuffers;
+
+    // Set up the options
+    const _options = {
+      promoteLongs: promoteLongs,
+      promoteValues: promoteValues,
+      promoteBuffers: promoteBuffers
+    };
+
+    while (this.index < this.data.length) {
+      const payloadType = this.data.readUInt8(this.index++);
+      if (payloadType === 1) {
+        console.error('TYPE 1');
+      } else if (payloadType === 0) {
+        const bsonSize = this.data.readUInt32LE(this.index);
+        const bin = this.data.slice(this.index, this.index + bsonSize);
+        this.documents.push(raw ? bin : this.bson.deserialize(bin, _options));
+
+        this.index += bsonSize;
+      }
+    }
+
+    this.parsed = true;
+  }
+}
+
+Msg.flags = {
+  CHECKSUM_PRESENT: 1,
+  MORE_TO_COME: 2,
+  EXHAUST_ALLOWED: 1 << 16
+};
+
 function writeInt32ListToUint8Buffer(buffer, int32List, start) {
   let index = start || 0;
-
   int32List.forEach(int32 => {
     buffer[index] = int32 & 0xff;
     buffer[index + 1] = (int32 >> 8) & 0xff;
@@ -198,7 +275,8 @@ function getValidSegmentListNamePairs(query) {
       }
     }
   }
+
   return false;
 }
 
-module.exports = { Msg };
+module.exports = { Msg, BinMsg };