NODE-1034 Fix GridStore issue caused by Node 8.0.0 breaking backward …

…compatible fs.read API

lib/gridfs/grid_store.js

@@ -427,20 +427,23 @@ var writeFile = function(self, file, callback) {
 
       // Write a chunk
       var writeChunk = function() {
-        fs.read(file, self.chunkSize, offset, 'binary', function(err, data, bytesRead) {
+        // Allocate the buffer
+        var _buffer = new Buffer(self.chunkSize);
+        // Read the file
+        fs.read(file, _buffer, 0, _buffer.length, offset, function(err, bytesRead, data) {
           if(err) return callback(err, self);
 
           offset = offset + bytesRead;
 
           // Create a new chunk for the data
           var chunk = new Chunk(self, {n:index++}, self.writeConcern);
-          chunk.write(data, function(err, chunk) {
+          chunk.write(data.slice(0, bytesRead), function(err, chunk) {
             if(err) return callback(err, self);
 
             chunk.save({}, function(err) {
               if(err) return callback(err, self);
 
-              self.position = self.position + data.length;
+              self.position = self.position + bytesRead;
 
               // Point to current chunk
               self.currentChunk = chunk;