refactor(buffer): add a more robust workaround for feross/safe-buffer#23

Fix #6826

Author: vkarpov15

lib/types/buffer.js

@@ -8,7 +8,8 @@ const Binary = require('../driver').get().Binary;
 const utils = require('../utils');
 const Buffer = require('safe-buffer').Buffer;
 
-const NodeBuffer = global.Buffer || Buffer;
+// Yes this is weird. See https://github.com/feross/safe-buffer/pull/23
+const proto = Buffer.from('').constructor.prototype;
 
 /**
  * Mongoose Buffer constructor.
@@ -134,7 +135,7 @@ MongooseBuffer.mixin = {
    */
 
   write: function() {
-    const written = NodeBuffer.prototype.write.apply(this, arguments);
+    const written = proto.write.apply(this, arguments);
 
     if (written > 0) {
       this._markModified();
@@ -157,7 +158,7 @@ MongooseBuffer.mixin = {
    */
 
   copy: function(target) {
-    const ret = NodeBuffer.prototype.copy.apply(this, arguments);
+    const ret = proto.copy.apply(this, arguments);
 
     if (target && target.isMongooseBuffer) {
       target._markModified();
@@ -181,11 +182,11 @@ MongooseBuffer.mixin = {
     'writeUInt16LE writeUInt16BE writeUInt32LE writeUInt32BE ' +
     'writeInt16LE writeInt16BE writeInt32LE writeInt32BE ' + 'writeFloatLE writeFloatBE writeDoubleLE writeDoubleBE')
 ).split(' ').forEach(function(method) {
-  if (!NodeBuffer.prototype[method]) {
+  if (!proto[method]) {
     return;
   }
   MongooseBuffer.mixin[method] = function() {
-    const ret = NodeBuffer.prototype[method].apply(this, arguments);
+    const ret = proto[method].apply(this, arguments);
     this._markModified();
     return ret;
   };