logging: throw when a circular reference is used in an entry (#1664)

packages/logging/package.json

@@ -58,6 +58,7 @@
     "google-gax": "^0.7.0",
     "google-proto-files": "^0.8.0",
     "is": "^3.0.1",
+    "is-circular": "^1.0.1",
     "string-format-obj": "^1.0.0"
   },
   "devDependencies": {

packages/logging/src/entry.js

@@ -23,6 +23,7 @@
 var common = require('@google-cloud/common');
 var extend = require('extend');
 var is = require('is');
+var isCircular = require('is-circular');
 
 /**
  * Create an entry object to define new data to insert into a log.
@@ -122,6 +123,10 @@ Entry.fromApiResponse_ = function(entry) {
  * @private
  */
 Entry.prototype.toJSON = function() {
+  if (is.object(this.data) && isCircular([this.data])) {
+    throw new Error('The JSON data for this entry has a circular reference.');
+  }
+
   var entry = extend(true, {}, this);
 
   var whitelist = [

packages/logging/test/entry.js

@@ -186,6 +186,15 @@ describe('Entry', function() {
       assert.strictEqual(json.jsonPayload, converted);
     });
 
+    it('should throw with a struct with a circular reference', function() {
+      entry.data = { val: true };
+      entry.data.data = entry.data;
+
+      assert.throws(function() {
+        entry.toJSON();
+      }, /The JSON data for this entry has a circular reference\./);
+    });
+
     it('should assign string data as textPayload', function() {
       entry.data = 'string';
       var json = entry.toJSON();