Use Fiddler to capture web traffic between a web browser and a web site

Overview:

When configuring GIS systems such as Geocortex Essentials or Analytics to use a web resource – REST, WMS or otherwise – sometimes it is useful to examine the network traffic between the viewer application(s) and the resource.

Solution:
One way of examining this network traffic is to use a freeware web debugging tool called Fiddler . Fiddler inserts itself as a proxy between your web browser and the Internet, letting you observe the traffic. To capture the traffic between your browser (a viewer) and an Essentials site, follow these steps:

1. Download and install Fiddler from https://www.telerik.com/fiddler .
2. Run Fiddler. It will now be able to capture HTTP traffic.  If your site uses HTTPS, you may want to enable HTTPS decryption - see this article for information on HTTPS decryption configuration.
3. Close any other running web browsers or other applications that send HTTP/HTTPS traffic.
4. Clear out any entries that Fiddler has recorded by selecting Edit | Remove | All Sessions from Fiddler’s main menu.
5. Clear out your browser cache using the “Clear Cache” button on the Fiddler toolbar (this will ensure that all traffic is captured by Fiddler):
   
   Caching can also be disabled by selecting the menu option Rules > Performance > Disable caching
6. Launch your web browser and start your Geocortex software that you want to monitor, such as a viewer.
7. If the issue is not a startup one, you can clear the log by typing Ctrl-X in the Fiddler window.
8. Reproduce the issue.
9. Switch to Fiddler and save the output via File | Save | All Sessions. The default save location is ..\Documents\Fiddler2\Captures, but save the file to the desktop for convenience. This will create a .saz file which can be attached to an email and sent to support.

You may wish to review the Fiddler session now to determine if the problem is apparent. Fiddler will highlight 404 and 500 error codes in red, which may help you track down the source of your problem.

Fiddler is also available in small simpler application dedicated to capturing sessions for support personnel.  The application can downloaded from here: https://www.telerik.com/fiddler/fiddlercap  and instructions for using it are found on the same page.

Learn More:

• For further information about the Fiddler program, consult its online documentation at https://www.telerik.com/fiddler
• For more information about the HTTP protocol, see the Wikipedia article here: https://en.wikipedia.org/wiki/Http
• For instructions on collecting traffic between Essentials and external services, see this article.