Windows: Add support for Unix sockets

Newer versions of Windows support AF_UNIX stream sockets. This change
adds Windows support for the `SockAddr::unix` function and the
`Domain::UNIX` constant.

Since Unix sockets are now available on all tier1 platforms, this also
removes `all` feature requirement from the `SockAddr::unix` function.

Author: jstarks

CONTRIBUTING.md

@@ -33,7 +33,7 @@ add new tests.
 
 All types and methods that are available on all tier 1 platforms are defined in
 the first level of the source, i.e. `src/*.rs` files. Additional API that is
-platform specific, e.g. `Domain::UNIX`, is defined in `src/sys/*.rs` and only
+platform specific, e.g. `Domain::VSOCK`, is defined in `src/sys/*.rs` and only
 for the platforms that support it. For API that is not available on all tier 1
 platforms the `all` feature is used, to indicate to the user that they're using
 API that might is not available on all platforms.

src/lib.rs

@@ -210,6 +210,9 @@ impl Domain {
     /// Domain for IPv6 communication, corresponding to `AF_INET6`.
     pub const IPV6: Domain = Domain(sys::AF_INET6);
 
+    /// Domain for Unix socket communication, corresponding to `AF_UNIX`.
+    pub const UNIX: Domain = Domain(sys::AF_UNIX);
+
     /// Returns the correct domain for `address`.
     pub const fn for_address(address: SocketAddr) -> Domain {
         match address {

src/sockaddr.rs

@@ -1,5 +1,6 @@
 use std::mem::{self, size_of, MaybeUninit};
 use std::net::{SocketAddr, SocketAddrV4, SocketAddrV6};
+use std::path::Path;
 use std::{fmt, io};
 
 #[cfg(windows)]
@@ -210,6 +211,16 @@ impl SockAddr {
             _ => None,
         }
     }
+
+    /// Constructs a `SockAddr` with the family `AF_UNIX` and the provided path.
+    ///
+    /// Returns an error if the path is longer than `SUN_LEN`.
+    pub fn unix<P>(path: P) -> io::Result<SockAddr>
+    where
+        P: AsRef<Path>,
+    {
+        crate::sys::unix_sockaddr(path.as_ref())
+    }
 }
 
 impl From<SocketAddr> for SockAddr {

src/sys/unix.rs

@@ -25,7 +25,6 @@ use std::num::NonZeroU32;
     )
 ))]
 use std::num::NonZeroUsize;
-#[cfg(feature = "all")]
 use std::os::unix::ffi::OsStrExt;
 #[cfg(all(
     feature = "all",
@@ -40,9 +39,7 @@ use std::os::unix::io::RawFd;
 use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd};
 #[cfg(feature = "all")]
 use std::os::unix::net::{UnixDatagram, UnixListener, UnixStream};
-#[cfg(feature = "all")]
 use std::path::Path;
-#[cfg(not(all(target_os = "redox", not(feature = "all"))))]
 use std::ptr;
 use std::time::{Duration, Instant};
 use std::{io, slice};
@@ -58,7 +55,7 @@ use crate::{Domain, Protocol, SockAddr, TcpKeepalive, Type};
 pub(crate) use libc::c_int;
 
 // Used in `Domain`.
-pub(crate) use libc::{AF_INET, AF_INET6};
+pub(crate) use libc::{AF_INET, AF_INET6, AF_UNIX};
 // Used in `Type`.
 #[cfg(all(feature = "all", not(target_os = "redox")))]
 pub(crate) use libc::SOCK_RAW;
@@ -222,10 +219,6 @@ type IovLen = c_int;
 
 /// Unix only API.
 impl Domain {
-    /// Domain for Unix socket communication, corresponding to `AF_UNIX`.
-    #[cfg_attr(docsrs, doc(cfg(unix)))]
-    pub const UNIX: Domain = Domain(libc::AF_UNIX);
-
     /// Domain for low-level packet interface, corresponding to `AF_PACKET`.
     #[cfg(all(
         feature = "all",
@@ -460,71 +453,56 @@ impl<'a> MaybeUninitSlice<'a> {
     }
 }
 
-/// Unix only API.
-impl SockAddr {
-    /// Constructs a `SockAddr` with the family `AF_UNIX` and the provided path.
-    ///
-    /// # Failure
-    ///
-    /// Returns an error if the path is longer than `SUN_LEN`.
-    #[cfg(feature = "all")]
-    #[cfg_attr(docsrs, doc(cfg(all(unix, feature = "all"))))]
-    #[allow(unused_unsafe)] // TODO: replace with `unsafe_op_in_unsafe_fn` once stable.
-    pub fn unix<P>(path: P) -> io::Result<SockAddr>
-    where
-        P: AsRef<Path>,
-    {
+#[allow(unused_unsafe)] // TODO: replace with `unsafe_op_in_unsafe_fn` once stable.
+pub(crate) fn unix_sockaddr(path: &Path) -> io::Result<SockAddr> {
+    // SAFETY: a `sockaddr_storage` of all zeros is valid.
+    let mut storage = unsafe { mem::zeroed::<sockaddr_storage>() };
+    let len = {
+        let storage: &mut libc::sockaddr_un =
+            unsafe { &mut *(&mut storage as *mut sockaddr_storage).cast() };
+
+        let bytes = path.as_os_str().as_bytes();
+        let too_long = match bytes.first() {
+            None => false,
+            // linux abstract namespaces aren't null-terminated
+            Some(&0) => bytes.len() > storage.sun_path.len(),
+            Some(_) => bytes.len() >= storage.sun_path.len(),
+        };
+        if too_long {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "path must be shorter than SUN_LEN",
+            ));
+        }
+
+        storage.sun_family = libc::AF_UNIX as sa_family_t;
+        // Safety: `bytes` and `addr.sun_path` are not overlapping and
+        // both point to valid memory.
+        // `storage` was initialized to zero above, so the path is
+        // already null terminated.
         unsafe {
-            SockAddr::try_init(|storage, len| {
-                // Safety: `SockAddr::try_init` zeros the address, which is a
-                // valid representation.
-                let storage: &mut libc::sockaddr_un = unsafe { &mut *storage.cast() };
-                let len: &mut socklen_t = unsafe { &mut *len };
-
-                let bytes = path.as_ref().as_os_str().as_bytes();
-                let too_long = match bytes.first() {
-                    None => false,
-                    // linux abstract namespaces aren't null-terminated
-                    Some(&0) => bytes.len() > storage.sun_path.len(),
-                    Some(_) => bytes.len() >= storage.sun_path.len(),
-                };
-                if too_long {
-                    return Err(io::Error::new(
-                        io::ErrorKind::InvalidInput,
-                        "path must be shorter than SUN_LEN",
-                    ));
-                }
+            ptr::copy_nonoverlapping(
+                bytes.as_ptr(),
+                storage.sun_path.as_mut_ptr() as *mut u8,
+                bytes.len(),
+            )
+        };
 
-                storage.sun_family = libc::AF_UNIX as sa_family_t;
-                // Safety: `bytes` and `addr.sun_path` are not overlapping and
-                // both point to valid memory.
-                // `SockAddr::try_init` zeroes the memory, so the path is
-                // already null terminated.
-                unsafe {
-                    ptr::copy_nonoverlapping(
-                        bytes.as_ptr(),
-                        storage.sun_path.as_mut_ptr() as *mut u8,
-                        bytes.len(),
-                    )
-                };
-
-                let base = storage as *const _ as usize;
-                let path = &storage.sun_path as *const _ as usize;
-                let sun_path_offset = path - base;
-                let length = sun_path_offset
-                    + bytes.len()
-                    + match bytes.first() {
-                        Some(&0) | None => 0,
-                        Some(_) => 1,
-                    };
-                *len = length as socklen_t;
-
-                Ok(())
-            })
-        }
-        .map(|(_, addr)| addr)
-    }
+        let base = storage as *const _ as usize;
+        let path = &storage.sun_path as *const _ as usize;
+        let sun_path_offset = path - base;
+        sun_path_offset
+            + bytes.len()
+            + match bytes.first() {
+                Some(&0) | None => 0,
+                Some(_) => 1,
+            }
+    };
+    Ok(unsafe { SockAddr::new(storage, len as socklen_t) })
+}
 
+/// Unix only API.
+impl SockAddr {
     /// Constructs a `SockAddr` with the family `AF_VSOCK` and the provided CID/port.
     ///
     /// # Errors
@@ -538,9 +516,8 @@ impl SockAddr {
         doc(cfg(all(feature = "all", any(target_os = "android", target_os = "linux"))))
     )]
     pub fn vsock(cid: u32, port: u32) -> SockAddr {
-        // SAFETY: a `sockaddr_storage` of all zeros is valid, hence we can
-        // safely assume it's initialised.
-        let mut storage = unsafe { MaybeUninit::<sockaddr_storage>::zeroed().assume_init() };
+        // SAFETY: a `sockaddr_storage` of all zeros is valid.
+        let mut storage = unsafe { mem::zeroed::<sockaddr_storage>() };
         {
             let storage: &mut libc::sockaddr_vm =
                 unsafe { &mut *((&mut storage as *mut sockaddr_storage).cast()) };

src/sys/windows.rs

@@ -14,6 +14,7 @@ use std::net::{self, Ipv4Addr, Ipv6Addr, Shutdown};
 use std::os::windows::io::{
     AsRawSocket, AsSocket, BorrowedSocket, FromRawSocket, IntoRawSocket, OwnedSocket, RawSocket,
 };
+use std::path::Path;
 use std::sync::Once;
 use std::time::{Duration, Instant};
 use std::{process, ptr, slice};
@@ -41,8 +42,8 @@ pub(crate) const MSG_TRUNC: c_int = 0x01;
 // Used in `Domain`.
 pub(crate) const AF_INET: c_int = windows_sys::Win32::Networking::WinSock::AF_INET as c_int;
 pub(crate) const AF_INET6: c_int = windows_sys::Win32::Networking::WinSock::AF_INET6 as c_int;
-const AF_UNIX: c_int = windows_sys::Win32::Networking::WinSock::AF_UNIX as c_int;
-const AF_UNSPEC: c_int = windows_sys::Win32::Networking::WinSock::AF_UNSPEC as c_int;
+pub(crate) const AF_UNIX: c_int = windows_sys::Win32::Networking::WinSock::AF_UNIX as c_int;
+pub(crate) const AF_UNSPEC: c_int = windows_sys::Win32::Networking::WinSock::AF_UNSPEC as c_int;
 // Used in `Type`.
 pub(crate) const SOCK_STREAM: c_int = windows_sys::Win32::Networking::WinSock::SOCK_STREAM as c_int;
 pub(crate) const SOCK_DGRAM: c_int = windows_sys::Win32::Networking::WinSock::SOCK_DGRAM as c_int;
@@ -774,6 +775,49 @@ pub(crate) fn to_mreqn(
     }
 }
 
+#[allow(unused_unsafe)] // TODO: replace with `unsafe_op_in_unsafe_fn` once stable.
+pub(crate) fn unix_sockaddr(path: &Path) -> io::Result<SockAddr> {
+    // SAFETY: a `sockaddr_storage` of all zeros is valid.
+    let mut storage = unsafe { mem::zeroed::<sockaddr_storage>() };
+    let len = {
+        let storage: &mut windows_sys::Win32::Networking::WinSock::sockaddr_un =
+            unsafe { &mut *(&mut storage as *mut sockaddr_storage).cast() };
+
+        // Windows expects a UTF-8 path here even though Windows paths are
+        // usually UCS-2 encoded. If Rust exposed OsStr's Wtf8 encoded
+        // buffer, this could be used directly, relying on Windows to
+        // validate the path, but Rust hides this implementation detail.
+        //
+        // See <https://github.com/rust-lang/rust/pull/95290>.
+        let bytes = path
+            .to_str()
+            .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidInput, "path must be valid UTF-8"))?
+            .as_bytes();
+
+        // Windows appears to allow non-null-terminated paths, but this is
+        // not documented, so do not rely on it yet.
+        //
+        // See <https://github.com/rust-lang/socket2/issues/331>.
+        if bytes.len() >= storage.sun_path.len() {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "path must be shorter than SUN_LEN",
+            ));
+        }
+
+        storage.sun_family = crate::sys::AF_UNIX as sa_family_t;
+        // `storage` was initialized to zero above, so the path is
+        // already null terminated.
+        storage.sun_path[..bytes.len()].copy_from_slice(bytes);
+
+        let base = storage as *const _ as usize;
+        let path = &storage.sun_path as *const _ as usize;
+        let sun_path_offset = path - base;
+        sun_path_offset + bytes.len() + 1
+    };
+    Ok(unsafe { SockAddr::new(storage, len as socklen_t) })
+}
+
 /// Windows only API.
 impl crate::Socket {
     /// Sets `HANDLE_FLAG_INHERIT` using `SetHandleInformation`.

tests/socket.rs

@@ -12,7 +12,6 @@ use std::fs::File;
 use std::io;
 #[cfg(not(target_os = "redox"))]
 use std::io::IoSlice;
-#[cfg(all(unix, feature = "all"))]
 use std::io::Read;
 use std::io::Write;
 use std::mem::{self, MaybeUninit};
@@ -36,7 +35,6 @@ use std::os::windows::io::AsRawSocket;
 use std::str;
 use std::thread;
 use std::time::Duration;
-#[cfg(all(unix, feature = "all"))]
 use std::{env, fs};
 
 #[cfg(windows)]
@@ -62,7 +60,6 @@ fn domain_fmt_debug() {
     let tests = &[
         (Domain::IPV4, "AF_INET"),
         (Domain::IPV6, "AF_INET6"),
-        #[cfg(unix)]
         (Domain::UNIX, "AF_UNIX"),
         #[cfg(all(feature = "all", any(target_os = "fuchsia", target_os = "linux")))]
         (Domain::PACKET, "AF_PACKET"),
@@ -130,7 +127,6 @@ fn from_invalid_raw_fd_should_panic() {
 }
 
 #[test]
-#[cfg(all(unix, feature = "all"))]
 fn socket_address_unix() {
     let string = "/tmp/socket";
     let addr = SockAddr::unix(string).unwrap();
@@ -429,9 +425,29 @@ fn pair() {
     assert_eq!(&buf[..n], DATA);
 }
 
+fn unix_sockets_supported() -> bool {
+    #[cfg(windows)]
+    {
+        // Only some versions of Windows support Unix sockets.
+        match Socket::new(Domain::UNIX, Type::STREAM, None) {
+            Ok(_) => {}
+            Err(err)
+                if err.raw_os_error()
+                    == Some(windows_sys::Win32::Networking::WinSock::WSAEAFNOSUPPORT as i32) =>
+            {
+                return false;
+            }
+            Err(err) => panic!("socket error: {}", err),
+        }
+    }
+    true
+}
+
 #[test]
-#[cfg(all(feature = "all", unix))]
 fn unix() {
+    if !unix_sockets_supported() {
+        return;
+    }
     let mut path = env::temp_dir();
     path.push("socket2");
     let _ = fs::remove_dir_all(&path);