Merge pull request #65 from c-cube/wip-cleanup-2023-06-20

cleanup and IO backend

Makefile

@@ -2,11 +2,12 @@
 
 all: build test
 
+OPTS?=--profile=release
 build:
-	@dune build @install
+	@dune build @install $(OPTS)
 
 test:
-	@dune runtest --no-buffer --force
+	@dune runtest --no-buffer --force $(OPTS)
 
 clean:
 	@dune clean
@@ -16,7 +17,7 @@ doc:
 
 WATCH?= "@install @runtest"
 watch:
-	@dune build $(WATCH) -w
+	@dune build $(OPTS) $(WATCH) -w
 
 .PHONY: benchs tests build watch
 

echo.sh

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec dune exec --profile=release "examples/echo.exe" -- $@
+exec dune exec --display=quiet --profile=release "examples/echo.exe" -- $@

examples/echo.ml

@@ -33,6 +33,16 @@ let middleware_stat () : S.Middleware.t * (unit -> string) =
   in
   m, get_stat
 
+(* ugly AF *)
+let base64 x =
+  let ic, oc = Unix.open_process "base64" in
+  output_string oc x;
+  flush oc;
+  close_out oc;
+  let r = input_line ic in
+  ignore (Unix.close_process (ic, oc));
+  r
+
 let () =
   let port_ = ref 8080 in
   let j = ref 32 in
@@ -106,6 +116,35 @@ let () =
         S.Response.fail ~code:500 "couldn't upload file: %s"
           (Printexc.to_string e));
 
+  (* protected by login *)
+  S.add_route_handler server
+    S.Route.(exact "protected" @/ return)
+    (fun req ->
+      let ok =
+        match S.Request.get_header req "authorization" with
+        | Some v ->
+          S._debug (fun k -> k "authenticate with %S" v);
+          v = "Basic " ^ base64 "user:foobar"
+        | None -> false
+      in
+      if ok then (
+        (* FIXME: a logout link *)
+        let s =
+          "<p>hello, this is super secret!</p><a href=\"/logout\">log out</a>"
+        in
+        S.Response.make_string (Ok s)
+      ) else (
+        let headers =
+          S.Headers.(empty |> set "www-authenticate" "basic realm=\"echo\"")
+        in
+        S.Response.fail ~code:401 ~headers "invalid"
+      ));
+
+  (* logout *)
+  S.add_route_handler server
+    S.Route.(exact "logout" @/ return)
+    (fun _req -> S.Response.fail ~code:401 "logged out");
+
   (* stats *)
   S.add_route_handler server
     S.Route.(exact "stats" @/ return)
@@ -171,6 +210,24 @@ let () =
                             txt " (GET) to access a VFS embedded in the binary";
                           ];
                       ];
+                    li []
+                      [
+                        pre []
+                          [
+                            a [ A.href "/protected" ] [ txt "/protected" ];
+                            txt
+                              " (GET) to see a protected page (login: user, \
+                               password: foobar)";
+                          ];
+                      ];
+                    li []
+                      [
+                        pre []
+                          [
+                            a [ A.href "/logout" ] [ txt "/logout" ];
+                            txt " (POST) to log out";
+                          ];
+                      ];
                   ];
               ];
           ]

src/Tiny_httpd.ml

@@ -4,3 +4,4 @@ include Tiny_httpd_server
 module Util = Tiny_httpd_util
 module Dir = Tiny_httpd_dir
 module Html = Tiny_httpd_html
+module IO = Tiny_httpd_io

src/Tiny_httpd.mli

@@ -85,6 +85,10 @@ module Buf = Tiny_httpd_buf
 
 module Byte_stream = Tiny_httpd_stream
 
+(** {2 IO Abstraction} *)
+
+module IO = Tiny_httpd_io
+
 (** {2 Main Server Type} *)
 
 (** @inline *)

src/Tiny_httpd_buf.ml

@@ -20,6 +20,16 @@ let add_bytes (self : t) s i len : unit =
   Bytes.blit s i self.bytes self.i len;
   self.i <- self.i + len
 
+let[@inline] add_string self str : unit =
+  add_bytes self (Bytes.unsafe_of_string str) 0 (String.length str)
+
+let add_buffer (self : t) (buf : Buffer.t) : unit =
+  let len = Buffer.length buf in
+  if self.i + len >= Bytes.length self.bytes then
+    resize self (self.i + (self.i / 2) + len + 10);
+  Buffer.blit buf 0 self.bytes self.i len;
+  self.i <- self.i + len
+
 let contents (self : t) : string = Bytes.sub_string self.bytes 0 self.i
 
 let contents_and_clear (self : t) : string =

src/Tiny_httpd_buf.mli

@@ -24,3 +24,11 @@ val contents_and_clear : t -> string
 val add_bytes : t -> bytes -> int -> int -> unit
 (** Append given bytes slice to the buffer.
     @since 0.5 *)
+
+val add_string : t -> string -> unit
+(** Add string.
+    @since NEXT_RELEASE *)
+
+val add_buffer : t -> Buffer.t -> unit
+(** Append bytes from buffer.
+    @since NEXT_RELEASE *)

src/Tiny_httpd_io.ml

@@ -0,0 +1,103 @@
+(** IO abstraction.
+
+    We abstract IO so we can support classic unix blocking IOs
+    with threads, and modern async IO with Eio.
+
+    {b NOTE}: experimental.
+
+    @since NEXT_RELEASE
+*)
+
+module Buf = Tiny_httpd_buf
+
+module In_channel = struct
+  type t = {
+    input: bytes -> int -> int -> int;
+        (** Read into the slice. Returns [0] only if the
+        channel is closed. *)
+    close: unit -> unit;
+  }
+
+  let of_in_channel ?(close_noerr = false) (ic : in_channel) : t =
+    {
+      input = (fun buf i len -> input ic buf i len);
+      close =
+        (fun () ->
+          if close_noerr then
+            close_in_noerr ic
+          else
+            close_in ic);
+    }
+
+  let of_unix_fd ?(close_noerr = false) (fd : Unix.file_descr) : t =
+    {
+      input = (fun buf i len -> Unix.read fd buf i len);
+      close =
+        (fun () ->
+          if close_noerr then (
+            try Unix.close fd with _ -> ()
+          ) else
+            Unix.close fd);
+    }
+
+  let[@inline] input (self : t) buf i len = self.input buf i len
+  let[@inline] close self : unit = self.close ()
+end
+
+module Out_channel = struct
+  type t = {
+    output: bytes -> int -> int -> unit;  (** Output slice *)
+    flush: unit -> unit;  (** Flush underlying buffer *)
+    close: unit -> unit;
+  }
+
+  let of_out_channel ?(close_noerr = false) (oc : out_channel) : t =
+    {
+      output = (fun buf i len -> output oc buf i len);
+      flush = (fun () -> flush oc);
+      close =
+        (fun () ->
+          if close_noerr then
+            close_out_noerr oc
+          else
+            close_out oc);
+    }
+
+  let[@inline] output (self : t) buf i len : unit = self.output buf i len
+
+  let[@inline] output_string (self : t) (str : string) : unit =
+    self.output (Bytes.unsafe_of_string str) 0 (String.length str)
+
+  let[@inline] close self : unit = self.close ()
+  let[@inline] flush self : unit = self.flush ()
+
+  let output_buf (self : t) (buf : Buf.t) : unit =
+    let b = Buf.bytes_slice buf in
+    output self b 0 (Buf.size buf)
+end
+
+(** A TCP server abstraction *)
+module TCP_server = struct
+  type conn_handler = {
+    handle: In_channel.t -> Out_channel.t -> unit;
+        (** Handle client connection *)
+  }
+
+  type t = {
+    endpoint: unit -> string * int;
+        (** Endpoint we listen on. This can only be called from within [serve]. *)
+    active_connections: unit -> int;
+        (** Number of connections currently active *)
+    running: unit -> bool;  (** Is the server currently running? *)
+    stop: unit -> unit;
+        (** Ask the server to stop. This might not take effect immediately. *)
+  }
+  (** Running server. *)
+
+  type builder = {
+    serve: after_init:(t -> unit) -> handle:conn_handler -> unit -> unit;
+        (** Blocking call to listen for incoming connections and handle them.
+            Uses the connection handler to handle individual client connections. *)
+  }
+  (** A TCP server implementation. *)
+end

src/Tiny_httpd_server.ml

@@ -18,6 +18,7 @@ let _debug k =
 
 module Buf = Tiny_httpd_buf
 module Byte_stream = Tiny_httpd_stream
+module IO = Tiny_httpd_io
 
 exception Bad_req of int * string
 
@@ -40,6 +41,7 @@ module Response_code = struct
     | 302 -> "Found"
     | 304 -> "Not Modified"
     | 400 -> "Bad request"
+    | 401 -> "Unauthorized"
     | 403 -> "Forbidden"
     | 404 -> "Not found"
     | 405 -> "Method not allowed"
@@ -422,9 +424,19 @@ module Response = struct
     Format.fprintf out "{@[code=%d;@ headers=[@[%a@]];@ body=%a@]}" self.code
       Headers.pp self.headers pp_body self.body
 
-  let output_ (oc : out_channel) (self : t) : unit =
-    Printf.fprintf oc "HTTP/1.1 %d %s\r\n" self.code
+  let output_ ?(buf = Buf.create ~size:256 ()) (oc : IO.Out_channel.t)
+      (self : t) : unit =
+    (* double indirection:
+       - print into [buffer] using [bprintf]
+       - transfer to [buf_] so we can output from there *)
+    let tmp_buffer = Buffer.create 32 in
+
+    (* write start of reply *)
+    Printf.bprintf tmp_buffer "HTTP/1.1 %d %s\r\n" self.code
       (Response_code.descr self.code);
+    Buf.add_buffer buf tmp_buffer;
+    Buffer.clear tmp_buffer;
+
     let body, is_chunked =
       match self.body with
       | `String s when String.length s > 1024 * 500 ->
@@ -446,19 +458,29 @@ module Response = struct
     _debug (fun k ->
         k "output response: %s"
           (Format.asprintf "%a" pp { self with body = `String "<…>" }));
-    List.iter (fun (k, v) -> Printf.fprintf oc "%s: %s\r\n" k v) headers;
-    output_string oc "\r\n";
+
+    (* write headers *)
+    List.iter
+      (fun (k, v) ->
+        Printf.bprintf tmp_buffer "%s: %s\r\n" k v;
+        Buf.add_buffer buf tmp_buffer;
+        Buffer.clear tmp_buffer)
+      headers;
+
+    IO.Out_channel.output_buf oc buf;
+    IO.Out_channel.output_string oc "\r\n";
+
     (match body with
     | `String "" | `Void -> ()
-    | `String s -> output_string oc s
+    | `String s -> IO.Out_channel.output_string oc s
     | `Stream str ->
       (try
-         Byte_stream.output_chunked oc str;
+         Byte_stream.output_chunked' oc str;
          Byte_stream.close str
        with e ->
          Byte_stream.close str;
          raise e));
-    flush oc
+    IO.Out_channel.flush oc
 end
 
 (* semaphore, for limiting concurrency. *)
@@ -592,7 +614,7 @@ module Middleware = struct
 end
 
 (* a request handler. handles a single request. *)
-type cb_path_handler = out_channel -> Middleware.handler
+type cb_path_handler = IO.Out_channel.t -> Middleware.handler
 
 module type SERVER_SENT_GENERATOR = sig
   val set_headers : Headers.t -> unit
@@ -605,18 +627,26 @@ end
 
 type server_sent_generator = (module SERVER_SENT_GENERATOR)
 
+module type IO_BACKEND = sig
+  val init_addr : unit -> string
+  val init_port : unit -> int
+
+  val spawn : (unit -> unit) -> unit
+  (** function used to spawn a new thread to handle a
+    new client connection. By default it is {!Thread.create} but one
+    could use a thread pool instead.*)
+
+  val get_time_s : unit -> float
+  (** obtain the current timestamp in seconds. *)
+
+  val tcp_server : unit -> Tiny_httpd_io.TCP_server.builder
+  (** Server  that can listen on a port and handle clients. *)
+end
+
 type t = {
-  addr: string;  (** Address at creation *)
-  port: int;  (** Port at creation *)
-  mutable sock: Unix.file_descr option;  (** Socket *)
-  timeout: float;
-  sem_max_connections: Sem_.t;
-      (* semaphore to restrict the number of active concurrent connections *)
-  new_thread: (unit -> unit) -> unit;
-      (* a function to run the given callback in a separate thread (or thread pool) *)
-  masksigpipe: bool;
+  backend: (module IO_BACKEND);
+  mutable tcp_server: IO.TCP_server.t option;
   buf_size: int;
-  get_time_s: unit -> float;
   mutable handler: string Request.t -> Response.t;
       (** toplevel handler, if any *)
   mutable middlewares: (int * Middleware.t) list;  (** Global middlewares *)
@@ -625,9 +655,6 @@ type t = {
   mutable path_handlers:
     (unit Request.t -> cb_path_handler resp_result option) list;
       (** path handlers *)
-  mutable running: bool;
-      (** true while the server is running. no need to protect with a mutex,
-     writes should be atomic enough. *)
 }
 
 let get_addr_ sock =
@@ -635,17 +662,24 @@ let get_addr_ sock =
   | Unix.ADDR_INET (addr, port) -> addr, port
   | _ -> invalid_arg "httpd: address is not INET"
 
-let addr self =
-  match self.sock with
-  | None -> self.addr
-  | Some s -> Unix.string_of_inet_addr (fst @@ get_addr_ s)
+let addr (self : t) =
+  match self.tcp_server with
+  | None ->
+    let (module B) = self.backend in
+    B.init_addr ()
+  | Some s -> fst @@ s.endpoint ()
 
-let port self =
-  match self.sock with
-  | None -> self.port
-  | Some sock -> snd @@ get_addr_ sock
+let port (self : t) =
+  match self.tcp_server with
+  | None ->
+    let (module B) = self.backend in
+    B.init_port ()
+  | Some s -> snd @@ s.endpoint ()
 
-let active_connections self = Sem_.num_acquired self.sem_max_connections - 1
+let active_connections (self : t) =
+  match self.tcp_server with
+  | None -> 0
+  | Some s -> s.active_connections ()
 
 let add_middleware ~stage self m =
   let stage =
@@ -725,8 +759,10 @@ let[@inline] _opt_iter ~f o =
   | None -> ()
   | Some x -> f x
 
+exception Exit_SSE
+
 let add_route_server_sent_handler ?accept self route f =
-  let tr_req oc req ~resp f =
+  let tr_req (oc : IO.Out_channel.t) req ~resp f =
     let req = Request.read_body_full ~buf_size:self.buf_size req in
     let headers =
       ref Headers.(empty |> set "content-type" "text/event-stream")
@@ -745,16 +781,20 @@ let add_route_server_sent_handler ?accept self route f =
       )
     in
 
+    let[@inline] writef fmt =
+      Printf.ksprintf (IO.Out_channel.output_string oc) fmt
+    in
+
     let send_event ?event ?id ?retry ~data () : unit =
       send_response_idempotent_ ();
-      _opt_iter event ~f:(fun e -> Printf.fprintf oc "event: %s\n" e);
-      _opt_iter id ~f:(fun e -> Printf.fprintf oc "id: %s\n" e);
-      _opt_iter retry ~f:(fun e -> Printf.fprintf oc "retry: %s\n" e);
+      _opt_iter event ~f:(fun e -> writef "event: %s\n" e);
+      _opt_iter id ~f:(fun e -> writef "id: %s\n" e);
+      _opt_iter retry ~f:(fun e -> writef "retry: %s\n" e);
       let l = String.split_on_char '\n' data in
-      List.iter (fun s -> Printf.fprintf oc "data: %s\n" s) l;
-      output_string oc "\n";
+      List.iter (fun s -> writef "data: %s\n" s) l;
+      IO.Out_channel.output_string oc "\n";
       (* finish group *)
-      flush oc
+      IO.Out_channel.flush oc
     in
     let module SSG = struct
       let set_headers h =
@@ -764,32 +804,26 @@ let add_route_server_sent_handler ?accept self route f =
         )
 
       let send_event = send_event
-      let close () = raise Exit
+      let close () = raise Exit_SSE
     end in
-    try f req (module SSG : SERVER_SENT_GENERATOR) with Exit -> close_out oc
+    try f req (module SSG : SERVER_SENT_GENERATOR)
+    with Exit_SSE -> IO.Out_channel.close oc
   in
   add_route_handler_ self ?accept ~meth:`GET route ~tr_req f
 
-let create ?(masksigpipe = true) ?(max_connections = 32) ?(timeout = 0.0)
-    ?(buf_size = 16 * 1_024) ?(get_time_s = Unix.gettimeofday)
-    ?(new_thread = fun f -> ignore (Thread.create f () : Thread.t))
-    ?(addr = "127.0.0.1") ?(port = 8080) ?sock ?(middlewares = []) () : t =
-  let handler _req = Response.fail ~code:404 "no top handler" in
+let get_max_connection_ ?(max_connections = 64) () : int =
   let max_connections = max 4 max_connections in
+  max_connections
+
+let create_from ?(buf_size = 16 * 1_024) ?(middlewares = []) ~backend () : t =
+  let handler _req = Response.fail ~code:404 "no top handler" in
   let self =
     {
-      new_thread;
-      addr;
-      port;
-      sock;
-      masksigpipe;
+      backend;
+      tcp_server = None;
       handler;
       buf_size;
-      running = true;
-      sem_max_connections = Sem_.create max_connections;
       path_handlers = [];
-      timeout;
-      get_time_s;
       middlewares = [];
       middlewares_sorted = lazy [];
     }
@@ -797,7 +831,149 @@ let create ?(masksigpipe = true) ?(max_connections = 32) ?(timeout = 0.0)
   List.iter (fun (stage, m) -> add_middleware self ~stage m) middlewares;
   self
 
-let stop s = s.running <- false
+let is_ipv6_str addr : bool = String.contains addr ':'
+
+module Unix_tcp_server_ = struct
+  type t = {
+    addr: string;
+    port: int;
+    max_connections: int;
+    sem_max_connections: Sem_.t;
+        (** semaphore to restrict the number of active concurrent connections *)
+    mutable sock: Unix.file_descr option;  (** Socket *)
+    new_thread: (unit -> unit) -> unit;
+    timeout: float;
+    masksigpipe: bool;
+    mutable running: bool; (* TODO: use an atomic? *)
+  }
+
+  let to_tcp_server (self : t) : IO.TCP_server.builder =
+    {
+      IO.TCP_server.serve =
+        (fun ~after_init ~handle () : unit ->
+          if self.masksigpipe then
+            ignore (Unix.sigprocmask Unix.SIG_BLOCK [ Sys.sigpipe ] : _ list);
+          let sock, should_bind =
+            match self.sock with
+            | Some s ->
+              ( s,
+                false
+                (* Because we're getting a socket from the caller (e.g. systemd) *)
+              )
+            | None ->
+              ( Unix.socket
+                  (if is_ipv6_str self.addr then
+                    Unix.PF_INET6
+                  else
+                    Unix.PF_INET)
+                  Unix.SOCK_STREAM 0,
+                true (* Because we're creating the socket ourselves *) )
+          in
+          Unix.clear_nonblock sock;
+          Unix.setsockopt_optint sock Unix.SO_LINGER None;
+          if should_bind then (
+            let inet_addr = Unix.inet_addr_of_string self.addr in
+            Unix.setsockopt sock Unix.SO_REUSEADDR true;
+            Unix.bind sock (Unix.ADDR_INET (inet_addr, self.port));
+            let n_listen = 2 * self.max_connections in
+            Unix.listen sock n_listen
+          );
+
+          self.sock <- Some sock;
+
+          let tcp_server =
+            {
+              IO.TCP_server.stop = (fun () -> self.running <- false);
+              running = (fun () -> self.running);
+              active_connections =
+                (fun () -> Sem_.num_acquired self.sem_max_connections - 1);
+              endpoint =
+                (fun () ->
+                  let addr, port = get_addr_ sock in
+                  Unix.string_of_inet_addr addr, port);
+            }
+          in
+          after_init tcp_server;
+
+          (* how to handle a single client *)
+          let handle_client_unix_ (client_sock : Unix.file_descr) : unit =
+            Unix.(setsockopt_float client_sock SO_RCVTIMEO self.timeout);
+            Unix.(setsockopt_float client_sock SO_SNDTIMEO self.timeout);
+            let oc =
+              IO.Out_channel.of_out_channel
+              @@ Unix.out_channel_of_descr client_sock
+            in
+            let ic = IO.In_channel.of_unix_fd client_sock in
+            handle.handle ic oc;
+            _debug (fun k -> k "done with client, exiting");
+            (try Unix.close client_sock
+             with e ->
+               _debug (fun k ->
+                   k "error when closing sock: %s" (Printexc.to_string e)));
+            ()
+          in
+
+          while self.running do
+            (* limit concurrency *)
+            Sem_.acquire 1 self.sem_max_connections;
+            try
+              let client_sock, _ = Unix.accept sock in
+              self.new_thread (fun () ->
+                  try
+                    handle_client_unix_ client_sock;
+                    Sem_.release 1 self.sem_max_connections
+                  with e ->
+                    (try Unix.close client_sock with _ -> ());
+                    Sem_.release 1 self.sem_max_connections;
+                    raise e)
+            with e ->
+              Sem_.release 1 self.sem_max_connections;
+              _debug (fun k ->
+                  k "Unix.accept or Thread.create raised an exception: %s"
+                    (Printexc.to_string e))
+          done;
+          ());
+    }
+end
+
+let create ?(masksigpipe = true) ?max_connections ?(timeout = 0.0) ?buf_size
+    ?(get_time_s = Unix.gettimeofday)
+    ?(new_thread = fun f -> ignore (Thread.create f () : Thread.t))
+    ?(addr = "127.0.0.1") ?(port = 8080) ?sock ?middlewares () : t =
+  let max_connections = get_max_connection_ ?max_connections () in
+  let server =
+    {
+      Unix_tcp_server_.addr;
+      new_thread;
+      running = true;
+      port;
+      sock;
+      max_connections;
+      sem_max_connections = Sem_.create max_connections;
+      masksigpipe;
+      timeout;
+    }
+  in
+  let tcp_server_builder = Unix_tcp_server_.to_tcp_server server in
+  let module B = struct
+    let init_addr () = addr
+    let init_port () = port
+    let get_time_s = get_time_s
+    let spawn f = new_thread f
+    let tcp_server () = tcp_server_builder
+  end in
+  let backend = (module B : IO_BACKEND) in
+  create_from ?buf_size ?middlewares ~backend ()
+
+let stop (self : t) =
+  match self.tcp_server with
+  | None -> ()
+  | Some s -> s.stop ()
+
+let running (self : t) =
+  match self.tcp_server with
+  | None -> false
+  | Some s -> s.running ()
 
 let find_map f l =
   let rec aux f = function
@@ -809,16 +985,15 @@ let find_map f l =
   in
   aux f l
 
-let handle_client_ (self : t) (client_sock : Unix.file_descr) : unit =
-  Unix.(setsockopt_float client_sock SO_RCVTIMEO self.timeout);
-  Unix.(setsockopt_float client_sock SO_SNDTIMEO self.timeout);
-  let oc = Unix.out_channel_of_descr client_sock in
+(* handle client on [ic] and [oc] *)
+let client_handle_for (self : t) ic oc : unit =
   let buf = Buf.create ~size:self.buf_size () in
-  let is = Byte_stream.of_fd ~buf_size:self.buf_size client_sock in
+  let is = Byte_stream.of_input ~buf_size:self.buf_size ic in
   let continue = ref true in
-  while !continue && self.running do
+  while !continue && running self do
     _debug (fun k -> k "read next request");
-    match Request.parse_req_start ~get_time_s:self.get_time_s ~buf is with
+    let (module B) = self.backend in
+    match Request.parse_req_start ~get_time_s:B.get_time_s ~buf is with
     | Ok None -> continue := false (* client is done *)
     | Error (c, s) ->
       (* connection error, close *)
@@ -832,7 +1007,7 @@ let handle_client_ (self : t) (client_sock : Unix.file_descr) : unit =
 
       (try
          (* is there a handler for this path? *)
-         let handler =
+         let base_handler =
            match find_map (fun ph -> ph req) self.path_handlers with
            | Some f -> unwrap_resp_result f
            | None ->
@@ -856,7 +1031,7 @@ let handle_client_ (self : t) (client_sock : Unix.file_descr) : unit =
            List.fold_right
              (fun (_, m) h -> m h)
              (Lazy.force self.middlewares_sorted)
-             (handler oc)
+             (base_handler oc)
          in
 
          (* now actually read request's body into a stream *)
@@ -888,62 +1063,24 @@ let handle_client_ (self : t) (client_sock : Unix.file_descr) : unit =
         continue := false;
         Response.output_ oc
         @@ Response.fail ~code:500 "server error: %s" (Printexc.to_string e))
-  done;
-  _debug (fun k -> k "done with client, exiting");
-  (try Unix.close client_sock
-   with e ->
-     _debug (fun k -> k "error when closing sock: %s" (Printexc.to_string e)));
-  ()
+  done
 
-let is_ipv6 self = String.contains self.addr ':'
+let client_handler (self : t) : IO.TCP_server.conn_handler =
+  { IO.TCP_server.handle = client_handle_for self }
 
+let is_ipv6 (self : t) =
+  let (module B) = self.backend in
+  is_ipv6_str (B.init_addr ())
+
+(* TODO: init TCP server *)
 let run ?(after_init = ignore) (self : t) : (unit, _) result =
   try
-    if self.masksigpipe then
-      ignore (Unix.sigprocmask Unix.SIG_BLOCK [ Sys.sigpipe ] : _ list);
-    let sock, should_bind =
-      match self.sock with
-      | Some s ->
-        ( s,
-          false
-          (* Because we're getting a socket from the caller (e.g. systemd) *) )
-      | None ->
-        ( Unix.socket
-            (if is_ipv6 self then
-              Unix.PF_INET6
-            else
-              Unix.PF_INET)
-            Unix.SOCK_STREAM 0,
-          true (* Because we're creating the socket ourselves *) )
-    in
-    Unix.clear_nonblock sock;
-    Unix.setsockopt_optint sock Unix.SO_LINGER None;
-    if should_bind then (
-      let inet_addr = Unix.inet_addr_of_string self.addr in
-      Unix.setsockopt sock Unix.SO_REUSEADDR true;
-      Unix.bind sock (Unix.ADDR_INET (inet_addr, self.port));
-      Unix.listen sock (2 * self.sem_max_connections.Sem_.n)
-    );
-    self.sock <- Some sock;
-    after_init ();
-    while self.running do
-      (* limit concurrency *)
-      Sem_.acquire 1 self.sem_max_connections;
-      try
-        let client_sock, _ = Unix.accept sock in
-        self.new_thread (fun () ->
-            try
-              handle_client_ self client_sock;
-              Sem_.release 1 self.sem_max_connections
-            with e ->
-              (try Unix.close client_sock with _ -> ());
-              Sem_.release 1 self.sem_max_connections;
-              raise e)
-      with e ->
-        Sem_.release 1 self.sem_max_connections;
-        _debug (fun k ->
-            k "Unix.accept or Thread.create raised an exception: %s"
-              (Printexc.to_string e))
-    done;
+    let (module B) = self.backend in
+    let server = B.tcp_server () in
+    server.serve
+      ~after_init:(fun tcp_server ->
+        self.tcp_server <- Some tcp_server;
+        after_init ())
+      ~handle:(client_handler self) ();
     Ok ()
   with e -> Error e

src/Tiny_httpd_server.mli

@@ -369,7 +369,7 @@ val create :
   ?middlewares:([ `Encoding | `Stage of int ] * Middleware.t) list ->
   unit ->
   t
-(** Create a new webserver.
+(** Create a new webserver using UNIX abstractions.
 
     The server will not do anything until {!run} is called on it.
     Before starting the server, one can use {!add_path_handler} and
@@ -401,6 +401,41 @@ val create :
       This parameter exists since 0.11.
 *)
 
+(** A backend that provides IO operations, network operations, etc. *)
+module type IO_BACKEND = sig
+  val init_addr : unit -> string
+  val init_port : unit -> int
+
+  val spawn : (unit -> unit) -> unit
+  (** function used to spawn a new thread to handle a
+    new client connection. By default it is {!Thread.create} but one
+    could use a thread pool instead.*)
+
+  val get_time_s : unit -> float
+  (** obtain the current timestamp in seconds. *)
+
+  val tcp_server : unit -> Tiny_httpd_io.TCP_server.builder
+  (** Server  that can listen on a port and handle clients. *)
+end
+
+val create_from :
+  ?buf_size:int ->
+  ?middlewares:([ `Encoding | `Stage of int ] * Middleware.t) list ->
+  backend:(module IO_BACKEND) ->
+  unit ->
+  t
+(** Create a new webserver using provided backend.
+
+    The server will not do anything until {!run} is called on it.
+    Before starting the server, one can use {!add_path_handler} and
+    {!set_top_handler} to specify how to handle incoming requests.
+
+    @param buf_size size for buffers (since 0.11)
+    @param middlewares see {!add_middleware} for more details.
+
+    @since NEXT_RELEASE
+*)
+
 val addr : t -> string
 (** Address on which the server listens. *)
 
@@ -556,6 +591,10 @@ val add_route_server_sent_handler :
 
 (** {2 Run the server} *)
 
+val running : t -> bool
+(** Is the server running?
+    @since NEXT_RELEASE *)
+
 val stop : t -> unit
 (** Ask the server to stop. This might not have an immediate effect
     as {!run} might currently be waiting on IO. *)

src/Tiny_httpd_stream.ml

@@ -1,4 +1,5 @@
 module Buf = Tiny_httpd_buf
+module IO = Tiny_httpd_io
 
 let spf = Printf.sprintf
 
@@ -45,37 +46,32 @@ let make ?(bs = Bytes.create @@ (16 * 1024)) ?(close = ignore) ~consume ~fill ()
   in
   self
 
-let of_chan_ ?(buf_size = 16 * 1024) ~close ic : t =
+let of_input ?(buf_size = 16 * 1024) (ic : IO.In_channel.t) : t =
   make ~bs:(Bytes.create buf_size)
-    ~close:(fun _ -> close ic)
+    ~close:(fun _ -> IO.In_channel.close ic)
     ~consume:(fun self n ->
       self.off <- self.off + n;
       self.len <- self.len - n)
     ~fill:(fun self ->
       if self.off >= self.len then (
         self.off <- 0;
-        self.len <- input ic self.bs 0 (Bytes.length self.bs)
+        self.len <- IO.In_channel.input ic self.bs 0 (Bytes.length self.bs)
       ))
     ()
 
-let of_chan = of_chan_ ~close:close_in
-let of_chan_close_noerr = of_chan_ ~close:close_in_noerr
+let of_chan_ ?buf_size ic ~close_noerr : t =
+  let inc = IO.In_channel.of_in_channel ~close_noerr ic in
+  of_input ?buf_size inc
 
-let of_fd_ ?(buf_size = 16 * 1024) ~close ic : t =
-  make ~bs:(Bytes.create buf_size)
-    ~close:(fun _ -> close ic)
-    ~consume:(fun self n ->
-      self.off <- self.off + n;
-      self.len <- self.len - n)
-    ~fill:(fun self ->
-      if self.off >= self.len then (
-        self.off <- 0;
-        self.len <- Unix.read ic self.bs 0 (Bytes.length self.bs)
-      ))
-    ()
+let of_chan ?buf_size ic = of_chan_ ?buf_size ic ~close_noerr:false
+let of_chan_close_noerr ?buf_size ic = of_chan_ ?buf_size ic ~close_noerr:true
 
-let of_fd = of_fd_ ~close:Unix.close
-let of_fd_close_noerr = of_fd_ ~close:(fun f -> try Unix.close f with _ -> ())
+let of_fd_ ?buf_size ~close_noerr ic : t =
+  let inc = IO.In_channel.of_unix_fd ~close_noerr ic in
+  of_input ?buf_size inc
+
+let of_fd ?buf_size fd : t = of_fd_ ?buf_size ~close_noerr:false fd
+let of_fd_close_noerr ?buf_size fd : t = of_fd_ ?buf_size ~close_noerr:true fd
 
 let rec iter f (self : t) : unit =
   self.fill_buf ();
@@ -90,6 +86,9 @@ let rec iter f (self : t) : unit =
 let to_chan (oc : out_channel) (self : t) =
   iter (fun s i len -> output oc s i len) self
 
+let to_chan' (oc : IO.Out_channel.t) (self : t) =
+  iter (fun s i len -> IO.Out_channel.output oc s i len) self
+
 let of_bytes ?(i = 0) ?len (bs : bytes) : t =
   (* invariant: !i+!len is constant *)
   let len =
@@ -298,19 +297,22 @@ let read_chunked ?(buf = Buf.create ()) ~fail (bs : t) : t =
       refill := false)
     ()
 
-(* print a stream as a series of chunks *)
-let output_chunked (oc : out_channel) (self : t) : unit =
+let output_chunked' (oc : IO.Out_channel.t) (self : t) : unit =
   let continue = ref true in
   while !continue do
     (* next chunk *)
     self.fill_buf ();
     let n = self.len in
-    Printf.fprintf oc "%x\r\n" n;
-    output oc self.bs self.off n;
+    IO.Out_channel.output_string oc (Printf.sprintf "%x\r\n" n);
+    IO.Out_channel.output oc self.bs self.off n;
     self.consume n;
     if n = 0 then continue := false;
-    output_string oc "\r\n"
+    IO.Out_channel.output_string oc "\r\n"
   done;
   (* write another crlf after the stream (see #56) *)
-  output_string oc "\r\n";
+  IO.Out_channel.output_string oc "\r\n";
   ()
+
+(* print a stream as a series of chunks *)
+let output_chunked (oc : out_channel) (self : t) : unit =
+  output_chunked' (IO.Out_channel.of_out_channel oc) self

src/Tiny_httpd_stream.mli

@@ -27,8 +27,7 @@ type t = {
   _rest: hidden;  (** Use {!make} to build a stream. *)
 }
 (** A buffered stream, with a view into the current buffer (or refill if empty),
-    and a function to consume [n] bytes.
-    See {!Byte_stream} for more details. *)
+    and a function to consume [n] bytes. *)
 
 val close : t -> unit
 (** Close stream *)
@@ -36,6 +35,10 @@ val close : t -> unit
 val empty : t
 (** Stream with 0 bytes inside *)
 
+val of_input : ?buf_size:int -> Tiny_httpd_io.In_channel.t -> t
+(** Make a buffered stream from the given channel.
+    @since NEXT_RELEASE *)
+
 val of_chan : ?buf_size:int -> in_channel -> t
 (** Make a buffered stream from the given channel. *)
 
@@ -62,6 +65,10 @@ val to_chan : out_channel -> t -> unit
 (** Write the stream to the channel.
     @since 0.3 *)
 
+val to_chan' : Tiny_httpd_io.Out_channel.t -> t -> unit
+(** Write to the IO channel.
+    @since NEXT_RELEASE *)
+
 val make :
   ?bs:bytes ->
   ?close:(t -> unit) ->
@@ -111,3 +118,7 @@ val read_exactly :
 
 val output_chunked : out_channel -> t -> unit
 (** Write the stream into the channel, using the chunked encoding. *)
+
+val output_chunked' : Tiny_httpd_io.Out_channel.t -> t -> unit
+(** Write the stream into the channel, using the chunked encoding.
+    @since NEXT_RELEASE *)

src/dune

@@ -1,8 +1,13 @@
+
+(env
+ (_
+  (flags :standard -warn-error -a+8 -w +a-4-32-40-42-44-70 -color always -safe-string
+    -strict-sequence)))
+
 (library
   (name tiny_httpd)
   (public_name tiny_httpd)
   (libraries threads seq)
-  (flags :standard -safe-string -strict-sequence -w +a-4-40-42 -warn-error -a+8)
   (wrapped false))
 
 (rule

tests/unit/dune

@@ -1,5 +1,5 @@
 
-(test
-  (name t_util)
+(tests
+  (names t_util t_buf)
   (package tiny_httpd)
-  (libraries tiny_httpd qcheck-core qcheck-core.runner))
+  (libraries tiny_httpd qcheck-core qcheck-core.runner test_util))

tests/unit/t_buf.ml

@@ -0,0 +1,27 @@
+open Test_util
+open Tiny_httpd_buf
+
+let spf = Printf.sprintf
+
+let () =
+  let b = create ~size:4 () in
+  add_string b "hello";
+  assert_eq ~to_string:(spf "%S") "hello" (contents b);
+
+  add_string b " world";
+  assert_eq ~to_string:(spf "%S") "hello world" (contents b);
+  ()
+
+let buffer_of_string str =
+  let buf = Buffer.create 32 in
+  Buffer.add_string buf str;
+  buf
+
+let () =
+  let b = create ~size:4 () in
+  add_buffer b (buffer_of_string "hello");
+  assert_eq ~to_string:(spf "%S") "hello" (contents b);
+
+  add_buffer b (buffer_of_string " world");
+  assert_eq ~to_string:(spf "%S") "hello world" (contents b);
+  ()

tests/unit/t_util.ml

@@ -1,25 +1,6 @@
-module Q = QCheck
-
-(* test utils *)
-let pp_res f = function
-  | Ok x -> f x
-  | Error e -> e
-
-let pp_res_query = Q.Print.(pp_res (list (pair string string)))
-
-let err_map f = function
-  | Ok x -> Ok (f x)
-  | Error e -> Error e
-
-let sort_l l = List.sort compare l
-let eq_sorted a b = err_map sort_l a = err_map sort_l b
-let is_ascii_char c = Char.code c < 128
-let assert_eq ?(cmp = ( = )) a b = assert (cmp a b)
-
+open Test_util
 open Tiny_httpd_util
 
-let qchecks = ref []
-let add_qcheck f = qchecks := f :: !qchecks
 let () = assert_eq "hello%20world" (percent_encode "hello world")
 let () = assert_eq "%23%25^%24%40^%40" (percent_encode "#%^$@^@")
 
@@ -67,4 +48,4 @@ let () =
          in
          eq_sorted (Ok l) (parse_query s))
 
-let () = exit @@ QCheck_base_runner.run_tests ~colors:false !qchecks
+let () = run_qcheck_and_exit ()

tests/unit/util/dune

@@ -0,0 +1,5 @@
+
+(library
+  (name test_util)
+  (modules test_util)
+  (libraries qcheck-core qcheck-core.runner))

tests/unit/util/test_util.ml

@@ -0,0 +1,31 @@
+module Q = QCheck
+
+(* test utils *)
+let pp_res f = function
+  | Ok x -> f x
+  | Error e -> e
+
+let pp_res_query = Q.Print.(pp_res (list (pair string string)))
+
+let err_map f = function
+  | Ok x -> Ok (f x)
+  | Error e -> Error e
+
+let sort_l l = List.sort compare l
+let eq_sorted a b = err_map sort_l a = err_map sort_l b
+let is_ascii_char c = Char.code c < 128
+
+let assert_eq ?to_string ?(cmp = ( = )) a b =
+  let ok = cmp a b in
+  if not ok then (
+    (match to_string with
+    | Some f -> Printf.eprintf "failed: %s != %s\n%!" (f a) (f b)
+    | None -> ());
+    failwith "test failed"
+  )
+
+let qchecks = ref []
+let add_qcheck f = qchecks := f :: !qchecks
+
+let run_qcheck_and_exit () : 'a =
+  exit @@ QCheck_base_runner.run_tests ~colors:false !qchecks