Real-Time Streaming Systems (WebRTC + Live Data) · 课时

发送和接收数据

为通过已建立的 WebRTC 数据通道发送和接收各种类型的数据（文本、二进制数据）编写代码示例。

发送和接收数据 是 CoddyKit 上的免费 Real-Time Streaming Systems (WebRTC + Live Data) 课时。这是第 2 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Real-Time Streaming Systems (WebRTC + Live Data) 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Real-Time Streaming Systems (WebRTC + Live Data) 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Messaging with Data Channels

WebRTC's RTCDataChannel isn't just for connection; it's also for sending messages! This lets peers exchange arbitrary data directly.

Think of it like a super-fast, secure chat line between two browsers, but for any kind of information you want to share.

Sending Data with `send()`

To send data, you use the send() method of an RTCDataChannel object. It's straightforward and can handle various data types.

Syntax: dataChannel.send(data);
The data can be a String, Blob, ArrayBuffer, or ArrayBufferView.

The channel must be in an 'open' state to send messages.

Text Messages are Easy

The simplest data to send is plain text. This is perfect for chat messages, commands, or small bits of structured data like JSON strings.

When you pass a JavaScript String to send(), it's sent as text data.

// Assuming 'dataChannel' is an open RTCDataChannel
dataChannel.send("Hello from CoddyKit!");
dataChannel.send(JSON.stringify({ type: "chat", message: "Hi!" }));

Try Sending a Text Message

Let's simulate sending a simple text message. In a real scenario, this would go to a connected peer. Here, we log what we're "sending."

const dataChannel = {
  readyState: "open",
  send: function(data) {
    if (this.readyState === "open") {
      console.log("DataChannel sending:", data);
    } else {
      console.error("DataChannel not open.");
    }
  }
};

if (dataChannel.readyState === "open") {
  dataChannel.send("Welcome to real-time data!");
  dataChannel.send("Your first message sent!");
} else {
  console.log("Data channel is not yet open.");
}

Handling Incoming Messages

To receive data, you listen for the message event on your RTCDataChannel object. This event fires whenever a peer sends data.

The event handler is typically set via dataChannel.onmessage.
The event object (MessageEvent) has a data property, which contains the received message.

The type of event.data depends on what was sent (String or Blob/ArrayBuffer).

Sending and Receiving Text

Here's a combined example. One "peer" sends a message, and another "peer" (simulated here) receives it using onmessage.

const senderChannel = {
  readyState: "open",
  send: function(data) {
    if (this.readyState === "open") {
      console.log("Sender sent:", data);
      receiverChannel.onmessage({ data: data });
    }
  }
};

const receiverChannel = {
  readyState: "open",
  onmessage: function(event) {
    console.log("Receiver received:", event.data);
  }
};

senderChannel.send("Hello from sender!");

Beyond Text: Binary Data

While strings are great for text, RTCDataChannel also supports sending binary data efficiently. This is crucial for things like file sharing, game state updates, or image data.

You can send:

Blob: Represents raw immutable data. Good for files.
ArrayBuffer: A fixed-length raw binary data buffer.
ArrayBufferView: A view into an ArrayBuffer (e.g., Uint8Array).

When binary data is received, event.data will be an ArrayBuffer or Blob, depending on the channel's binaryType property.

Using ArrayBuffer for Binary

ArrayBuffer is a common way to handle raw binary data in JavaScript. You can create views (like Uint8Array) to manipulate its contents.

// Create an ArrayBuffer
const buffer = new ArrayBuffer(4); // 4 bytes
const view = new Uint8Array(buffer);

// Put some data into the view
view[0] = 65; // ASCII 'A'
view[1] = 66; // ASCII 'B'
view[2] = 67; // ASCII 'C'
view[3] = 68; // ASCII 'D'

// Send the ArrayBuffer
dataChannel.send(buffer);

The receiver will get this ArrayBuffer and can then interpret it.

Binary Data in Action

Let's simulate sending an ArrayBuffer and then interpreting it on the receiving end. We'll convert the received bytes back to characters for display.

const senderBinaryChannel = {
  readyState: "open",
  send: function(data) {
    if (this.readyState === "open") {
      console.log("Sender sent binary data.");
      receiverBinaryChannel.onmessage({ data: data });
    }
  }
};

const receiverBinaryChannel = {
  readyState: "open",
  onmessage: function(event) {
    console.log("Receiver received binary data.");
    const receivedBuffer = event.data;
    if (receivedBuffer instanceof ArrayBuffer) {
      const view = new Uint8Array(receivedBuffer);
      let receivedChars = "";
      for (let i = 0; i < view.length; i++) {
        receivedChars += String.fromCharCode(view[i]);
      }
      console.log("Decoded binary:", receivedChars);
    }
  }
};

const buffer = new ArrayBuffer(3);
const view = new Uint8Array(buffer);
view[0] = 72; // H
view[1] = 73; // I
view[2] = 33; // !

senderBinaryChannel.send(buffer);

Data Channel Check

You've learned how to send and receive different types of data. Let's test your understanding!

Sending & Receiving Data Recap

Great job! You've mastered the basics of sending and receiving data over WebRTC Data Channels.

We use dataChannel.send(data) to transmit information.
The onmessage event listener handles incoming data from peers.
Data Channels support both text (String) and various binary types (Blob, ArrayBuffer).

This capability opens up a world of possibilities for real-time collaboration and direct data exchange!

常见问题解答

「发送和接收数据」课时是免费的吗？

是的 — 「发送和接收数据」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Real-Time Streaming Systems (WebRTC + Live Data) 课程的其余内容，请升级到 CoddyKit PRO。 Real-Time Streaming Systems (WebRTC + Live Data) 课程共包含 4 节课。

「发送和接收数据」这节课中我会学到什么？

为通过已建立的 WebRTC 数据通道发送和接收各种类型的数据（文本、二进制数据）编写代码示例。你通过在浏览器中直接运行的动手代码来练习 Real-Time Streaming Systems (WebRTC + Live Data)，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Real-Time Streaming Systems (WebRTC + Live Data) 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Real-Time Streaming Systems (WebRTC + Live Data) 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 2 节课，共 4 节。

「发送和接收数据」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Real-Time Streaming Systems (WebRTC + Live Data) 课中编写并运行代码吗？

能。每节 Real-Time Streaming Systems (WebRTC + Live Data) 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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