Update example using the read and seek methods

examples/experimental/fs/fs.js

@@ -1,20 +1,52 @@
-import { open } from "k6/experimental/fs";
+import { open, SeekMode } from "k6/experimental/fs";
 
 export const options = {
 	vus: 100,
 	iterations: 1000,
 };
 
-// As k6 does not support asynchronous code in the init context, yet, we need to
-// use a top-level async function to be able to use the `await` keyword.
+// k6 doesn't support async in the init context. We use a top-level async function for `await`.
+//
+// Each Virtual User gets its own `file` copy.
+// So, operations like `seek` or `read` won't impact other VUs.
 let file;
 (async function () {
 	file = await open("bonjour.txt");
 })();
 
 export default async function () {
+	// About information about the file
 	const fileinfo = await file.stat();
 	if (fileinfo.name != "bonjour.txt") {
 		throw new Error("Unexpected file name");
 	}
+
+	const buffer = new Uint8Array(4);
+
+	let totalBytesRead = 0;
+	while (true) {
+		// Read into the buffer
+		const bytesRead = await file.read(buffer);
+		if (bytesRead == null) {
+			// EOF
+			break;
+		}
+
+		// Do something useful with the content of the buffer
+
+		totalBytesRead += bytesRead;
+
+		// If bytesRead is less than the buffer size, we've read the whole file
+		if (bytesRead < buffer.byteLength) {
+			break;
+		}
+	}
+
+	// Check that we read the expected number of bytes
+	if (totalBytesRead != fileinfo.size) {
+		throw new Error("Unexpected number of bytes read");
+	}
+
+	// Seek back to the beginning of the file
+	await file.seek(0, SeekMode.Start);
 }