Menu
Open source
read
The read
method is used to read a chunk of the file into an Uint8Array buffer.
It resolves to either the number of bytes read during the operation, or null
if there was nothing more to read.
Parameters
Parameter | Type | Description |
---|---|---|
buffer | Uint8Array | The buffer to read the data into. |
Returns
A Promise resolving to the number of bytes read or null
if the end of the file has been reached.
Example
Reading a file
In the following example, we open a file and read it in chunks of 128 bytes until we reach the end of the file.
JavaScript
import { open, SeekMode } from 'k6/experimental/fs';
let file;
(async function () {
file = await open('bonjour.txt');
})();
export default async function () {
const buffer = new Uint8Array(128);
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;
}
}
// Seek back to the beginning of the file
await file.seek(0, SeekMode.Start);
}
readAll
helper function
The following helper function can be used to read the entire contents of a file into a Uint8Array buffer.
JavaScript
import { open, SeekMode } from 'k6/experimental/fs';
let file;
(async function () {
file = await open('bonjour.txt');
})();
async function readAll(file) {
const fileInfo = await file.stat();
const buffer = new Uint8Array(fileInfo.size);
const bytesRead = await file.read(buffer);
if (bytesRead !== fileInfo.size) {
throw new Error(
'unexpected number of bytes read; expected ' +
fileInfo.size +
' but got ' +
bytesRead +
' bytes'
);
}
return buffer;
}
export default async function () {
// Read the whole file
const fileContent = await readAll(file);
console.log(JSON.stringify(fileContent));
// Seek back to the beginning of the file
await file.seek(0, SeekMode.Start);
}
Was this page helpful?
Related documentation
Related resources from Grafana Labs
Additional helpful documentation, links, and articles:
Video
Performance testing and observability in Grafana Cloud
In this webinar, learn how Grafana Cloud k6 offers you the best developer experience for performance testing.
User-centered observability: load testing, real user monitoring, and synthetics
Learn how to use load testing, synthetic monitoring, and real user monitoring (RUM) to understand end users' experience of your apps. Watch on demand.