fix(deserializeStream): allow multiple documents to be deserialized

deserializeStream was calling deserialize, which required the buffer
size to exactly match the object size per the corpus test. Fixing
this by adding a flag that deserializeStream passes to allow the
buffer to be larger than the object size.

Fixes #244

Author: daprahamian

Diff for: lib/bson/bson.js

@@ -128,6 +128,7 @@ BSON.prototype.serializeWithBufferAndIndex = function(object, finalBuffer, optio
  * @param {Object} [options.promoteValues=false] when deserializing will promote BSON values to their Node.js closest equivalent types.
  * @param {Object} [options.fieldsAsRaw=null] allow to specify if there what fields we wish to return as unserialized raw buffer.
  * @param {Object} [options.bsonRegExp=false] return BSON regular expressions as BSONRegExp instances.
+ * @param {boolean} [options.allowObjectSmallerThanBufferSize=false] allows the buffer to be larger than the parsed BSON object
  * @return {Object} returns the deserialized Javascript Object.
  * @api public
  */
@@ -183,15 +184,15 @@ BSON.prototype.deserializeStream = function(
   docStartIndex,
   options
 ) {
-  options = options != null ? options : {};
+  options = Object.assign({ allowObjectSmallerThanBufferSize: true }, options);
   var index = startIndex;
   // Loop over all documents
   for (var i = 0; i < numberOfDocuments; i++) {
     // Find size of the document
     var size =
       data[index] | (data[index + 1] << 8) | (data[index + 2] << 16) | (data[index + 3] << 24);
     // Update options with index
-    options['index'] = index;
+    options.index = index;
     // Parse the document at this point
     documents[docStartIndex + i] = this.deserialize(data, options);
     // Adjust index by the document size

Diff for: lib/bson/parser/deserializer.js

@@ -23,9 +23,22 @@ var deserialize = function(buffer, options, isArray) {
     (buffer[index + 2] << 16) |
     (buffer[index + 3] << 24);
 
-  // Ensure buffer is valid size
-  if (size < 5 || buffer.length !== size || size + index > buffer.length) {
-    throw new Error('corrupt bson message');
+  if (size < 5) {
+    throw new Error(`bson size must be >= 5, is ${size}`);
+  }
+
+  if (options.allowObjectSmallerThanBufferSize && buffer.length < size) {
+    throw new Error(`buffer length ${buffer.length} must be >= bson size ${size}`);
+  }
+
+  if (!options.allowObjectSmallerThanBufferSize && buffer.length !== size) {
+    throw new Error(`buffer length ${buffer.length} must === bson size ${size}`);
+  }
+
+  if (size + index > buffer.length) {
+    throw new Error(
+      `(bson size ${size} + options.index ${index} must be <= buffer length ${buffer.length})`
+    );
   }
 
   // Illegal end value

Diff for: test/binary_parser.js

@@ -47,7 +47,11 @@ BinaryParser.decodeFloat = function decodeFloat(data, precisionBits, exponentBit
   } while ((precisionBits -= startBit));
 
   return exponent === (bias << 1) + 1
-    ? significand ? NaN : signal ? -Infinity : +Infinity
+    ? significand
+      ? NaN
+      : signal
+        ? -Infinity
+        : +Infinity
     : (1 + signal * -2) *
         (exponent || significand
           ? !exponent

Diff for: test/node/bson_test.js

@@ -2174,6 +2174,23 @@ describe('BSON', function() {
   //   done();
   // }
 
+  it('should properly deserialize multiple documents using deserializeStream', function() {
+    const bson = createBSON();
+    const docs = [{ foo: 'bar' }, { foo: 'baz' }, { foo: 'quux' }];
+
+    // Serialize the test data
+    const serializedDocs = [];
+    for (let i = 0; i < docs.length; i++) {
+      serializedDocs[i] = bson.serialize(docs[i]);
+    }
+    const buf = Buffer.concat(serializedDocs);
+
+    const parsedDocs = [];
+    bson.deserializeStream(buf, 0, docs.length, parsedDocs, 0);
+
+    docs.forEach((doc, i) => expect(doc).to.deep.equal(parsedDocs[i]));
+  });
+
   /**
    * @ignore
    */