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//! Provides safe access to the `getifaddrs` libc function.

extern crate errno;
extern crate libc;

use std::mem;
use std::net::*;
use std::os::raw::*;
use std::ptr;

/// A single configured address.
///
/// Mostly analogous to `struct ifaddrs` from libc, with some field omitted or renamed.
pub struct IfAddr {
    /// Name of the interface the address is configured on. The name need not be valid UTF-8 and is
    /// thus handled as pure binary data.
    pub name: Vec<u8>,
    /// Interface flags.
    pub flags: u32,
    /// Configured address. May be `None` if no address is configured or the configured address is
    /// not IPv4 or IPv6.
    pub address: Option<IpAddr>,
    /// Configured netmask. May be `None` if no address is configured or the configured address is
    /// not IPv4 or IPv6.
    pub netmask: Option<IpAddr>,
    /// Configured broadcast address or destination address (depending on flags). May be `None` if
    /// no address is configured or the configured address is not IPv4 or IPv6. Corresponds to
    /// `ifa_broadaddr` and `ifa_dstaddr` in `struct ifaddrs`.
    pub broadcast_or_dest: Option<IpAddr>,
    /// Index of the interface as determined by `if_nametoindex`.
    pub index: u32,
}

struct IfaddrHandle<'a> {
    addrs: &'a mut libc::ifaddrs,
    cur: Option<&'a libc::ifaddrs>,
}

impl<'a> IfaddrHandle<'a> {
    fn new() -> Result<IfaddrHandle<'a>, errno::Errno> {
        let mut addrs: *mut libc::ifaddrs = unsafe { mem::uninitialized() };
        match unsafe { libc::getifaddrs(&mut addrs as *mut *mut libc::ifaddrs) } {
            0 => Ok(IfaddrHandle{addrs: unsafe { &mut *addrs }, cur: Some(unsafe { &*addrs })}),
            _ => Err(errno::errno()),
        }
    }
}

impl<'a> Drop for IfaddrHandle<'a> {
    fn drop(&mut self) {
        unsafe { libc::freeifaddrs(self.addrs) }
    }
}

impl<'a> Iterator for IfaddrHandle<'a> {
    type Item = &'a libc::ifaddrs;

    fn next(&mut self) -> Option<Self::Item> {
        match self.cur {
            None => None,
            Some(addr) => {
                match addr.ifa_next as usize {
                    0 => self.cur = None,
                    _ => self.cur = Some(unsafe { &*addr.ifa_next }),
                }
                Some(addr)
            }
        }
    }
}

fn get_v4(addr: &libc::sockaddr_in) -> IpAddr {
    let raw = u32::from_be(addr.sin_addr.s_addr);
    IpAddr::V4(Ipv4Addr::new((raw >> 24) as u8, (raw >> 16) as u8, (raw >> 8) as u8, raw as u8))
}

fn get_v6(addr: &libc::sockaddr_in6) -> IpAddr {
    let addr = &addr.sin6_addr.s6_addr;
    IpAddr::V6(
        Ipv6Addr::new(
            (addr[0] as u16) << 8 | (addr[1] as u16), (addr[2] as u16) << 8 | (addr[3] as u16),
            (addr[4] as u16) << 8 | (addr[5] as u16), (addr[6] as u16) << 8 | (addr[7] as u16),
            (addr[8] as u16) << 8 | (addr[9] as u16), (addr[10] as u16) << 8 | (addr[11] as u16),
            (addr[12] as u16) << 8 | (addr[13] as u16), (addr[14] as u16) << 8 | (addr[15] as u16)))
}

fn get_addr(addr: *const libc::sockaddr) -> Option<IpAddr> {
    match addr as usize {
        0 => None,
        _ => {
            let addr = unsafe { &*addr };
            match addr.sa_family as c_int {
                libc::AF_INET => Some(get_v4(unsafe { mem::transmute(addr) })),
                libc::AF_INET6 => Some(get_v6(unsafe { mem::transmute(addr) })),
                _ => None,
            }
        }
    }
}

fn copy_name(name: *const c_char) -> Vec<u8> {
    unsafe {
        let len = libc::strlen(name);
        let mut result = Vec::with_capacity(len);
        result.set_len(len);
        ptr::copy(name, result.as_mut_ptr() as *mut c_char, len);
        result
    }
}

/// Lists available interfaces, their IP addresses and coresponding interface indexes.
///
/// The interface indexes are valid is `scope_id` values for IPv6 addresses.
///
/// # Examples
///
/// ```
/// let lo = getifaddrs::getifaddrs().unwrap().into_iter().filter(|i| { i.index == 1 });
/// ```
pub fn getifaddrs() -> Result<Vec<IfAddr>, errno::Errno> {
    IfaddrHandle::new().and_then(|addrs| {
        let mut result = Vec::new();

        for ifaddr in addrs {
            let index = match unsafe { libc::if_nametoindex(ifaddr.ifa_name) } {
                0 => return Err(errno::errno()),
                i => i,
            };

            result.push(IfAddr{
                flags: ifaddr.ifa_flags,
                name: copy_name(ifaddr.ifa_name),
                address: get_addr(ifaddr.ifa_addr),
                netmask: get_addr(ifaddr.ifa_netmask),
                broadcast_or_dest: get_addr(ifaddr.ifa_ifu),
                index: index,
            });
        }

        Ok(result)
    })
}

#[cfg(test)]
mod tests {
    use std::net;

    #[test]
    fn lo_exists() {
        let addrs = ::getifaddrs().unwrap();

        assert!(addrs.into_iter().filter(|i| {
            i.index == 1 &&
                i.address.unwrap_or(net::IpAddr::V4(net::Ipv4Addr::new(0, 0, 0, 0))).is_loopback()
        }).count() > 0);
    }
}