api: automatically pull youtube session tokens from a session server

if provided, cobalt will pull poToken & visitor_data from an instance of invidious' youtube-trusted-session-generator or its counterpart

api/src/processing/helpers/youtube-session.js

@@ -0,0 +1,74 @@
+import * as cluster from "../../misc/cluster.js";
+
+import { env } from "../../config.js";
+import { Green, Yellow } from "../../misc/console-text.js";
+
+let session;
+
+const validateSession = (sessionResponse) => {
+    if (!sessionResponse.potoken) {
+        throw "no poToken in session response";
+    }
+
+    if (!sessionResponse.visitor_data) {
+        throw "no visitor_data in session response";
+    }
+
+    if (!sessionResponse.updated) {
+        throw "no last update timestamp in session response";
+    }
+
+    // https://github.com/iv-org/youtube-trusted-session-generator/blob/c2dfe3f/potoken_generator/main.py#L25
+    if (sessionResponse.potoken.length < 160) {
+        console.error(`${Yellow('[!]')} poToken is too short and might not work (${new Date().toISOString()})`);
+    }
+}
+
+const updateSession = (newSession) => {
+    session = newSession;
+}
+
+const loadSession = async () => {
+    const sessionServerUrl = new URL(env.ytSessionServer);
+    sessionServerUrl.pathname = "/token";
+
+    const newSession = await fetch(sessionServerUrl).then(a => a.json());
+    validateSession(newSession);
+
+    if (!session || session.updated < newSession?.updated) {
+        cluster.broadcast({ youtube_session: newSession });
+        updateSession(newSession);
+    }
+}
+
+const wrapLoad = (initial = false) => {
+    loadSession()
+    .then(() => {
+        if (initial) {
+            console.log(`${Green('[✓]')} poToken & visitor_data loaded successfully!`);
+        }
+    })
+    .catch((e) => {
+        console.error(`${Yellow('[!]')} Failed loading poToken & visitor_data at ${new Date().toISOString()}.`);
+        console.error('Error:', e);
+    })
+}
+
+export const getYouTubeSession = () => {
+    return session;
+}
+
+export const setup = () => {
+    if (cluster.isPrimary) {
+        wrapLoad(true);
+        if (env.ytSessionReloadInterval > 0) {
+            setInterval(wrapLoad, env.ytSessionReloadInterval * 1000);
+        }
+    } else if (cluster.isWorker) {
+        process.on('message', (message) => {
+            if ('youtube_session' in message) {
+                updateSession(message.youtube_session);
+            }
+        });
+    }
+}