api/stream: add Estimated-Content-Length header to tunnels

present where Content-Length cannot be accurately calculated,
pure proxy streams do not have this header and instead have
the accurate Content-Length one.

api/src/stream/internal-hls.js

@@ -1,5 +1,6 @@
 import HLS from "hls-parser";
 import { createInternalStream } from "./manage.js";
+import { request } from "undici";
 
 function getURL(url) {
     try {
@@ -74,3 +75,59 @@ export async function handleHlsPlaylist(streamInfo, req, res) {
 
     res.send(hlsPlaylist);
 }
+
+async function getSegmentSize(url, config) {
+    const segmentResponse = await request(url, {
+        ...config,
+        throwOnError: true
+    });
+
+    if (segmentResponse.headers['content-length']) {
+        segmentResponse.body.dump();
+        return +segmentResponse.headers['content-length'];
+    }
+
+    // if the response does not have a content-length
+    // header, we have to compute it ourselves
+    let size = 0;
+
+    for await (const data of segmentResponse.body) {
+        size += data.length;
+    }
+
+    return size;
+}
+
+export async function probeInternalHLSTunnel(streamInfo) {
+    const { url, headers, dispatcher, signal } = streamInfo;
+
+    // remove all falsy headers
+    Object.keys(headers).forEach(key => {
+        if (!headers[key]) delete headers[key];
+    });
+
+    const config = { headers, dispatcher, signal, maxRedirections: 16 };
+
+    const manifestResponse = await fetch(url, config);
+
+    const manifest = HLS.parse(await manifestResponse.text());
+    if (manifest.segments.length === 0)
+        return -1;
+
+    const segmentSamples = await Promise.all(
+        Array(5).fill().map(async () => {
+            const manifestIdx = Math.floor(Math.random() * manifest.segments.length);
+            const randomSegment = manifest.segments[manifestIdx];
+            if (!randomSegment.uri)
+                throw "segment is missing URI";
+
+            const segmentSize = await getSegmentSize(randomSegment.uri, config) / randomSegment.duration;
+            return segmentSize;
+        })
+    );
+
+    const averageBitrate = segmentSamples.reduce((a, b) => a + b) / segmentSamples.length;
+    const totalDuration = manifest.segments.reduce((acc, segment) => acc + segment.duration, 0);
+
+    return averageBitrate * totalDuration;
+}