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/manage.js

@@ -72,6 +72,16 @@ export function getInternalTunnel(id) {
     return internalStreamCache.get(id);
 }
 
+export function getInternalTunnelFromURL(url) {
+    url = new URL(url);
+    if (url.hostname !== '127.0.0.1') {
+        return;
+    }
+
+    const id = url.searchParams.get('id');
+    return getInternalTunnel(id);
+}
+
 export function createInternalStream(url, obj = {}) {
     assert(typeof url === 'string');