Set 'Content-Length' Header Field in Body Handler

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, [email protected]