fix(agent): do not throw error on circular dependencies

Author: dszakallas

lib/agent/api/index.js

@@ -6,6 +6,7 @@ var isNumber = require('lodash.isnumber')
 var debug = require('debug')('risingstack/trace')
 var assign = require('lodash.assign')
 var HttpsProxyAgent = require('https-proxy-agent')
+var stringify = require('json-stringify-safe')
 
 var bl = require('bl')
 var libPackage = require('../../../package')
@@ -38,7 +39,7 @@ function CollectorApi (options) {
 
 // USE THIS WITH CAUTION, IT WILL BE BLOCKING
 CollectorApi.prototype._sendSync = function (destinationUrl, data) {
-  debug('sending data to trace servers sync: ', JSON.stringify(data))
+  debug('sending data to trace servers sync: ', stringify(data))
   try {
     requestSync('POST', destinationUrl, {
       json: data,
@@ -64,7 +65,7 @@ CollectorApi.prototype._withInstanceInfo = function (data) {
 
 CollectorApi.prototype._send = function (destinationUrl, data, callback) {
   var opts = url.parse(destinationUrl)
-  var payload = JSON.stringify(data)
+  var payload = stringify(data)
 
   callback = callback || function () {}