`Dream.serve` exit whole program when sending long string to closed connection

[panglesd]

Hello, and thanks for your work on this great package!

I have a strange (and critical!) issue. When using Dream.serve, if I send a long string to a closed connection, the program simply exits, without any error.

Here is a minimal reproduction:

1. Create a server with Dream.serve, which waits 3 seconds before answering a long string of as:

open Lwt.Syntax

let () =
  let f =
    let+ () =
      Dream.serve
      @@ Dream.logger (fun _ ->
             Logs.app (fun m -> m "Starting waiting");
             let* () = Lwt_unix.sleep 3.0 in
             Logs.app (fun m -> m "Finished waiting");
             let x = String.init 1015765 (fun _ -> 'a') in
             Dream.respond x)
    in
    print_endline "Finished"
  in
  Lwt_main.run f

2. Start the program. Connect to localhost:8080 with a web browser, but close the tab before the 3 seconds elapses

3. Have a look at the log, and cry 😢:

$ dune exec ./middleware.exe
10.01.25 10:36:56.511    dream.logger  INFO REQ 1 GET / ::1:48826 fd 6 Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/127.0
10.01.25 10:36:56.511                       REQ 1 Starting waiting
10.01.25 10:36:59.515                       REQ 1 Finished waiting
10.01.25 10:36:59.528    dream.logger  INFO REQ 1 200 in 3017101 μs
$ # back to prompt. "Finished" was not even written to output... Error result is 0.

Some more comments:

• Any length of answer above 1015765 result in this behavior,

• Any length below works as expected

• The same program but with Dream.run works!

  open Lwt.Syntax
  
  let () =
    Dream.run
    @@ Dream.logger (fun _ ->
           Logs.app (fun m -> m "Starting waiting");
           let* () = Lwt_unix.sleep 3.0 in
           Logs.app (fun m -> m "Finished waiting");
           let x = String.init 1015765 (* 1061514 *) (fun _ -> 'a') in
           Dream.respond x)

I am puzzled...

[panglesd]

Apparently, that is because of an unhandled "broken pipe" signal. I investigated the difference between Dream.serve and Dream.run, and it seems this line (taken from here) solves the problem:

let () = if Sys.unix then Sys.(set_signal sigpipe Signal_ignore) in

It makes sense, but probably should be added to Dream.serve. Or, have a mention in the doc.