|Revision 1.0||01.15.2013||Admin||Fiddler tutorial|
|Revision 1.1 – 1.3||09.09.2013 - 10.04.2013||Admin||bugfixes and enhancements|
Fiddler is a free and open-source packet analyzer. It is used for network troubleshooting, analysis, software, communications protocol development and education. Fiddler captures HTTP and HTTPS traffic data between the browser and server. These data are extremely valuable to troubleshoot HTTP errors, Java script errors and performance issues related to browser page rendering, this article is a step by step tutorial to guide how to use Fiddler and how to capture HTTP Traffic.
Fiddler sits between the http client and http server listening on a port for traffic. As the finger displays in below, it enables a proxy between two layers to intercept the traffic, the request being taken does not proceed to server directly, instead, it is sent to Fiddler proxy bridge, Fiddler records the incoming and outgoing data and then forward to server again.
Fiddler is a Windows Forms application, available for Windows XP and later, go to download page http://www.fiddler2.com/fiddler2/, there have two versions fiddler2 and fiddler4 available, fiddler2 was written in .Net 2, fiddler4 was higher, please choose either the one to download.
After downloaded, double-click the exe file and agree to the installing license, follow the step-by-step wizard to complete the installation, during installing, you may be asked to close all browsers.
Lunch the shortcut of Fiddler from from Start > All Program, you will see the below main Fiddler UI, when starting Fiddler, it will automatically check the latest version against the Fiddler server and ask you upgrade if there have new version available.
Use Internet Explorer or Mozilla FireFox, open a web page to make a request via the explorer, we will instantly see a list of the web requests in the web sessions panel, while you visit more web pages, the list will continue to growing and keep in order.
The web sessions show all HTTP and HTTPS sessions which were captured by Fiddler, the messages include certain key information:
It’s an overall summary list about without much details, it generic give a sense what’s all the HTTP requests .
when you double click on a HTTP session, the Inspectors tab from right hand side of the screen will be displayed, it visualize content of captured requests and responses in meaningful ways. In the top half of the right hand side is the request what was sent to server, there have multiple tabs of view where show format message and data(Headers, Text View, web forms, HexView, Auth, Cookies, Raw, JSON and XML). The first one is header, it logged cache, Client, Cookies/Login, Miscellaneous and Transport, these infos are particular helpful to troubleshoot.
[RW] Headers—Shows request headers and status.
[RW] TextView—Shows the request body in a text box.
[RW] HexView—Shows the request body in a hexadecimal view.
[RO] XML—Shows the request body as an XML DOM in a tree view.
[RW] Transformer—Removes GZip, DEFLATE, and CHUNKED encodings for easier debugging.
[RW] Headers—Shows response headers and status.
[RW] TextView—Shows the response body in a text box.
[RW] HexView—Shows the response body in a hexadecimal view.
[RO] ImageView—Shows the response body as an Image. Supports all .NET image formats.
[RO] XML—Shows the response body as an XML DOM in a tree view.
[RO] Privacy—Explains the P3P statement in the response headers, if present.
The bottom half is response, this is the entire response being sent back to the client browser, it may possible be HTML page, image, JSON string, Cascading Style Sheet (CSS) and other resources, we can click textview, syntaxview, Imageview and other clickable tab to view it in different format, the below example demos we syntax view the html source page of this site.
In this tutorial introduces the basic features and examples of Fiddler, Fiddler is a very good debug tool. You may take a try if you have not tried it.