websocket_cohttp_lwt.ml

(*
 * Copyright (c) 2016-2018 Maciej Wos <maciej.wos@gmail.com>
 * Copyright (c) 2012-2018 Vincent Bernardoff <vb@luminar.eu.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 *)

open Lwt.Infix
open Websocket
module Lwt_IO = Websocket.Make (Cohttp_lwt_unix.IO)

let send_frames stream oc =
  let buf = Buffer.create 128 in
  let send_frame fr =
    Buffer.clear buf;
    Lwt_IO.write_frame_to_buf ~mode:Server buf fr;
    Lwt_io.write oc @@ Buffer.contents buf
  in
  Lwt_stream.iter_s send_frame stream

let read_frames ic oc handler_fn =
  let read_frame = Lwt_IO.make_read_frame ~mode:Server ic oc in
  let rec inner () = read_frame () >>= Lwt.wrap1 handler_fn >>= inner in
  inner ()

let upgrade_connection request incoming_handler =
  let headers = Cohttp.Request.headers request in
  (match Cohttp.Header.get headers "sec-websocket-key" with
  | None ->
      Lwt.fail_invalid_arg
        "upgrade_connection: missing header `sec-websocket-key`"
  | Some key -> Lwt.return key)
  >>= fun key ->
  let hash = b64_encoded_sha1sum (key ^ websocket_uuid) in
  let response_headers =
    Cohttp.Header.of_list
      [
        ("Upgrade", "websocket");
        ("Connection", "Upgrade");
        ("Sec-WebSocket-Accept", hash);
      ]
  in
  let resp =
    Cohttp.Response.make ~status:`Switching_protocols
      ~encoding:Cohttp.Transfer.Unknown ~headers:response_headers ~flush:true ()
  in
  let frames_out_stream, frames_out_fn = Lwt_stream.create () in
  let f ic oc =
    Lwt.pick
      [
        (* input: data from the client is read from the input channel
         * of the tcp connection; pass it to handler function *)
        read_frames ic oc incoming_handler;
        (* output: data for the client is written to the output
         * channel of the tcp connection *)
        send_frames frames_out_stream oc;
      ]
  in
  Lwt.return (`Expert (resp, f), frames_out_fn)