在Cowboy中的HTTP处理程序和websocket处理程序之间进行通信 [英] communicating between http handler and websocket handler in Cowboy

问题描述

我想在Cowboy中创建一个websocket应用，该应用从另一个Cowboy处理程序获取其数据。假设我要结合牛仔的Echo_get示例： https：// github.com/ninenines/cowboy/tree/master/examples/echo_get/src

I'd like to create a websocket app in Cowboy that gets its data from another Cowboy handler. Let's say that I want to combine the Echo_get example from cowboy: https://github.com/ninenines/cowboy/tree/master/examples/echo_get/src

带有websocket示例

with websocket example

https://github.com/ninenines/cowboy/tree / master / examples / websocket / src

这样，对Echo的GET请求应通过websocket处理程序向html页面发送推送在那个例子中。

in such a way that a GET request to Echo should send a "push" via websocket handler to the html page in that example.

最简单的方法是什么？我可以通过一些简单的方法使用 pipe运算符吗？我是否需要创建和中间gen_something在它们之间传递消息？我希望得到一个示例代码的答案，该代码显示了处理程序的粘合代码-我真的不知道从哪里开始将两个处理程序连接在一起。

What is the least complicated way to do it? Can I use "pipe" operator in some easy way ? Do I need to create and intermediate gen_something to pass messages between them? I would appreciate an answer with sample code that shows the glue code for the handlers - I do not really know where to start plumbing the two handlers together.

推荐答案

牛仔的Websocket处理程序是一个长期存在的请求过程，您可以向其发送Websocket或erlang消息。

A websocket handler in cowboy is a long lived request process to which you can send websocket or erlang messages.

在您的情况下，有两种类型进程数：

In your case, there are 2 types of processes:

• websocket进程：向客户端打开了具有websocket连接的websocket处理程序。


• echo进程：当客户端使用参数访问回显处理程序时进行的处理。

其思想是，回显进程将erlang消息发送给

The idea is that the echo process sends an erlang message to the websocket processes, that in turn will send a message to the client.

为使回显进程可以向websocket进程发送消息，您需要保留一个websocket列表。您要向其发送消息的进程。 Gproc 是用于此目的的非常有用的库。

For your echo process can send a message to your websocket processes, you need to keep a list of websocket processes to which you want to send messages. Gproc is a quite useful library for that purpose.

您可以使用<$ c将进程注册到 gproc pubsub $ c> gproc_ps：subscribe / 2 ，然后使用 gproc_ps：publish / 3 将消息发送到已注册的进程。

You can register processes to gproc pubsub with gproc_ps:subscribe/2, and send messages to the registered processes with gproc_ps:publish/3.

Cowboy Websocket进程使用 websocket_info / 3 函数。

Cowboy websocket processes receive erlang messages with the websocket_info/3 function.

因此，例如，websocket处理程序可能是这样的：

So for example, the websocket handler could be like this:

websocket_init(_, Req, _Opts) ->
  ...
  % l is for local process registration
  % echo is the name of the event you register the process to
  gproc_ps:subscribe(l, echo),
  ...

websocket_info({gproc_ps_event, echo, Echo}, Req, State) ->
  % sending the Echo to the client
  {reply, {text, Echo}, Req, State};

回声处理程序如下：

echo(<<"GET">>, Echo, Req) ->
    % sending the echo message to the websockets handlers
    gproc_ps:publish(l, echo, Echo),
    cowboy_req:reply(200, [
        {<<"content-type">>, <<"text/plain; charset=utf-8">>}
    ], Echo, Req);

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