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.js

@@ -1,7 +1,7 @@
 import { request } from "undici";
 import { Readable } from "node:stream";
 import { closeRequest, getHeaders, pipe } from "./shared.js";
-import { handleHlsPlaylist, isHlsResponse } from "./internal-hls.js";
+import { handleHlsPlaylist, isHlsResponse, probeInternalHLSTunnel } from "./internal-hls.js";
 
 const CHUNK_SIZE = BigInt(8e6); // 8 MB
 const min = (a, b) => a < b ? a : b;
@@ -130,3 +130,40 @@ export function internalStream(streamInfo, res) {
 
     return handleGenericStream(streamInfo, res);
 }
+
+export async function probeInternalTunnel(streamInfo) {
+    try {
+        const signal = AbortSignal.timeout(3000);
+        const headers = {
+            ...Object.fromEntries(streamInfo.headers || []),
+            ...getHeaders(streamInfo.service),
+            host: undefined,
+            range: undefined
+        };
+
+        if (streamInfo.isHLS) {
+            return probeInternalHLSTunnel({
+                ...streamInfo,
+                signal,
+                headers
+            });
+        }
+
+        const response = await request(streamInfo.url, {
+            method: 'HEAD',
+            headers,
+            dispatcher: streamInfo.dispatcher,
+            signal,
+            maxRedirections: 16
+        });
+
+        if (response.statusCode !== 200)
+            throw "status is not 200 OK";
+
+        const size = +response.headers['content-length'];
+        if (isNaN(size))
+            throw "content-length is not a number";
+
+        return size;
+    } catch {}
+}