// Copyright 2018 Developers of the Rand project.

//

// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or

// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license

// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your

// option. This file may not be copied, modified, or distributed

// except according to those terms.

//! Implementation for Linux / Android

use crate::{

    util::LazyBool,

    util_libc::{last_os_error, sys_fill_exact},

    {use_file, Error},

};

use core::mem::MaybeUninit;

pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {

    // getrandom(2) was introduced in Linux 3.17

    static HAS_GETRANDOM: LazyBool = LazyBool::new();

    if HAS_GETRANDOM.unsync_init(is_getrandom_available) {

        sys_fill_exact(dest, |buf| unsafe {

            getrandom(buf.as_mut_ptr() as *mut libc::c_void, buf.len(), 0)

        })

    } else {

        use_file::getrandom_inner(dest)

    }

}

fn is_getrandom_available() -> bool {

    let res = unsafe { getrandom(core::ptr::null_mut(), 0, libc::GRND_NONBLOCK) };

    if res < 0 {

        match last_os_error().raw_os_error() {

            Some(libc::ENOSYS) => false, // No kernel support

            Some(libc::EPERM) => false,  // Blocked by seccomp

            _ => true,

        }

    } else {

        true

    }

}

unsafe fn getrandom(

    buf: *mut libc::c_void,

    buflen: libc::size_t,

    flags: libc::c_uint,

) -> libc::ssize_t {

    libc::syscall(libc::SYS_getrandom, buf, buflen, flags) as libc::ssize_t

}