std: implement hostname

Author: joboet

library/std/src/net/hostname.rs

@@ -0,0 +1,22 @@
+use crate::ffi::OsString;
+
+/// Returns the system hostname.
+///
+/// This can error out in platform-specific error cases;
+/// for example, uefi and wasm, where hostnames aren't
+/// supported.
+///
+/// # Underlying system calls
+///
+/// | Platform | System call                                                                                             |
+/// |----------|---------------------------------------------------------------------------------------------------------|
+/// | UNIX     | [`gethostname`](https://www.man7.org/linux/man-pages/man2/gethostname.2.html)                           |
+/// | Windows  | [`GetHostNameW`](https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-gethostnamew) |
+///
+/// Note that platform-specific behavior [may change in the future][changes].
+///
+/// [changes]: crate::io#platform-specific-behavior
+#[unstable(feature = "gethostname", issue = "135142")]
+pub fn hostname() -> crate::io::Result<OsString> {
+    crate::sys::net::hostname()
+}

library/std/src/net/mod.rs

@@ -1,7 +1,8 @@
 //! Networking primitives for TCP/UDP communication.
 //!
 //! This module provides networking functionality for the Transmission Control and User
-//! Datagram Protocols, as well as types for IP and socket addresses.
+//! Datagram Protocols, as well as types for IP and socket addresses and functions related
+//! to network properties.
 //!
 //! # Organization
 //!
@@ -24,6 +25,8 @@
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::net::AddrParseError;
 
+#[unstable(feature = "gethostname", issue = "135142")]
+pub use self::hostname::hostname;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::ip_addr::{IpAddr, Ipv4Addr, Ipv6Addr, Ipv6MulticastScope};
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -35,6 +38,7 @@ pub use self::tcp::{Incoming, TcpListener, TcpStream};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::udp::UdpSocket;
 
+mod hostname;
 mod ip_addr;
 mod socket_addr;
 mod tcp;

library/std/src/sys/net/connection/socket/windows.rs

@@ -8,9 +8,8 @@ use crate::net::{Shutdown, SocketAddr};
 use crate::os::windows::io::{
     AsRawSocket, AsSocket, BorrowedSocket, FromRawSocket, IntoRawSocket, OwnedSocket, RawSocket,
 };
-use crate::sync::atomic::Atomic;
-use crate::sync::atomic::Ordering::{AcqRel, Relaxed};
 use crate::sys::c;
+use crate::sys::pal::winsock::last_error;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
 use crate::time::Duration;
 use crate::{cmp, mem, ptr, sys};
@@ -112,84 +111,11 @@ pub(super) mod netc {
     }
 }
 
+pub use crate::sys::pal::winsock::{cleanup, cvt, cvt_gai, cvt_r, startup as init};
+
 #[expect(missing_debug_implementations)]
 pub struct Socket(OwnedSocket);
 
-static WSA_INITIALIZED: Atomic<bool> = Atomic::<bool>::new(false);
-
-/// Checks whether the Windows socket interface has been started already, and
-/// if not, starts it.
-#[inline]
-pub fn init() {
-    if !WSA_INITIALIZED.load(Relaxed) {
-        wsa_startup();
-    }
-}
-
-#[cold]
-fn wsa_startup() {
-    unsafe {
-        let mut data: c::WSADATA = mem::zeroed();
-        let ret = c::WSAStartup(
-            0x202, // version 2.2
-            &mut data,
-        );
-        assert_eq!(ret, 0);
-        if WSA_INITIALIZED.swap(true, AcqRel) {
-            // If another thread raced with us and called WSAStartup first then call
-            // WSACleanup so it's as though WSAStartup was only called once.
-            c::WSACleanup();
-        }
-    }
-}
-
-pub fn cleanup() {
-    // We don't need to call WSACleanup here because exiting the process will cause
-    // the OS to clean everything for us, which is faster than doing it manually.
-    // See #141799.
-}
-
-/// Returns the last error from the Windows socket interface.
-fn last_error() -> io::Error {
-    io::Error::from_raw_os_error(unsafe { c::WSAGetLastError() })
-}
-
-#[doc(hidden)]
-pub trait IsMinusOne {
-    fn is_minus_one(&self) -> bool;
-}
-
-macro_rules! impl_is_minus_one {
-    ($($t:ident)*) => ($(impl IsMinusOne for $t {
-        fn is_minus_one(&self) -> bool {
-            *self == -1
-        }
-    })*)
-}
-
-impl_is_minus_one! { i8 i16 i32 i64 isize }
-
-/// Checks if the signed integer is the Windows constant `SOCKET_ERROR` (-1)
-/// and if so, returns the last error from the Windows socket interface. This
-/// function must be called before another call to the socket API is made.
-pub fn cvt<T: IsMinusOne>(t: T) -> io::Result<T> {
-    if t.is_minus_one() { Err(last_error()) } else { Ok(t) }
-}
-
-/// A variant of `cvt` for `getaddrinfo` which return 0 for a success.
-pub fn cvt_gai(err: c_int) -> io::Result<()> {
-    if err == 0 { Ok(()) } else { Err(last_error()) }
-}
-
-/// Just to provide the same interface as sys/pal/unix/net.rs
-pub fn cvt_r<T, F>(mut f: F) -> io::Result<T>
-where
-    T: IsMinusOne,
-    F: FnMut() -> T,
-{
-    cvt(f())
-}
-
 impl Socket {
     pub fn new(addr: &SocketAddr, ty: c_int) -> io::Result<Socket> {
         let family = match *addr {

library/std/src/sys/net/hostname/mod.rs

@@ -0,0 +1,14 @@
+cfg_select! {
+    target_family = "unix" => {
+        mod unix;
+        pub use unix::hostname;
+    }
+    target_os = "windows" => {
+        mod windows;
+        pub use windows::hostname;
+    }
+    _ => {
+        mod unsupported;
+        pub use unsupported::hostname;
+    }
+}

library/std/src/sys/net/hostname/unix.rs

@@ -0,0 +1,62 @@
+use crate::ffi::OsString;
+use crate::io;
+use crate::os::unix::ffi::OsStringExt;
+use crate::sys::pal::os::errno;
+
+pub fn hostname() -> io::Result<OsString> {
+    // Query the system for the maximum host name length.
+    let host_name_max = match unsafe { libc::sysconf(libc::_SC_HOST_NAME_MAX) } {
+        // If this fails (possibly because there is no maximum length), then
+        // assume a maximum length of _POSIX_HOST_NAME_MAX (255).
+        -1 => 255,
+        max => max as usize,
+    };
+
+    // Reserve space for the nul terminator too.
+    let mut buf = Vec::<u8>::try_with_capacity(host_name_max + 1)?;
+    loop {
+        // SAFETY: `buf.capacity()` bytes of `buf` are writable.
+        let r = unsafe { libc::gethostname(buf.as_mut_ptr().cast(), buf.capacity()) };
+        match (r != 0).then(errno) {
+            None => {
+                // Unfortunately, the UNIX specification says that the name will
+                // be truncated if it does not fit in the buffer, without returning
+                // an error. As additionally, the truncated name may still be null-
+                // terminated, there is no reliable way to  detect truncation.
+                // Fortunately, most platforms ignore what the specication says
+                // and return an error (mostly ENAMETOOLONG). Should that not be
+                // the case, the following detects truncation if the null-terminator
+                // was omitted. Note that this check does not impact performance at
+                // all as we need to find the length of the string anyways.
+                //
+                // Use `strnlen` as it does not place an initialization requirement
+                // on the bytes after the nul terminator.
+                //
+                // SAFETY: `buf.capacity()` bytes of `buf` are accessible, and are
+                // initialized up to and including a possible nul terminator.
+                let len = unsafe { libc::strnlen(buf.as_ptr().cast(), buf.capacity()) };
+                if len < buf.capacity() {
+                    // If the string is nul-terminated, we assume that is has not
+                    // been truncated, as the capacity *should be* enough to hold
+                    // `HOST_NAME_MAX` bytes.
+                    // SAFETY: `len + 1` bytes have been initialized (we exlude
+                    // the nul terminator from the string).
+                    unsafe { buf.set_len(len) };
+                    return Ok(OsString::from_vec(buf));
+                }
+            }
+            // As `buf.capacity()` is always positive (as Rust allocations cannot
+            // be larger than `isize::MAX` bytes), the only way `EINVAL` can be
+            // returned is if the system uses `EINVAL` to report that the name
+            // does not fit in the provided buffer. In that case (or in the case
+            // of `ENAMETOOLONG`), resize the buffer and try again.
+            Some(libc::EINVAL | libc::ENAMETOOLONG) => {}
+            // Other error codes (e.g. EPERM) have nothing to do with the buffer
+            // size and should be returned to the user.
+            Some(err) => return Err(io::Error::from_raw_os_error(err)),
+        }
+
+        // Resize the buffer (according to `Vec`'s resizing rules) and try again.
+        buf.try_reserve(buf.capacity() + 1)?;
+    }
+}

library/std/src/sys/net/hostname/unsupported.rs

@@ -0,0 +1,6 @@
+use crate::ffi::OsString;
+use crate::io::{Error, Result};
+
+pub fn hostname() -> Result<OsString> {
+    Err(Error::UNSUPPORTED_PLATFORM)
+}

library/std/src/sys/net/hostname/windows.rs

@@ -0,0 +1,20 @@
+use crate::ffi::OsString;
+use crate::io::Result;
+use crate::os::windows::ffi::OsStringExt;
+use crate::sys::pal::c;
+use crate::sys::pal::winsock::{self, cvt_gai};
+
+pub fn hostname() -> Result<OsString> {
+    winsock::startup();
+
+    // The documentation of GetHostNameW says that a buffer size of 256 is
+    // always enough.
+    let mut buffer = [0; 256];
+    // SAFETY: these parameters specify a valid, writable region of memory.
+    cvt_gai(unsafe { c::GetHostNameW(buffer.as_mut_ptr(), buffer.len() as i32) })?;
+    let len = buffer
+        .iter()
+        .position(|&w| w == 0)
+        .expect("GetHostNameW failed to return a null-terminated name");
+    Ok(OsString::from_wide(&buffer[..len]))
+}

library/std/src/sys/net/mod.rs

@@ -2,3 +2,6 @@
 /// `UdpSocket` as well as related functionality like DNS resolving.
 mod connection;
 pub use connection::*;
+
+mod hostname;
+pub use hostname::hostname;

library/std/src/sys/pal/windows/c/bindings.txt

@@ -2170,6 +2170,7 @@ GetFileType
 GETFINALPATHNAMEBYHANDLE_FLAGS
 GetFinalPathNameByHandleW
 GetFullPathNameW
+GetHostNameW
 GetLastError
 GetModuleFileNameW
 GetModuleHandleA

library/std/src/sys/pal/windows/c/windows_sys.rs

@@ -49,6 +49,7 @@ windows_targets::link!("kernel32.dll" "system" fn GetFileSizeEx(hfile : HANDLE,
 windows_targets::link!("kernel32.dll" "system" fn GetFileType(hfile : HANDLE) -> FILE_TYPE);
 windows_targets::link!("kernel32.dll" "system" fn GetFinalPathNameByHandleW(hfile : HANDLE, lpszfilepath : PWSTR, cchfilepath : u32, dwflags : GETFINALPATHNAMEBYHANDLE_FLAGS) -> u32);
 windows_targets::link!("kernel32.dll" "system" fn GetFullPathNameW(lpfilename : PCWSTR, nbufferlength : u32, lpbuffer : PWSTR, lpfilepart : *mut PWSTR) -> u32);
+windows_targets::link!("ws2_32.dll" "system" fn GetHostNameW(name : PWSTR, namelen : i32) -> i32);
 windows_targets::link!("kernel32.dll" "system" fn GetLastError() -> WIN32_ERROR);
 windows_targets::link!("kernel32.dll" "system" fn GetModuleFileNameW(hmodule : HMODULE, lpfilename : PWSTR, nsize : u32) -> u32);
 windows_targets::link!("kernel32.dll" "system" fn GetModuleHandleA(lpmodulename : PCSTR) -> HMODULE);