Add download limit bar on file viewer

svelte/src/file_viewer/DownloadLimitStore.js

@@ -0,0 +1,62 @@
+import { readable } from 'svelte/store';
+
+let limits = {
+	download_limit: 0,
+	download_limit_used: 0,
+	transfer_limit: 0,
+	transfer_limit_used: 0,
+	ipv6_bonus: 0,
+	loaded: false,
+}
+
+export const download_limits = readable(
+	limits,
+	function start(set) {
+		set_func = set;
+		loop();
+
+		return function stop() {
+			clearTimeout(timeout_ref);
+		};
+	}
+);
+
+let set_func;
+let timeout_ref = 0;
+let timeout_ms = 10000;
+
+const loop = async () => {
+	let new_limits;
+	try {
+		let resp = await fetch(window.api_endpoint + "/misc/rate_limits")
+		if (resp.status >= 400) {
+			throw new Error(await resp.text())
+		}
+		new_limits = await resp.json()
+		new_limits.loaded = true
+	} catch (err) {
+		console.error("Failed to get rate limits: " + err)
+		timeout_ref = setTimeout(loop, 30000)
+		return
+	}
+
+	// If the usage has not changed we increase the timeout with one second. If
+	// it did change we halve the timeout
+	if (new_limits.transfer_limit_used === limits.transfer_limit_used) {
+		timeout_ms += 1000
+		if (timeout_ms > 60000) {
+			timeout_ms = 60000
+		}
+	} else {
+		timeout_ms /= 2
+		if (timeout_ms < 5000) {
+			timeout_ms = 5000
+		}
+
+		limits = new_limits
+		set_func(new_limits)
+	}
+
+	console.debug("Sleep", timeout_ms / 1000, "seconds")
+	timeout_ref = setTimeout(loop, timeout_ms)
+}