Cohttp-eio: response body not flushed?

[smondet]

Using the current master branch.

I have server code that hangs with:

Server.respond_string ~body:"Not found, sorry" ~status:`Not_found ()

"hangs" = curl client hangs, the ~stop argument of the server (the _ Promise.t) does not stop the server but the server logs show that it can handle more than one request.

It seems better with:

    Server.respond
      ~body:(Eio.Flow.string_source "Not found, sorry")
      ~status:`Not_found ()

"better = at least the client is "unlocked" and the ~stop argument (the _ Promise.t) does it's job. But the body is not actually transmitted.

It seems that this loop in cohttp-eio/src/utils.ml exits before sending any bytes:

let flow_to_writer flow writer write_body =
  let input = Eio.Buf_read.of_flow ~max_size:max_int flow in
  let rec loop () =
    let () =
      let () = Eio.Buf_read.ensure input 1 in
      let contents = Eio.Buf_read.(take (buffered_bytes input) input) in
      let () =
        Logs.debug (fun m -> m "send %d bytes of body" (String.length contents))
      in
      write_body writer contents
    in
    loop ()
  in
  try loop ()
  with End_of_file ->
    let () = Logs.debug (fun m -> m "end of outbound body") in
    ()

This is the debug output (in both cases of ~body: argument):

main.exe: [DEBUG] send headers
main.exe: [DEBUG] send body
main.exe: [DEBUG] end of outbound body

Any ideas?

(Eio 0.13, OCaml 5.1)

[smondet]

Ok the "bug" was on my side.

For the historians: I had something that worked with 6.0.0~alpha1 and an earlier Eio that included being able to log the body of the response before sending it; with master since it's an Eio.Flow.t logging it, even with Eio.Flow.copy, consumes the stream so it is empty when flow_to_writer is called.

@talex5 should Eio.Flow.copy be called transfer or move instead?

[talex5]

That's an interesting point about the name. However, it's not always a more (e.g. if the source is a file then the file data isn't deleted).