用erlang gen_tcp 实现支持websocket功能

要使用Erlang的gen_tcp模块实现WebSocket功能，需要进行以下步骤：

1. 创建一个TCP服务器，监听WebSocket连接请求。

2. 当有WebSocket连接请求时，接受连接并进行WebSocket协议的握手。

3. 一旦完成握手，服务器和客户端之间的通信就可以使用WebSocket协议进行。

以下是一个简单的Erlang代码示例，用于实现WebSocket功能：

-module(websocket_server).
-export([start/0, stop/0]).

start() ->
    {ok, ListenSocket} = gen_tcp:listen(8080, [{active, false}, {reuseaddr, true}]),
    accept_loop(ListenSocket).

stop() ->
    ok = gen_tcp:close(ListenSocket).

accept_loop(ListenSocket) ->
    {ok, Socket} = gen_tcp:accept(ListenSocket),
    spawn(fun() -> handle(Socket) end),
    accept_loop(ListenSocket).

handle(Socket) ->
    {ok, Request} = gen_tcp:recv(Socket, 0),
    case extract_websocket_key(Request) of
        {ok, Key} ->
            Response = create_websocket_response(Key),
            ok = gen_tcp:send(Socket, Response),
            websocket_loop(Socket);
        {error, Reason} ->
            ok = gen_tcp:close(Socket),
            error_logger:error_msg("WebSocket handshake failed: ~p~n", [Reason])
    end.

websocket_loop(Socket) ->
    {ok, Data} = gen_tcp:recv(Socket, 0),
    case Data of
        <<_:1/binary, 0:1/binary, Payload/binary>> ->
            % This is a WebSocket text message
            process_message(Payload),
            ok = gen_tcp:send(Socket, create_websocket_frame(Payload));
        <<_:1/binary, 1:1/binary, Payload/binary>> ->
            % This is a WebSocket binary message
            process_message(Payload),
            ok = gen_tcp:send(Socket, create_websocket_frame(Payload));
        <<_:1/binary, 8:1/binary>> ->
            % This is a WebSocket close message
            ok = gen_tcp:close(Socket);
        _ ->
            % This is an invalid WebSocket frame
            error_logger:error_msg("Invalid WebSocket frame received: ~p~n", [Data]),
            ok = gen_tcp:close(Socket)
    end,
    websocket_loop(Socket).

extract_websocket_key(Request) ->
    case re:run(Request, "Sec-WebSocket-Key: ([^\\r\\n]+)", [{capture, [1]}]) of
        {match, [Key]} ->
            {ok, Key};
        nomatch ->
            {error, "WebSocket key not found"}
    end.

create_websocket_response(Key) ->
    Hash = crypto:sha1_bin(list_to_binary([Key, "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"])),
    Response = <<"HTTP/1.1 101 Switching Protocols\r\n">>,
    Response = <<Response/binary, "Upgrade: websocket\r\n">>,
    Response = <<Response/binary, "Connection: Upgrade\r\n">>,
    Response = <<Response/binary, "Sec-WebSocket-Accept: ", base64:encode(Hash), "\r\n">>,
    Response = <<Response/binary, "\r\n">>,
    Response.

create_websocket_frame(Payload) ->
    <<129:1/binary, Length:1/integer, Data/binary>> = Payload,
    Frame = <<129:1/binary>>,
    case Length of
        Len when Len =< 125 ->
            Frame = <<Frame/binary, Length:1/integer>>;
        Len when Len =< 65535 ->
            Frame = <<Frame/binary, 126:1/binary, Len:2/integer>>;
        Len ->
            Frame = <<Frame/binary, 127:1/binary, Len:8/integer>>
    end,
    <<Frame/binary, Data/binary>>.

process_message(Payload) ->
    io:format("Received message: ~p~n", [Payload]).

这个示例实现了一个简单的WebSocket服务器，它监听端口8080，接受WebSocket连接请求，并将消息发送回客户端。它使用gen_tcp模块进行网络通信，并使用crypto和base64模块进行加密和解密。在处理WebSocket消息时，它使用了WebSocket协议中定义的帧格式。