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';

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.

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);
}