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read

Mon, 21 Sep 2026 15:16:28 +0000

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.

import { open, SeekMode } from 'k6/experimental/fs';

const file = await open('bonjour.txt');

export default async function () {
  // Seek to the beginning of the file
  await file.seek(0, SeekMode.Start);

  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;
    }
  }
}

`readAll` helper function

The following helper function can be used to read the entire contents of a file into a Uint8Array buffer.

import { open, SeekMode } from 'k6/experimental/fs';

let file;
(async function () {
  file = await open('bonjour.txt');
})();

async function readAll(file) {
  // Seek to the beginning of the file
  await file.seek(0, SeekMode.Start);

  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

Mon, 21 Sep 2026 15:16:28 +0000

seek

The seek method sets the file position indicator for the file to the passed offset bytes, under the mode given by whence. The call resolves to the new position within the resource (bytes from the start).

Based on the SeekMode passed, the offset is interpreted as follows:

when using SeekMode.Start, the offset must be greater than or equal to zero.
when using SeekMode.Current, the offset can be positive or negative.
when using SeekMode.End, the offset must be less than or equal to zero.

Parameters

Parameter	Type	Description
offset	number	The offset in bytes from the position specified by `whence`.
whence	SeekMode	The position from which the offset is applied.

Returns

A Promise resolving to the new offset within the file.

Example

import { open, SeekMode } from 'k6/experimental/fs';

const file = await open('bonjour.txt');

export default async function () {
  // Seek 6 bytes from the start of the file
  await file.seek(6, SeekMode.Start);

  // Seek 2 more bytes from the current position
  await file.seek(2, SeekMode.Current);

  // Seek backwards 2 bytes from the end of the file
  await file.seek(-2, SeekMode.End);
}

stat

Mon, 21 Sep 2026 15:16:28 +0000

stat

The stat method returns a promise resolving to a FileInfo object with information about the file.

Returns

A Promise resolving to a FileInfo object with information about the file.

Examples

import { open, SeekMode } from 'k6/experimental/fs';

const 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');
  }

  console.log(JSON.stringify(fileinfo));
}

File on Grafana Labs

read

read

Parameters

Returns

Example

Reading a file

readAll helper function

seek

seek

Parameters

Returns

Example

stat

stat

Returns

Examples

`readAll` helper function