diff --git a/lib/httpServerAgent.js b/lib/httpServerAgent.js
index 1fffea3..b091170 100644
--- a/lib/httpServerAgent.js
+++ b/lib/httpServerAgent.js
@@ -20,6 +20,10 @@ var https = require('https')
 var cluster = require('cluster')
 var domain = require('domain')
 
+// constants
+var FINISH_EVENT_NAME = 'finish'
+var ABRUPT_CLOSE_EVENT_NAME = 'close'
+
 module.exports = function httpServerAgent () {
   var SpmAgent = require('spm-agent')
   var Agent = SpmAgent.Agent
@@ -37,20 +41,18 @@ module.exports = function httpServerAgent () {
     timer: timer,
     stats: stats,
     logger: logger,
-    histogram: histogram,
-    FINISH_EVENT_NAME: 'finish',
-    ABRUPT_CLOSE_EVENT_NAME: 'close'
+    histogram: histogram
   }
 
   // bind monitorHttp safely
-  safeProcess(ctx, monitorHttp)
+  var monitor = safeProcess(ctx, monitorHttp)
 
   // setup monitoring agent
   var hAgent = new Agent({
     start: function (agent) {
       this._agent = agent
-      patchHttpServer(monitorHttp)
-      patchHttpsServer(monitorHttp)
+      patchHttpServer(monitor)
+      patchHttpsServer(monitor)
       var timerId = setInterval(function () {
         var httpStats = stats.toJSON()
         var responseTimes = histogram.toJSON()
@@ -61,8 +63,8 @@ module.exports = function httpServerAgent () {
           httpStats['3xxRate'] ? httpStats['3xxRate'].count : 0, // http.3xx (int)
           httpStats['4xxRate'] ? httpStats['4xxRate'].count : 0, // http.4xx (int)
           httpStats['5xxRate'] ? httpStats['5xxRate'].count : 0, // http.5xx (int)
-          reqSize,
-          resSize,
+          ctx.reqSize,
+          ctx.resSize,
           responseTimes.min,
           responseTimes.max,
           responseTimes.sum