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Repeater Content-Length is not recalculated when json content is modified

Christophe | Last updated: Dec 01, 2016 09:21AM UTC

Hi, Quite often in the repeater when you deal with a POST with a Content-Type: application/json;charset=utf-8, when you modify the json body the repeater doesn't recalculate the content-length header. If you add some characters after the json structure the repeater recalculâtes the content length, but if you modify the json structure the content-length is not recalculated. This is very annoying. Is there a workaround to this behaviour ? Regards. Christophe Rieunier CERT La Poste France

PortSwigger Agent | Last updated: Dec 01, 2016 09:23AM UTC

We're not seeing this problem. Repeater (by default) always updates the Content-Length when the body is modified, regardless of the content type in the body. We've tested this with JSON content in the body and Repeater is working as expected.

Burp User | Last updated: Dec 01, 2016 10:14AM UTC

Ok, I understand what happens. It works but the new content-length is displayed when the server answers. So when the server takes a long time (one minute for example) to answer because of the modified request, the displayed content-length is the old one. It would be nice to display the new content length just before sending the request. Thanks for your quick answer. Regards.

PortSwigger Agent | Last updated: Dec 01, 2016 10:58AM UTC

Ok, thanks. We'll look into updating the request with the new Content-Length at the time the user clicks "send".

Burp User | Last updated: Dec 01, 2016 12:20PM UTC

Thanks. In addition, what is really disturbing for the user is that when the answer is very long, if the user clicks on the 'Cancel' button, the new content-length is not displayed, so the user don't know if the server is waiting for more datas (when the new request body is smaller) or if there is another problem. Regards.

PortSwigger Agent | Last updated: Dec 01, 2016 02:16PM UTC

Just to let you know that in the latest release of Burp we have made Repeater display the updated Content-Length as soon as you click the "send" button.

Burp User | Last updated: Jan 16, 2017 03:47PM UTC