/**
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* Performs the actual SDP exchange.
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*
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* 1. Constructs the client's SDP offer
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* 2. Sends the SDP offer to the server,
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* 3. Awaits the server's offer.
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*
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* SDP describes what kind of media we can send and how the server and client communicate.
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*
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* https://developer.mozilla.org/en-US/docs/Glossary/SDP
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* https://www.ietf.org/archive/id/draft-ietf-wish-whip-01.html#name-protocol-operation
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*/
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export default async function negotiateConnectionWithClientOffer(
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peerConnection,
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endpoint
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) {
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/** https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/createOffer */
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const offer = await peerConnection.createOffer();
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/** https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/setLocalDescription */
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await peerConnection.setLocalDescription(offer);
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/** Wait for ICE gathering to complete */
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let ofr = await waitToCompleteICEGathering(peerConnection);
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if (!ofr) {
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throw Error("failed to gather ICE candidates for offer");
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}
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/**
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* As long as the connection is open, attempt to...
|
*/
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while (peerConnection.connectionState !== "closed") {
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/**
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* This response contains the server's SDP offer.
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* This specifies how the client should communicate,
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* and what kind of media client and server have negotiated to exchange.
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*/
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let response = await postSDPOffer(endpoint, ofr.sdp);
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if (response.status === 201) {
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let answerSDP = await response.text();
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await peerConnection.setRemoteDescription(
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new RTCSessionDescription({ type: "answer", sdp: answerSDP })
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);
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return response.headers.get("Location");
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} else if (response.status === 405) {
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console.error("Update the URL passed into the WHIP or WHEP client");
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} else {
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const errorMessage = await response.text();
|
console.error(errorMessage);
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}
|
/** Limit reconnection attempts to at-most once every 5 seconds */
|
await new Promise((r) => setTimeout(r, 5000));
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}
|
}
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async function postSDPOffer(endpoint, data) {
|
return await fetch(endpoint, {
|
method: "POST",
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mode: "cors",
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headers: {
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"content-type": "application/sdp",
|
},
|
body: data,
|
});
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}
|
/**
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* Receives an RTCPeerConnection and waits until
|
* the connection is initialized or a timeout passes.
|
*
|
* https://www.ietf.org/archive/id/draft-ietf-wish-whip-01.html#section-4.1
|
* https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/iceGatheringState
|
* https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/icegatheringstatechange_event
|
*/
|
async function waitToCompleteICEGathering(peerConnection) {
|
return new Promise((resolve) => {
|
/** Wait at most 1 second for ICE gathering. */
|
setTimeout(function () {
|
resolve(peerConnection.localDescription);
|
}, 1000);
|
peerConnection.onicegatheringstatechange = (ev) =>
|
peerConnection.iceGatheringState === "complete" &&
|
resolve(peerConnection.localDescription);
|
});
|
}
|
