Add a network benchmark using an HTTP-like protocol

This runs 4 client domains and 4 server domains. Each client opens 25
connections and makes 1000 HTTP POSTs on each one. For each request it
uses Buf_write to write the headers and body, then Buf_read to parse the
response. Likewise, the server uses Buf_read and Buf_write to handle the
each request.

On my system, I get this using eio_linux (eio_posix is about the same):

    clients, servers, requests, requests/s
          4,       4,   100000, 367051.7

Makefile

@@ -4,6 +4,7 @@ all:
 	dune build @runtest @all
 
 bench:
+	dune exec -- ./bench/bench_server.exe
 	dune exec -- ./bench/bench_condition.exe
 	dune exec -- ./bench/bench_buf_read.exe
 	dune exec -- ./bench/bench_mutex.exe

bench/bench_server.ml

@@ -0,0 +1,104 @@
+(* A multi-domain server handles HTTP-like requests from many clients running across multiple domains. *)
+
+open Eio.Std
+
+let n_client_domains = 4
+let n_server_domains = 4
+let n_connections_per_domain = 25
+let n_requests_per_connection = 1000
+
+(* Note: this is not a real HTTP parser! *)
+let key_char = function
+  | 'A'..'Z' | 'a'..'z' | '-' -> true
+  | _ -> false
+
+let parse_headers r =
+  let len = ref (-1) in
+  let rec aux () =
+    let key = Eio.Buf_read.take_while key_char r in
+    if key = "" then Eio.Buf_read.string "\r\n" r
+    else (
+      Eio.Buf_read.char ':' r;
+      let value = Eio.Buf_read.line r in
+      if key = "Content-Length" then len := int_of_string (String.trim value);
+      aux ()
+    )
+  in
+  aux ();
+  !len
+
+let handle_connection conn _addr =
+  Eio.Buf_write.with_flow conn @@ fun w ->
+  let rec requests r =
+    let _req = Eio.Buf_read.line r in
+    let len = parse_headers r in
+    let body = Eio.Buf_read.take len r in
+    let response = body ^ " / received" in
+    Eio.Buf_write.string w "HTTP/1.1 200 OK\r\n";
+    Eio.Buf_write.string w (Printf.sprintf "Content-Length: %d\r\n" (String.length response));
+    Eio.Buf_write.string w "\r\n";
+    Eio.Buf_write.string w response;
+    if not (Eio.Buf_read.at_end_of_input r) then requests r
+  in
+  Eio.Buf_read.parse_exn requests conn ~max_size:max_int
+
+let run_client id conn =
+  let total = ref 0 in
+  let r = Eio.Buf_read.of_flow conn ~max_size:max_int in
+  Eio.Buf_write.with_flow conn @@ fun w ->
+  for i = 1 to n_requests_per_connection do
+    let msg = Printf.sprintf "%s / request %d" id i in
+    Eio.Buf_write.string w "POST / HTTP/1.1\r\n";
+    Eio.Buf_write.string w "Host: localhost:8085\r\n";
+    Eio.Buf_write.string w "User-Agent: bench_server\r\n";
+    Eio.Buf_write.string w "Connection: keep-alive\r\n";
+    Eio.Buf_write.string w (Printf.sprintf "Content-Length: %d\r\n" (String.length msg));
+    Eio.Buf_write.string w "\r\n";
+    Eio.Buf_write.string w msg;
+    let status = Eio.Buf_read.line r in
+    assert (status = "HTTP/1.1 200 OK");
+    let len = parse_headers r in
+    let body = Eio.Buf_read.take len r in
+    assert (body = msg ^ " / received");
+    incr total
+  done;
+  !total
+
+let main net domain_mgr =
+  let total = Atomic.make 0 in
+  let t0 = Unix.gettimeofday () in
+  Switch.run (fun sw ->
+      let addr = `Tcp (Eio.Net.Ipaddr.V4.loopback, 8085) in
+      let server_socket = Eio.Net.listen ~reuse_addr:true ~backlog:100 ~sw net addr in
+      Fiber.fork_daemon ~sw (fun () ->
+          Eio.Net.run_server server_socket handle_connection
+            ~additional_domains:(domain_mgr, n_server_domains - 1)
+            ~on_error:raise
+        );
+      for domain = 1 to n_client_domains do
+        Fiber.fork ~sw (fun () ->
+            Eio.Domain_manager.run domain_mgr (fun () ->
+                Switch.run @@ fun sw ->
+                for i = 1 to n_connections_per_domain do
+                  Fiber.fork ~sw (fun () ->
+                      let id = Printf.sprintf "domain %d / conn %d" domain i in
+                      let conn = Eio.Net.connect ~sw net addr in
+                      let requests = run_client id conn in
+                      ignore (Atomic.fetch_and_add total requests : int)
+                    )
+                done
+              )
+          )
+      done
+    );
+  let t1 = Unix.gettimeofday () in
+  Fmt.pr "clients, servers, requests, requests/s@.";
+  let requests = n_connections_per_domain * n_client_domains * n_requests_per_connection in
+  assert (requests = Atomic.get total);
+  let req_per_s = float requests /. (t1 -. t0) in
+  Fmt.pr "%7d, %7d, %8d, %.1f@." n_client_domains n_server_domains requests req_per_s
+
+let () =
+  print_endline "";     (* work around dune bug *)
+  Eio_main.run @@ fun env ->
+  main env#net env#domain_mgr

bench/dune

@@ -1,4 +1,4 @@
 (executables
   (names bench_stream bench_promise bench_semaphore bench_yield bench_cancel bench_mutex
-         bench_buf_read bench_condition bench_fd)
+         bench_buf_read bench_condition bench_fd bench_server)
   (libraries eio_main))