---
title: "random_get()"
description: "Fill a buffer with high-quality random data. This function may be slow and block."
url: "https://wasix.org/docs/api-reference/wasi/random_get/"
markdown: "https://wasix.org/docs/api-reference/wasi/random_get.md"
---

# `random_get()`

Fill a buffer with high-quality random data. This function may be slow and block.

## Description

The `random_get()` function is used to fill a buffer with high-quality random data. It takes a pointer to a buffer and the number of bytes to be written as input. The function will generate random bytes and write them to the specified buffer.

Generating high-quality random data may be a slow operation and may block in certain cases, especially when the system’s entropy pool is depleted. Therefore, this function should be used with caution in performance-sensitive scenarios.

## Syntax

```ebnf
  ;;; number generator, rather than to provide the random data directly.
  ;;; required, it's advisable to use this function to seed a pseudo-random
  ;;; This function may execute slowly, so when large mounts of random data are
  ;;; provide sufficient high-quality random data.
  ;;; This function blocks when the implementation is unable to immediately
  ;;; Write high-quality random data into a buffer.
  (@interface func (export "random_get")
    ;;; The buffer to fill with random data.
    (param $buf (@witx pointer u8))
    (param $buf_len $size)
    (result $error (expected (error $errno)))
  )
```

## Parameters

- `ctx`: The function environment.
- `buf`: A pointer to the buffer where the random bytes will be written.
- `buf_len`: The number of bytes to be written.

## Return Value

The function returns an `Errno` value indicating the result of the operation. If the operation is successful and the random data is generated and written to the buffer, it returns `Errno::Success`. If there is an error generating the random data, it returns `Errno::Io`.

## Logging

This function is instrumented with `trace` level logging. It includes the following field for debugging purposes:

- `buf_len`: The length of the buffer in bytes.

## Note

- The `random_get()` function fills a buffer with high-quality random data.
- It uses the `getrandom` crate to generate the random data.
- The function creates a `u8` buffer with the specified length and calls `getrandom::getrandom()` to generate random bytes.
- If the random data is generated successfully, it writes the data to the buffer specified by `buf`.
- The function returns `Errno::Success` if the operation is successful.
- If there is an error generating the random data, such as when the system’s entropy pool is depleted, it returns `Errno::Io`.

---

[Documentation index](https://wasix.org/llms.txt) · [HTML version](https://wasix.org/docs/api-reference/wasi/random_get/)