RTCIceCandidate.candidate

The read-only property candidate on the RTCIceCandidate interface returns a DOMString describing the candidate in detail. Most of the other properties of RTCIceCandidate are actually extracted from this string.

This property can be configured using the candidate property of the object passed into the RTCIceCandidate() constructor or RTCPeerConnection.addIceCandidate().

A DOMString describing the properties of the candidate, taken directly from the SDP attribute "candidate". The candidate string specifies the network connectivity information for the candidate. If the candidate is an empty string (""), the end of the candidate list has been reached; this candidate is known as the "end-of-candidates" marker.

The syntax of the candidate string is described in RFC 5245, section 15.1. For an a-line (attribute line) that looks like this:

a=candidate:4234997325 1 udp 2043278322 192.168.0.56 44323 typ host

the corresponding candidate string's value will be: "candidate:4234997325 1 udp 2043278322 192.168.0.56 44323 typ host".

The user agent always prefers candidates with the highest priority, all else being equal. In the example above, the priority is 2043278322. The attributes are all separated by a single space character, and are in a specific order. The complete list of attributes for this example candidate is:

• foundation = 4234997325
• component = "rtp" (the number 1 is encoded to this string; 2 becomes "rtcp")
• protocol = "udp"
• priority = 2043278322
• ip = "192.168.0.56"
• port = 44323
• type = "host"

In this example, we see a function which receives as input an SDP string containing an ICE candidate received from the remote peer during the signaling process.

function handleNewIceCandidate(candidateSDP) {
  var candidateObj = new RTCIceCandidate(candidateSDP);

  myPeerConnection.addIceCandidate(candidateObj).catch({
    /* handle the error thrown by addIceCandidate() */
  });
}

The handleNewIceCandidate() function shown here passes the received candidate's SDP text into RTCIceCandidate() to receive an RTCIceCandidate object in return, which represents the candidate.

The new candidate is then passed into RTCPeerConnection.addIceCandidate() to add the candidate to the list of candidates for WebRTC to consider using for the connection being established.

This example could be simplified somewhat; you may more often see the code look something like this, taking advantage of more advanced ECMAScript 2016 features:

let handleNewIceCandidate = candidateSDP =>
  myPeerConnection.addIceCandidate(new RTCIceCandidate(candidateSDP));