Set 'Content-Length' Header Field in Body Handler

[Christos Kontas]

Hello!

I am currently working on a filter module, in which I would like to rewrite the content
received from an upstream.  Similar to `gzip` module, I don't know the exact value to
set to the 'Content-Length' header field during filtering the headers of the request,
not only before processing part of the request's body.

Is there any way I can postpone the transmission of the response headers until
the time this value can be calculated during the filtering of the request body?

Thank you in advance!
Christos Kontas, kontas at ceid.upatras.gr