// Copyright 2016-2020 Parity Technologies (UK) Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/// Outcome of raising file descriptor resource limit
pub enum Outcome {
    /// Limit was raised successfully
    LimitRaised {
        /// Previous limit (likely soft limit)
        from: u64,
        /// New limit (likely hard limit)
        to: u64,
    },
    /// Raising limit is not supported on this platform
    Unsupported,
}

/// Errors that happen when trying to raise file descriptor resource limit
#[derive(Debug, thiserror::Error)]
pub enum Error {
    /// Failed to call sysctl to get max supported value configured in sysctl
    #[error("Failed to call sysctl to get max supported value configured in sysctl: {0}")]
    #[cfg(any(target_os = "macos", target_os = "ios"))]
    FailedToCallSysctl(std::io::Error),
    /// Failed to get current limit
    #[error("Failed to get current limit: {0}")]
    FailedToGetLimit(std::io::Error),
    /// Failed to set new limit
    #[error("Failed to set new limit ({from}->{to}): {error}")]
    FailedToSetLimit {
        /// Current limit
        from: u64,
        /// New desired limit
        to: u64,
        /// Low level OS error
        error: std::io::Error,
    },
}

/// Raise the soft open file descriptor resource limit to the smaller of the
/// kernel limit and the hard resource limit.
///
/// darwin_fd_limit exists to work around an issue where launchctl on Mac OS X
/// defaults the rlimit maxfiles to 256/unlimited. The default soft limit of 256
/// ends up being far too low for our multithreaded scheduler testing, depending
/// on the number of cores available.
#[cfg(any(target_os = "macos", target_os = "ios"))]
#[allow(clippy::useless_conversion, non_camel_case_types)]
pub fn raise_fd_limit() -> Result<Outcome, Error> {
    use std::cmp;
    use std::io;
    use std::mem::size_of_val;
    use std::ptr::null_mut;

    unsafe {
        static CTL_KERN: libc::c_int = 1;
        static KERN_MAXFILESPERPROC: libc::c_int = 29;

        // The strategy here is to fetch the current resource limits, read the
        // kern.maxfilesperproc sysctl value, and bump the soft resource limit for
        // maxfiles up to the sysctl value.

        // Fetch the kern.maxfilesperproc value
        let mut mib: [libc::c_int; 2] = [CTL_KERN, KERN_MAXFILESPERPROC];
        let mut maxfiles: libc::c_int = 0;
        let mut size: libc::size_t = size_of_val(&maxfiles) as libc::size_t;
        if libc::sysctl(
            &mut mib[0],
            2,
            &mut maxfiles as *mut _ as *mut _,
            &mut size,
            null_mut(),
            0,
        ) != 0
        {
            return Err(Error::FailedToCallSysctl(io::Error::last_os_error()));
        }

        // Fetch the current resource limits
        let mut rlim = libc::rlimit {
            rlim_cur: 0,
            rlim_max: 0,
        };
        if libc::getrlimit(libc::RLIMIT_NOFILE, &mut rlim) != 0 {
            return Err(Error::FailedToGetLimit(io::Error::last_os_error()));
        }

        let old_value = rlim.rlim_cur;

        // Bump the soft limit to the smaller of kern.maxfilesperproc and the hard
        // limit
        rlim.rlim_cur = cmp::min(maxfiles as libc::rlim_t, rlim.rlim_max);

        // Set our newly-increased resource limit
        if libc::setrlimit(libc::RLIMIT_NOFILE, &rlim) != 0 {
            return Err(Error::FailedToSetLimit {
                from: old_value.into(),
                to: rlim.rlim_cur.into(),
                error: io::Error::last_os_error(),
            });
        }

        Ok(Outcome::LimitRaised {
            from: old_value.into(),
            to: rlim.rlim_cur.into(),
        })
    }
}

/// Raise the soft open file descriptor resource limit to the hard resource
/// limit.
#[cfg(target_os = "linux")]
#[allow(clippy::useless_conversion, non_camel_case_types)]
pub fn raise_fd_limit() -> Result<Outcome, Error> {
    use std::io;

    unsafe {
        // Fetch the current resource limits
        let mut rlim = libc::rlimit {
            rlim_cur: 0,
            rlim_max: 0,
        };
        if libc::getrlimit(libc::RLIMIT_NOFILE, &mut rlim) != 0 {
            return Err(Error::FailedToGetLimit(io::Error::last_os_error()));
        }

        let old_value = rlim.rlim_cur;

        // Set soft limit to hard imit
        rlim.rlim_cur = rlim.rlim_max;

        // Set our newly-increased resource limit
        if libc::setrlimit(libc::RLIMIT_NOFILE, &rlim) != 0 {
            return Err(Error::FailedToSetLimit {
                from: old_value.into(),
                to: rlim.rlim_cur.into(),
                error: io::Error::last_os_error(),
            });
        }

        Ok(Outcome::LimitRaised {
            from: old_value.into(),
            to: rlim.rlim_cur.into(),
        })
    }
}

/// Does nothing on unsupported platform
#[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "linux")))]
pub fn raise_fd_limit() -> Result<Outcome, Error> {
    Ok(Outcome::Unsupported)
}
