gotatun 0.5.0

an implementation of the WireGuard® protocol designed for portability and speed
Documentation 
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// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.
//
// This file incorporates work covered by the following copyright and
// permission notice:
//
//   Copyright (c) Mullvad VPN AB. All rights reserved.
//   Copyright (c) 2019 Cloudflare, Inc. All rights reserved.
//
// SPDX-License-Identifier: MPL-2.0

use std::time::Duration;

use nix::sys::time::TimeSpec;
use nix::time::{ClockId, clock_gettime};

#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos"))]
const CLOCK_ID: ClockId = ClockId::CLOCK_MONOTONIC;
#[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "tvos")))]
const CLOCK_ID: ClockId = ClockId::CLOCK_BOOTTIME;

#[derive(Clone, Copy, Debug)]
pub(crate) struct Instant {
    t: TimeSpec,
}

impl Instant {
    pub(crate) fn now() -> Self {
        // std::time::Instant unwraps as well, so feel safe doing so here
        let t = clock_gettime(CLOCK_ID).unwrap();
        Self { t }
    }

    pub(crate) fn checked_duration_since(&self, earlier: Instant) -> Option<Duration> {
        const NANOSECOND: nix::libc::c_long = 1_000_000_000;
        let (tv_sec, tv_nsec) = if self.t.tv_nsec() < earlier.t.tv_nsec() {
            (
                self.t.tv_sec() - earlier.t.tv_sec() - 1,
                self.t.tv_nsec() - earlier.t.tv_nsec() + NANOSECOND,
            )
        } else {
            (
                self.t.tv_sec() - earlier.t.tv_sec(),
                self.t.tv_nsec() - earlier.t.tv_nsec(),
            )
        };

        if tv_sec < 0 {
            None
        } else {
            Some(Duration::new(tv_sec as _, tv_nsec as _))
        }
    }
}