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open( filePath, [mode] )

Opens a file, reading all its contents into memory for use in the script.

Caution

open() can only be called from the init context. This restriction is necessary to determine the local files needed to bundle when distributing the test across multiple nodes.

Note

open() often consumes a large amount of memory because every VU keeps a separate copy of the file in memory.

To reduce the memory consumption, you can:

  • Use open() within a SharedArray, which shares the allocated file memory between VUs.
  • Use open() from the k6/experimental/fs module. It provides a memory-efficient way to handle file interactions in your test script and can read files in small chunks.
ParameterTypeDescription
filePathstringThe path to the file, absolute or relative, that will be read into memory. The file will only be loaded once, even when running with several VUs.
modestringBy default, the contents of the file are read as text, but if you specify b, the file will be read as binary data instead.

Returns

TypeDescription
string / ArrayBufferThe contents of the file, returned as string or ArrayBuffer (if b was specified as the mode).

Examples

json 
[
  {
    "username": "user1",
    "password": "password1"
  },
  {
    "username": "user2",
    "password": "password2"
  },
  {
    "username": "user3",
    "password": "password3"
  }
]
JavaScript 
import { SharedArray } from 'k6/data';
import { sleep } from 'k6';

const data = new SharedArray('users', function () {
  // here you can open files, and then do additional processing or generate the array with data dynamically
  const f = JSON.parse(open('./users.json'));
  return f; // f must be an array[]
});

export default () => {
  const randomUser = data[Math.floor(Math.random() * data.length)];
  console.log(`${randomUser.username}, ${randomUser.password}`);
  sleep(3);
};
JavaScript 
import { sleep } from 'k6';

const users = JSON.parse(open('./users.json')); // consider using SharedArray for large files

export default function () {
  const user = users[__VU - 1];
  console.log(`${user.username}, ${user.password}`);
  sleep(3);
}
JavaScript 
import http from 'k6/http';
import { sleep } from 'k6';

const binFile = open('/path/to/file.bin', 'b');

export default function () {
  const data = {
    field: 'this is a standard form field',
    file: http.file(binFile, 'test.bin'),
  };
  const res = http.post('https://example.com/upload', data);
  sleep(3);
}