RTCDataChannel - Web APIs 编辑

Event handlers

The RTCDataChannel interface represents a network channel which can be used for bidirectional peer-to-peer transfers of arbitrary data. Every data channel is associated with an RTCPeerConnection, and each peer connection can have up to a theoretical maximum of 65,534 data channels (the actual limit may vary from browser to browser).

To create a data channel and ask a remote peer to join you, call the RTCPeerConnection's createDataChannel() method. The peer being invited to exchange data receives a datachannel event (which has type RTCDataChannelEvent) to let it know the data channel has been added to the connection.

Properties

Also inherits properties from: EventTarget

binaryType

The property binaryType on the RTCDataChannel interface is a DOMString which specifies the type of JavaScript object which should be used to represent binary data received on the RTCDataChannel. Values allowed by the WebSocket.binaryType property are also permitted here: "blob" if Blob objects are being used or "arraybuffer" if ArrayBuffer objects are being used. The default is "blob".

bufferedAmount undefined

The read-only RTCDataChannel property bufferedAmount returns the number of bytes of data currently queued to be sent over the data channel.

bufferedAmountLowThreshold

The RTCDataChannel property bufferedAmountLowThreshold is used to specify the number of bytes of buffered outgoing data that is considered "low." The default value is 0.

id undefined

The read-only RTCDataChannel property id returns an ID number (between 0 and 65,534) which uniquely identifies the RTCDataChannel.

label undefined

The read-only RTCDataChannel property label returns a DOMString containing a name describing the data channel. These labels are not required to be unique.

maxPacketLifeTime undefined

The read-only RTCDataChannel property maxPacketLifeTime returns the amount of time, in milliseconds, the browser is allowed to take to attempt to transmit a message, as set when the data channel was created, or null.

maxRetransmits undefined

The read-only RTCDataChannel property maxRetransmits returns the maximum number of times the browser should try to retransmit a message before giving up, as set when the data channel was created, or null, which indicates that there is no maximum.

negotiated undefined

The read-only RTCDataChannel property negotiated indicates whether the RTCDataChannel's connection was negotiated by the Web app (true) or by the WebRTC layer (false).

ordered undefined

The read-only RTCDataChannel property ordered indicates whether or not the data channel guarantees in-order delivery of messages; the default is true, which indicates that the data channel is indeed ordered.

protocol undefined

The read-only RTCDataChannel property protocol returns a DOMString containing the name of the subprotocol in use. If no protocol was specified when the data channel was created, then this property's value is "" (the empty string).

readyState undefined

The read-only RTCDataChannel property readyState returns an enum of type RTCDataChannelState which indicates the state of the data channel's underlying data connection.

reliable undefined

The read-only RTCDataChannel property reliable indicates whether or not the data channel is reliable.

stream undefined

The deprecated (and never part of the official specification) read-only RTCDataChannel property stream returns an ID number (between 0 and 65,535) which uniquely identifies the RTCDataChannel.

Also inherits event handlers from: EventTarget

onbufferedamountlow

The RTCDataChannel.onbufferedamountlow property is an EventHandler which specifies a function the browser calls when the bufferedamountlow event is sent to the RTCDataChannel. This event, which is represented by a simple Event object, is sent when the amount of data buffered to be sent falls to or below the threshold specified by the channel's RTCDataChannel.bufferedAmountLowThreshold.

onclose

The RTCDataChannel.onclose property is an EventHandler which specifies a function to be called by the browser when the close event is received by the RTCDataChannel. This is a simple Event which indicates that the data channel has closed down.

onclosing

The RTCDataChannel.onclosing property is an EventHandler which specifies a function to be called by the browser when the closing event is received by the RTCDataChannel. This is a simple Event which indicates that the data channel is being closed, that is, RTCDataChannel transitions to "closing" state. For example, after RTCDataChannel.close was called but the underlying data transport might not have been closed yet.

onerror

The RTCDataChannel.onerror property is an EventHandler which specifies a function to be called when the error event is received. When an error occurs on the data channel, the function receives as input an ErrorEvent object describing the error which occurred.

onmessage

The RTCDataChannel.onmessage property stores an EventHandler which specifies a function to be called when the message event is fired on the channel. This event is represented by the MessageEvent interface. This event is sent to the channel when a message is received from the other peer.

onopen

The RTCDataChannel.onopen property is an EventHandler which specifies a function to be called when the open event is fired; this is a simple Event which is sent when the data channel's underlying data transport—the link over which the RTCDataChannel's messages flow—is established or re-established.

Methods

Also inherits methods from: EventTarget

close()

The RTCDataChannel.close() method closes the RTCDataChannel. Either peer is permitted to call this method to initiate closure of the channel.

send()

The send() method of the RTCDataChannel interface sends data across the data channel to the remote peer.

Events

bufferedamountlow

Sent to the channel's onbufferedamountlow event handler when the number of bytes of data in the outgoing data buffer falls below the value specified by bufferedAmountLowThreshold.

close

Sent to the onclose event handler when the underlying data transport closes.

error

Sent to the onerror event handler when an error occurs on the data channel.

message

Sent to the onmessage event handler when a message has been received from the remote peer. The message contents can be found in the event's data property.

open

Sent to the onopen event handler when the data channel is first opened, or when an existing data channel's underlying connection re-opens.

Data format

The underlying data format is defined by the IEEE draft specification draft-ietf-mmusic-sctp-sdp. The current format specifies its protocol as either "UDP/DTLS/SCTP" (UDP carrying DTLS carrying SCTP) or "TCP/DTLS/SCTP" (TCP carrying DTLS carrying SCTP). Older browsers may only specify "DTLS/SCTP".

Example

var pc = new RTCPeerConnection();
var dc = pc.createDataChannel("my channel");

dc.onmessage = function (event) {
  console.log("received: " + event.data);
};

dc.onopen = function () {
  console.log("datachannel open");
};

dc.onclose = function () {
  console.log("datachannel close");
};

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• WebRTC API