Function useProxyLatency

site/src/contexts/useProxyLatency.ts:43–253

(
	proxies?: readonly Region[],
)

};

export const useProxyLatency = (
	proxies?: readonly Region[],
): {
	// Refetch can be called to refetch the proxy latencies.
	// Until the new values are loaded, the old values will still be used.
	refetch: () => Date;
	proxyLatencies: Record<string, ProxyLatencyReport>;
	// loaded signals all latency requests have completed. Once set to true, this will not change.
	// Latencies at this point should be loaded from local storage, and updated asynchronously as needed.
	// If local storage has updated latencies, then this will be set to true with 0 actual network requests.
	// The loaded latencies will all be from the cache.
	loaded: boolean;
} => {
	// maxStoredLatencies is the maximum number of latencies to store per proxy in local storage.
	let maxStoredLatencies = 1;
	// The reason we pull this from local storage is so for development purposes, a user can manually
	// set a larger number to collect data in their normal usage. This data can later be analyzed to come up
	// with some better magic numbers.
	const maxStoredLatenciesVar = localStorage.getItem(
		"workspace-proxy-latencies-max",
	);
	if (maxStoredLatenciesVar) {
		maxStoredLatencies = Number(maxStoredLatenciesVar);
	}

	const [proxyLatencies, dispatchProxyLatencies] = useReducer(
		proxyLatenciesReducer,
		{},
	);

	// This latestFetchRequest is used to trigger a refetch of the proxy latencies.
	const [latestFetchRequest, setLatestFetchRequest] = useState(
		// The initial state is the current time minus the interval. Any proxies that have a latency after this
		// in the cache are still valid.
		new Date(Date.now() - proxyIntervalSeconds * 1000).toISOString(),
	);

	const [loaded, setLoaded] = useState(false);

	// Refetch will always set the latestFetchRequest to the current time, making all the cached latencies
	// stale and triggering a refetch of all proxies in the list.
	const refetch = () => {
		const d = new Date();
		setLatestFetchRequest(d.toISOString());
		return d;
	};

	// Only run latency updates when the proxies change.
	useEffect(() => {
		if (!proxies) {
			return;
		}

		const storedLatencies = loadStoredLatencies();

		// proxyMap is a map of the proxy path_app_url to the proxy object.
		// This is for the observer to know which requests are important to
		// record.