Send headers in output body filter ?

[Maxim Dounin]

Hello!

On Fri, Mar 26, 2021 at 06:05:27PM +0100, Alfred Sawaya wrote:

> I am developping a nginx C module that aims to modify the backend
> response (handled by the proxy module) in order to redact specified strings.
> 
> I have a working module, but I am stuck on a case where the module modfy
> the length of the backend response. As the output header filter is
> called before the output body filter, the content-length is already sent
> when the module get the backend response and modifies it.
> 
> Is there any normal way to workaround this? I would like to avoid
> writing a complete upstream handler... I wonder if it is a known use case?

The usual approach is to remove the Content-Length header if you 
expect that the response length might be changed by your body 
filter.  You also have to either remove ETag or change it to a 
weak one, if present.  For examples see SSI filter, sub filter, 
addition filter, and many others.

-- 
Maxim Dounin
http://mdounin.ru/