use crate::cmp::Ordering;
use crate::fmt::{self, Write};
use crate::mem::transmute;

use super::display_buffer::DisplayBuffer;

/// IP 地址，IPv4 或 IPv6。
///
/// 该枚举可以包含 [`Ipv4Addr`] 或 [`Ipv6Addr`]，有关更多详细信息，请参见其各自的文档。
///
///
/// # Examples
///
/// ```
/// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
///
/// let localhost_v4 = IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1));
/// let localhost_v6 = IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
///
/// assert_eq!("127.0.0.1".parse(), Ok(localhost_v4));
/// assert_eq!("::1".parse(), Ok(localhost_v6));
///
/// assert_eq!(localhost_v4.is_ipv6(), false);
/// assert_eq!(localhost_v4.is_ipv4(), true);
/// ```
#[cfg_attr(not(test), rustc_diagnostic_item = "IpAddr")]
#[stable(feature = "ip_addr", since = "1.7.0")]
#[derive(Copy, Clone, Eq, PartialEq, Hash, PartialOrd, Ord)]
pub enum IpAddr {
    /// IPv4 地址。
    #[stable(feature = "ip_addr", since = "1.7.0")]
    V4(#[stable(feature = "ip_addr", since = "1.7.0")] Ipv4Addr),
    /// IPv6 地址。
    #[stable(feature = "ip_addr", since = "1.7.0")]
    V6(#[stable(feature = "ip_addr", since = "1.7.0")] Ipv6Addr),
}

/// IPv4 地址。
///
/// IPv4 地址在 [IETF RFC 791] 中定义为 32 位整数。
/// 它们通常表示为四个八位位组。
///
/// 有关同时包含 IPv4 和 IPv6 地址的类型，请参见 [`IpAddr`]。
///
/// [IETF RFC 791]: https://tools.ietf.org/html/rfc791
///
/// # 文字表达
///
/// `Ipv4Addr` 提供了一个 [`FromStr`] 的实现。四个八位位组用十进制表示法除以 `.` (称为 "点十进制表示法")。
/// 值得注意的是，每个 [IETF RFC 6943] 不允许使用八进制数 (以 `0` 开头) 和十六进制数 (以 `0x` 开头)。
///
///
/// [IETF RFC 6943]: https://tools.ietf.org/html/rfc6943#section-3.1.1
/// [`FromStr`]: crate::str::FromStr
///
/// # Examples
///
/// ```
/// use std::net::Ipv4Addr;
///
/// let localhost = Ipv4Addr::new(127, 0, 0, 1);
/// assert_eq!("127.0.0.1".parse(), Ok(localhost));
/// assert_eq!(localhost.is_loopback(), true);
/// assert!("012.004.002.000".parse::<Ipv4Addr>().is_err()); // 所有八位字节都是八进制的
/// assert!("0000000.0.0.0".parse::<Ipv4Addr>().is_err()); // 第一个八位字节是八进制中的零
/// assert!("0xcb.0x0.0x71.0x00".parse::<Ipv4Addr>().is_err()); // 所有八位字节都是十六进制的
/// ```
///
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Ipv4Addr {
    octets: [u8; 4],
}

/// IPv6 地址。
///
/// IPv6 地址在 [IETF RFC 4291] 中定义为 128 位整数。
/// 它们通常表示为八个 16 位段。
///
/// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
///
/// # 嵌入 IPv4 地址
///
/// 有关同时包含 IPv4 和 IPv6 地址的类型，请参见 [`IpAddr`]。
///
/// 为了帮助从 IPv4 过渡到 IPv6，定义了两种类型的 IPv6 地址，它们嵌入了 IPv4 地址：
/// IPv4 兼容地址和 IPv4 映射地址。其中这些与 IPv4 兼容的地址已被正式弃用。
///
/// 除了相关标准规定的内容外，此实现并未为这两种类型的地址分配任何特殊含义。
/// 这意味着像 `::ffff:127.0.0.1` 这样的地址，虽然代表 IPv4 回环地址，但它本身并不是 IPv6 回环地址； 只有 `::1` 是。
/// 要处理这些所谓的 "IPv4-in-IPv6" 地址，必须首先将它们转换为规范的 IPv4 地址。
///
/// ### 兼容 IPv4 的 IPv6 地址
///
/// IPv4 兼容的 IPv6 地址在 [IETF RFC 4291 第 2.5.5.1 节][IETF RFC 4291 Section 2.5.5.1] 中定义，并已被正式弃用。
/// RFC 描述了 "IPv4 兼容 IPv6 地址" 的格式如下：
///
/// ```text
/// |                80 bits               | 16 |      32 bits        |
/// +--------------------------------------+--------------------------+
/// |0000..............................0000|0000|    IPv4 address     |
/// +--------------------------------------+----+---------------------+
/// ```
/// 因此 `::a.b.c.d` 将是表示 IPv4 地址 `a.b.c.d` 的 IPv4 兼容 IPv6 地址。
///
/// 要将 IPv4 地址转换为与 IPv4 兼容的 IPv6 地址，请使用 [`Ipv4Addr::to_ipv6_compatible`]。
/// 使用 [`Ipv6Addr::to_ipv4`] 将兼容 IPv4 的 IPv6 地址转换为规范的 IPv4 地址。
///
/// [IETF RFC 4291 Section 2.5.5.1]: https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.1
///
/// ### IPv4 映射的 IPv6 地址
///
/// IPv4 映射的 IPv6 地址在 [IETF RFC 4291 第 2.5.5.2 节][IETF RFC 4291 Section 2.5.5.2] 中定义。
/// RFC 描述了 "IPv4-Mapped IPv6 address" 的格式如下：
///
/// ```text
/// |                80 bits               | 16 |      32 bits        |
/// +--------------------------------------+--------------------------+
/// |0000..............................0000|FFFF|    IPv4 address     |
/// +--------------------------------------+----+---------------------+
/// ```
/// 因此 `::ffff:a.b.c.d` 将是表示 IPv4 地址 `a.b.c.d` 的 IPv4 映射 IPv6 地址。
///
/// 要将 IPv4 地址转换为 IPv4 映射的 IPv6 地址，请使用 [`Ipv4Addr::to_ipv6_mapped`]。
/// 使用 [`Ipv6Addr::to_ipv4`] 将 IPv4 映射的 IPv6 地址转换为规范的 IPv4 地址。
/// 请注意，这也会将 IPv6 回环地址 `::1` 转换为 `0.0.0.1`。使用 [`Ipv6Addr::to_ipv4_mapped`] 可以避免这种情况。
///
/// [IETF RFC 4291 Section 2.5.5.2]: https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.2
///
/// # 文字表达
///
/// `Ipv6Addr` 提供了一个 [`FromStr`] 的实现。
/// 有多种方法可以用文本表示 IPv6 地址，但通常，每个段都以十六进制表示法，并且段之间用 `:` 分隔。
///
/// 有关更多信息，请参见 [IETF RFC 5952]。
///
/// [`FromStr`]: crate::str::FromStr
/// [IETF RFC 5952]: https://tools.ietf.org/html/rfc5952
///
/// # Examples
///
/// ```
/// use std::net::Ipv6Addr;
///
/// let localhost = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1);
/// assert_eq!("::1".parse(), Ok(localhost));
/// assert_eq!(localhost.is_loopback(), true);
/// ```
///
///
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Ipv6Addr {
    octets: [u8; 16],
}

/// [IETF RFC 7346 第 2 节][IETF RFC 7346 section 2] 中定义的 [IPv6 多播地址][IPv6 multicast address] 的范围。
///
/// # 稳定性保证
///
/// 并非多播作用域的所有可能值都已分配。
/// 未来的 RFC 可能会引入新的作用域，它将作为变体添加到此枚举中；
/// 因此，枚举被标记为 `#[non_exhaustive]`。
///
/// # Examples
/// ```
/// #![feature(ip)]
///
/// use std::net::Ipv6Addr;
/// use std::net::Ipv6MulticastScope::*;
///
/// // 具有全局作用域 (`ff0e::`) 的 IPv6 多播地址。
/// let address = Ipv6Addr::new(0xff0e, 0, 0, 0, 0, 0, 0, 0);
///
/// // 将打印 "Global scope"。
/// match address.multicast_scope() {
///     Some(InterfaceLocal) => println!("Interface-Local scope"),
///     Some(LinkLocal) => println!("Link-Local scope"),
///     Some(RealmLocal) => println!("Realm-Local scope"),
///     Some(AdminLocal) => println!("Admin-Local scope"),
///     Some(SiteLocal) => println!("Site-Local scope"),
///     Some(OrganizationLocal) => println!("Organization-Local scope"),
///     Some(Global) => println!("Global scope"),
///     Some(_) => println!("Unknown scope"),
///     None => println!("Not a multicast address!")
/// }
///
/// ```
///
/// [IPv6 multicast address]: Ipv6Addr
/// [IETF RFC 7346 section 2]: https://tools.ietf.org/html/rfc7346#section-2
#[derive(Copy, PartialEq, Eq, Clone, Hash, Debug)]
#[unstable(feature = "ip", issue = "27709")]
#[non_exhaustive]
pub enum Ipv6MulticastScope {
    /// Interface-Local 作用域。
    InterfaceLocal,
    /// Link-Local 作用域。
    LinkLocal,
    /// Realm-Local 作用域。
    RealmLocal,
    /// Admin-Local 作用域。
    AdminLocal,
    /// Site-Local 作用域。
    SiteLocal,
    /// Organization-Local 作用域。
    OrganizationLocal,
    /// Global 作用域。
    Global,
}

impl IpAddr {
    /// 返回 [`true`] 作为特殊的 'unspecified' 地址。
    ///
    /// 有关更多详细信息，请参见 [`Ipv4Addr::is_unspecified()`] 和 [`Ipv6Addr::is_unspecified()`] 的文档。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(0, 0, 0, 0)).is_unspecified(), true);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0)).is_unspecified(), true);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "ip_shared", since = "1.12.0")]
    #[must_use]
    #[inline]
    pub const fn is_unspecified(&self) -> bool {
        match self {
            IpAddr::V4(ip) => ip.is_unspecified(),
            IpAddr::V6(ip) => ip.is_unspecified(),
        }
    }

    /// 如果这是一个回环地址，则返回 [`true`]。
    ///
    /// 有关更多详细信息，请参见 [`Ipv4Addr::is_loopback()`] 和 [`Ipv6Addr::is_loopback()`] 的文档。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)).is_loopback(), true);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0x1)).is_loopback(), true);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "ip_shared", since = "1.12.0")]
    #[must_use]
    #[inline]
    pub const fn is_loopback(&self) -> bool {
        match self {
            IpAddr::V4(ip) => ip.is_loopback(),
            IpAddr::V6(ip) => ip.is_loopback(),
        }
    }

    /// 如果该地址似乎是可全局路由的，则返回 [`true`]。
    ///
    /// 有关更多详细信息，请参见 [`Ipv4Addr::is_global()`] 和 [`Ipv6Addr::is_global()`] 的文档。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(80, 9, 12, 3)).is_global(), true);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0x1c9, 0, 0, 0xafc8, 0, 0x1)).is_global(), true);
    /// ```
    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_global(&self) -> bool {
        match self {
            IpAddr::V4(ip) => ip.is_global(),
            IpAddr::V6(ip) => ip.is_global(),
        }
    }

    /// 如果这是一个多播地址，则返回 [`true`]。
    ///
    /// 有关更多详细信息，请参见 [`Ipv4Addr::is_multicast()`] 和 [`Ipv6Addr::is_multicast()`] 的文档。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(224, 254, 0, 0)).is_multicast(), true);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0)).is_multicast(), true);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "ip_shared", since = "1.12.0")]
    #[must_use]
    #[inline]
    pub const fn is_multicast(&self) -> bool {
        match self {
            IpAddr::V4(ip) => ip.is_multicast(),
            IpAddr::V6(ip) => ip.is_multicast(),
        }
    }

    /// 如果此地址在文档指定的范围内，则返回 [`true`]。
    ///
    /// 有关更多详细信息，请参见 [`Ipv4Addr::is_documentation()`] 和 [`Ipv6Addr::is_documentation()`] 的文档。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 6)).is_documentation(), true);
    /// assert_eq!(
    ///     IpAddr::V6(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0)).is_documentation(),
    ///     true
    /// );
    /// ```
    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_documentation(&self) -> bool {
        match self {
            IpAddr::V4(ip) => ip.is_documentation(),
            IpAddr::V6(ip) => ip.is_documentation(),
        }
    }

    /// 如果此地址在为基准测试指定的范围内，则返回 [`true`]。
    ///
    /// 有关更多详细信息，请参见 [`Ipv4Addr::is_benchmarking()`] 和 [`Ipv6Addr::is_benchmarking()`] 的文档。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(198, 19, 255, 255)).is_benchmarking(), true);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0x2001, 0x2, 0, 0, 0, 0, 0, 0)).is_benchmarking(), true);
    /// ```
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_benchmarking(&self) -> bool {
        match self {
            IpAddr::V4(ip) => ip.is_benchmarking(),
            IpAddr::V6(ip) => ip.is_benchmarking(),
        }
    }

    /// 如果此地址是 [`IPv4` address]，则返回 [`true`]，否则返回 [`false`]。
    ///
    ///
    /// [`IPv4` address]: IpAddr::V4
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 6)).is_ipv4(), true);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0)).is_ipv4(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "ipaddr_checker", since = "1.16.0")]
    #[must_use]
    #[inline]
    pub const fn is_ipv4(&self) -> bool {
        matches!(self, IpAddr::V4(_))
    }

    /// 如果此地址是 [`IPv6` address]，则返回 [`true`]，否则返回 [`false`]。
    ///
    ///
    /// [`IPv6` address]: IpAddr::V6
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 6)).is_ipv6(), false);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0)).is_ipv6(), true);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "ipaddr_checker", since = "1.16.0")]
    #[must_use]
    #[inline]
    pub const fn is_ipv6(&self) -> bool {
        matches!(self, IpAddr::V6(_))
    }

    /// 如果它是 IPv4 映射的 IPv6 地址，则将此地址转换为 `IpAddr::V4`，否则按原样返回 `self`。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)).to_canonical().is_loopback(), true);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1)).is_loopback(), false);
    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1)).to_canonical().is_loopback(), true);
    /// ```
    #[inline]
    #[must_use = "this returns the result of the operation, \
                  without modifying the original"]
    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    pub const fn to_canonical(&self) -> IpAddr {
        match self {
            &v4 @ IpAddr::V4(_) => v4,
            IpAddr::V6(v6) => v6.to_canonical(),
        }
    }
}

impl Ipv4Addr {
    /// 从四个八位八位字节创建一个新的 IPv4 地址。
    ///
    /// 结果将代表 IP 地址 `a`.`b`.`c`.`d`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::new(127, 0, 0, 1);
    /// ```
    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[inline]
    pub const fn new(a: u8, b: u8, c: u8, d: u8) -> Ipv4Addr {
        Ipv4Addr { octets: [a, b, c, d] }
    }

    /// 一个 IPv4 地址，地址指向 localhost: `127.0.0.1`
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::LOCALHOST;
    /// assert_eq!(addr, Ipv4Addr::new(127, 0, 0, 1));
    /// ```
    #[stable(feature = "ip_constructors", since = "1.30.0")]
    pub const LOCALHOST: Self = Ipv4Addr::new(127, 0, 0, 1);

    /// 代表未指定地址的 IPv4 地址: `0.0.0.0`
    ///
    /// 这对应于其他语言中的常量 `INADDR_ANY`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::UNSPECIFIED;
    /// assert_eq!(addr, Ipv4Addr::new(0, 0, 0, 0));
    /// ```
    #[doc(alias = "INADDR_ANY")]
    #[stable(feature = "ip_constructors", since = "1.30.0")]
    pub const UNSPECIFIED: Self = Ipv4Addr::new(0, 0, 0, 0);

    /// 代表广播地址的 IPv4 地址: `255.255.255.255`
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::BROADCAST;
    /// assert_eq!(addr, Ipv4Addr::new(255, 255, 255, 255));
    /// ```
    #[stable(feature = "ip_constructors", since = "1.30.0")]
    pub const BROADCAST: Self = Ipv4Addr::new(255, 255, 255, 255);

    /// 返回组成该地址的四个八位整数。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::new(127, 0, 0, 1);
    /// assert_eq!(addr.octets(), [127, 0, 0, 1]);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[inline]
    pub const fn octets(&self) -> [u8; 4] {
        self.octets
    }

    /// 为特殊的 'unspecified' 地址 (`0.0.0.0`) 返回 [`true`]。
    ///
    /// 此属性在 _UNIX Network Programming, Second Edition_，W 中定义。Richard Stevens,  p.
    /// 891; 另请参见 [ip7]。
    ///
    /// [ip7]: https://man7.org/linux/man-pages/man7/ip.7.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(0, 0, 0, 0).is_unspecified(), true);
    /// assert_eq!(Ipv4Addr::new(45, 22, 13, 197).is_unspecified(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
    #[stable(feature = "ip_shared", since = "1.12.0")]
    #[must_use]
    #[inline]
    pub const fn is_unspecified(&self) -> bool {
        u32::from_be_bytes(self.octets) == 0
    }

    /// 如果这是回环地址 (`127.0.0.0/8`)，则返回 [`true`]。
    ///
    /// 此属性由 [IETF RFC 1122] 定义。
    ///
    /// [IETF RFC 1122]: https://tools.ietf.org/html/rfc1122
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(127, 0, 0, 1).is_loopback(), true);
    /// assert_eq!(Ipv4Addr::new(45, 22, 13, 197).is_loopback(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_loopback(&self) -> bool {
        self.octets()[0] == 127
    }

    /// 如果这是一个专用地址，则返回 [`true`]。
    ///
    /// 专用地址范围在 [IETF RFC 1918] 中定义，包括：
    ///
    ///  - `10.0.0.0/8`
    ///  - `172.16.0.0/12`
    ///  - `192.168.0.0/16`
    ///
    /// [IETF RFC 1918]: https://tools.ietf.org/html/rfc1918
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(10, 0, 0, 1).is_private(), true);
    /// assert_eq!(Ipv4Addr::new(10, 10, 10, 10).is_private(), true);
    /// assert_eq!(Ipv4Addr::new(172, 16, 10, 10).is_private(), true);
    /// assert_eq!(Ipv4Addr::new(172, 29, 45, 14).is_private(), true);
    /// assert_eq!(Ipv4Addr::new(172, 32, 0, 2).is_private(), false);
    /// assert_eq!(Ipv4Addr::new(192, 168, 0, 2).is_private(), true);
    /// assert_eq!(Ipv4Addr::new(192, 169, 0, 2).is_private(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_private(&self) -> bool {
        match self.octets() {
            [10, ..] => true,
            [172, b, ..] if b >= 16 && b <= 31 => true,
            [192, 168, ..] => true,
            _ => false,
        }
    }

    /// 如果地址是本地链接 (`169.254.0.0/16`)，则返回 [`true`]。
    ///
    /// 此属性由 [IETF RFC 3927] 定义。
    ///
    /// [IETF RFC 3927]: https://tools.ietf.org/html/rfc3927
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(169, 254, 0, 0).is_link_local(), true);
    /// assert_eq!(Ipv4Addr::new(169, 254, 10, 65).is_link_local(), true);
    /// assert_eq!(Ipv4Addr::new(16, 89, 10, 65).is_link_local(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_link_local(&self) -> bool {
        matches!(self.octets(), [169, 254, ..])
    }

    /// 如果地址看起来是由 [IANA IPv4 Special-Purpose Address Registry] 指定的全局可访问的，则返回 [`true`]。
    /// 一个地址是否实际可访问将取决于您的网络配置。
    ///
    /// 大多数 IPv4 地址都是全局可达的;
    /// 除非它们被明确定义为 *not* 全局可达。
    ///
    /// 全球无法访问的显着地址的非详尽列表:
    ///
    /// - [unspecified address] ([`is_unspecified`](Ipv4Addr::is_unspecified))
    /// - 保留供 private 使用的地址 ([`is_private`](Ipv4Addr::is_private))
    /// - 共享地址空间 ([`is_shared`](Ipv4Addr::is_shared)) 中的地址
    /// - 回环地址 ([`is_loopback`](Ipv4Addr::is_loopback))
    /// - 链路本地地址 ([`is_link_local`](Ipv4Addr::is_link_local))
    /// - 为文档 ([`is_documentation`](Ipv4Addr::is_documentation)) 保留的地址
    /// - 为 ([`is_benchmarking`](Ipv4Addr::is_benchmarking)) 基准测试保留的地址
    /// - 保留地址 ([`is_reserved`](Ipv4Addr::is_reserved))
    /// - [broadcast address] ([`is_broadcast`](Ipv4Addr::is_broadcast))
    ///
    /// 有关哪些地址可全局访问的完整概览，请参见 [IANA IPv4 Special-Purpose Address Registry] 中的表格。
    ///
    /// [IANA IPv4 Special-Purpose Address Registry]: https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
    /// [unspecified address]: Ipv4Addr::UNSPECIFIED
    /// [broadcast address]: Ipv4Addr::BROADCAST
    ///

    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv4Addr;
    ///
    /// // 大多数 IPv4 地址都是全局可达的:
    /// assert_eq!(Ipv4Addr::new(80, 9, 12, 3).is_global(), true);
    ///
    /// // 但是，某些地址已被赋予特殊含义，使它们无法全局访问。
    /// // 一些例子是:
    ///
    /// // 未指定的地址 (`0.0.0.0`)
    /// assert_eq!(Ipv4Addr::UNSPECIFIED.is_global(), false);
    ///
    /// // 保留供 private 使用的地址 (`10.0.0.0/8`, `172.16.0.0/12`, 192.168.0.0/16)
    /// assert_eq!(Ipv4Addr::new(10, 254, 0, 0).is_global(), false);
    /// assert_eq!(Ipv4Addr::new(192, 168, 10, 65).is_global(), false);
    /// assert_eq!(Ipv4Addr::new(172, 16, 10, 65).is_global(), false);
    ///
    /// // 共享地址空间 (`100.64.0.0/10`) 中的地址
    /// assert_eq!(Ipv4Addr::new(100, 100, 0, 0).is_global(), false);
    ///
    /// // 回环地址 (`127.0.0.0/8`)
    /// assert_eq!(Ipv4Addr::LOCALHOST.is_global(), false);
    ///
    /// // 链路本地地址 (`169.254.0.0/16`)
    /// assert_eq!(Ipv4Addr::new(169, 254, 45, 1).is_global(), false);
    ///
    /// // 为文档保留的地址 (`192.0.2.0/24`、`198.51.100.0/24`、`203.0.113.0/24`)
    /// assert_eq!(Ipv4Addr::new(192, 0, 2, 255).is_global(), false);
    /// assert_eq!(Ipv4Addr::new(198, 51, 100, 65).is_global(), false);
    /// assert_eq!(Ipv4Addr::new(203, 0, 113, 6).is_global(), false);
    ///
    /// // 为 (`198.18.0.0/15`) 基准测试保留的地址
    /// assert_eq!(Ipv4Addr::new(198, 18, 0, 0).is_global(), false);
    ///
    /// // 保留地址 (`240.0.0.0/4`)
    /// assert_eq!(Ipv4Addr::new(250, 10, 20, 30).is_global(), false);
    ///
    /// // 广播地址 (`255.255.255.255`)
    /// assert_eq!(Ipv4Addr::BROADCAST.is_global(), false);
    ///
    /// // 有关完整概述，请参见 IANA IPv4 专用地址注册表。
    /// ```
    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_global(&self) -> bool {
        !(self.octets()[0] == 0 // "This network"
            || self.is_private()
            || self.is_shared()
            || self.is_loopback()
            || self.is_link_local()
            // 为 future 协议 (`192.0.0.0/24`) 保留的地址
            ||(self.octets()[0] == 192 && self.octets()[1] == 0 && self.octets()[2] == 0)
            || self.is_documentation()
            || self.is_benchmarking()
            || self.is_reserved()
            || self.is_broadcast())
    }

    /// 如果此地址是 [IETF RFC 6598] (`100.64.0.0/10`) 中定义的共享地址空间的一部分，则返回 [`true`]。
    ///
    ///
    /// [IETF RFC 6598]: https://tools.ietf.org/html/rfc6598
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(100, 64, 0, 0).is_shared(), true);
    /// assert_eq!(Ipv4Addr::new(100, 127, 255, 255).is_shared(), true);
    /// assert_eq!(Ipv4Addr::new(100, 128, 0, 0).is_shared(), false);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_shared(&self) -> bool {
        self.octets()[0] == 100 && (self.octets()[1] & 0b1100_0000 == 0b0100_0000)
    }

    /// 如果此地址属于 `198.18.0.0/15` 范围 (为网络设备基准测试保留)，则返回 [`true`]。
    /// [IETF RFC 2544] 将该范围定义为 `192.18.0.0` 至 `198.19.255.255`，但 [勘误表 423][errata 423] 将其更正为 `198.18.0.0/15`。
    ///
    ///
    /// [IETF RFC 2544]: https://tools.ietf.org/html/rfc2544
    /// [errata 423]: https://www.rfc-editor.org/errata/eid423
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(198, 17, 255, 255).is_benchmarking(), false);
    /// assert_eq!(Ipv4Addr::new(198, 18, 0, 0).is_benchmarking(), true);
    /// assert_eq!(Ipv4Addr::new(198, 19, 255, 255).is_benchmarking(), true);
    /// assert_eq!(Ipv4Addr::new(198, 20, 0, 0).is_benchmarking(), false);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_benchmarking(&self) -> bool {
        self.octets()[0] == 198 && (self.octets()[1] & 0xfe) == 18
    }

    /// 如果此地址由 IANA 保留供 future 使用，则返回 [`true`]。[IETF RFC 1112] 将保留地址块定义为 `240.0.0.0/4`。
    /// 此范围通常包括广播地址 `255.255.255.255`，但是此实现方案明确将其排除在外，因为它显然不保留供 future 使用。
    ///
    ///
    /// [IETF RFC 1112]: https://tools.ietf.org/html/rfc1112
    ///
    /// # Warning
    ///
    /// 随着 IANA 分配新地址，此方法将被更新。
    /// 这可能会导致未保留的地址被视为依赖于此方法的过时版本的代码中的保留地址。
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(240, 0, 0, 0).is_reserved(), true);
    /// assert_eq!(Ipv4Addr::new(255, 255, 255, 254).is_reserved(), true);
    ///
    /// assert_eq!(Ipv4Addr::new(239, 255, 255, 255).is_reserved(), false);
    /// // 此实现不将广播地址视为保留给 future 使用
    /// assert_eq!(Ipv4Addr::new(255, 255, 255, 255).is_reserved(), false);
    /// ```
    ///
    ///
    ///
    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_reserved(&self) -> bool {
        self.octets()[0] & 240 == 240 && !self.is_broadcast()
    }

    /// 如果这是多播地址 (`224.0.0.0/4`)，则返回 [`true`]。
    ///
    /// 多播地址在 `224` 和 `239` 之间有一个最重要的八位字节，由 [IETF RFC 5771] 定义。
    ///
    ///
    /// [IETF RFC 5771]: https://tools.ietf.org/html/rfc5771
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(224, 254, 0, 0).is_multicast(), true);
    /// assert_eq!(Ipv4Addr::new(236, 168, 10, 65).is_multicast(), true);
    /// assert_eq!(Ipv4Addr::new(172, 16, 10, 65).is_multicast(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_multicast(&self) -> bool {
        self.octets()[0] >= 224 && self.octets()[0] <= 239
    }

    /// 如果这是广播地址 (`255.255.255.255`)，则返回 [`true`]。
    ///
    /// 广播地址的所有八位字节都设置为 `255`，如 [IETF RFC 919] 中所定义。
    ///
    /// [IETF RFC 919]: https://tools.ietf.org/html/rfc919
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(255, 255, 255, 255).is_broadcast(), true);
    /// assert_eq!(Ipv4Addr::new(236, 168, 10, 65).is_broadcast(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_broadcast(&self) -> bool {
        u32::from_be_bytes(self.octets()) == u32::from_be_bytes(Self::BROADCAST.octets())
    }

    /// 如果此地址在文档指定的范围内，则返回 [`true`]。
    ///
    /// 这在 [IETF RFC 5737] 中定义：
    ///
    /// - `192.0.2.0/24` (TEST-NET-1)
    /// - `198.51.100.0/24` (TEST-NET-2)
    /// - `203.0.113.0/24` (TEST-NET-3)
    ///
    /// [IETF RFC 5737]: https://tools.ietf.org/html/rfc5737
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// assert_eq!(Ipv4Addr::new(192, 0, 2, 255).is_documentation(), true);
    /// assert_eq!(Ipv4Addr::new(198, 51, 100, 65).is_documentation(), true);
    /// assert_eq!(Ipv4Addr::new(203, 0, 113, 6).is_documentation(), true);
    /// assert_eq!(Ipv4Addr::new(193, 34, 17, 19).is_documentation(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_documentation(&self) -> bool {
        matches!(self.octets(), [192, 0, 2, _] | [198, 51, 100, _] | [203, 0, 113, _])
    }

    /// 将此地址转换为 [IPv4 兼容][IPv4-compatible] 的 [`IPv6` 地址][`IPv6` address]。
    ///
    /// `a.b.c.d` 变成 `::a.b.c.d`
    ///
    /// 请注意，与 IPv4 兼容的地址已被正式弃用。
    /// 如果出于遗留原因，您没有明确需要与 IPv4 兼容的地址，请考虑改用 `to_ipv6_mapped`。
    ///
    /// [IPv4-compatible]: Ipv6Addr#ipv4-compatible-ipv6-addresses
    /// [`IPv6` address]: Ipv6Addr
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(
    ///     Ipv4Addr::new(192, 0, 2, 255).to_ipv6_compatible(),
    ///     Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0xc000, 0x2ff)
    /// );
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use = "this returns the result of the operation, \
                  without modifying the original"]
    #[inline]
    pub const fn to_ipv6_compatible(&self) -> Ipv6Addr {
        let [a, b, c, d] = self.octets();
        Ipv6Addr { octets: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, a, b, c, d] }
    }

    /// 将此地址转换为 [IPv4 映射][IPv4-mapped] 的 [`IPv6` 地址][`IPv6` address]。
    ///
    /// `a.b.c.d` 变成 `::ffff:a.b.c.d`
    ///
    /// [IPv4-mapped]: Ipv6Addr#ipv4-mapped-ipv6-addresses
    /// [`IPv6` address]: Ipv6Addr
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(Ipv4Addr::new(192, 0, 2, 255).to_ipv6_mapped(),
    ///            Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc000, 0x2ff));
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use = "this returns the result of the operation, \
                  without modifying the original"]
    #[inline]
    pub const fn to_ipv6_mapped(&self) -> Ipv6Addr {
        let [a, b, c, d] = self.octets();
        Ipv6Addr { octets: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xFF, 0xFF, a, b, c, d] }
    }
}

#[stable(feature = "ip_addr", since = "1.7.0")]
impl fmt::Display for IpAddr {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            IpAddr::V4(ip) => ip.fmt(fmt),
            IpAddr::V6(ip) => ip.fmt(fmt),
        }
    }
}

#[stable(feature = "ip_addr", since = "1.7.0")]
impl fmt::Debug for IpAddr {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, fmt)
    }
}

#[stable(feature = "ip_from_ip", since = "1.16.0")]
impl From<Ipv4Addr> for IpAddr {
    /// 将此地址复制到新的 `IpAddr::V4`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr};
    ///
    /// let addr = Ipv4Addr::new(127, 0, 0, 1);
    ///
    /// assert_eq!(
    ///     IpAddr::V4(addr),
    ///     IpAddr::from(addr)
    /// )
    /// ```
    #[inline]
    fn from(ipv4: Ipv4Addr) -> IpAddr {
        IpAddr::V4(ipv4)
    }
}

#[stable(feature = "ip_from_ip", since = "1.16.0")]
impl From<Ipv6Addr> for IpAddr {
    /// 将此地址复制到新的 `IpAddr::V6`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv6Addr};
    ///
    /// let addr = Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff);
    ///
    /// assert_eq!(
    ///     IpAddr::V6(addr),
    ///     IpAddr::from(addr)
    /// );
    /// ```
    #[inline]
    fn from(ipv6: Ipv6Addr) -> IpAddr {
        IpAddr::V6(ipv6)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for Ipv4Addr {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        let octets = self.octets();

        // 如果没有对齐要求，直接将 IP 地址写入 `f`。
        // 否则，将其写入本地缓冲区，然后使用 `f.pad`。
        if fmt.precision().is_none() && fmt.width().is_none() {
            write!(fmt, "{}.{}.{}.{}", octets[0], octets[1], octets[2], octets[3])
        } else {
            const LONGEST_IPV4_ADDR: &str = "255.255.255.255";

            let mut buf = DisplayBuffer::<{ LONGEST_IPV4_ADDR.len() }>::new();
            // 缓冲区足够长，可以容纳最长的 IPv4 地址，所以这永远不会失败。
            write!(buf, "{}.{}.{}.{}", octets[0], octets[1], octets[2], octets[3]).unwrap();

            fmt.pad(buf.as_str())
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for Ipv4Addr {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, fmt)
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialEq<Ipv4Addr> for IpAddr {
    #[inline]
    fn eq(&self, other: &Ipv4Addr) -> bool {
        match self {
            IpAddr::V4(v4) => v4 == other,
            IpAddr::V6(_) => false,
        }
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialEq<IpAddr> for Ipv4Addr {
    #[inline]
    fn eq(&self, other: &IpAddr) -> bool {
        match other {
            IpAddr::V4(v4) => self == v4,
            IpAddr::V6(_) => false,
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl PartialOrd for Ipv4Addr {
    #[inline]
    fn partial_cmp(&self, other: &Ipv4Addr) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialOrd<Ipv4Addr> for IpAddr {
    #[inline]
    fn partial_cmp(&self, other: &Ipv4Addr) -> Option<Ordering> {
        match self {
            IpAddr::V4(v4) => v4.partial_cmp(other),
            IpAddr::V6(_) => Some(Ordering::Greater),
        }
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialOrd<IpAddr> for Ipv4Addr {
    #[inline]
    fn partial_cmp(&self, other: &IpAddr) -> Option<Ordering> {
        match other {
            IpAddr::V4(v4) => self.partial_cmp(v4),
            IpAddr::V6(_) => Some(Ordering::Less),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Ord for Ipv4Addr {
    #[inline]
    fn cmp(&self, other: &Ipv4Addr) -> Ordering {
        self.octets.cmp(&other.octets)
    }
}

#[stable(feature = "ip_u32", since = "1.1.0")]
impl From<Ipv4Addr> for u32 {
    /// 将 `Ipv4Addr` 转换为主机字节顺序 `u32`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::new(0x12, 0x34, 0x56, 0x78);
    /// assert_eq!(0x12345678, u32::from(addr));
    /// ```
    #[inline]
    fn from(ip: Ipv4Addr) -> u32 {
        u32::from_be_bytes(ip.octets)
    }
}

#[stable(feature = "ip_u32", since = "1.1.0")]
impl From<u32> for Ipv4Addr {
    /// 将主机字节顺序 `u32` 转换为 `Ipv4Addr`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::from(0x12345678);
    /// assert_eq!(Ipv4Addr::new(0x12, 0x34, 0x56, 0x78), addr);
    /// ```
    #[inline]
    fn from(ip: u32) -> Ipv4Addr {
        Ipv4Addr { octets: ip.to_be_bytes() }
    }
}

#[stable(feature = "from_slice_v4", since = "1.9.0")]
impl From<[u8; 4]> for Ipv4Addr {
    /// 从一个四元素字节数组创建一个 `Ipv4Addr`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// let addr = Ipv4Addr::from([13u8, 12u8, 11u8, 10u8]);
    /// assert_eq!(Ipv4Addr::new(13, 12, 11, 10), addr);
    /// ```
    #[inline]
    fn from(octets: [u8; 4]) -> Ipv4Addr {
        Ipv4Addr { octets }
    }
}

#[stable(feature = "ip_from_slice", since = "1.17.0")]
impl From<[u8; 4]> for IpAddr {
    /// 从一个四元素字节数组创建一个 `IpAddr::V4`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv4Addr};
    ///
    /// let addr = IpAddr::from([13u8, 12u8, 11u8, 10u8]);
    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(13, 12, 11, 10)), addr);
    /// ```
    #[inline]
    fn from(octets: [u8; 4]) -> IpAddr {
        IpAddr::V4(Ipv4Addr::from(octets))
    }
}

impl Ipv6Addr {
    /// 从八个 16 位段创建一个新的 IPv6 地址。
    ///
    /// 结果将代表 IP 地址 `a:b:c:d:e:f:g:h`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// let addr = Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff);
    /// ```
    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[inline]
    pub const fn new(a: u16, b: u16, c: u16, d: u16, e: u16, f: u16, g: u16, h: u16) -> Ipv6Addr {
        let addr16 = [
            a.to_be(),
            b.to_be(),
            c.to_be(),
            d.to_be(),
            e.to_be(),
            f.to_be(),
            g.to_be(),
            h.to_be(),
        ];
        Ipv6Addr {
            // `addr16` 中的所有元素均为大端。
            // SAFETY: `[u16; 8]` 始终可以安全地转换为 `[u8; 16]`。
            octets: unsafe { transmute::<_, [u8; 16]>(addr16) },
        }
    }

    /// 代表本地主机的 IPv6 地址: `::1`。
    ///
    /// 这对应其他语言的常量 `IN6ADDR_LOOPBACK_INIT` 或 `in6addr_loopback`。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// let addr = Ipv6Addr::LOCALHOST;
    /// assert_eq!(addr, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
    /// ```
    #[doc(alias = "IN6ADDR_LOOPBACK_INIT")]
    #[doc(alias = "in6addr_loopback")]
    #[stable(feature = "ip_constructors", since = "1.30.0")]
    pub const LOCALHOST: Self = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1);

    /// 代表未指定地址的 IPv6 地址: `::`
    ///
    /// 这对应其他语言的常量 `IN6ADDR_ANY_INIT` 或 `in6addr_any`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// let addr = Ipv6Addr::UNSPECIFIED;
    /// assert_eq!(addr, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0));
    /// ```
    #[doc(alias = "IN6ADDR_ANY_INIT")]
    #[doc(alias = "in6addr_any")]
    #[stable(feature = "ip_constructors", since = "1.30.0")]
    pub const UNSPECIFIED: Self = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0);

    /// 返回组成该地址的八个 16 位段。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).segments(),
    ///            [0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff]);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[inline]
    pub const fn segments(&self) -> [u16; 8] {
        // `self.octets` 中的所有元素都必须是大端。
        // SAFETY: `[u8; 16]` 始终可以安全地转换为 `[u16; 8]`。
        let [a, b, c, d, e, f, g, h] = unsafe { transmute::<_, [u16; 8]>(self.octets) };
        // 我们想要本地字节序 u16
        [
            u16::from_be(a),
            u16::from_be(b),
            u16::from_be(c),
            u16::from_be(d),
            u16::from_be(e),
            u16::from_be(f),
            u16::from_be(g),
            u16::from_be(h),
        ]
    }

    /// 为特殊的 'unspecified' 地址 (`::`) 返回 [`true`]。
    ///
    /// 此属性在 [IETF RFC 4291] 中定义。
    ///
    /// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_unspecified(), false);
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0).is_unspecified(), true);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_unspecified(&self) -> bool {
        u128::from_be_bytes(self.octets()) == u128::from_be_bytes(Ipv6Addr::UNSPECIFIED.octets())
    }

    /// 如果这是 [环回地址][loopback address] (`::1`)，如 [IETF RFC 4291 第 2.5.3 节][IETF RFC 4291 section 2.5.3] 中所定义，则返回 [`true`]。
    ///
    ///
    /// 与 IPv4 相反，IPv6 只有一个回环地址。
    ///
    /// [loopback address]: Ipv6Addr::LOCALHOST
    /// [IETF RFC 4291 section 2.5.3]: https://tools.ietf.org/html/rfc4291#section-2.5.3
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_loopback(), false);
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0x1).is_loopback(), true);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_loopback(&self) -> bool {
        u128::from_be_bytes(self.octets()) == u128::from_be_bytes(Ipv6Addr::LOCALHOST.octets())
    }

    /// 如果地址看起来是由 [IANA IPv6 Special-Purpose Address Registry] 指定的全局可访问的，则返回 [`true`]。
    /// 一个地址是否实际可访问将取决于您的网络配置。
    ///
    /// 大多数 IPv6 地址都是全局可达的;
    /// 除非它们被明确定义为 *not* 全局可达。
    ///
    /// 全球无法访问的显着地址的非详尽列表:
    /// - [unspecified address] ([`is_unspecified`](Ipv6Addr::is_unspecified))
    /// - [loopback address] ([`is_loopback`](Ipv6Addr::is_loopback))
    /// - IPv4 映射地址
    /// - 为基准测试保留的地址
    /// - 为文档 ([`is_documentation`](Ipv6Addr::is_documentation)) 保留的地址
    /// - 唯一的本地地址 ([`is_unique_local`](Ipv6Addr::is_unique_local))
    /// - 具有链路本地作用域 ([`is_unicast_link_local`](Ipv6Addr::is_unicast_link_local)) 的单播地址
    ///
    /// 有关哪些地址可全局访问的完整概览，请参见 [IANA IPv6 Special-Purpose Address Registry] 中的表格。
    ///
    /// 请注意，地址具有以下作用: 存在与全局可访问相同的地址，并且这两个概念之间没有直接关系是全球可访问的，没有具有非域范围的多播地址 (多播地址)。
    ///
    ///
    /// [IANA IPv6 Special-Purpose Address Registry]: https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml
    /// [unspecified address]: Ipv6Addr::UNSPECIFIED
    /// [loopback address]: Ipv6Addr::LOCALHOST
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv6Addr;
    ///
    /// // 大多数 IPv6 地址都是全局可达的:
    /// assert_eq!(Ipv6Addr::new(0x26, 0, 0x1c9, 0, 0, 0xafc8, 0x10, 0x1).is_global(), true);
    ///
    /// // 但是，某些地址已被赋予特殊含义，使它们无法全局访问。
    /// // 一些例子是:
    ///
    /// // 未指定的地址 (`::`)
    /// assert_eq!(Ipv6Addr::UNSPECIFIED.is_global(), false);
    ///
    /// // 回环地址 (`::1`)
    /// assert_eq!(Ipv6Addr::LOCALHOST.is_global(), false);
    ///
    /// // IPv4 映射地址 (`::ffff:0:0/96`)
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_global(), false);
    ///
    /// // 为 (`2001:2::/48`) 基准测试保留的地址
    /// assert_eq!(Ipv6Addr::new(0x2001, 2, 0, 0, 0, 0, 0, 1,).is_global(), false);
    ///
    /// // 为文档 (`2001:db8::/32`) 保留的地址
    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 1).is_global(), false);
    ///
    /// // 唯一的本地地址 (`fc00::/7`)
    /// assert_eq!(Ipv6Addr::new(0xfc02, 0, 0, 0, 0, 0, 0, 1).is_global(), false);
    ///
    /// // 具有链路本地作用域 (`fe80::/10`) 的单播地址
    /// assert_eq!(Ipv6Addr::new(0xfe81, 0, 0, 0, 0, 0, 0, 1).is_global(), false);
    ///
    /// // 有关完整概述，请参见 IANA IPv6 专用地址注册表。
    /// ```
    ///
    ///
    ///
    ///
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_global(&self) -> bool {
        !(self.is_unspecified()
            || self.is_loopback()
            // IPv4 映射地址 (`::ffff:0:0/96`)
            || matches!(self.segments(), [0, 0, 0, 0, 0, 0xffff, _, _])
            // IPv4-IPv6 Translat。 (`64:ff9b:1::/48`)
            || matches!(self.segments(), [0x64, 0xff9b, 1, _, _, _, _, _])
            // 仅丢弃地址块 (`100::/64`)
            || matches!(self.segments(), [0x100, 0, 0, 0, _, _, _, _])
            // IETF 协议分配 (`2001::/23`)
            || (matches!(self.segments(), [0x2001, b, _, _, _, _, _, _] if b < 0x200)
                && !(
                    // 端口控制协议任播 (`2001:1::1`)
                    u128::from_be_bytes(self.octets()) == 0x2001_0001_0000_0000_0000_0000_0000_0001
                    // 在 NAT Anycast (`2001:1::2`) 周围使用中继进行遍历
                    || u128::from_be_bytes(self.octets()) == 0x2001_0001_0000_0000_0000_0000_0000_0002
                    // AMT (`2001:3::/32`)
                    || matches!(self.segments(), [0x2001, 3, _, _, _, _, _, _])
                    // AS112-v6 (`2001:4:112::/48`)
                    || matches!(self.segments(), [0x2001, 4, 0x112, _, _, _, _, _])
                    // ORCHIDv2 (`2001:20::/28`)
                    || matches!(self.segments(), [0x2001, b, _, _, _, _, _, _] if b >= 0x20 && b <= 0x2F)
                ))
            || self.is_documentation()
            || self.is_unique_local()
            || self.is_unicast_link_local())
    }

    /// 如果这是唯一的本地地址 (`fc00::/7`)，则返回 [`true`]。
    ///
    /// 此属性在 [IETF RFC 4193] 中定义。
    ///
    /// [IETF RFC 4193]: https://tools.ietf.org/html/rfc4193
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_unique_local(), false);
    /// assert_eq!(Ipv6Addr::new(0xfc02, 0, 0, 0, 0, 0, 0, 0).is_unique_local(), true);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_unique_local(&self) -> bool {
        (self.segments()[0] & 0xfe00) == 0xfc00
    }

    /// 如果这是 [IETF RFC 4291] 定义的单播地址，则返回 [`true`]。
    /// 任何不是 [多播地址][multicast address] (`ff00::/8`) 的地址都是单播的。
    ///
    /// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
    /// [multicast address]: Ipv6Addr::is_multicast
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv6Addr;
    ///
    /// // 未指定地址和回环地址是单播的。
    /// assert_eq!(Ipv6Addr::UNSPECIFIED.is_unicast(), true);
    /// assert_eq!(Ipv6Addr::LOCALHOST.is_unicast(), true);
    ///
    /// // 任何不是多播地址 (`ff00::/8`) 的地址都是单播的。
    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_unicast(), true);
    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).is_unicast(), false);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_unicast(&self) -> bool {
        !self.is_multicast()
    }

    /// 如果地址是具有链接本地作用域的单播地址，则返回 `true`，如 [RFC 4291] 中所定义。
    ///
    /// 如果单播地址具有前缀 `fe80::/10`，则它具有链路本地作用域，如 [RFC 4291 section 2.4]。
    /// 请注意，这包含比 [RFC 4291 第 2.5.6 节][RFC 4291 section 2.5.6] 中定义的地址更多的地址，[RFC 4291 第 2.5.6 节] 将 "链路本地 IPv6 单播地址" 描述为具有以下更严格的格式：
    ///
    /// ```text
    /// | 10 bits  |         54 bits         |          64 bits           |
    /// +----------+-------------------------+----------------------------+
    /// |1111111010|           0             |       interface ID         |
    /// +----------+-------------------------+----------------------------+
    /// ```
    /// 因此，虽然目前应用程序将遇到的唯一具有本地链接作用域的地址都在 `fe80::/64` 中，但随着新标准的发布，这可能会在 future 中发生变化。
    /// `fe80::/10` 中可以分配更多的地址，这些地址将具有本地链接作用域。
    ///
    /// 另请注意，虽然 [RFC 4291 第 2.5.3 章][RFC 4291 section 2.5.3] 提到 "它被视为具有 Link-Local 作用域" 的 [环回地址][loopback address] (`::1`)，但这并不意味着回环地址实际上具有链接本地作用域，并且此方法将在其上返回 `false`。
    ///
    ///
    /// [RFC 4291]: https://tools.ietf.org/html/rfc4291
    /// [RFC 4291 section 2.4]: https://tools.ietf.org/html/rfc4291#section-2.4
    /// [RFC 4291 section 2.5.3]: https://tools.ietf.org/html/rfc4291#section-2.5.3
    /// [RFC 4291 section 2.5.6]: https://tools.ietf.org/html/rfc4291#section-2.5.6
    /// [loopback address]: Ipv6Addr::LOCALHOST
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv6Addr;
    ///
    /// // 回环地址 (`::1`) 实际上并没有链接本地作用域。
    /// assert_eq!(Ipv6Addr::LOCALHOST.is_unicast_link_local(), false);
    ///
    /// // 只有 `fe80::/10` 中的地址具有本地链接作用域。
    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_unicast_link_local(), false);
    /// assert_eq!(Ipv6Addr::new(0xfe80, 0, 0, 0, 0, 0, 0, 0).is_unicast_link_local(), true);
    ///
    /// // 更严格的 `fe80::/64` 之外的地址也具有链接本地作用域。
    /// assert_eq!(Ipv6Addr::new(0xfe80, 0, 0, 1, 0, 0, 0, 0).is_unicast_link_local(), true);
    /// assert_eq!(Ipv6Addr::new(0xfe81, 0, 0, 0, 0, 0, 0, 0).is_unicast_link_local(), true);
    /// ```
    ///
    ///
    ///
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_unicast_link_local(&self) -> bool {
        (self.segments()[0] & 0xffc0) == 0xfe80
    }

    /// 如果这是为文档 (`2001:db8::/32`) 保留的地址，则返回 [`true`]。
    ///
    ///
    /// 此属性在 [IETF RFC 3849] 中定义。
    ///
    /// [IETF RFC 3849]: https://tools.ietf.org/html/rfc3849
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_documentation(), false);
    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_documentation(), true);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_documentation(&self) -> bool {
        (self.segments()[0] == 0x2001) && (self.segments()[1] == 0xdb8)
    }

    /// 如果这是为基准测试 (`2001:2::/48`) 保留的地址，则返回 [`true`]。
    ///
    /// 此属性在 [IETF RFC 5180] 中定义，其中错误地将其指定为覆盖范围 `2001:0200::/48`。
    /// 这在 [IETF RFC Errata 1752] 到 `2001:0002::/48` 中得到纠正。
    ///
    /// [IETF RFC 5180]: https://tools.ietf.org/html/rfc5180
    /// [IETF RFC Errata 1752]: https://www.rfc-editor.org/errata_search.php?eid=1752
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc613, 0x0).is_benchmarking(), false);
    /// assert_eq!(Ipv6Addr::new(0x2001, 0x2, 0, 0, 0, 0, 0, 0).is_benchmarking(), true);
    /// ```
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_benchmarking(&self) -> bool {
        (self.segments()[0] == 0x2001) && (self.segments()[1] == 0x2) && (self.segments()[2] == 0)
    }

    /// 如果该地址是全局可路由的单播地址，则返回 [`true`]。
    ///
    /// 以下返回 false：
    ///
    /// - 回环地址
    /// - 链接本地地址
    /// - 唯一的本地地址
    /// - 未指定地址
    /// - 保留用于文档的地址范围
    ///
    /// 此方法根据 [RFC 4291 第 2.5.7 节][RFC 4291 section 2.5.7] 返回 [`true`] 作为站点本地地址
    ///
    /// ```no_rust
    /// The special behavior of [the site-local unicast] prefix defined in [RFC3513] must no longer
    /// be supported in new implementations (i.e., new implementations must treat this prefix as
    /// Global Unicast).
    /// ```
    ///
    /// [RFC 4291 section 2.5.7]: https://tools.ietf.org/html/rfc4291#section-2.5.7
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_unicast_global(), false);
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_unicast_global(), true);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn is_unicast_global(&self) -> bool {
        self.is_unicast()
            && !self.is_loopback()
            && !self.is_unicast_link_local()
            && !self.is_unique_local()
            && !self.is_unspecified()
            && !self.is_documentation()
            && !self.is_benchmarking()
    }

    /// 如果该地址是多播的，则返回该地址的多播作用域。
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    ///
    /// use std::net::{Ipv6Addr, Ipv6MulticastScope};
    ///
    /// assert_eq!(
    ///     Ipv6Addr::new(0xff0e, 0, 0, 0, 0, 0, 0, 0).multicast_scope(),
    ///     Some(Ipv6MulticastScope::Global)
    /// );
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).multicast_scope(), None);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use]
    #[inline]
    pub const fn multicast_scope(&self) -> Option<Ipv6MulticastScope> {
        if self.is_multicast() {
            match self.segments()[0] & 0x000f {
                1 => Some(Ipv6MulticastScope::InterfaceLocal),
                2 => Some(Ipv6MulticastScope::LinkLocal),
                3 => Some(Ipv6MulticastScope::RealmLocal),
                4 => Some(Ipv6MulticastScope::AdminLocal),
                5 => Some(Ipv6MulticastScope::SiteLocal),
                8 => Some(Ipv6MulticastScope::OrganizationLocal),
                14 => Some(Ipv6MulticastScope::Global),
                _ => None,
            }
        } else {
            None
        }
    }

    /// 如果这是多播地址 (`ff00::/8`)，则返回 [`true`]。
    ///
    /// 此属性由 [IETF RFC 4291] 定义。
    ///
    /// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).is_multicast(), true);
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_multicast(), false);
    /// ```
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(since = "1.7.0", feature = "ip_17")]
    #[must_use]
    #[inline]
    pub const fn is_multicast(&self) -> bool {
        (self.segments()[0] & 0xff00) == 0xff00
    }

    /// 如果它是 [IPv4 映射][IPv4-mapped] 地址 (如 [IETF RFC 4291 第 2.5.5.2 节][IETF RFC 4291 section 2.5.5.2] 中所定义)，则将此地址转换为 [`IPv4` address]，否则返回 [`None`]。
    ///
    ///
    /// `::ffff:a.b.c.d` 变成 `a.b.c.d`。
    /// 所有非以 `::ffff` 开头的地址都将返回 `None`。
    ///
    /// [`IPv4` address]: Ipv4Addr
    /// [IPv4-mapped]: Ipv6Addr
    /// [IETF RFC 4291 section 2.5.5.2]: https://tools.ietf.org/html/rfc4291#section-2.5.5.2
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).to_ipv4_mapped(), None);
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).to_ipv4_mapped(),
    ///            Some(Ipv4Addr::new(192, 10, 2, 255)));
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1).to_ipv4_mapped(), None);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[stable(feature = "ipv6_to_ipv4_mapped", since = "1.63.0")]
    #[must_use = "this returns the result of the operation, \
                  without modifying the original"]
    #[inline]
    pub const fn to_ipv4_mapped(&self) -> Option<Ipv4Addr> {
        match self.octets() {
            [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, a, b, c, d] => {
                Some(Ipv4Addr::new(a, b, c, d))
            }
            _ => None,
        }
    }

    /// 如果此地址是 [IETF RFC 4291 第 2.5.5.1 节][IETF RFC 4291 section 2.5.5.1] 中定义的 [IPv4 兼容][IPv4-compatible] 地址或 [IETF RFC 4291 第 2.5.5.2 节][IETF RFC 4291 section 2.5.5.2] 中定义的 [ IPv4 映射][IPv4-mapped] 地址，则将此地址转换为 [`IPv4` 地址][`IPv4` address]，否则返回 [`None`]。
    ///
    ///
    /// 请注意，这将为 IPv6 回环地址 `::1` 返回一个 [`IPv4` address]。使用 [`Ipv6Addr::to_ipv4_mapped`] 可以避免这种情况。
    ///
    /// `::a.b.c.d` 和 `::ffff:a.b.c.d` 变成了 `a.b.c.d`。`::1` 变成了 `0.0.0.1`。
    /// 所有*不*以全零或 `::ffff` 开头的地址都将返回 `None`。
    ///
    /// [`IPv4` address]: Ipv4Addr
    /// [IPv4-compatible]: Ipv6Addr#ipv4-compatible-ipv6-addresses
    /// [IPv4-mapped]: Ipv6Addr#ipv4-mapped-ipv6-addresses
    /// [IETF RFC 4291 section 2.5.5.1]: https://tools.ietf.org/html/rfc4291#section-2.5.5.1
    /// [IETF RFC 4291 section 2.5.5.2]: https://tools.ietf.org/html/rfc4291#section-2.5.5.2
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{Ipv4Addr, Ipv6Addr};
    ///
    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).to_ipv4(), None);
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).to_ipv4(),
    ///            Some(Ipv4Addr::new(192, 10, 2, 255)));
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1).to_ipv4(),
    ///            Some(Ipv4Addr::new(0, 0, 0, 1)));
    /// ```
    ///
    ///
    ///
    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use = "this returns the result of the operation, \
                  without modifying the original"]
    #[inline]
    pub const fn to_ipv4(&self) -> Option<Ipv4Addr> {
        if let [0, 0, 0, 0, 0, 0 | 0xffff, ab, cd] = self.segments() {
            let [a, b] = ab.to_be_bytes();
            let [c, d] = cd.to_be_bytes();
            Some(Ipv4Addr::new(a, b, c, d))
        } else {
            None
        }
    }

    /// 如果此地址是 IPv4 映射地址，则将此地址转换为 `IpAddr::V4`，否则返回自包装在 `IpAddr::V6` 中。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ip)]
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1).is_loopback(), false);
    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1).to_canonical().is_loopback(), true);
    /// ```
    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
    #[unstable(feature = "ip", issue = "27709")]
    #[must_use = "this returns the result of the operation, \
                  without modifying the original"]
    #[inline]
    pub const fn to_canonical(&self) -> IpAddr {
        if let Some(mapped) = self.to_ipv4_mapped() {
            return IpAddr::V4(mapped);
        }
        IpAddr::V6(*self)
    }

    /// 返回 IPv6 地址组成的 16 个八位整数。
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).octets(),
    ///            [255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]);
    /// ```
    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
    #[stable(feature = "ipv6_to_octets", since = "1.12.0")]
    #[must_use]
    #[inline]
    pub const fn octets(&self) -> [u8; 16] {
        self.octets
    }
}

/// 编写一个符合 [RFC 5952](https://tools.ietf.org/html/rfc5952) 描述的规范样式的 Ivv6Addr。
///
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for Ipv6Addr {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // 如果没有对齐要求，直接将 IP 地址写入 `f`。
        // 否则，将其写入本地缓冲区，然后使用 `f.pad`。
        if f.precision().is_none() && f.width().is_none() {
            let segments = self.segments();

            // :: 和 ::1 的特殊情况； 否则，它们将使用 IPv4 格式化程序编写
            //
            if self.is_unspecified() {
                f.write_str("::")
            } else if self.is_loopback() {
                f.write_str("::1")
            } else if let Some(ipv4) = self.to_ipv4() {
                match segments[5] {
                    // IPv4 兼容地址
                    0 => write!(f, "::{}", ipv4),
                    // IPv4 映射地址
                    0xffff => write!(f, "::ffff:{}", ipv4),
                    _ => unreachable!(),
                }
            } else {
                #[derive(Copy, Clone, Default)]
                struct Span {
                    start: usize,
                    len: usize,
                }

                // 找出内部 0 跨度
                let zeroes = {
                    let mut longest = Span::default();
                    let mut current = Span::default();

                    for (i, &segment) in segments.iter().enumerate() {
                        if segment == 0 {
                            if current.len == 0 {
                                current.start = i;
                            }

                            current.len += 1;

                            if current.len > longest.len {
                                longest = current;
                            }
                        } else {
                            current = Span::default();
                        }
                    }

                    longest
                };

                /// 写一个用冒号分隔的地址部分
                #[inline]
                fn fmt_subslice(f: &mut fmt::Formatter<'_>, chunk: &[u16]) -> fmt::Result {
                    if let Some((first, tail)) = chunk.split_first() {
                        write!(f, "{:x}", first)?;
                        for segment in tail {
                            f.write_char(':')?;
                            write!(f, "{:x}", segment)?;
                        }
                    }
                    Ok(())
                }

                if zeroes.len > 1 {
                    fmt_subslice(f, &segments[..zeroes.start])?;
                    f.write_str("::")?;
                    fmt_subslice(f, &segments[zeroes.start + zeroes.len..])
                } else {
                    fmt_subslice(f, &segments)
                }
            }
        } else {
            const LONGEST_IPV6_ADDR: &str = "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff";

            let mut buf = DisplayBuffer::<{ LONGEST_IPV6_ADDR.len() }>::new();
            // 缓冲区足够长，可以容纳最长的 IPv6 地址，所以这永远不会失败。
            write!(buf, "{}", self).unwrap();

            f.pad(buf.as_str())
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for Ipv6Addr {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, fmt)
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialEq<IpAddr> for Ipv6Addr {
    #[inline]
    fn eq(&self, other: &IpAddr) -> bool {
        match other {
            IpAddr::V4(_) => false,
            IpAddr::V6(v6) => self == v6,
        }
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialEq<Ipv6Addr> for IpAddr {
    #[inline]
    fn eq(&self, other: &Ipv6Addr) -> bool {
        match self {
            IpAddr::V4(_) => false,
            IpAddr::V6(v6) => v6 == other,
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl PartialOrd for Ipv6Addr {
    #[inline]
    fn partial_cmp(&self, other: &Ipv6Addr) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialOrd<Ipv6Addr> for IpAddr {
    #[inline]
    fn partial_cmp(&self, other: &Ipv6Addr) -> Option<Ordering> {
        match self {
            IpAddr::V4(_) => Some(Ordering::Less),
            IpAddr::V6(v6) => v6.partial_cmp(other),
        }
    }
}

#[stable(feature = "ip_cmp", since = "1.16.0")]
impl PartialOrd<IpAddr> for Ipv6Addr {
    #[inline]
    fn partial_cmp(&self, other: &IpAddr) -> Option<Ordering> {
        match other {
            IpAddr::V4(_) => Some(Ordering::Greater),
            IpAddr::V6(v6) => self.partial_cmp(v6),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Ord for Ipv6Addr {
    #[inline]
    fn cmp(&self, other: &Ipv6Addr) -> Ordering {
        self.segments().cmp(&other.segments())
    }
}

#[stable(feature = "i128", since = "1.26.0")]
impl From<Ipv6Addr> for u128 {
    /// 将 `Ipv6Addr` 转换为主机字节顺序 `u128`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// let addr = Ipv6Addr::new(
    ///     0x1020, 0x3040, 0x5060, 0x7080,
    ///     0x90A0, 0xB0C0, 0xD0E0, 0xF00D,
    /// );
    /// assert_eq!(0x102030405060708090A0B0C0D0E0F00D_u128, u128::from(addr));
    /// ```
    #[inline]
    fn from(ip: Ipv6Addr) -> u128 {
        u128::from_be_bytes(ip.octets)
    }
}
#[stable(feature = "i128", since = "1.26.0")]
impl From<u128> for Ipv6Addr {
    /// 将主机字节顺序 `u128` 转换为 `Ipv6Addr`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// let addr = Ipv6Addr::from(0x102030405060708090A0B0C0D0E0F00D_u128);
    /// assert_eq!(
    ///     Ipv6Addr::new(
    ///         0x1020, 0x3040, 0x5060, 0x7080,
    ///         0x90A0, 0xB0C0, 0xD0E0, 0xF00D,
    ///     ),
    ///     addr);
    /// ```
    #[inline]
    fn from(ip: u128) -> Ipv6Addr {
        Ipv6Addr::from(ip.to_be_bytes())
    }
}

#[stable(feature = "ipv6_from_octets", since = "1.9.0")]
impl From<[u8; 16]> for Ipv6Addr {
    /// 从 16 个元素的字节数组创建 `Ipv6Addr`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// let addr = Ipv6Addr::from([
    ///     25u8, 24u8, 23u8, 22u8, 21u8, 20u8, 19u8, 18u8,
    ///     17u8, 16u8, 15u8, 14u8, 13u8, 12u8, 11u8, 10u8,
    /// ]);
    /// assert_eq!(
    ///     Ipv6Addr::new(
    ///         0x1918, 0x1716,
    ///         0x1514, 0x1312,
    ///         0x1110, 0x0f0e,
    ///         0x0d0c, 0x0b0a
    ///     ),
    ///     addr
    /// );
    /// ```
    #[inline]
    fn from(octets: [u8; 16]) -> Ipv6Addr {
        Ipv6Addr { octets }
    }
}

#[stable(feature = "ipv6_from_segments", since = "1.16.0")]
impl From<[u16; 8]> for Ipv6Addr {
    /// 从 8 个元素的 16 位数组创建 `Ipv6Addr`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::Ipv6Addr;
    ///
    /// let addr = Ipv6Addr::from([
    ///     525u16, 524u16, 523u16, 522u16,
    ///     521u16, 520u16, 519u16, 518u16,
    /// ]);
    /// assert_eq!(
    ///     Ipv6Addr::new(
    ///         0x20d, 0x20c,
    ///         0x20b, 0x20a,
    ///         0x209, 0x208,
    ///         0x207, 0x206
    ///     ),
    ///     addr
    /// );
    /// ```
    #[inline]
    fn from(segments: [u16; 8]) -> Ipv6Addr {
        let [a, b, c, d, e, f, g, h] = segments;
        Ipv6Addr::new(a, b, c, d, e, f, g, h)
    }
}

#[stable(feature = "ip_from_slice", since = "1.17.0")]
impl From<[u8; 16]> for IpAddr {
    /// 从 16 个元素的字节数组创建 `IpAddr::V6`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv6Addr};
    ///
    /// let addr = IpAddr::from([
    ///     25u8, 24u8, 23u8, 22u8, 21u8, 20u8, 19u8, 18u8,
    ///     17u8, 16u8, 15u8, 14u8, 13u8, 12u8, 11u8, 10u8,
    /// ]);
    /// assert_eq!(
    ///     IpAddr::V6(Ipv6Addr::new(
    ///         0x1918, 0x1716,
    ///         0x1514, 0x1312,
    ///         0x1110, 0x0f0e,
    ///         0x0d0c, 0x0b0a
    ///     )),
    ///     addr
    /// );
    /// ```
    #[inline]
    fn from(octets: [u8; 16]) -> IpAddr {
        IpAddr::V6(Ipv6Addr::from(octets))
    }
}

#[stable(feature = "ip_from_slice", since = "1.17.0")]
impl From<[u16; 8]> for IpAddr {
    /// 从 8 个元素的 16 位数组创建 `IpAddr::V6`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::net::{IpAddr, Ipv6Addr};
    ///
    /// let addr = IpAddr::from([
    ///     525u16, 524u16, 523u16, 522u16,
    ///     521u16, 520u16, 519u16, 518u16,
    /// ]);
    /// assert_eq!(
    ///     IpAddr::V6(Ipv6Addr::new(
    ///         0x20d, 0x20c,
    ///         0x20b, 0x20a,
    ///         0x209, 0x208,
    ///         0x207, 0x206
    ///     )),
    ///     addr
    /// );
    /// ```
    #[inline]
    fn from(segments: [u16; 8]) -> IpAddr {
        IpAddr::V6(Ipv6Addr::from(segments))
    }
}