Downstream compression does not work for custom response

[vicanso]

What is the problem your feature solves, or the need it fulfills?

I make a custom response in request_filter like this:

session.downstream_compression.adjust_decompression(true);
session.downstream_compression.adjust_level(9);
session.write_response_header(Box::new(header)).await?;
session.write_response_body(self.body).await?;
return Ok(true);

But the response body is not compressed. Does compression only take effect for response from upstream?

Describe the solution you'd like

I want downstream compression to take effect for all responses to downstream.

[eaufavor]

You are right. The compression module in the proxy logic needs some rework to take care of this case.

[palant]

At the moment this can be achieved by calling session.downstream_compression methods manually along these lines:

session.downstream_compression.adjust_level(3);

session
    .downstream_compression
    .request_filter(session.downstream_session.req_header());

let mut task = HttpTask::Header(Box::new(header), false);
session.downstream_compression.response_filter(&mut task);
if let HttpTask::Header(header, _) = task {
    session.write_response_header(header).await?;
} else {
    panic!("Unexpected: compression response filter replaced header task by {task:?}");
}

let mut task = HttpTask::Body(Some(self.body), true);
session.downstream_compression.response_filter(&mut task);
if let HttpTask::Body(Some(bytes), _) = task {
    session.write_response_body(bytes).await?;
}

return Ok(true);

If the response body consists of multiple chunks, response_filter() has to be called multiple times, probably followed up by a call with HttpTask::Done parameter. It is also necessary to make sure not to write out any empty chunks potentially produced by the compression (these indicate end of stream with chunked encoding).

All in all, not really trivial. But it works.