Real-Time Streaming Systems (WebRTC + Live Data) · レッスン

一方向プッシュのためのServer-Sent Events（SSE）

サーバーからクライアントへ一方向にデータをプッシュする、WebSocketよりシンプルな選択肢としてServer-Sent Events（SSE）を学びます。

「一方向プッシュのためのServer-Sent Events（SSE）」はCoddyKit上の無料Real-Time Streaming Systems (WebRTC + Live Data)レッスンです。これはレッスン3/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはReal-Time Streaming Systems (WebRTC + Live Data)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Real-Time Streaming Systems (WebRTC + Live Data)コースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Intro to Server-Sent Events

Welcome! In this lesson, we'll explore Server-Sent Events (SSE), a powerful yet simple way for servers to push real-time updates to clients.

Unlike traditional HTTP requests where the client always asks the server for data, SSE allows the server to send data to the client whenever new information is available, without the client needing to constantly poll.

SSE: Simpler Unidirectional Push

You might be familiar with WebSockets for real-time communication. While WebSockets enable full two-way communication, SSE is designed specifically for unidirectional data flow, from the server to the client.

This makes SSE a simpler and often more efficient choice for scenarios where the client only needs to receive updates, not send them back in real-time.

How SSE Connections Work

SSE operates over a standard HTTP connection. The client initiates a regular HTTP request, but the server responds with a special Content-Type: text/event-stream header.

Instead of closing the connection after sending data, the server keeps it open. It then pushes new data to the client whenever updates are ready, effectively streaming events over this single, persistent connection.

Listening with EventSource

On the client-side (typically in a web browser), you use the built-in EventSource API to connect to an SSE stream and listen for incoming events.

Here's a basic JavaScript snippet to connect to an SSE endpoint and log messages:

const eventSource = new EventSource('/stream');

eventSource.onmessage = (event) => {
  console.log('New data:', event.data);
  // Update your UI here
};

eventSource.onerror = (error) => {
  console.error('SSE Error:', error);
  eventSource.close(); // Close connection on error
};

Building an SSE Server

Let's see how a simple server can send SSE messages. This Node.js example creates an HTTP server that sends the current time every second.

Run this code, then open a browser and navigate to http://localhost:8080 to see the events stream in your console.

const http = require('http');

http.createServer((req, res) => {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive'
  });

  // Send a message every second
  const intervalId = setInterval(() => {
    res.write('data: The time is ' + new Date().toLocaleTimeString() + '\n\n');
  }, 1000);

  // Clean up on client disconnect
  req.on('close', () => {
    clearInterval(intervalId);
    res.end();
  });

}).listen(8080, () => {
  console.log('SSE server running on http://localhost:8080');
});

Sending Custom SSE Event Types

Beyond the default message event, SSE allows you to define custom event types using the event: field. This helps clients handle different kinds of updates differently.

On the client, you'd use eventSource.addEventListener('myCustomEvent', handler).

const http = require('http');

http.createServer((req, res) => {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive'
  });

  let counter = 0;
  const intervalId = setInterval(() => {
    if (counter % 2 === 0) {
      res.write('event: heartbeat\n');
      res.write('data: Ping! ' + counter + '\n\n');
    } else {
      res.write('event: update\n');
      res.write('data: New data point: ' + Math.random().toFixed(2) + '\n\n');
    }
    counter++;
  }, 2000);

  req.on('close', () => {
    clearInterval(intervalId);
    res.end();
  });

}).listen(8080, () => {
  console.log('SSE server (custom events) running on http://localhost:8080');
});

Automatic Reconnection Magic

One of the most convenient features of EventSource is its built-in automatic reconnection. If the connection drops (due to network issues, server restart, etc.), the browser will automatically attempt to reconnect after a short delay.

You don't need to write any extra code to handle connection failures and retries, making SSE very robust for continuous updates.

Benefits of Using SSE

SSE offers several compelling advantages for server-to-client push:

Simplicity: Easier to implement than WebSockets for one-way data.
Built-in Reconnection: Automatic handling of connection drops by EventSource.
HTTP Compatibility: Works over standard HTTP/HTTPS, compatible with existing infrastructure (proxies, firewalls).
HTTP/2 Multiplexing: Can share a single connection with other HTTP requests efficiently.

SSE Limitations

While powerful, SSE isn't suitable for all real-time scenarios:

Unidirectional Only: Only supports server-to-client communication. For client-to-server or true bidirectional, WebSockets are required.
No Binary Data: Limited to UTF-8 encoded text. You cannot send raw binary data directly via SSE.
Browser Connection Limits: Browsers typically limit the number of concurrent SSE connections per domain (e.g., 6).

Real-World SSE Examples

SSE shines in applications that need continuous, one-way updates:

Live Stock Tickers: Continuously pushing price updates to trading dashboards.
News Feeds: Instant delivery of breaking news or article updates.
Activity Streams: Real-time notifications (e.g., new emails, social media activity).
Dashboards: Live updates for monitoring system metrics or user statistics.

SSE Quick Check

Time to test your understanding of Server-Sent Events!

Lesson Summary: SSE

Great job! You've now learned about Server-Sent Events (SSE).

SSE enables unidirectional, server-to-client data push over a single HTTP connection.
It's simpler than WebSockets for one-way updates and features automatic reconnection.
You use the client-side EventSource API to listen for events.
SSE is perfect for live dashboards, news feeds, and real-time notifications.

Keep exploring how these live data architectures can enhance your applications!

よくある質問

「一方向プッシュのためのServer-Sent Events（SSE）」レッスンは無料ですか？

はい。「一方向プッシュのためのServer-Sent Events（SSE）」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Real-Time Streaming Systems (WebRTC + Live Data)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Real-Time Streaming Systems (WebRTC + Live Data)コースには全4レッスンが含まれています。

「一方向プッシュのためのServer-Sent Events（SSE）」で何を学びますか？

サーバーからクライアントへ一方向にデータをプッシュする、WebSocketよりシンプルな選択肢としてServer-Sent Events（SSE）を学びます。ブラウザで直接実行するハンズオンコードでReal-Time Streaming Systems (WebRTC + Live Data)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Real-Time Streaming Systems (WebRTC + Live Data)を始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのReal-Time Streaming Systems (WebRTC + Live Data)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン3/4です。

「一方向プッシュのためのServer-Sent Events（SSE）」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このReal-Time Streaming Systems (WebRTC + Live Data)レッスンでコードを書いて実行できますか？

はい。すべてのReal-Time Streaming Systems (WebRTC + Live Data)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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