web telegram save cached video

download_telegram_cache_video.js

// web telegram stream video from cache
// it probably uses shared/webworkers to save bytes chunks into cache storage
// so once video is fully cached it could be saved from cache to device
// browser could ask to allow parallel files downloads from web telegram domain, just allow it

(async function downloadCachedVideos() {
    // global downloaded set is to prevent downloading videos were alreadt downloaded 
    window.downloaded = window.downloaded || new Set([])
    function saveVideo(outname, dataArray) {
        console.log(`Start downloading ${outname} with ${dataArray.length} chunks`)
        var blob = new Blob(dataArray, {type: "video/mp4"});
        var link = document.createElement('a');
        link.href = URL.createObjectURL(blob);
        var fileName = outname;
        link.download = fileName;
        link.click();
        URL.revokeObjectURL(link.href)
        delete link
    }

    const cache = await caches.open('cachedStreamChunks');
    const requests = await cache.keys();
    function getOffset(r) {
        return parseInt(new URL(r.url).searchParams.get('offset'), 10)
    }
    function getPathNum(r) {
        return new URL(r.url).pathname.slice(1)
    }
    requests.sort((a, b) => {
        const [oA, oB] = [getOffset(a), getOffset(b)]
        return oA < oB ? -1 : oA > oB ? 1 : 0;
    })
    /** @type {Object.<number, Blob>} */
    const bts = {};
    for (const req of requests) {
        const id = getPathNum(req)
        if (window.downloaded.has(String(id))) continue;
        bts[id] = bts[id] || []
        const response = await cache.match(req)
        if (!response) continue;
        bts[id].push(await response.blob())
    }
    for (const [id, blobsArray] of Object.entries(bts)) {
        window.downloaded.add(String(id))
        saveVideo(id+'.mp4',blobsArray)
    }
})()