feat: implement latency measurement for resource fetching

src/lib/index.ts

@@ -14,12 +14,20 @@ export async function bandwidthTest(
 	onProgress: BandwidthCallback,
 	onLatency: (latency: number) => void
 ) {
-	performance.setResourceTimingBufferSize(100);
-	performance.clearResourceTimings();
-	// start timer
-	const startTime = performance.now();
-	const url = 'https://cdn-test-cloudfront.hf.co/5gb.safetensors';
-	// const url = 'https://cdn-test-cloudfront.hf.co/15mb.json';
+	// performance.setResourceTimingBufferSize(100);
+	// performance.clearResourceTimings();
+	// const url = 'https://cdn-test-cloudfront.hf.co/5gb.safetensors';
+	const url = 'https://cdn-test-cloudfront.hf.co/15mb.json';
+	// first HEAD to get latency
+	let startTime = performance.now();
+	const latencyResponse = await fetch(url, { method: 'HEAD' });
+	if (!latencyResponse.ok) {
+		throw new Error(`Network response was not ok: ${latencyResponse.status}`);
+	}
+	const latency = performance.now() - startTime;
+	onLatency(latency);
+
+	startTime = performance.now();
 	const response = await fetch(url);
 	if (!response.ok) {
 		throw new Error(`Network response was not ok: ${response.status}`);
@@ -35,8 +43,6 @@ export async function bandwidthTest(
 	// 	const latency = responseStart - requestStart;
 	// 	onLatency(latency);
 	// }, 2000);
-	const latency = performance.now() - startTime;
-	onLatency(latency);
 	const contentLengthHeader = response.headers.get('content-length');
 	const totalBytes = contentLengthHeader ? parseInt(contentLengthHeader, 10) : 1e99;
 	const reader = response.body.getReader();