HOWTO: Understanding whether uploader sends anything

Sometimes you may encounter the following behaviour of the uploader: when you send some files to the server, the uploader reports that the upload is successfully completed, but no files appear on the server. Why it may happen?

All possible reasons can be divided into two groups:

1. The uploader does not send anything to the server. For example, it sends only variables (such as file name, additional form you appended to the upload, cookies, etc), but no files are added to the HTTP POST request.

2. Your server-side code which processes files does not save files properly due to some reasons. If this server side code returns HTTP code 200, uploader will think that the session succeeded and will display you a "success" message, although no files are saved.

Obviously, in the latter case, you should debug your server-side code and see what actually happens. But before you start doing it, you are surely would like to exclude the problem with the uploader.

Possible reasons

The uploader may falsely report you that it uploads files in the following cases:

1. Your configuration does not allow any files (may be a problem with convertors).

2. Some bug in the uploader

It happens very rarely, but it is worthy to check it before you start debugging your server side code.

Detecting whether uploader sends no files

The quick way to understand if it really sends anything is to see how fast the progress bar reaches 100%. If you select a lot of files and the upload "completes" in a second, most likely it means that no files are actually uploaded. Contrary, if it the upload works long enough, most likely the problem is on the server side.

To be totally sure, you can use the Fiddler software. It is a nice free tool created by Telerik which shows you the HTTP activity on your machine. You can look into all HTTP request sent from your machine and troubleshoot them. It can work with both ActiveX/Java and HTML5/Flash uploader and even with any non-Aurigma software.

It is very simple to use it.

1. Download Fiddler tool from its official website fiddler2.com.

2. Install and run it.

3. Open the page with the uploader in the browser and upload anyting.

4. As a result, you will see a lot of information in the Filddler's left panel. The string you need looks like this screenshot.

Explanations:

1. The correct line should have right arrow icon (meaning that it is a POST request) on the left and your URL/page path.

2. To see the POST request content, you should switch to Inspectors->WebForms.

3. Scroll the list of POST variables and look for a variable named File0_0. If you see it and it contains some binary data, it means that the uploader works as expected.

Uploader sends no files! What's next?

If you don't see the File0_0 variable in Fiddler, please submit a support ticket and post there your code with the uploader settings. If you can give us a link to the page where it can be reproduced, it would help a lot. Also, please report what exact browser and operating system you have.

Uploader does send files. How do I debug my server code?

Do it in the same way as you debug any other part of your website. The only difference with the regular code is that when your upload script returns any HTML code to the server, it is not displayed by the browser, but it is received by the uploader. Use the instructions from documentation how to display server response from the uploader.

Another recommendation - make sure if your server is configured to return HTTP error code 500 when the server-side code stops execution. It will tell the uploader that the upload was not succesfully completed.