fix(error): attach command response to MongoWriteConcernError (#322)

Fixes NODE-1521

Author: kvwalker

lib/connection/pool.js

@@ -581,11 +581,11 @@ function messageHandler(self) {
           }
 
           if (responseDoc.writeConcernError) {
-            return handleOperationCallback(
-              self,
-              workItem.cb,
-              new MongoWriteConcernError(responseDoc.writeConcernError)
-            );
+            const err =
+              responseDoc.ok === 1
+                ? new MongoWriteConcernError(responseDoc.writeConcernError, responseDoc)
+                : new MongoWriteConcernError(responseDoc.writeConcernError);
+            return handleOperationCallback(self, workItem.cb, err);
           }
         }
 

lib/error.js

@@ -130,13 +130,19 @@ function isRetryableError(error) {
  *
  * @class
  * @param {Error|string|object} message The error message
+ * @param {object} result The result document (provided if ok: 1)
  * @property {string} message The error message
+ * @property {object} [result] The result document (provided if ok: 1)
  * @return {MongoWriteConcernError} A MongoWriteConcernError instance
  * @extends {MongoError}
  */
-const MongoWriteConcernError = function(message) {
+const MongoWriteConcernError = function(message, result) {
   MongoError.call(this, message);
   this.name = 'MongoWriteConcernError';
+
+  if (result != null) {
+    this.result = result;
+  }
 };
 util.inherits(MongoWriteConcernError, MongoError);