#[cfg(all(test, not(target_os = "emscripten")))]
mod tests;

use crate::cmp::Ordering;
use crate::fmt;
use crate::hash;
use crate::io::{self, Write};
use crate::iter;
use crate::mem;
use crate::net::{IpAddr, Ipv4Addr, Ipv6Addr};
use crate::option;
use crate::slice;
use crate::sys::net::netc as c;
use crate::sys_common::net::LookupHost;
use crate::sys_common::{FromInner, IntoInner};
use crate::vec;

/// An internet socket address, either IPv4 or IPv6.
///
/// Internet socket addresses consist of an [IP address], a 16-bit port number, as well
/// as possibly some version-dependent additional information. See [`SocketAddrV4`]'s and
/// [`SocketAddrV6`]'s respective documentation for more details.
///
/// The size of a `SocketAddr` instance may vary depending on the target operating
/// system.
///
/// [IP address]: IpAddr
///
/// # Examples
///
/// ```
/// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
///
/// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
///
/// assert_eq!("127.0.0.1:8080".parse(), Ok(socket));
/// assert_eq!(socket.port(), 8080);
/// assert_eq!(socket.is_ipv4(), true);
/// ```
#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
#[stable(feature = "rust1", since = "1.0.0")]
pub enum SocketAddr {
    /// An IPv4 socket address.
    #[stable(feature = "rust1", since = "1.0.0")]
    V4(#[stable(feature = "rust1", since = "1.0.0")] SocketAddrV4),
    /// An IPv6 socket address.
    #[stable(feature = "rust1", since = "1.0.0")]
    V6(#[stable(feature = "rust1", since = "1.0.0")] SocketAddrV6),
}

/// An IPv4 socket address.
///
/// IPv4 socket addresses consist of an [`IPv4` address] and a 16-bit port number, as
/// stated in [IETF RFC 793].
///
/// See [`SocketAddr`] for a type encompassing both IPv4 and IPv6 socket addresses.
///
/// The size of a `SocketAddrV4` struct may vary depending on the target operating
/// system. Do not assume that this type has the same memory layout as the underlying
/// system representation.
///
/// [IETF RFC 793]: https://tools.ietf.org/html/rfc793
/// [`IPv4` address]: Ipv4Addr
///
/// # Examples
///
/// ```
/// use std::net::{Ipv4Addr, SocketAddrV4};
///
/// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
///
/// assert_eq!("127.0.0.1:8080".parse(), Ok(socket));
/// assert_eq!(socket.ip(), &Ipv4Addr::new(127, 0, 0, 1));
/// assert_eq!(socket.port(), 8080);
/// ```
#[derive(Copy, Clone, Eq, PartialEq)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct SocketAddrV4 {
    ip: Ipv4Addr,
    port: u16,
}

/// An IPv6 socket address.
///
/// IPv6 socket addresses consist of an [`IPv6` address], a 16-bit port number, as well
/// as fields containing the traffic class, the flow label, and a scope identifier
/// (see [IETF RFC 2553, Section 3.3] for more details).
///
/// See [`SocketAddr`] for a type encompassing both IPv4 and IPv6 socket addresses.
///
/// The size of a `SocketAddrV6` struct may vary depending on the target operating
/// system. Do not assume that this type has the same memory layout as the underlying
/// system representation.
///
/// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
/// [`IPv6` address]: Ipv6Addr
///
/// # Examples
///
/// ```
/// use std::net::{Ipv6Addr, SocketAddrV6};
///
/// let socket = SocketAddrV6::new(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
///
/// assert_eq!("[2001:db8::1]:8080".parse(), Ok(socket));
/// assert_eq!(socket.ip(), &Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 1));
/// assert_eq!(socket.port(), 8080);
/// ```
#[derive(Copy, Clone, Eq, PartialEq)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct SocketAddrV6 {
    ip: Ipv6Addr,
    port: u16,
    flowinfo: u32,
    scope_id: u32,
}

impl SocketAddr {
    /// Creates a new socket address from an [IP address] and a port number.
    ///
    /// [IP address]: IpAddr
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
    ///
    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
    /// assert_eq!(socket.ip(), IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)));
    /// assert_eq!(socket.port(), 8080);
    /// ```
    #[stable(feature = "ip_addr", since = "1.7.0")]
    #[must_use]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn new(ip: IpAddr, port: u16) -> SocketAddr {
        match ip {
            IpAddr::V4(a) => SocketAddr::V4(SocketAddrV4::new(a, port)),
            IpAddr::V6(a) => SocketAddr::V6(SocketAddrV6::new(a, port, 0, 0)),
        }
    }

    /// Returns the IP address associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
    ///
    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
    /// assert_eq!(socket.ip(), IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)));
    /// ```
    #[must_use]
    #[stable(feature = "ip_addr", since = "1.7.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn ip(&self) -> IpAddr {
        match *self {
            SocketAddr::V4(ref a) => IpAddr::V4(*a.ip()),
            SocketAddr::V6(ref a) => IpAddr::V6(*a.ip()),
        }
    }

    /// Changes the IP address associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
    ///
    /// let mut socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
    /// socket.set_ip(IpAddr::V4(Ipv4Addr::new(10, 10, 0, 1)));
    /// assert_eq!(socket.ip(), IpAddr::V4(Ipv4Addr::new(10, 10, 0, 1)));
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_ip(&mut self, new_ip: IpAddr) {
        // `match (*self, new_ip)` would have us mutate a copy of self only to throw it away.
        match (self, new_ip) {
            (&mut SocketAddr::V4(ref mut a), IpAddr::V4(new_ip)) => a.set_ip(new_ip),
            (&mut SocketAddr::V6(ref mut a), IpAddr::V6(new_ip)) => a.set_ip(new_ip),
            (self_, new_ip) => *self_ = Self::new(new_ip, self_.port()),
        }
    }

    /// Returns the port number associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
    ///
    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
    /// assert_eq!(socket.port(), 8080);
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn port(&self) -> u16 {
        match *self {
            SocketAddr::V4(ref a) => a.port(),
            SocketAddr::V6(ref a) => a.port(),
        }
    }

    /// Changes the port number associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
    ///
    /// let mut socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
    /// socket.set_port(1025);
    /// assert_eq!(socket.port(), 1025);
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_port(&mut self, new_port: u16) {
        match *self {
            SocketAddr::V4(ref mut a) => a.set_port(new_port),
            SocketAddr::V6(ref mut a) => a.set_port(new_port),
        }
    }

    /// Returns [`true`] if the [IP address] in this `SocketAddr` is an
    /// [`IPv4` address], and [`false`] otherwise.
    ///
    /// [IP address]: IpAddr
    /// [`IPv4` address]: IpAddr::V4
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
    ///
    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
    /// assert_eq!(socket.is_ipv4(), true);
    /// assert_eq!(socket.is_ipv6(), false);
    /// ```
    #[must_use]
    #[stable(feature = "sockaddr_checker", since = "1.16.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn is_ipv4(&self) -> bool {
        matches!(*self, SocketAddr::V4(_))
    }

    /// Returns [`true`] if the [IP address] in this `SocketAddr` is an
    /// [`IPv6` address], and [`false`] otherwise.
    ///
    /// [IP address]: IpAddr
    /// [`IPv6` address]: IpAddr::V6
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv6Addr, SocketAddr};
    ///
    /// let socket = SocketAddr::new(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 65535, 0, 1)), 8080);
    /// assert_eq!(socket.is_ipv4(), false);
    /// assert_eq!(socket.is_ipv6(), true);
    /// ```
    #[must_use]
    #[stable(feature = "sockaddr_checker", since = "1.16.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn is_ipv6(&self) -> bool {
        matches!(*self, SocketAddr::V6(_))
    }
}

impl SocketAddrV4 {
    /// Creates a new socket address from an [`IPv4` address] and a port number.
    ///
    /// [`IPv4` address]: Ipv4Addr
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV4, Ipv4Addr};
    ///
    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn new(ip: Ipv4Addr, port: u16) -> SocketAddrV4 {
        SocketAddrV4 { ip, port }
    }

    /// Returns the IP address associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV4, Ipv4Addr};
    ///
    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
    /// assert_eq!(socket.ip(), &Ipv4Addr::new(127, 0, 0, 1));
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn ip(&self) -> &Ipv4Addr {
        &self.ip
    }

    /// Changes the IP address associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV4, Ipv4Addr};
    ///
    /// let mut socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
    /// socket.set_ip(Ipv4Addr::new(192, 168, 0, 1));
    /// assert_eq!(socket.ip(), &Ipv4Addr::new(192, 168, 0, 1));
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_ip(&mut self, new_ip: Ipv4Addr) {
        self.ip = new_ip;
    }

    /// Returns the port number associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV4, Ipv4Addr};
    ///
    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
    /// assert_eq!(socket.port(), 8080);
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn port(&self) -> u16 {
        self.port
    }

    /// Changes the port number associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV4, Ipv4Addr};
    ///
    /// let mut socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
    /// socket.set_port(4242);
    /// assert_eq!(socket.port(), 4242);
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_port(&mut self, new_port: u16) {
        self.port = new_port;
    }
}

impl SocketAddrV6 {
    /// Creates a new socket address from an [`IPv6` address], a 16-bit port number,
    /// and the `flowinfo` and `scope_id` fields.
    ///
    /// For more information on the meaning and layout of the `flowinfo` and `scope_id`
    /// parameters, see [IETF RFC 2553, Section 3.3].
    ///
    /// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
    /// [`IPv6` address]: Ipv6Addr
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn new(ip: Ipv6Addr, port: u16, flowinfo: u32, scope_id: u32) -> SocketAddrV6 {
        SocketAddrV6 { ip, port, flowinfo, scope_id }
    }

    /// Returns the IP address associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
    /// assert_eq!(socket.ip(), &Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn ip(&self) -> &Ipv6Addr {
        &self.ip
    }

    /// Changes the IP address associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
    /// socket.set_ip(Ipv6Addr::new(76, 45, 0, 0, 0, 0, 0, 0));
    /// assert_eq!(socket.ip(), &Ipv6Addr::new(76, 45, 0, 0, 0, 0, 0, 0));
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_ip(&mut self, new_ip: Ipv6Addr) {
        self.ip = new_ip;
    }

    /// Returns the port number associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
    /// assert_eq!(socket.port(), 8080);
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn port(&self) -> u16 {
        self.port
    }

    /// Changes the port number associated with this socket address.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
    /// socket.set_port(4242);
    /// assert_eq!(socket.port(), 4242);
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_port(&mut self, new_port: u16) {
        self.port = new_port;
    }

    /// Returns the flow information associated with this address.
    ///
    /// This information corresponds to the `sin6_flowinfo` field in C's `netinet/in.h`,
    /// as specified in [IETF RFC 2553, Section 3.3].
    /// It combines information about the flow label and the traffic class as specified
    /// in [IETF RFC 2460], respectively [Section 6] and [Section 7].
    ///
    /// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
    /// [IETF RFC 2460]: https://tools.ietf.org/html/rfc2460
    /// [Section 6]: https://tools.ietf.org/html/rfc2460#section-6
    /// [Section 7]: https://tools.ietf.org/html/rfc2460#section-7
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 10, 0);
    /// assert_eq!(socket.flowinfo(), 10);
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn flowinfo(&self) -> u32 {
        self.flowinfo
    }

    /// Changes the flow information associated with this socket address.
    ///
    /// See [`SocketAddrV6::flowinfo`]'s documentation for more details.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 10, 0);
    /// socket.set_flowinfo(56);
    /// assert_eq!(socket.flowinfo(), 56);
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_flowinfo(&mut self, new_flowinfo: u32) {
        self.flowinfo = new_flowinfo;
    }

    /// Returns the scope ID associated with this address.
    ///
    /// This information corresponds to the `sin6_scope_id` field in C's `netinet/in.h`,
    /// as specified in [IETF RFC 2553, Section 3.3].
    ///
    /// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 78);
    /// assert_eq!(socket.scope_id(), 78);
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn scope_id(&self) -> u32 {
        self.scope_id
    }

    /// Changes the scope ID associated with this socket address.
    ///
    /// See [`SocketAddrV6::scope_id`]'s documentation for more details.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV6, Ipv6Addr};
    ///
    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 78);
    /// socket.set_scope_id(42);
    /// assert_eq!(socket.scope_id(), 42);
    /// ```
    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
    pub fn set_scope_id(&mut self, new_scope_id: u32) {
        self.scope_id = new_scope_id;
    }
}

impl FromInner<c::sockaddr_in> for SocketAddrV4 {
    fn from_inner(addr: c::sockaddr_in) -> SocketAddrV4 {
        SocketAddrV4 { ip: Ipv4Addr::from_inner(addr.sin_addr), port: u16::from_be(addr.sin_port) }
    }
}

impl FromInner<c::sockaddr_in6> for SocketAddrV6 {
    fn from_inner(addr: c::sockaddr_in6) -> SocketAddrV6 {
        SocketAddrV6 {
            ip: Ipv6Addr::from_inner(addr.sin6_addr),
            port: u16::from_be(addr.sin6_port),
            flowinfo: addr.sin6_flowinfo,
            scope_id: addr.sin6_scope_id,
        }
    }
}

impl IntoInner<c::sockaddr_in> for SocketAddrV4 {
    fn into_inner(self) -> c::sockaddr_in {
        c::sockaddr_in {
            sin_family: c::AF_INET as c::sa_family_t,
            sin_port: self.port.to_be(),
            sin_addr: self.ip.into_inner(),
            ..unsafe { mem::zeroed() }
        }
    }
}

impl IntoInner<c::sockaddr_in6> for SocketAddrV6 {
    fn into_inner(self) -> c::sockaddr_in6 {
        c::sockaddr_in6 {
            sin6_family: c::AF_INET6 as c::sa_family_t,
            sin6_port: self.port.to_be(),
            sin6_addr: self.ip.into_inner(),
            sin6_flowinfo: self.flowinfo,
            sin6_scope_id: self.scope_id,
            ..unsafe { mem::zeroed() }
        }
    }
}

#[stable(feature = "ip_from_ip", since = "1.16.0")]
impl From<SocketAddrV4> for SocketAddr {
    /// Converts a [`SocketAddrV4`] into a [`SocketAddr::V4`].
    fn from(sock4: SocketAddrV4) -> SocketAddr {
        SocketAddr::V4(sock4)
    }
}

#[stable(feature = "ip_from_ip", since = "1.16.0")]
impl From<SocketAddrV6> for SocketAddr {
    /// Converts a [`SocketAddrV6`] into a [`SocketAddr::V6`].
    fn from(sock6: SocketAddrV6) -> SocketAddr {
        SocketAddr::V6(sock6)
    }
}

#[stable(feature = "addr_from_into_ip", since = "1.17.0")]
impl<I: Into<IpAddr>> From<(I, u16)> for SocketAddr {
    /// Converts a tuple struct (Into<[`IpAddr`]>, `u16`) into a [`SocketAddr`].
    ///
    /// This conversion creates a [`SocketAddr::V4`] for an [`IpAddr::V4`]
    /// and creates a [`SocketAddr::V6`] for an [`IpAddr::V6`].
    ///
    /// `u16` is treated as port of the newly created [`SocketAddr`].
    fn from(pieces: (I, u16)) -> SocketAddr {
        SocketAddr::new(pieces.0.into(), pieces.1)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for SocketAddr {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            SocketAddr::V4(ref a) => a.fmt(f),
            SocketAddr::V6(ref a) => a.fmt(f),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for SocketAddr {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, fmt)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for SocketAddrV4 {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Fast path: if there's no alignment stuff, write to the output buffer
        // directly
        if f.precision().is_none() && f.width().is_none() {
            write!(f, "{}:{}", self.ip(), self.port())
        } else {
            const IPV4_SOCKET_BUF_LEN: usize = (3 * 4)  // the segments
                + 3  // the separators
                + 1 + 5; // the port
            let mut buf = [0; IPV4_SOCKET_BUF_LEN];
            let mut buf_slice = &mut buf[..];

            // Unwrap is fine because writing to a sufficiently-sized
            // buffer is infallible
            write!(buf_slice, "{}:{}", self.ip(), self.port()).unwrap();
            let len = IPV4_SOCKET_BUF_LEN - buf_slice.len();

            // This unsafe is OK because we know what is being written to the buffer
            let buf = unsafe { crate::str::from_utf8_unchecked(&buf[..len]) };
            f.pad(buf)
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for SocketAddrV4 {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, fmt)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for SocketAddrV6 {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Fast path: if there's no alignment stuff, write to the output
        // buffer directly
        if f.precision().is_none() && f.width().is_none() {
            match self.scope_id() {
                0 => write!(f, "[{}]:{}", self.ip(), self.port()),
                scope_id => write!(f, "[{}%{}]:{}", self.ip(), scope_id, self.port()),
            }
        } else {
            const IPV6_SOCKET_BUF_LEN: usize = (4 * 8)  // The address
            + 7  // The colon separators
            + 2  // The brackets
            + 1 + 10 // The scope id
            + 1 + 5; // The port

            let mut buf = [0; IPV6_SOCKET_BUF_LEN];
            let mut buf_slice = &mut buf[..];

            match self.scope_id() {
                0 => write!(buf_slice, "[{}]:{}", self.ip(), self.port()),
                scope_id => write!(buf_slice, "[{}%{}]:{}", self.ip(), scope_id, self.port()),
            }
            // Unwrap is fine because writing to a sufficiently-sized
            // buffer is infallible
            .unwrap();
            let len = IPV6_SOCKET_BUF_LEN - buf_slice.len();

            // This unsafe is OK because we know what is being written to the buffer
            let buf = unsafe { crate::str::from_utf8_unchecked(&buf[..len]) };
            f.pad(buf)
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for SocketAddrV6 {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, fmt)
    }
}

#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
impl PartialOrd for SocketAddrV4 {
    fn partial_cmp(&self, other: &SocketAddrV4) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
impl PartialOrd for SocketAddrV6 {
    fn partial_cmp(&self, other: &SocketAddrV6) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
impl Ord for SocketAddrV4 {
    fn cmp(&self, other: &SocketAddrV4) -> Ordering {
        self.ip().cmp(other.ip()).then(self.port().cmp(&other.port()))
    }
}

#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
impl Ord for SocketAddrV6 {
    fn cmp(&self, other: &SocketAddrV6) -> Ordering {
        self.ip().cmp(other.ip()).then(self.port().cmp(&other.port()))
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl hash::Hash for SocketAddrV4 {
    fn hash<H: hash::Hasher>(&self, s: &mut H) {
        (self.port, self.ip).hash(s)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl hash::Hash for SocketAddrV6 {
    fn hash<H: hash::Hasher>(&self, s: &mut H) {
        (self.port, &self.ip, self.flowinfo, self.scope_id).hash(s)
    }
}

/// A trait for objects which can be converted or resolved to one or more
/// [`SocketAddr`] values.
///
/// This trait is used for generic address resolution when constructing network
/// objects. By default it is implemented for the following types:
///
///  * [`SocketAddr`]: [`to_socket_addrs`] is the identity function.
///
///  * [`SocketAddrV4`], [`SocketAddrV6`], <code>([IpAddr], [u16])</code>,
///    <code>([Ipv4Addr], [u16])</code>, <code>([Ipv6Addr], [u16])</code>:
///    [`to_socket_addrs`] constructs a [`SocketAddr`] trivially.
///
///  * <code>(&[str], [u16])</code>: <code>&[str]</code> should be either a string representation
///    of an [`IpAddr`] address as expected by [`FromStr`] implementation or a host
///    name. [`u16`] is the port number.
///
///  * <code>&[str]</code>: the string should be either a string representation of a
///    [`SocketAddr`] as expected by its [`FromStr`] implementation or a string like
///    `<host_name>:<port>` pair where `<port>` is a [`u16`] value.
///
/// This trait allows constructing network objects like [`TcpStream`] or
/// [`UdpSocket`] easily with values of various types for the bind/connection
/// address. It is needed because sometimes one type is more appropriate than
/// the other: for simple uses a string like `"localhost:12345"` is much nicer
/// than manual construction of the corresponding [`SocketAddr`], but sometimes
/// [`SocketAddr`] value is *the* main source of the address, and converting it to
/// some other type (e.g., a string) just for it to be converted back to
/// [`SocketAddr`] in constructor methods is pointless.
///
/// Addresses returned by the operating system that are not IP addresses are
/// silently ignored.
///
/// [`FromStr`]: crate::str::FromStr "std::str::FromStr"
/// [`TcpStream`]: crate::net::TcpStream "net::TcpStream"
/// [`to_socket_addrs`]: ToSocketAddrs::to_socket_addrs
/// [`UdpSocket`]: crate::net::UdpSocket "net::UdpSocket"
///
/// # Examples
///
/// Creating a [`SocketAddr`] iterator that yields one item:
///
/// ```
/// use std::net::{ToSocketAddrs, SocketAddr};
///
/// let addr = SocketAddr::from(([127, 0, 0, 1], 443));
/// let mut addrs_iter = addr.to_socket_addrs().unwrap();
///
/// assert_eq!(Some(addr), addrs_iter.next());
/// assert!(addrs_iter.next().is_none());
/// ```
///
/// Creating a [`SocketAddr`] iterator from a hostname:
///
/// ```no_run
/// use std::net::{SocketAddr, ToSocketAddrs};
///
/// // assuming 'localhost' resolves to 127.0.0.1
/// let mut addrs_iter = "localhost:443".to_socket_addrs().unwrap();
/// assert_eq!(addrs_iter.next(), Some(SocketAddr::from(([127, 0, 0, 1], 443))));
/// assert!(addrs_iter.next().is_none());
///
/// // assuming 'foo' does not resolve
/// assert!("foo:443".to_socket_addrs().is_err());
/// ```
///
/// Creating a [`SocketAddr`] iterator that yields multiple items:
///
/// ```
/// use std::net::{SocketAddr, ToSocketAddrs};
///
/// let addr1 = SocketAddr::from(([0, 0, 0, 0], 80));
/// let addr2 = SocketAddr::from(([127, 0, 0, 1], 443));
/// let addrs = vec![addr1, addr2];
///
/// let mut addrs_iter = (&addrs[..]).to_socket_addrs().unwrap();
///
/// assert_eq!(Some(addr1), addrs_iter.next());
/// assert_eq!(Some(addr2), addrs_iter.next());
/// assert!(addrs_iter.next().is_none());
/// ```
///
/// Attempting to create a [`SocketAddr`] iterator from an improperly formatted
/// socket address `&str` (missing the port):
///
/// ```
/// use std::io;
/// use std::net::ToSocketAddrs;
///
/// let err = "127.0.0.1".to_socket_addrs().unwrap_err();
/// assert_eq!(err.kind(), io::ErrorKind::InvalidInput);
/// ```
///
/// [`TcpStream::connect`] is an example of an function that utilizes
/// `ToSocketAddrs` as a trait bound on its parameter in order to accept
/// different types:
///
/// ```no_run
/// use std::net::{TcpStream, Ipv4Addr};
///
/// let stream = TcpStream::connect(("127.0.0.1", 443));
/// // or
/// let stream = TcpStream::connect("127.0.0.1:443");
/// // or
/// let stream = TcpStream::connect((Ipv4Addr::new(127, 0, 0, 1), 443));
/// ```
///
/// [`TcpStream::connect`]: crate::net::TcpStream::connect
#[stable(feature = "rust1", since = "1.0.0")]
pub trait ToSocketAddrs {
    /// Returned iterator over socket addresses which this type may correspond
    /// to.
    #[stable(feature = "rust1", since = "1.0.0")]
    type Iter: Iterator<Item = SocketAddr>;

    /// Converts this object to an iterator of resolved [`SocketAddr`]s.
    ///
    /// The returned iterator might not actually yield any values depending on the
    /// outcome of any resolution performed.
    ///
    /// Note that this function may block the current thread while resolution is
    /// performed.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn to_socket_addrs(&self) -> io::Result<Self::Iter>;
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for SocketAddr {
    type Iter = option::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<option::IntoIter<SocketAddr>> {
        Ok(Some(*self).into_iter())
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for SocketAddrV4 {
    type Iter = option::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<option::IntoIter<SocketAddr>> {
        SocketAddr::V4(*self).to_socket_addrs()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for SocketAddrV6 {
    type Iter = option::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<option::IntoIter<SocketAddr>> {
        SocketAddr::V6(*self).to_socket_addrs()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for (IpAddr, u16) {
    type Iter = option::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<option::IntoIter<SocketAddr>> {
        let (ip, port) = *self;
        match ip {
            IpAddr::V4(ref a) => (*a, port).to_socket_addrs(),
            IpAddr::V6(ref a) => (*a, port).to_socket_addrs(),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for (Ipv4Addr, u16) {
    type Iter = option::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<option::IntoIter<SocketAddr>> {
        let (ip, port) = *self;
        SocketAddrV4::new(ip, port).to_socket_addrs()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for (Ipv6Addr, u16) {
    type Iter = option::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<option::IntoIter<SocketAddr>> {
        let (ip, port) = *self;
        SocketAddrV6::new(ip, port, 0, 0).to_socket_addrs()
    }
}

fn resolve_socket_addr(lh: LookupHost) -> io::Result<vec::IntoIter<SocketAddr>> {
    let p = lh.port();
    let v: Vec<_> = lh
        .map(|mut a| {
            a.set_port(p);
            a
        })
        .collect();
    Ok(v.into_iter())
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for (&str, u16) {
    type Iter = vec::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<vec::IntoIter<SocketAddr>> {
        let (host, port) = *self;

        // try to parse the host as a regular IP address first
        if let Ok(addr) = host.parse::<Ipv4Addr>() {
            let addr = SocketAddrV4::new(addr, port);
            return Ok(vec![SocketAddr::V4(addr)].into_iter());
        }
        if let Ok(addr) = host.parse::<Ipv6Addr>() {
            let addr = SocketAddrV6::new(addr, port, 0, 0);
            return Ok(vec![SocketAddr::V6(addr)].into_iter());
        }

        resolve_socket_addr((host, port).try_into()?)
    }
}

#[stable(feature = "string_u16_to_socket_addrs", since = "1.46.0")]
impl ToSocketAddrs for (String, u16) {
    type Iter = vec::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<vec::IntoIter<SocketAddr>> {
        (&*self.0, self.1).to_socket_addrs()
    }
}

// accepts strings like 'localhost:12345'
#[stable(feature = "rust1", since = "1.0.0")]
impl ToSocketAddrs for str {
    type Iter = vec::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<vec::IntoIter<SocketAddr>> {
        // try to parse as a regular SocketAddr first
        if let Ok(addr) = self.parse() {
            return Ok(vec![addr].into_iter());
        }

        resolve_socket_addr(self.try_into()?)
    }
}

#[stable(feature = "slice_to_socket_addrs", since = "1.8.0")]
impl<'a> ToSocketAddrs for &'a [SocketAddr] {
    type Iter = iter::Cloned<slice::Iter<'a, SocketAddr>>;

    fn to_socket_addrs(&self) -> io::Result<Self::Iter> {
        Ok(self.iter().cloned())
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ToSocketAddrs + ?Sized> ToSocketAddrs for &T {
    type Iter = T::Iter;
    fn to_socket_addrs(&self) -> io::Result<T::Iter> {
        (**self).to_socket_addrs()
    }
}

#[stable(feature = "string_to_socket_addrs", since = "1.16.0")]
impl ToSocketAddrs for String {
    type Iter = vec::IntoIter<SocketAddr>;
    fn to_socket_addrs(&self) -> io::Result<vec::IntoIter<SocketAddr>> {
        (&**self).to_socket_addrs()
    }
}