RTCPeerConnection.createDataChannel()

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RTCPeerConnection 的 createDataChannel() 方法创建一个可以发送任意数据的数据通道(data channel)。常用于后台传输内容, 例如: 图像, 文件传输, 聊天文字, 游戏数据更新包, 等等。

基于某个连接创建第一个data channel时, 会通过发送一个negotiationneeded event来开始重新谈判(renegotiation)。

语法

dataChannel = RTCPeerConnection.createDataChannel(label[, options]);

参数

label
一个便于理解的通道名. 该字符串不能长于 65,535 字节.
options 可选
提供data channel设置的一个 RTCDataChannelInit dictionary 

RTCDataChannelInit dictionary

RTCDataChannelInit 字典提供以下字段, 用以构造可选的options参数来设置data channel以满足你的需求:

ordered 可选
表示通过 RTCDataChannel 的信息的到达顺序需要和发送顺序一致(true), 或者到达顺序不需要和发送顺序一致 (false). 默认: true.
maxPacketLifeTime 可选
The maximum number of milliseconds that attempts to transfer a message may take in unreliable mode. While this value is a 16-bit unsigned number, each user agent may clamp it to whatever maximum it deems appropriate. Default: null.
maxRetransmits 可选
The maximum number of times the user agent should attempt to retransmit a message which fails the first time in unreliable mode. While this value is a16-bit unsigned number, each user agent may clamp it to whatever maximum it deems appropriate. Default: null.
protocol 可选
The name of the sub-protocol being used on the RTCDataChannel, if any; otherwise, the empty string (""). Default: empty string, "". This string may not be longer than 65,535 bytes.
negotiated 可选
By default (false), data channels are negotiated in-band, where one side calls createDataChannel, and the other side listens to the RTCDataChannelEvent event using the ondatachannel EventHandler . Alternatively (true), they can be negotiated out of-band, where both sides call createDataChannel with an agreed-upon id. Default: false.
id 可选
An 16-bit numeric ID for the channel; permitted values are 0-65534. If you don't include this option, the user agent will select an ID for you.

The options which can be configured using the RTCDataChannelInit dictionary represent the script-settable subset of the properties on the RTCDataChannel interface.

Return value

A new RTCDataChannel object with the specified label, configured using the options specified by options if that parameter is included; otherwise, the defaults listed above are established.

Exceptions

InvalidStateError
The RTCPeerConnection is closed.
TypeError
This can happen in a couple of situations:
  • The label and/or protocol string is too long; these cannot be longer than 65,535 bytes (bytes, rather than characters).
  • The id is 65535. While this is a valid unsigned 16-bit value, it's not a permitted value for id.
SyntaxError
Values were specified for both the maxPacketLifeTime and maxRetransmits options. You may only specify a non-null value for one of these.
ResourceInUse
An id was specified, but another RTCDataChannel is already using the same value.
OperationError
Either the specified id is already in use or, if no id was specified, the WebRTC layer was unable to automatically generate an ID because all IDs are in use.

Examples

This example shows how to create a data channel and set up handlers for the open and message events to send and receive messages on it (For brievity, the example assumes onnegotiationneeded is set up).

// Offerer side

var pc = new RTCPeerConnection(options);
var channel = pc.createDataChannel("chat");
channel.onopen = function(event) {
  channel.send('Hi you!');
}
channel.onmessage = function(event) {
  console.log(event.data);
}
// Answerer side

var pc = new RTCPeerConnection(options);
pc.ondatachannel = function(event) {
  var channel = event.channel;
  channel.onopen = function(event) {
    channel.send('Hi back!');
  }
  channel.onmessage = function(event) {
    console.log(event.data);
  }
}

Alternatively, more symmetrical out-of-band negotiation can be used, using an agreed-upon id (0 here):

// Both sides

var pc = new RTCPeerConnection(options);
var channel = pc.createDataChannel("chat", {negotiated: true, id: 0});
channel.onopen = function(event) {
  channel.send('Hi!');
}
channel.onmessage = function(event) {
  console.log(event.data);
}

For a more thorough example showing how the connection and channel are established, see A simple RTCDataChannel sample.

Specifications

Specification Status Comment
WebRTC 1.0: Real-time Communication Between Browsers
createDataChannel()
Candidate Recommendation Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
createDataChannelChrome Full support 25Edge No support NoFirefox Full support 22IE No support NoOpera Full support 43
Notes
Full support 43
Notes
Notes Promise-based version.
No support 37 — 43
Safari Full support 11WebView Android Full support YesChrome Android Full support 25Firefox Android Full support 44Opera Android Full support 43
Notes
Full support 43
Notes
Notes Promise-based version.
No support 37 — 43
Safari iOS Full support 11Samsung Internet Android Full support 6.0

Legend

Full support  
Full support
No support  
No support
See implementation notes.
See implementation notes.

See also

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