std: net: Add support for getting the system hostname

library/std/src/net/hostname.rs

@@ -0,0 +1,10 @@
+use crate::ffi::OsString;
+
+/// Returns the system hostname.
+///
+/// The only time this should ever error out is if the system is broken
+/// in some way. Such errors depend on those cases.
+#[unstable(feature = "gethostname", issue = "135142")]
+pub fn hostname() -> crate::io::Result<OsString> {
+    crate::sys_common::net::gethostname()
+}

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")]
@@ -36,6 +39,7 @@ pub use self::tcp::{Incoming, TcpListener, TcpStream};
 pub use self::udp::UdpSocket;
 use crate::io::{self, ErrorKind};
 
+mod hostname;
 mod ip_addr;
 mod socket_addr;
 mod tcp;

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

@@ -1978,6 +1978,7 @@ Windows.Win32.Networking.WinSock.FD_SET
 Windows.Win32.Networking.WinSock.FIONBIO
 Windows.Win32.Networking.WinSock.freeaddrinfo
 Windows.Win32.Networking.WinSock.getaddrinfo
+Windows.Win32.Networking.WinSock.gethostname
 Windows.Win32.Networking.WinSock.getpeername
 Windows.Win32.Networking.WinSock.getsockname
 Windows.Win32.Networking.WinSock.getsockopt

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

@@ -126,6 +126,7 @@ windows_targets::link!("ws2_32.dll" "system" fn closesocket(s : SOCKET) -> i32);
 windows_targets::link!("ws2_32.dll" "system" fn connect(s : SOCKET, name : *const SOCKADDR, namelen : i32) -> i32);
 windows_targets::link!("ws2_32.dll" "system" fn freeaddrinfo(paddrinfo : *const ADDRINFOA));
 windows_targets::link!("ws2_32.dll" "system" fn getaddrinfo(pnodename : PCSTR, pservicename : PCSTR, phints : *const ADDRINFOA, ppresult : *mut *mut ADDRINFOA) -> i32);
+windows_targets::link!("ws2_32.dll" "system" fn gethostname(name : PSTR, namelen : i32) -> i32);
 windows_targets::link!("ws2_32.dll" "system" fn getpeername(s : SOCKET, name : *mut SOCKADDR, namelen : *mut i32) -> i32);
 windows_targets::link!("ws2_32.dll" "system" fn getsockname(s : SOCKET, name : *mut SOCKADDR, namelen : *mut i32) -> i32);
 windows_targets::link!("ws2_32.dll" "system" fn getsockopt(s : SOCKET, level : i32, optname : i32, optval : PSTR, optlen : *mut i32) -> i32);

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

@@ -31,8 +31,8 @@ pub mod netc {
         IP_DROP_MEMBERSHIP, IP_MULTICAST_LOOP, IP_MULTICAST_TTL, IP_TTL, IPPROTO_IP, IPPROTO_IPV6,
         IPV6_ADD_MEMBERSHIP, IPV6_DROP_MEMBERSHIP, IPV6_MULTICAST_LOOP, IPV6_V6ONLY, SO_BROADCAST,
         SO_RCVTIMEO, SO_SNDTIMEO, SOCK_DGRAM, SOCK_STREAM, SOCKADDR as sockaddr,
-        SOCKADDR_STORAGE as sockaddr_storage, SOL_SOCKET, bind, connect, freeaddrinfo, getpeername,
-        getsockname, getsockopt, listen, setsockopt,
+        SOCKADDR_STORAGE as sockaddr_storage, SOL_SOCKET, bind, connect, freeaddrinfo, gethostname,
+        getpeername, getsockname, getsockopt, listen, setsockopt,
     };
 
     #[allow(non_camel_case_types)]

library/std/src/sys_common/net.rs

@@ -1,7 +1,7 @@
 #[cfg(test)]
 mod tests;
 
-use crate::ffi::{c_int, c_void};
+use crate::ffi::{CStr, OsString, c_char, c_int, c_void};
 use crate::io::{self, BorrowedCursor, ErrorKind, IoSlice, IoSliceMut};
 use crate::net::{Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr};
 use crate::sys::common::small_c_string::run_with_cstr;
@@ -215,6 +215,31 @@ impl<'a> TryFrom<(&'a str, u16)> for LookupHost {
     }
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// gethostname
+////////////////////////////////////////////////////////////////////////////////
+
+pub fn gethostname() -> crate::io::Result<OsString> {
+    init();
+    // 255 bytes is the maximum allowable length for a hostname (as per the DNS spec),
+    // so we shouldn't ever have problems with this. I (@orowith2os) considered using a constant
+    // and letting the platform set the length, but it was determined after some discussion that
+    // this could break things if the platform changes their length. Possible alternative is to
+    // read the sysconf setting for the max hostname length, but that might be a bit too much work.
+    // The 256 byte length is to allow for the NUL terminator.
+    let mut temp_buffer: [c_char; 256] = [0; 256];
+
+    // SAFETY: should never be unsafe, as we're passing in a valid (0-initialized) buffer, and the
+    // length of said buffer.
+    unsafe {
+        cvt(c::gethostname(temp_buffer.as_mut_ptr() as _, temp_buffer.len() as _))?;
+    }
+
+    // SAFETY: we already know the pointer here is valid, we made it from safe Rust earlier.
+    let cstring = unsafe { CStr::from_ptr(temp_buffer.as_mut_ptr()) };
+    Ok(OsString::from(cstring.to_string_lossy().as_ref()))
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // TCP streams
 ////////////////////////////////////////////////////////////////////////////////