Thanks for your prompt reply.

Why do I have to do the work in the post handler? Now I have a stub post handler. ngx_http_read_client_request_body() does nothing but load the request body into the original request, which is used by the next handler. Everything seems to be working fine to me.

I'm not sure how to use the post handler to send a subrequest like a real handler which is polled multiple times until the response is arrived.