wasi-http: make the buffer and budget capacity of the OutgoingBody writer configurable

[iawia002]

Please refer to issue #9653 for the background and reasons for the changes.

fix #9653

cc @alexcrichton @pchickey

[pchickey]

Thanks, we never got back to making these buffer depths configurable in WasiHttpView but this is the right path.

Some style notes:

Ideally we'd rewrite the internals to just give the user a single bound on the amount buffered, rather than a combination of number of chunks and chunk size. If you are up for doing that, I believe its the best path forward, but it is trickier than what we have. (Wanting that ideal implementation is mostly why we didn't make this configurable yet.)

Instead of calling it writer_buffer call it outgoing_body_buffer_chunks, described as the number of distinct write calls to the outgoing body's output-stream that the implementation will buffer. write_budget should be outgoing_body_chunk_size, the maximum size allowed in a write call to the outgoing body's output-stream.

The minimum of 2 chunks is an implementation detail related to the way channel reservations work, lets make the default configuration 1, assert! that any value given is greater than 1, and then always add 1 when creating the channel because one empty slot is required by the way this implementation uses the channel.

Also, I don't think we should change the configuration in wasi-http/tests/all/main.rs, but instead fix the implementation of test_programs::http::request which has the exact same bug I pointed out in your guest in #9653 (comment). We should make sure that we have a tests that send a body exceeding the limits on both chunk size and buffer chunks.

[iawia002]

Hi @pchickey, thanks for the detailed explanation and guidance, I think all comments addressed, PTAL

[pchickey]

Thanks! Its a holiday weekend here and I’ll review this next week.