loled/static/js/grab-canvas.js

(async () => {
    const globalConnnection = Symbol("grab-canvas-connection")

    const currentScriptSrc = document.currentScript.src;
    const sourceElt = document.querySelector("canvas,video");

    if(!sourceElt){
        console.error("No canvas found on this page")
    }

    const conn = new RTCPeerConnection({
        iceServers: [
            {urls: ["stun:stun.nextcloud.com:443"]}
        ]
    });

    const iceCandidates = []
    conn.addEventListener("icecandidate", e => {
        iceCandidates.push(e.candidate)
    })

    const allCandidatesCollected = new Promise(res => 
        conn.addEventListener("icecandidate", e => e.candidate == null && res() ))

    let captureFn = sourceElt.captureStream;
    if(!captureFn){
        captureFn = sourceElt.mozCaptureStream;
    }

    const canvasStream = captureFn()
    const canvasStreamTracks = canvasStream.getVideoTracks()
    if(canvasStreamTracks.length > 0){
        conn.addTrack(canvasStreamTracks[0], canvasStream)
    }

    const offer = await conn.createOffer();
    await conn.setLocalDescription(offer);

    await allCandidatesCollected

    const res = await fetch(new URL("/_loled/grab-display", currentScriptSrc), {
        method: "POST",
        headers: { "content-type": "application/json" },
        body: JSON.stringify({
            offer,
            iceCandidates
        })
    })
    const response = new RTCSessionDescription(await res.json());
    conn.setRemoteDescription(response);

    window[globalConnnection] = conn
})()