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

use crate::cmp::Ordering;
use crate::convert::TryInto;
use crate::fmt;
use crate::hash;
use crate::io::{self, Write};
use crate::iter;
use crate::mem;
use crate::net::{htons, ntohs, 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::{AsInner, FromInner, IntoInner};
use crate::vec;

/// Internet 套接字地址，IPv4 或 IPv6。
///
/// Internet 套接字地址包含一个 [IP address]，一个 16 位端口号以及一些可能与版本有关的附加信息。
/// 有关更多详细信息，请参见 [`SocketAddrV4`] 和 [`SocketAddrV6`] 的文档。
///
/// `SocketAddr` 实例的大小可能会因目标操作系统而异。
///
/// [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 {
    /// IPv4 套接字地址。
    #[stable(feature = "rust1", since = "1.0.0")]
    V4(#[stable(feature = "rust1", since = "1.0.0")] SocketAddrV4),
    /// IPv6 套接字地址。
    #[stable(feature = "rust1", since = "1.0.0")]
    V6(#[stable(feature = "rust1", since = "1.0.0")] SocketAddrV6),
}

/// IPv4 套接字地址。
///
/// IPv4 如 [IETF RFC 793] 中所述，套接字地址由 [`IPv4` address] 和 16 位端口号组成。
///
///
/// 有关同时包含 IPv4 和 IPv6 套接字地址的类型，请参见 [`SocketAddr`]。
///
/// `SocketAddrV4` 结构体的大小可能会因目标操作系统而异。
/// 不要假设此类型与底层系统表示具有相同的内存布局。
///
/// [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)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct SocketAddrV4 {
    // 不要假设这个结构体是作为底层系统表示实现的。
    // 内存布局不是 std 公开的稳定接口的一部分。
    inner: c::sockaddr_in,
}

/// IPv6 套接字地址。
///
/// IPv6 套接字地址由 [`IPv6` address]，16 位端口号以及包含流量类别，流标签和作用域标识符的字段组成 (有关更多详细信息，请参见 [IETF RFC 2553, Section 3.3])。
///
///
/// 有关同时包含 IPv4 和 IPv6 套接字地址的类型，请参见 [`SocketAddr`]。
///
/// `SocketAddrV6` 结构体的大小可能会因目标操作系统而异。不要假设此类型与底层系统表示具有相同的内存布局。
///
/// [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)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct SocketAddrV6 {
    // 不要假设这个结构体是作为底层系统表示实现的。
    // 内存布局不是 std 公开的稳定接口的一部分。
    inner: c::sockaddr_in6,
}

impl SocketAddr {
    /// 从 [IP address] 和端口号创建一个新的套接字地址。
    ///
    /// [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")]
    pub 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)),
        }
    }

    /// 返回与此套接字地址关联的 IP 地址。
    ///
    /// # 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)));
    /// ```
    #[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()),
        }
    }

    /// 更改与此套接字地址关联的 IP 地址。
    ///
    /// # 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)` 让我们可变一个自我的副本而只是丢掉它。
        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()),
        }
    }

    /// 返回与此套接字地址关联的端口号。
    ///
    /// # 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);
    /// ```
    #[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(),
        }
    }

    /// 更改与此套接字地址关联的端口号。
    ///
    /// # 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),
        }
    }

    /// 如果此 `SocketAddr` 中的 [IP address] 是 [`IPv4` address]，则返回 [`true`]，否则返回 [`false`]。
    ///
    ///
    /// [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);
    /// ```
    #[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(_))
    }

    /// 如果此 `SocketAddr` 中的 [IP address] 是 [`IPv6` address]，则返回 [`true`]，否则返回 [`false`]。
    ///
    ///
    /// [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);
    /// ```
    #[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 {
    /// 从 [`IPv4` address] 和端口号创建一个新的套接字地址。
    ///
    /// [`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")]
    pub fn new(ip: Ipv4Addr, port: u16) -> SocketAddrV4 {
        SocketAddrV4 {
            inner: c::sockaddr_in {
                sin_family: c::AF_INET as c::sa_family_t,
                sin_port: htons(port),
                sin_addr: ip.into_inner(),
                ..unsafe { mem::zeroed() }
            },
        }
    }

    /// 返回与此套接字地址关联的 IP 地址。
    ///
    /// # 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));
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn ip(&self) -> &Ipv4Addr {
        // SAFETY: `Ipv4Addr` 是 `#[repr(C)] struct { _: in_addr; }`。
        // 从 `&in_addr` 转换为 `&Ipv4Addr` 是安全的。
        unsafe { &*(&self.inner.sin_addr as *const c::in_addr as *const Ipv4Addr) }
    }

    /// 更改与此套接字地址关联的 IP 地址。
    ///
    /// # 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.inner.sin_addr = new_ip.into_inner()
    }

    /// 返回与此套接字地址关联的端口号。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{SocketAddrV4, Ipv4Addr};
    ///
    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
    /// assert_eq!(socket.port(), 8080);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn port(&self) -> u16 {
        ntohs(self.inner.sin_port)
    }

    /// 更改与此套接字地址关联的端口号。
    ///
    /// # 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.inner.sin_port = htons(new_port);
    }
}

impl SocketAddrV6 {
    /// 从 [`IPv6` address]，16 位端口号以及 `flowinfo` 和 `scope_id` 字段创建新的套接字地址。
    ///
    /// 有关 `flowinfo` 和 `scope_id` 参数的含义和布局的更多信息，请参见 [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")]
    pub fn new(ip: Ipv6Addr, port: u16, flowinfo: u32, scope_id: u32) -> SocketAddrV6 {
        SocketAddrV6 {
            inner: c::sockaddr_in6 {
                sin6_family: c::AF_INET6 as c::sa_family_t,
                sin6_port: htons(port),
                sin6_addr: *ip.as_inner(),
                sin6_flowinfo: flowinfo,
                sin6_scope_id: scope_id,
                ..unsafe { mem::zeroed() }
            },
        }
    }

    /// 返回与此套接字地址关联的 IP 地址。
    ///
    /// # 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));
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn ip(&self) -> &Ipv6Addr {
        unsafe { &*(&self.inner.sin6_addr as *const c::in6_addr as *const Ipv6Addr) }
    }

    /// 更改与此套接字地址关联的 IP 地址。
    ///
    /// # 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.inner.sin6_addr = *new_ip.as_inner()
    }

    /// 返回与此套接字地址关联的端口号。
    ///
    /// # 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);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn port(&self) -> u16 {
        ntohs(self.inner.sin6_port)
    }

    /// 更改与此套接字地址关联的端口号。
    ///
    /// # 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.inner.sin6_port = htons(new_port);
    }

    /// 返回与此地址关联的流信息。
    ///
    /// 该信息对应于 [IETF RFC 2553, Section 3.3] 中指定的 C 的 `netinet/in.h` 中的 `sin6_flowinfo` 字段。
    /// 它结合了关于流标签和流量类别的信息，分别在 [IETF RFC 2460]，[Section 6] 和 [Section 7] 中指定。
    ///
    ///
    /// [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);
    /// ```
    ///
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn flowinfo(&self) -> u32 {
        self.inner.sin6_flowinfo
    }

    /// 更改与此套接字地址关联的流信息。
    ///
    /// 有关更多详细信息，请参见 [`SocketAddrV6::flowinfo`] 的文档。
    ///
    /// # 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.inner.sin6_flowinfo = new_flowinfo;
    }

    /// 返回与此地址关联的作用域 ID。
    ///
    /// 该信息对应于 [IETF RFC 2553, Section 3.3] 中指定的 C 的 `netinet/in.h` 中的 `sin6_scope_id` 字段。
    ///
    ///
    /// [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);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_socketaddr", issue = "82485")]
    pub const fn scope_id(&self) -> u32 {
        self.inner.sin6_scope_id
    }

    /// 更改与此套接字地址关联的作用域 ID。
    ///
    /// 有关更多详细信息，请参见 [`SocketAddrV6::scope_id`] 的文档。
    ///
    /// # 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.inner.sin6_scope_id = new_scope_id;
    }
}

impl FromInner<c::sockaddr_in> for SocketAddrV4 {
    fn from_inner(addr: c::sockaddr_in) -> SocketAddrV4 {
        SocketAddrV4 { inner: addr }
    }
}

impl FromInner<c::sockaddr_in6> for SocketAddrV6 {
    fn from_inner(addr: c::sockaddr_in6) -> SocketAddrV6 {
        SocketAddrV6 { inner: addr }
    }
}

#[stable(feature = "ip_from_ip", since = "1.16.0")]
impl From<SocketAddrV4> for SocketAddr {
    /// 将 [`SocketAddrV4`] 转换为 [`SocketAddr::V4`]。
    fn from(sock4: SocketAddrV4) -> SocketAddr {
        SocketAddr::V4(sock4)
    }
}

#[stable(feature = "ip_from_ip", since = "1.16.0")]
impl From<SocketAddrV6> for SocketAddr {
    /// 将 [`SocketAddrV6`] 转换为 [`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 {
    /// 将元组结构体 (Into <[`IpAddr`]>，`u16`) 转换为 [`SocketAddr`]。
    ///
    /// 此转换为 [`IpAddr::V4`] 创建 [`SocketAddr::V4`]，为 [`IpAddr::V6`] 创建 [`SocketAddr::V6`]。
    ///
    ///
    /// `u16` 被视为新创建的 [`SocketAddr`] 的端口。
    fn from(pieces: (I, u16)) -> SocketAddr {
        SocketAddr::new(pieces.0.into(), pieces.1)
    }
}

impl<'a> IntoInner<(*const c::sockaddr, c::socklen_t)> for &'a SocketAddr {
    fn into_inner(self) -> (*const c::sockaddr, c::socklen_t) {
        match *self {
            SocketAddr::V4(ref a) => {
                (a as *const _ as *const _, mem::size_of_val(a) as c::socklen_t)
            }
            SocketAddr::V6(ref a) => {
                (a as *const _ as *const _, mem::size_of_val(a) as c::socklen_t)
            }
        }
    }
}

#[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 {
        // 快速路径: 如果没有对齐内容，则直接写入输出缓冲区
        //
        if f.precision().is_none() && f.width().is_none() {
            write!(f, "{}:{}", self.ip(), self.port())
        } else {
            const IPV4_SOCKET_BUF_LEN: usize = (3 * 4)  // 段
                + 3  // 分隔符
                + 1 + 5; // 端口
            let mut buf = [0; IPV4_SOCKET_BUF_LEN];
            let mut buf_slice = &mut buf[..];

            // Unwrap 很好，因为写入足够大小的缓冲区是绝对可靠的
            //
            write!(buf_slice, "{}:{}", self.ip(), self.port()).unwrap();
            let len = IPV4_SOCKET_BUF_LEN - buf_slice.len();

            // 这种不安全的行为是可以的，因为我们知道正在将什么内容写入缓冲区
            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 {
        // 快速路径: 如果没有对齐内容，则直接写入输出缓冲区
        //
        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)  // 地址
            + 7  // 冒号分隔符
            + 2  // 括号
            + 1 + 10 // 作用域 ID
            + 1 + 5; // 端口

            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 很好，因为写入足够大小的缓冲区是绝对可靠的
            //
            .unwrap();
            let len = IPV6_SOCKET_BUF_LEN - buf_slice.len();

            // 这种不安全的行为是可以的，因为我们知道正在将什么内容写入缓冲区
            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 = "rust1", since = "1.0.0")]
impl Clone for SocketAddrV4 {
    fn clone(&self) -> SocketAddrV4 {
        *self
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Clone for SocketAddrV6 {
    fn clone(&self) -> SocketAddrV6 {
        *self
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl PartialEq for SocketAddrV4 {
    fn eq(&self, other: &SocketAddrV4) -> bool {
        self.inner.sin_port == other.inner.sin_port
            && self.inner.sin_addr.s_addr == other.inner.sin_addr.s_addr
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl PartialEq for SocketAddrV6 {
    fn eq(&self, other: &SocketAddrV6) -> bool {
        self.inner.sin6_port == other.inner.sin6_port
            && self.inner.sin6_addr.s6_addr == other.inner.sin6_addr.s6_addr
            && self.inner.sin6_flowinfo == other.inner.sin6_flowinfo
            && self.inner.sin6_scope_id == other.inner.sin6_scope_id
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Eq for SocketAddrV4 {}
#[stable(feature = "rust1", since = "1.0.0")]
impl Eq for SocketAddrV6 {}

#[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.inner.sin_port, self.inner.sin_addr.s_addr).hash(s)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl hash::Hash for SocketAddrV6 {
    fn hash<H: hash::Hasher>(&self, s: &mut H) {
        (
            self.inner.sin6_port,
            &self.inner.sin6_addr.s6_addr,
            self.inner.sin6_flowinfo,
            self.inner.sin6_scope_id,
        )
            .hash(s)
    }
}

/// trait，用于可以转换或解析为一个或多个 [`SocketAddr`] 值的对象。
///
/// trait 在构造网络对象时用于泛型地址解析。默认情况下，它针对以下类型实现:
///
///  * [`SocketAddr`]: [`to_socket_addrs`] 是标识函数。
///
///  * [`SocketAddrV4`], [`SocketAddrV6`], `(`[`IpAddr`]`, `[`u16`]`)`, `(`[`Ipv4Addr`]`, `[`u16`]`)`, `(`[`Ipv6Addr`]`, `[`u16`]`)`:
///    [`to_socket_addrs`] 简单地创建一个 [`SocketAddr`]。
///
///  * `(`[`&str`]`, `[`u16`]`)`: [`&str`] 应该是 [`FromStr`] 实现所期望的 [`IpAddr`] 地址的字符串表示形式，或者是主机名。[`u16`] 是端口号。
///
///  * [`&str`]: 该字符串应该是 [`SocketAddr`] 实现所期望的 [`SocketAddr`] 的字符串表示形式，或者是 `<host_name>:<port>` 对之类的字符串，其中 `<port>` 是 [`u16`] 值。
///
/// trait 允许使用 bind/connection 地址的各种类型的值轻松构造 [`TcpStream`] 或 [`UdpSocket`] 之类的网络对象。
/// 之所以需要它，是因为有时一种类型比另一种类型更合适: 对于简单的用法，像 `"localhost:12345"` 这样的字符串比相应的 [`SocketAddr`] 的手工构造好得多，但是有时 [`SocketAddr`] 值是地址的 * 主要来源，并将其转换为其他一些类型 (例如，字符串) 仅用于在构造函数方法中将其转换回 [`SocketAddr`] 是没有意义的。
///
///
/// 操作系统返回的不是 IP 地址的地址将被静默忽略。
///
/// [`FromStr`]: crate::str::FromStr
/// [`&str`]: str
/// [`TcpStream`]: crate::net::TcpStream
/// [`to_socket_addrs`]: ToSocketAddrs::to_socket_addrs
/// [`UdpSocket`]: crate::net::UdpSocket
///
/// # Examples
///
/// 创建一个产生一个项的 [`SocketAddr`] 迭代器:
///
/// ```
/// 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());
/// ```
///
/// 从主机名创建 [`SocketAddr`] 迭代器:
///
/// ```no_run
/// use std::net::{SocketAddr, ToSocketAddrs};
///
/// // 假设 'localhost' 解析为 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());
///
/// // 假设 'foo' 无法解析
/// assert!("foo:443".to_socket_addrs().is_err());
/// ```
///
/// 创建一个产生多个项的 [`SocketAddr`] 迭代器:
///
/// ```
/// 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());
/// ```
///
/// 尝试从格式不正确的套接字地址 `&str` (缺少端口) 创建 [`SocketAddr`] 迭代器:
///
/// ```
/// 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`] 是一个函数的示例，该函数在其参数上利用 `ToSocketAddrs` 作为 trait bound 来接受不同的类型:
///
/// ```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 {
    /// 在此类型可能对应的套接字地址上返回的迭代器。
    ///
    #[stable(feature = "rust1", since = "1.0.0")]
    type Iter: Iterator<Item = SocketAddr>;

    /// 将此 object 转换为解析的 `SocketAddr` 的迭代器。
    ///
    /// 根据执行的任何解析的结果，返回的迭代器实际上可能不会产生任何值。
    ///
    ///
    /// 请注意，执行解析时，此函数可能会阻塞当前线程。
    ///
    #[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;

        // 尝试首先将主机解析为常规 IP 地址
        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()
    }
}

// 接受 'localhost:12345' 之类的字符串
#[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>> {
        // 尝试首先解析为常规的 SocketAddr
        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()
    }
}