Rollup merge of #145327 - joboet:net-addr-sgx-hack, r=tgross35

std: make address resolution weirdness local to SGX

Currently, the implementations of `TcpStream::connect` and its cousins take an `io::Result<&SocketAddr>` as argument, which is very weird, as most of them then `?`-try the result immediately to access the actual address. This weirdness is however necessitated by a peculiarity of the SGX networking implementation:

SGX doesn't support DNS resolution but rather accepts hostnames in the same place as socket addresses. So, to make e.g.
```rust
TcpStream::connect("example.com:80")`
```
work, the DNS lookup returns a special error (`NonIpSockAddr`) instead, which contains the hostname being looked up. When `.to_socket_addrs()` fails, the `each_addr` function used to select an address will pass the error to the inner `TcpStream::connect` implementation, which in SGX's case will inspect the error and try recover the hostname from it. If
that succeeds, it continues with the found hostname.

This is pretty obviously a terrible hack and leads to buggy code (for instance, when users use the result of `.to_socket_addrs()` in their own `ToSocketAddrs` implementation to select from a list of possible URLs, the only URL used will be that of the last item tried). Still, without changes to the SGX usercall ABI, it cannot be avoided.

Therefore, this PR aims to minimise the impact of that weirdness and remove it from all non-SGX platforms. The inner `TcpStream::connect`, et al. functions now receive the `ToSocketAddrs` type directly and call `each_addr` (which is moved to `sys::net::connection`) themselves. On SGX, the implementation uses a special `each_addr` which contains the whole pass-hostname-through-error hack.

As well as making the code cleaner, this also opens up the possibility of reusing newly created sockets even if a connection request fails – but I've left that for another PR.

CC `@raoulstrackx`

1 files changed, 854 insertions, 0 deletions

diff --git a/library/std/src/sys/net/connection/socket/mod.rs b/library/std/src/sys/net/connection/socket/mod.rs
new file mode 100644
index 00000000000..564f2e3a01f
--- /dev/null
+++ b/library/std/src/sys/net/connection/socket/mod.rs
@@ -0,0 +1,854 @@
+#[cfg(test)]
+mod tests;
+
+use crate::ffi::{c_int, c_void};
+use crate::io::{self, BorrowedCursor, ErrorKind, IoSlice, IoSliceMut};
+use crate::net::{
+    Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr, SocketAddrV4, SocketAddrV6, ToSocketAddrs,
+};
+use crate::sys::common::small_c_string::run_with_cstr;
+use crate::sys::net::connection::each_addr;
+use crate::sys_common::{AsInner, FromInner};
+use crate::time::Duration;
+use crate::{cmp, fmt, mem, ptr};
+
+cfg_select! {
+    target_os = "hermit" => {
+        mod hermit;
+        pub use hermit::*;
+    }
+    target_os = "solid_asp3" => {
+        mod solid;
+        pub use solid::*;
+    }
+    target_family = "unix" => {
+        mod unix;
+        pub use unix::*;
+    }
+    all(target_os = "wasi", target_env = "p2") => {
+        mod wasip2;
+        pub use wasip2::*;
+    }
+    target_os = "windows" => {
+        mod windows;
+        pub use windows::*;
+    }
+    _ => {}
+}
+
+use netc as c;
+
+cfg_select! {
+    any(
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_os = "netbsd",
+        target_os = "illumos",
+        target_os = "solaris",
+        target_os = "haiku",
+        target_os = "l4re",
+        target_os = "nto",
+        target_os = "nuttx",
+        target_vendor = "apple",
+    ) => {
+        use c::IPV6_JOIN_GROUP as IPV6_ADD_MEMBERSHIP;
+        use c::IPV6_LEAVE_GROUP as IPV6_DROP_MEMBERSHIP;
+    }
+    _ => {
+        use c::IPV6_ADD_MEMBERSHIP;
+        use c::IPV6_DROP_MEMBERSHIP;
+    }
+}
+
+cfg_select! {
+    any(
+        target_os = "linux", target_os = "android",
+        target_os = "hurd",
+        target_os = "dragonfly", target_os = "freebsd",
+        target_os = "openbsd", target_os = "netbsd",
+        target_os = "solaris", target_os = "illumos",
+        target_os = "haiku", target_os = "nto",
+        target_os = "cygwin",
+    ) => {
+        use libc::MSG_NOSIGNAL;
+    }
+    _ => {
+        const MSG_NOSIGNAL: c_int = 0x0;
+    }
+}
+
+cfg_select! {
+    any(
+        target_os = "dragonfly", target_os = "freebsd",
+        target_os = "openbsd", target_os = "netbsd",
+        target_os = "solaris", target_os = "illumos",
+        target_os = "nto",
+    ) => {
+        use crate::ffi::c_uchar;
+        type IpV4MultiCastType = c_uchar;
+    }
+    _ => {
+        type IpV4MultiCastType = c_int;
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// address conversions
+////////////////////////////////////////////////////////////////////////////////
+
+fn ip_v4_addr_to_c(addr: &Ipv4Addr) -> c::in_addr {
+    // `s_addr` is stored as BE on all machines and the array is in BE order.
+    // So the native endian conversion method is used so that it's never swapped.
+    c::in_addr { s_addr: u32::from_ne_bytes(addr.octets()) }
+}
+
+fn ip_v6_addr_to_c(addr: &Ipv6Addr) -> c::in6_addr {
+    c::in6_addr { s6_addr: addr.octets() }
+}
+
+fn ip_v4_addr_from_c(addr: c::in_addr) -> Ipv4Addr {
+    Ipv4Addr::from(addr.s_addr.to_ne_bytes())
+}
+
+fn ip_v6_addr_from_c(addr: c::in6_addr) -> Ipv6Addr {
+    Ipv6Addr::from(addr.s6_addr)
+}
+
+fn socket_addr_v4_to_c(addr: &SocketAddrV4) -> c::sockaddr_in {
+    c::sockaddr_in {
+        sin_family: c::AF_INET as c::sa_family_t,
+        sin_port: addr.port().to_be(),
+        sin_addr: ip_v4_addr_to_c(addr.ip()),
+        ..unsafe { mem::zeroed() }
+    }
+}
+
+fn socket_addr_v6_to_c(addr: &SocketAddrV6) -> c::sockaddr_in6 {
+    c::sockaddr_in6 {
+        sin6_family: c::AF_INET6 as c::sa_family_t,
+        sin6_port: addr.port().to_be(),
+        sin6_addr: ip_v6_addr_to_c(addr.ip()),
+        sin6_flowinfo: addr.flowinfo(),
+        sin6_scope_id: addr.scope_id(),
+        ..unsafe { mem::zeroed() }
+    }
+}
+
+fn socket_addr_v4_from_c(addr: c::sockaddr_in) -> SocketAddrV4 {
+    SocketAddrV4::new(ip_v4_addr_from_c(addr.sin_addr), u16::from_be(addr.sin_port))
+}
+
+fn socket_addr_v6_from_c(addr: c::sockaddr_in6) -> SocketAddrV6 {
+    SocketAddrV6::new(
+        ip_v6_addr_from_c(addr.sin6_addr),
+        u16::from_be(addr.sin6_port),
+        addr.sin6_flowinfo,
+        addr.sin6_scope_id,
+    )
+}
+
+/// A type with the same memory layout as `c::sockaddr`. Used in converting Rust level
+/// SocketAddr* types into their system representation. The benefit of this specific
+/// type over using `c::sockaddr_storage` is that this type is exactly as large as it
+/// needs to be and not a lot larger. And it can be initialized more cleanly from Rust.
+#[repr(C)]
+union SocketAddrCRepr {
+    v4: c::sockaddr_in,
+    v6: c::sockaddr_in6,
+}
+
+impl SocketAddrCRepr {
+    fn as_ptr(&self) -> *const c::sockaddr {
+        self as *const _ as *const c::sockaddr
+    }
+}
+
+fn socket_addr_to_c(addr: &SocketAddr) -> (SocketAddrCRepr, c::socklen_t) {
+    match addr {
+        SocketAddr::V4(a) => {
+            let sockaddr = SocketAddrCRepr { v4: socket_addr_v4_to_c(a) };
+            (sockaddr, size_of::<c::sockaddr_in>() as c::socklen_t)
+        }
+        SocketAddr::V6(a) => {
+            let sockaddr = SocketAddrCRepr { v6: socket_addr_v6_to_c(a) };
+            (sockaddr, size_of::<c::sockaddr_in6>() as c::socklen_t)
+        }
+    }
+}
+
+unsafe fn socket_addr_from_c(
+    storage: *const c::sockaddr_storage,
+    len: usize,
+) -> io::Result<SocketAddr> {
+    match (*storage).ss_family as c_int {
+        c::AF_INET => {
+            assert!(len >= size_of::<c::sockaddr_in>());
+            Ok(SocketAddr::V4(socket_addr_v4_from_c(unsafe {
+                *(storage as *const _ as *const c::sockaddr_in)
+            })))
+        }
+        c::AF_INET6 => {
+            assert!(len >= size_of::<c::sockaddr_in6>());
+            Ok(SocketAddr::V6(socket_addr_v6_from_c(unsafe {
+                *(storage as *const _ as *const c::sockaddr_in6)
+            })))
+        }
+        _ => Err(io::const_error!(ErrorKind::InvalidInput, "invalid argument")),
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// sockaddr and misc bindings
+////////////////////////////////////////////////////////////////////////////////
+
+pub fn setsockopt<T>(
+    sock: &Socket,
+    level: c_int,
+    option_name: c_int,
+    option_value: T,
+) -> io::Result<()> {
+    unsafe {
+        cvt(c::setsockopt(
+            sock.as_raw(),
+            level,
+            option_name,
+            (&raw const option_value) as *const _,
+            size_of::<T>() as c::socklen_t,
+        ))?;
+        Ok(())
+    }
+}
+
+pub fn getsockopt<T: Copy>(sock: &Socket, level: c_int, option_name: c_int) -> io::Result<T> {
+    unsafe {
+        let mut option_value: T = mem::zeroed();
+        let mut option_len = size_of::<T>() as c::socklen_t;
+        cvt(c::getsockopt(
+            sock.as_raw(),
+            level,
+            option_name,
+            (&raw mut option_value) as *mut _,
+            &mut option_len,
+        ))?;
+        Ok(option_value)
+    }
+}
+
+fn sockname<F>(f: F) -> io::Result<SocketAddr>
+where
+    F: FnOnce(*mut c::sockaddr, *mut c::socklen_t) -> c_int,
+{
+    unsafe {
+        let mut storage: c::sockaddr_storage = mem::zeroed();
+        let mut len = size_of_val(&storage) as c::socklen_t;
+        cvt(f((&raw mut storage) as *mut _, &mut len))?;
+        socket_addr_from_c(&storage, len as usize)
+    }
+}
+
+#[cfg(target_os = "android")]
+fn to_ipv6mr_interface(value: u32) -> c_int {
+    value as c_int
+}
+
+#[cfg(not(target_os = "android"))]
+fn to_ipv6mr_interface(value: u32) -> crate::ffi::c_uint {
+    value as crate::ffi::c_uint
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// get_host_addresses
+////////////////////////////////////////////////////////////////////////////////
+
+pub struct LookupHost {
+    original: *mut c::addrinfo,
+    cur: *mut c::addrinfo,
+    port: u16,
+}
+
+impl LookupHost {
+    pub fn port(&self) -> u16 {
+        self.port
+    }
+}
+
+impl Iterator for LookupHost {
+    type Item = SocketAddr;
+    fn next(&mut self) -> Option<SocketAddr> {
+        loop {
+            unsafe {
+                let cur = self.cur.as_ref()?;
+                self.cur = cur.ai_next;
+                match socket_addr_from_c(cur.ai_addr.cast(), cur.ai_addrlen as usize) {
+                    Ok(addr) => return Some(addr),
+                    Err(_) => continue,
+                }
+            }
+        }
+    }
+}
+
+unsafe impl Sync for LookupHost {}
+unsafe impl Send for LookupHost {}
+
+impl Drop for LookupHost {
+    fn drop(&mut self) {
+        unsafe { c::freeaddrinfo(self.original) }
+    }
+}
+
+impl TryFrom<&str> for LookupHost {
+    type Error = io::Error;
+
+    fn try_from(s: &str) -> io::Result<LookupHost> {
+        macro_rules! try_opt {
+            ($e:expr, $msg:expr) => {
+                match $e {
+                    Some(r) => r,
+                    None => return Err(io::const_error!(io::ErrorKind::InvalidInput, $msg)),
+                }
+            };
+        }
+
+        // split the string by ':' and convert the second part to u16
+        let (host, port_str) = try_opt!(s.rsplit_once(':'), "invalid socket address");
+        let port: u16 = try_opt!(port_str.parse().ok(), "invalid port value");
+        (host, port).try_into()
+    }
+}
+
+impl<'a> TryFrom<(&'a str, u16)> for LookupHost {
+    type Error = io::Error;
+
+    fn try_from((host, port): (&'a str, u16)) -> io::Result<LookupHost> {
+        init();
+
+        run_with_cstr(host.as_bytes(), &|c_host| {
+            let mut hints: c::addrinfo = unsafe { mem::zeroed() };
+            hints.ai_socktype = c::SOCK_STREAM;
+            let mut res = ptr::null_mut();
+            unsafe {
+                cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res))
+                    .map(|_| LookupHost { original: res, cur: res, port })
+            }
+        })
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// TCP streams
+////////////////////////////////////////////////////////////////////////////////
+
+pub struct TcpStream {
+    inner: Socket,
+}
+
+impl TcpStream {
+    pub fn connect<A: ToSocketAddrs>(addr: A) -> io::Result<TcpStream> {
+        init();
+        return each_addr(addr, inner);
+
+        fn inner(addr: &SocketAddr) -> io::Result<TcpStream> {
+            let sock = Socket::new(addr, c::SOCK_STREAM)?;
+            sock.connect(addr)?;
+            Ok(TcpStream { inner: sock })
+        }
+    }
+
+    pub fn connect_timeout(addr: &SocketAddr, timeout: Duration) -> io::Result<TcpStream> {
+        init();
+
+        let sock = Socket::new(addr, c::SOCK_STREAM)?;
+        sock.connect_timeout(addr, timeout)?;
+        Ok(TcpStream { inner: sock })
+    }
+
+    #[inline]
+    pub fn socket(&self) -> &Socket {
+        &self.inner
+    }
+
+    pub fn into_socket(self) -> Socket {
+        self.inner
+    }
+
+    pub fn set_read_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
+        self.inner.set_timeout(dur, c::SO_RCVTIMEO)
+    }
+
+    pub fn set_write_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
+        self.inner.set_timeout(dur, c::SO_SNDTIMEO)
+    }
+
+    pub fn read_timeout(&self) -> io::Result<Option<Duration>> {
+        self.inner.timeout(c::SO_RCVTIMEO)
+    }
+
+    pub fn write_timeout(&self) -> io::Result<Option<Duration>> {
+        self.inner.timeout(c::SO_SNDTIMEO)
+    }
+
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.peek(buf)
+    }
+
+    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.read(buf)
+    }
+
+    pub fn read_buf(&self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        self.inner.read_buf(buf)
+    }
+
+    pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
+        self.inner.read_vectored(bufs)
+    }
+
+    #[inline]
+    pub fn is_read_vectored(&self) -> bool {
+        self.inner.is_read_vectored()
+    }
+
+    pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
+        let len = cmp::min(buf.len(), <wrlen_t>::MAX as usize) as wrlen_t;
+        let ret = cvt(unsafe {
+            c::send(self.inner.as_raw(), buf.as_ptr() as *const c_void, len, MSG_NOSIGNAL)
+        })?;
+        Ok(ret as usize)
+    }
+
+    pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
+        self.inner.write_vectored(bufs)
+    }
+
+    #[inline]
+    pub fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        sockname(|buf, len| unsafe { c::getpeername(self.inner.as_raw(), buf, len) })
+    }
+
+    pub fn socket_addr(&self) -> io::Result<SocketAddr> {
+        sockname(|buf, len| unsafe { c::getsockname(self.inner.as_raw(), buf, len) })
+    }
+
+    pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
+        self.inner.shutdown(how)
+    }
+
+    pub fn duplicate(&self) -> io::Result<TcpStream> {
+        self.inner.duplicate().map(|s| TcpStream { inner: s })
+    }
+
+    pub fn set_linger(&self, linger: Option<Duration>) -> io::Result<()> {
+        self.inner.set_linger(linger)
+    }
+
+    pub fn linger(&self) -> io::Result<Option<Duration>> {
+        self.inner.linger()
+    }
+
+    pub fn set_nodelay(&self, nodelay: bool) -> io::Result<()> {
+        self.inner.set_nodelay(nodelay)
+    }
+
+    pub fn nodelay(&self) -> io::Result<bool> {
+        self.inner.nodelay()
+    }
+
+    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
+        setsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL, ttl as c_int)
+    }
+
+    pub fn ttl(&self) -> io::Result<u32> {
+        let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL)?;
+        Ok(raw as u32)
+    }
+
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.inner.take_error()
+    }
+
+    pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
+        self.inner.set_nonblocking(nonblocking)
+    }
+}
+
+impl AsInner<Socket> for TcpStream {
+    #[inline]
+    fn as_inner(&self) -> &Socket {
+        &self.inner
+    }
+}
+
+impl FromInner<Socket> for TcpStream {
+    fn from_inner(socket: Socket) -> TcpStream {
+        TcpStream { inner: socket }
+    }
+}
+
+impl fmt::Debug for TcpStream {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut res = f.debug_struct("TcpStream");
+
+        if let Ok(addr) = self.socket_addr() {
+            res.field("addr", &addr);
+        }
+
+        if let Ok(peer) = self.peer_addr() {
+            res.field("peer", &peer);
+        }
+
+        let name = if cfg!(windows) { "socket" } else { "fd" };
+        res.field(name, &self.inner.as_raw()).finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// TCP listeners
+////////////////////////////////////////////////////////////////////////////////
+
+pub struct TcpListener {
+    inner: Socket,
+}
+
+impl TcpListener {
+    pub fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<TcpListener> {
+        init();
+        return each_addr(addr, inner);
+
+        fn inner(addr: &SocketAddr) -> io::Result<TcpListener> {
+            let sock = Socket::new(addr, c::SOCK_STREAM)?;
+
+            // On platforms with Berkeley-derived sockets, this allows to quickly
+            // rebind a socket, without needing to wait for the OS to clean up the
+            // previous one.
+            //
+            // On Windows, this allows rebinding sockets which are actively in use,
+            // which allows “socket hijacking”, so we explicitly don't set it here.
+            // https://docs.microsoft.com/en-us/windows/win32/winsock/using-so-reuseaddr-and-so-exclusiveaddruse
+            #[cfg(not(windows))]
+            setsockopt(&sock, c::SOL_SOCKET, c::SO_REUSEADDR, 1 as c_int)?;
+
+            // Bind our new socket
+            let (addr, len) = socket_addr_to_c(addr);
+            cvt(unsafe { c::bind(sock.as_raw(), addr.as_ptr(), len as _) })?;
+
+            let backlog = if cfg!(target_os = "horizon") {
+                // The 3DS doesn't support a big connection backlog. Sometimes
+                // it allows up to about 37, but other times it doesn't even
+                // accept 32. There may be a global limitation causing this.
+                20
+            } else if cfg!(target_os = "haiku") {
+                // Haiku does not support a queue length > 32
+                // https://github.com/haiku/haiku/blob/979a0bc487864675517fb2fab28f87dc8bf43041/headers/posix/sys/socket.h#L81
+                32
+            } else {
+                // The default for all other platforms
+                128
+            };
+
+            // Start listening
+            cvt(unsafe { c::listen(sock.as_raw(), backlog) })?;
+            Ok(TcpListener { inner: sock })
+        }
+    }
+
+    #[inline]
+    pub fn socket(&self) -> &Socket {
+        &self.inner
+    }
+
+    pub fn into_socket(self) -> Socket {
+        self.inner
+    }
+
+    pub fn socket_addr(&self) -> io::Result<SocketAddr> {
+        sockname(|buf, len| unsafe { c::getsockname(self.inner.as_raw(), buf, len) })
+    }
+
+    pub fn accept(&self) -> io::Result<(TcpStream, SocketAddr)> {
+        // The `accept` function will fill in the storage with the address,
+        // so we don't need to zero it here.
+        // reference: https://linux.die.net/man/2/accept4
+        let mut storage: mem::MaybeUninit<c::sockaddr_storage> = mem::MaybeUninit::uninit();
+        let mut len = size_of_val(&storage) as c::socklen_t;
+        let sock = self.inner.accept(storage.as_mut_ptr() as *mut _, &mut len)?;
+        let addr = unsafe { socket_addr_from_c(storage.as_ptr(), len as usize)? };
+        Ok((TcpStream { inner: sock }, addr))
+    }
+
+    pub fn duplicate(&self) -> io::Result<TcpListener> {
+        self.inner.duplicate().map(|s| TcpListener { inner: s })
+    }
+
+    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
+        setsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL, ttl as c_int)
+    }
+
+    pub fn ttl(&self) -> io::Result<u32> {
+        let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL)?;
+        Ok(raw as u32)
+    }
+
+    pub fn set_only_v6(&self, only_v6: bool) -> io::Result<()> {
+        setsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_V6ONLY, only_v6 as c_int)
+    }
+
+    pub fn only_v6(&self) -> io::Result<bool> {
+        let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_V6ONLY)?;
+        Ok(raw != 0)
+    }
+
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.inner.take_error()
+    }
+
+    pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
+        self.inner.set_nonblocking(nonblocking)
+    }
+}
+
+impl FromInner<Socket> for TcpListener {
+    fn from_inner(socket: Socket) -> TcpListener {
+        TcpListener { inner: socket }
+    }
+}
+
+impl fmt::Debug for TcpListener {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut res = f.debug_struct("TcpListener");
+
+        if let Ok(addr) = self.socket_addr() {
+            res.field("addr", &addr);
+        }
+
+        let name = if cfg!(windows) { "socket" } else { "fd" };
+        res.field(name, &self.inner.as_raw()).finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// UDP
+////////////////////////////////////////////////////////////////////////////////
+
+pub struct UdpSocket {
+    inner: Socket,
+}
+
+impl UdpSocket {
+    pub fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<UdpSocket> {
+        init();
+        return each_addr(addr, inner);
+
+        fn inner(addr: &SocketAddr) -> io::Result<UdpSocket> {
+            let sock = Socket::new(addr, c::SOCK_DGRAM)?;
+            let (addr, len) = socket_addr_to_c(addr);
+            cvt(unsafe { c::bind(sock.as_raw(), addr.as_ptr(), len as _) })?;
+            Ok(UdpSocket { inner: sock })
+        }
+    }
+
+    #[inline]
+    pub fn socket(&self) -> &Socket {
+        &self.inner
+    }
+
+    pub fn into_socket(self) -> Socket {
+        self.inner
+    }
+
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        sockname(|buf, len| unsafe { c::getpeername(self.inner.as_raw(), buf, len) })
+    }
+
+    pub fn socket_addr(&self) -> io::Result<SocketAddr> {
+        sockname(|buf, len| unsafe { c::getsockname(self.inner.as_raw(), buf, len) })
+    }
+
+    pub fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.inner.recv_from(buf)
+    }
+
+    pub fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.inner.peek_from(buf)
+    }
+
+    pub fn send_to(&self, buf: &[u8], dst: &SocketAddr) -> io::Result<usize> {
+        let len = cmp::min(buf.len(), <wrlen_t>::MAX as usize) as wrlen_t;
+        let (dst, dstlen) = socket_addr_to_c(dst);
+        let ret = cvt(unsafe {
+            c::sendto(
+                self.inner.as_raw(),
+                buf.as_ptr() as *const c_void,
+                len,
+                MSG_NOSIGNAL,
+                dst.as_ptr(),
+                dstlen,
+            )
+        })?;
+        Ok(ret as usize)
+    }
+
+    pub fn duplicate(&self) -> io::Result<UdpSocket> {
+        self.inner.duplicate().map(|s| UdpSocket { inner: s })
+    }
+
+    pub fn set_read_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
+        self.inner.set_timeout(dur, c::SO_RCVTIMEO)
+    }
+
+    pub fn set_write_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
+        self.inner.set_timeout(dur, c::SO_SNDTIMEO)
+    }
+
+    pub fn read_timeout(&self) -> io::Result<Option<Duration>> {
+        self.inner.timeout(c::SO_RCVTIMEO)
+    }
+
+    pub fn write_timeout(&self) -> io::Result<Option<Duration>> {
+        self.inner.timeout(c::SO_SNDTIMEO)
+    }
+
+    pub fn set_broadcast(&self, broadcast: bool) -> io::Result<()> {
+        setsockopt(&self.inner, c::SOL_SOCKET, c::SO_BROADCAST, broadcast as c_int)
+    }
+
+    pub fn broadcast(&self) -> io::Result<bool> {
+        let raw: c_int = getsockopt(&self.inner, c::SOL_SOCKET, c::SO_BROADCAST)?;
+        Ok(raw != 0)
+    }
+
+    pub fn set_multicast_loop_v4(&self, multicast_loop_v4: bool) -> io::Result<()> {
+        setsockopt(
+            &self.inner,
+            c::IPPROTO_IP,
+            c::IP_MULTICAST_LOOP,
+            multicast_loop_v4 as IpV4MultiCastType,
+        )
+    }
+
+    pub fn multicast_loop_v4(&self) -> io::Result<bool> {
+        let raw: IpV4MultiCastType = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_MULTICAST_LOOP)?;
+        Ok(raw != 0)
+    }
+
+    pub fn set_multicast_ttl_v4(&self, multicast_ttl_v4: u32) -> io::Result<()> {
+        setsockopt(
+            &self.inner,
+            c::IPPROTO_IP,
+            c::IP_MULTICAST_TTL,
+            multicast_ttl_v4 as IpV4MultiCastType,
+        )
+    }
+
+    pub fn multicast_ttl_v4(&self) -> io::Result<u32> {
+        let raw: IpV4MultiCastType = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_MULTICAST_TTL)?;
+        Ok(raw as u32)
+    }
+
+    pub fn set_multicast_loop_v6(&self, multicast_loop_v6: bool) -> io::Result<()> {
+        setsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_MULTICAST_LOOP, multicast_loop_v6 as c_int)
+    }
+
+    pub fn multicast_loop_v6(&self) -> io::Result<bool> {
+        let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_MULTICAST_LOOP)?;
+        Ok(raw != 0)
+    }
+
+    pub fn join_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr) -> io::Result<()> {
+        let mreq = c::ip_mreq {
+            imr_multiaddr: ip_v4_addr_to_c(multiaddr),
+            imr_interface: ip_v4_addr_to_c(interface),
+        };
+        setsockopt(&self.inner, c::IPPROTO_IP, c::IP_ADD_MEMBERSHIP, mreq)
+    }
+
+    pub fn join_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32) -> io::Result<()> {
+        let mreq = c::ipv6_mreq {
+            ipv6mr_multiaddr: ip_v6_addr_to_c(multiaddr),
+            ipv6mr_interface: to_ipv6mr_interface(interface),
+        };
+        setsockopt(&self.inner, c::IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, mreq)
+    }
+
+    pub fn leave_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr) -> io::Result<()> {
+        let mreq = c::ip_mreq {
+            imr_multiaddr: ip_v4_addr_to_c(multiaddr),
+            imr_interface: ip_v4_addr_to_c(interface),
+        };
+        setsockopt(&self.inner, c::IPPROTO_IP, c::IP_DROP_MEMBERSHIP, mreq)
+    }
+
+    pub fn leave_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32) -> io::Result<()> {
+        let mreq = c::ipv6_mreq {
+            ipv6mr_multiaddr: ip_v6_addr_to_c(multiaddr),
+            ipv6mr_interface: to_ipv6mr_interface(interface),
+        };
+        setsockopt(&self.inner, c::IPPROTO_IPV6, IPV6_DROP_MEMBERSHIP, mreq)
+    }
+
+    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
+        setsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL, ttl as c_int)
+    }
+
+    pub fn ttl(&self) -> io::Result<u32> {
+        let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL)?;
+        Ok(raw as u32)
+    }
+
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.inner.take_error()
+    }
+
+    pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
+        self.inner.set_nonblocking(nonblocking)
+    }
+
+    pub fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.read(buf)
+    }
+
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.peek(buf)
+    }
+
+    pub fn send(&self, buf: &[u8]) -> io::Result<usize> {
+        let len = cmp::min(buf.len(), <wrlen_t>::MAX as usize) as wrlen_t;
+        let ret = cvt(unsafe {
+            c::send(self.inner.as_raw(), buf.as_ptr() as *const c_void, len, MSG_NOSIGNAL)
+        })?;
+        Ok(ret as usize)
+    }
+
+    pub fn connect<A: ToSocketAddrs>(&self, addr: A) -> io::Result<()> {
+        return each_addr(addr, |addr| inner(self, addr));
+
+        fn inner(this: &UdpSocket, addr: &SocketAddr) -> io::Result<()> {
+            let (addr, len) = socket_addr_to_c(addr);
+            cvt_r(|| unsafe { c::connect(this.inner.as_raw(), addr.as_ptr(), len) }).map(drop)
+        }
+    }
+}
+
+impl FromInner<Socket> for UdpSocket {
+    fn from_inner(socket: Socket) -> UdpSocket {
+        UdpSocket { inner: socket }
+    }
+}
+
+impl fmt::Debug for UdpSocket {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut res = f.debug_struct("UdpSocket");
+
+        if let Ok(addr) = self.socket_addr() {
+            res.field("addr", &addr);
+        }
+
+        let name = if cfg!(windows) { "socket" } else { "fd" };
+        res.field(name, &self.inner.as_raw()).finish()
+    }
+}