服务器已发送事件是打开与Web服务器的持久连接的有用工具，该服务器具有在可用时将新数据推送到客户端的功能。
在Node.js中使用这项技术非常简单，可以通过以下代码示例实现：
#!/usr/bin/env node
'use strict';
const http = (options, listener) => require('http').createServer(listener).listen(options.port);
http({ port: 8080 }, (req, res) => {
switch (req.url) {
case '/server-sent-events': {
res.writeHead(200, {
'Content-Type': 'text/event-stream',
'Connection': 'keep-alive',
'Cache-Control': 'no-cache',
});
const sendDate = () => res.write(`data: ${new Date()}\n\n`);
sendDate();
const interval = setInterval(sendDate, 1000);
req.on('close', () => clearInterval(interval));
} break;
default: {
res.writeHead(200, {
'Content-Type': 'text/html; charset=utf-8',
});
res.end(`
<!DOCTYPE html>
<html>
<head>
<title>Server Send Events</title>
<meta charset="utf-8">
<script>
const sse = new EventSource('/server-sent-events');
sse.onerror = () => document.body.innerHTML = 'Connection Error';
sse.onmessage = ({ data }) => document.body.innerHTML = data;
</script>
</head>
<body></body>
</html>
`);
}
}
});
不幸的是，我无法使用Deno达到相同的目标，因为请求对象上没有简单的write方法，但是我想必须使用req.w缓冲区来实现它。您能帮我完成以下示例代码，以便服务器发送事件也可以与Deno一起使用吗？
#!/usr/bin/env deno run --allow-net
import { listenAndServe as http } from 'https://deno.land/std/http/server.ts';
http({ port: 8080 }, (req) => {
switch (req.url) {
case '/server-sent-events': {
// missing steps:
// * setup the server sent event headers
// * create the interval and send the date periodically
// * clear the interval when the connection gets closed
} break;
default: {
req.respond({
headers: new Headers({
'Content-Type': 'text/html; charset=utf-8',
}),
body: `
<!DOCTYPE html>
<html>
<head>
<title>Server Send Events</title>
<meta charset="utf-8">
<script>
const sse = new EventSource('/server-sent-events');
sse.onerror = () => document.body.innerHTML = 'Connection Error';
sse.onmessage = ({ data }) => document.body.innerHTML = data;
</script>
</head>
<body></body>
</html>
`,
});
}
}
});
非常感谢您的支持！
[更新]：
我在不同来源（https://deno.land/std@0.76.0/http/server.ts，https://github.com/denoland/deno/issues/4817）上进行了一些研究，取得了一些进展，并且距离解决方案又迈进了一步。使用下面的更新示例，至少服务器发送事件的设置和使用现在可以正常工作。剩下的问题（除了清理和重构代码外）仍然是在关闭传入请求时的安全检测（请参见下面的源代码中的注释）：
#!/usr/bin/env deno run --allow-net
import { listenAndServe as http } from 'https://deno.land/std/http/server.ts';
http({ port: 8080 }, (req) => {
switch (req.url) {
case '/server-sent-events': {
// set up a quick´n´dirty write method without error checking
req.write = (data) => {
req.w.write(new TextEncoder().encode(data));
req.w.flush();
};
// setup the server sent event headers
let headers = '';
headers += 'HTTP/1.1 200 OK\r\n';
headers += 'Connection: keep-alive\r\n';
headers += 'Cache-Control: no-cache\r\n';
headers += 'Content-Type: text/event-stream\r\n';
headers += '\r\n';
req.write(headers);
// create the interval and send the date periodically
const sendDate = () => req.write(`data: ${new Date()}\n\n`);
sendDate();
const interval = setInterval(sendDate, 1000);
// final missing step:
// * clear the interval when the connection gets closed
// currently dropping the connection from the client will
// result in the error: Uncaught (in promise) BrokenPipe:
// Broken pipe (os error 32)
// this error also does not seem to be catchable in the
// req.write method above, so there needs to be another safe
// way to prevent this error from occurring.
} break;
default: {
req.respond({
headers: new Headers({
'Content-Type': 'text/html; charset=utf-8',
}),
body: `
<!DOCTYPE html>
<html>
<head>
<title>Server Send Events</title>
<meta charset="utf-8">
<script>
const sse = new EventSource('/server-sent-events');
sse.onerror = () => document.body.innerHTML = 'Connection Error';
sse.onmessage = ({ data }) => document.body.innerHTML = data;
</script>
</head>
<body></body>
</html>
`,
});
}
}
});
答案 0 :(得分：3)
Deno的http库不支持SSE，但是您可以使用Oak框架，也可以自己实现。
import { Application, Router } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
const router = new Router();
router.get('/', ctx => {
ctx.response.body = `
<!DOCTYPE html>
<html>
<head>
<title>Server Send Events</title>
<meta charset="utf-8">
<script>
const sse = new EventSource('/server-sent-events');
sse.onerror = () => document.body.innerHTML = 'Connection Error';
sse.onmessage = ({ data }) => document.body.innerHTML = data;
</script>
</head>
<body></body>
</html>
`;
})
router.get("/server-sent-events", (ctx) => {
const target = ctx.sendEvents();
const sendDate = () => target.dispatchMessage(`${new Date()}`);
sendDate();
const interval = setInterval(sendDate, 1000);
});
app.use(router.routes());
await app.listen({ port: 8080 });
答案 1 :(得分：1)
最后，我找到了我的问题的答案，因此下面是带有大量评论的完整答案，因此您将在 Deno 中获得服务器发送事件的工作版本。下面的解决方案还解决了 os error 32，这是由于未捕获连接编写器 flash 方法引起的：
#!/usr/bin/env deno run --allow-net
// imports
import { ServerRequest, listenAndServe as http } from 'https://deno.land/std/http/server.ts';
// commodity
const encoder = new TextEncoder();
const print = console.log;
// start the web-server
// this one allows the endpoint `/server-sent-events`, which hosts a clock that
// will be refreshed every second (the efficiency of the clock solution could of
// course be optimised, as every client gets its own clock interval, but this
// this does not matter as this example wants to show how to setup and clean a
// task for every connecting client)
// all other requests will be answered with a simple html page that subscribes
// to the sse-based clock
http({ port: 8080 }, async (req) => {
// ip address of the client (formatted as `ip:port`, so we cut the `:port` part
// of it)
const ip = req.headers.get('host').split(':').slice(0, -1).join(':');
// determine the endpoint to access
switch (req.url) {
// host the server sent event based clock
case '/server-sent-events': {
// logging
print(`+ Client ${ip} connected`);
// prepare the disconnect promise. we will use this one later on to await
// the clients disconnect, so we can properly clean up. so the promise will
// be resolved manually by us when we detect a disconnect from the client
// on an attempt to send new data to him (unfortunately there seems to be
// no other way to detect when the client actually closed the connection)
let resolver;
const disconnect = new Promise((resolve) => resolver = resolve);
// write helper
req.write = async (data) => {
// send the current data to the client
req.w.write(encoder.encode(data));
// to actually send the data we need to flush the writer first. we need
// to try/catch this part, as not handling errors on flush will lead to
// the `Broken pipe (os error 32)` error
try {
await req.w.flush();
} catch(err) {
// throw any errors but the broken pipe, which gets thrown when the
// client has already disconnected and we try to send him new data
// later on
if (err.name !== 'BrokenPipe') {
throw err;
}
// close the connection from our side as well
req.conn.close();
// resolve our `disconnect` promise, so we can clean up
resolver();
}
};
// date writer (interval method which pushes the current date to the client)
const sendDate = async () => await req.write(`data: ${new Date()}\n\n`);
// prepare and send the headers
let headers = '';
headers += `HTTP/1.1 200 OK\r\n`;
headers += `Connection: keep-alive\r\n`;
headers += `Cache-Control: no-cache\r\n`;
headers += `Content-Type: text/event-stream\r\n`;
headers += `\r\n`;
await req.write(headers);
// send the date now for the first time and then every second
sendDate();
const interval = setInterval(sendDate, 1000);
// await until the clients disconnects to clean up. so we will be "stuck"
// here until a disconnect gets detected as we use a promise based approach
// to detect the disconnect
await disconnect;
clearInterval(interval);
// logging
print(`- Client ${ip} disconnected`);
} break;
// all other requests host a simple html page which subscribes to the clock
default: {
print(`* Serve website to ${ip}`);
req.respond({
headers: new Headers({
'Content-Type': 'text/html; charset=utf-8',
}),
body: `
<!DOCTYPE html>
<html>
<head>
<title>Server Sent Events</title>
<meta charset="utf-8">
<script>
const sse = new EventSource('/server-sent-events');
sse.onerror = () => document.body.innerHTML = 'Connection Error';
sse.onmessage = ({ data }) => document.body.innerHTML = data;
</script>
</head>
<body></body>
</html>
`,
});
}
}
});