http/2 sometimes hangs

[shyba]

Hello 👋

I was trying out the new version for a service that uses http/2 and it hanged. I tried investigating the hang without much success on exactly what causes it, but I was able to create a test that reproduces it: shyba@72be83a#diff-1a76f7e21ec9d1bb57ab33fa404bfb6201893aec6028063cf0c8ffba16d97fe7R171-R173

This same commit has an ownership change that makes the test pass, but I did not open a pull request because I don't really know if this is a proper fix.

Since I was on it, I just let Claude continue coding on top of that, it finished this branch with other things it identified: https://github.com/shyba/hackney/tree/fix/larger

Feel free to ignore all code changes, I just wanted to report the bug itself. If you think this makes sense as a PR I can open one.

[benoitc]

how does it hangs ? do you have any log ?

[shyba]

Here is a small example that should reproduce

  %% HTTP/2 pooled connection stall — hackney 3.2.1
  %% Paste into: rebar3 shell
  application:ensure_all_started(hackney).
  Pool = h2_repro, hackney_pool:start_pool(Pool, [{max_connections, 10}]).
  URL = <<"https://cloudflare-quic.com/">>.
  Opts = [{pool, Pool}, {recv_timeout, 3}].
  {ok, _, _, _} = hackney:request(get, URL, [], <<>>, Opts).
  timer:sleep(50).
  Parent = self().
  Deadline = erlang:monotonic_time(millisecond) + 3000.
  W = fun() -> (fun Self(C) ->
      case erlang:monotonic_time(millisecond) < Deadline of
          true ->
              {ok, _, _, _} = hackney:request(get, URL, [], <<>>, Opts),
              Self(C+1);
          false -> Parent ! {w, self(), {done, C}}
      end end)(0) end.
  P1 = spawn(W), P2 = spawn(W).
  R1 = receive {w, P1, X1} -> X1 after 10000 -> stall end.
  R2 = receive {w, P2, X2} -> X2 after 10000 -> stall end.
  io:format("~p ~p~n", [R1, R2]).
  hackney_pool:stop_pool(Pool).
  %% Expected: {done,N} {done,N}
  %% Actual on 3.2.1: stall stall

It passes on my branches, but I am not sure if I got the fix right. Let me know if it doesnt work so I can try another snippet

[benoitc]

thanks I will take car eof it in coming release

[shyba]

Thank you very much! Amazing work and very good library.
Let me know if anything else I can help with snippets or a PR from those branches.