Document rand module

//! Cryptographically strong random bytes.

//!

//! This module exposes functionality to put cryptographically strong

//! pseudo-random bytes into a buffer.

//!

//! # Examples

//!

//! To generate a buffer with cryptographically strong bytes:

//!

//! ```

//! let muf buf = [0; 256]

//! rand_bytes(&mut buf).unwrap();

//! ```

//!

//! # External OpenSSL Documentation

//!

//! [RAND_bytes](https://www.openssl.org/docs/man1.1.0/crypto/RAND_bytes.html)

use libc::c_int;

use ffi;

use cvt;

use error::ErrorStack;

/// Fills buffer with cryptographically strong pseudo-random bytes.

pub fn rand_bytes(buf: &mut [u8]) -> Result<(), ErrorStack> {

    unsafe {

        ffi::init();