ASPNET Core 服务器发送事件/响应刷新

2023-07-11C#/.NET开发问题

本文介绍了ASPNET Core 服务器发送事件/响应刷新的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着跟版网的小编来一起学习吧！

问题描述

虽然没有官方文档，但有谁知道如何使用 ASP.NET Core 实现 SSE?

While there is no official documentation, does anyone know how SSE may be implemented using ASP.NET Core?

我怀疑一种实现可能会使用自定义中间件，但也许可以在控制器操作中做到这一点?

I suspect one implementation may use custom middleware, but maybe it is possible to do that in controller action?

客户端 - wwwroot/index.html

在页面加载时，为 http://www.somehost.ca/sse 网址创建一个 EventSource.然后将其事件写入控制台.

Client Side - wwwroot/index.html

On page load, create an EventSource for the http://www.somehost.ca/sse url. Then write its events to the console.

<body>
    <script type="text/javascript">

        var source = new EventSource('sse');

        source.onmessage = function (event) {
            console.log('onmessage: ' + event.data);
        };

        source.onopen = function(event) {
            console.log('onopen');
        };

        source.onerror = function(event) {
            console.log('onerror');
        }

    </script>
</body>

服务器端替代方案 #1 - 使用中间件

中间件处理 sse 路径.它将 Content-Type 标头设置为服务器套接字事件所需的 text/event-stream.它写入响应流，而不关闭连接.它通过在写入之间延迟五秒钟来模仿工作.

Server Side Alternative #1 - Use Middleware

The middleware handles the sse path. It sets the Content-Type header to text/event-stream, which the server socket event requires. It writes to the response stream, without closing the connection. It mimics doing work, by delaying for five seconds between writes.

app.Use(async (context, next) =>
{
    if (context.Request.Path.ToString().Equals("/sse"))
    {
        var response = context.Response;
        response.Headers.Add("Content-Type", "text/event-stream");

        for(var i = 0; true; ++i)
        {
            // WriteAsync requires `using Microsoft.AspNetCore.Http`
            await response
                .WriteAsync($"data: Middleware {i} at {DateTime.Now}

");

            await response.Body.FlushAsync();
            await Task.Delay(5 * 1000);
        }
    }

    await next.Invoke();
});

服务器端替代方案 #2 - 使用控制器

控制器的作用与中间件完全相同.

Server Side Alternative #2 - Use a Controller

The controller does the exact same thing as the middleware does.

[Route("/api/sse")]
public class ServerSentEventController : Controller
{
    [HttpGet]
    public async Task Get()
    {
        var response = Response;
        response.Headers.Add("Content-Type", "text/event-stream");

        for(var i = 0; true; ++i)
        {
            await response
                .WriteAsync($"data: Controller {i} at {DateTime.Now}

");

            response.Body.Flush();
            await Task.Delay(5 * 1000);
        }
    }
}

Firefox 中的客户端控制台输出

这是 Firefox 控制台窗口中的结果.每五秒钟就有一条新消息到达.

Client Side Console Output in Firefox

This is the result in the Firefox console window. Every five seconds a new messages arrives.

onopen
onmessage: Message 0 at 4/15/2016 3:39:04 PM
onmessage: Message 1 at 4/15/2016 3:39:09 PM
onmessage: Message 2 at 4/15/2016 3:39:14 PM
onmessage: Message 3 at 4/15/2016 3:39:19 PM
onmessage: Message 4 at 4/15/2016 3:39:24 PM

参考文献:

GitHub 上的上述示例
HTML 生活标准，第 9.2 节服务器发送的事件
维基百科上的Http推送技术
分块传输编码

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