jellyfin-media-player/native/find-webclient.js

async function tryConnect(server) {
    document.getElementById('connect-button').disabled = true;

    try {
        if (!server.startsWith("http")) {
            server = "http://" + server;
        }

        const url = new URL("/System/Info/Public", server);
        const response = await fetch(url);
        if (response.ok && (await response.json()).Id) {
            const htmlResponse = await fetch(server);
            if (!htmlResponse.ok) {
                throw new Error("Status not ok");
            }

            if (response.headers.get("content-security-policy")) {
                // Sigh... If we just navigate to the URL, the server's CSP will block us loading other resources.
                // So we have to parse the HTML, set a new base href, and then write it back to the page.
                // We also have to override the history functions to make sure they use the correct URL.
                console.log("Using CSP workaround");
                const webUrl = htmlResponse.url.replace(/\/[^\/]*$/, "/");
                const realUrl = window.location.href;

                const html = await htmlResponse.text();
                const parser = new DOMParser();
                const doc = parser.parseFromString(html, "text/html");
                const base = doc.createElement("base");
                base.href = webUrl
                doc.head.insertBefore(base, doc.head.firstChild);
                
                const oldPushState = window.history.pushState;
                window.history.pushState = function(state, title, url) {
                    url = (new URL(url, realUrl)).toString();
                    return oldPushState.call(window.history, state, title, url);
                };

                const oldReplaceState = window.history.replaceState;
                window.history.replaceState = function(state, title, url) {
                    url = (new URL(url, realUrl)).toString();
                    return oldReplaceState.call(window.history, state, title, url);
                };

                document.open();
                document.write((new XMLSerializer()).serializeToString(doc));
                document.close();
            } else {
                console.log("Using normal navigation");
                window.location = server;
            }

            await window.initCompleted;
            window.jmpInfo.settings.main.userWebClient = server;

            return true;
        }
    } catch (e) {
        console.error(e);
        document.getElementById('connect-button').disabled = false;
        return false;
    }
}

document.getElementById('connect-form').addEventListener('submit', async (e) => {
    e.preventDefault();
    const server = document.getElementById('address').value;
    const result = await tryConnect(server);
    if (!result) {
        document.getElementById('backdrop').style.display = 'block';
    }
});

document.getElementById('connect-fail-button').addEventListener('click', () => {
    document.getElementById('backdrop').style.display = 'none';
});


// load the server if we have one
(async() => {
    const savedServer = window.jmpInfo.settings.main.userWebClient;

    if (!savedServer || !(await tryConnect(savedServer))) {
        document.getElementById('splash').style.display = 'none';
        document.getElementById('main').style.display = 'block';
    }
})();