dope 0.4.3

The manifold runtime
Documentation 
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use std::ffi::CStr;
use std::io;

#[derive(Debug)]
pub struct Snapshot {
    pub syncookies: bool,
    pub max_syn_backlog: u32,
    pub somaxconn: u32,
    pub rlimit_nofile: u64,
}

impl Snapshot {
    pub fn detect() -> io::Result<Self> {
        let somaxconn = Self::sysctl_u32(c"kern.ipc.somaxconn")?;
        Ok(Self {
            syncookies: true,
            max_syn_backlog: somaxconn,
            somaxconn,
            rlimit_nofile: Self::read_rlimit()?,
        })
    }

    pub fn raise_nofile() -> io::Result<()> {
        let mut rlim = Self::rlimit()?;
        rlim.rlim_cur = rlim.rlim_max;
        // SAFETY: `rlim` is a valid rlimit with cur set to hard max.
        let rc = unsafe { libc::setrlimit(libc::RLIMIT_NOFILE, &rlim) };
        if rc != 0 {
            return Err(io::Error::last_os_error());
        }
        Ok(())
    }

    fn rlimit() -> io::Result<libc::rlimit> {
        let mut rlim = libc::rlimit {
            rlim_cur: 0,
            rlim_max: 0,
        };
        // SAFETY: `rlim` is a valid, writable rlimit for the duration of the call.
        let rc = unsafe { libc::getrlimit(libc::RLIMIT_NOFILE, &mut rlim) };
        if rc != 0 {
            return Err(io::Error::last_os_error());
        }
        Ok(rlim)
    }

    #[allow(clippy::unnecessary_cast)]
    fn read_rlimit() -> io::Result<u64> {
        Ok(Self::rlimit()?.rlim_max as u64)
    }

    fn sysctl_u32(name: &CStr) -> io::Result<u32> {
        let mut val: libc::c_int = 0;
        let mut len = std::mem::size_of::<libc::c_int>();
        // SAFETY: `name` is a valid C string; `val`/`len` are valid out-params sized for c_int.
        let rc = unsafe {
            libc::sysctlbyname(
                name.as_ptr(),
                (&mut val as *mut libc::c_int).cast(),
                &mut len,
                std::ptr::null_mut(),
                0,
            )
        };
        if rc != 0 {
            return Err(io::Error::last_os_error());
        }
        Ok(val.max(0) as u32)
    }
}

impl Snapshot {
    pub fn check(&self, cfg: &super::Config) -> Result<(), Mismatch> {
        let requested_slots = cfg.fixed_file_slots;
        if (requested_slots as u64) > self.rlimit_nofile {
            return Err(Mismatch::NoFileTooLow {
                requested: requested_slots,
                rlimit: self.rlimit_nofile,
            });
        }
        if !self.syncookies && self.max_syn_backlog < SYN_BACKLOG_FLOOR {
            return Err(Mismatch::SynFloodVulnerable {
                backlog: self.max_syn_backlog,
                expected: SYN_BACKLOG_FLOOR,
            });
        }
        if self.somaxconn < SOMAXCONN_FLOOR {
            return Err(Mismatch::SomaxconnTooLow {
                requested: SOMAXCONN_FLOOR,
                kernel: self.somaxconn,
            });
        }
        Ok(())
    }
}

const SYN_BACKLOG_FLOOR: u32 = 4096;
const SOMAXCONN_FLOOR: u32 = 4096;

#[derive(Debug)]
pub enum Mismatch {
    NoFileTooLow { requested: u32, rlimit: u64 },
    SomaxconnTooLow { requested: u32, kernel: u32 },
    SynFloodVulnerable { backlog: u32, expected: u32 },
}

impl std::fmt::Display for Mismatch {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::NoFileTooLow { requested, rlimit } => write!(
                f,
                "RLIMIT_NOFILE hard cap ({rlimit}) below configured fixed_file_slots ({requested}); raise the rlimit or lower the slot count"
            ),
            Self::SomaxconnTooLow { requested, kernel } => write!(
                f,
                "kern.ipc.somaxconn ({kernel}) below required floor ({requested}); raise via sysctl -w kern.ipc.somaxconn={requested}"
            ),
            Self::SynFloodVulnerable { backlog, expected } => write!(
                f,
                "SYN-flood vulnerable: syncookies off and max_syn_backlog ({backlog}) below floor ({expected}); enable syncookies or raise the backlog"
            ),
        }
    }
}

impl std::error::Error for Mismatch {}

impl From<Mismatch> for io::Error {
    fn from(m: Mismatch) -> Self {
        io::Error::new(io::ErrorKind::InvalidInput, m.to_string())
    }
}