logname: add Windows support via WTSQuerySessionInformationW

Cargo.toml

@@ -577,6 +577,7 @@ feat_Tier1 = [
   "env",
   "hostname",
   "kill",
+  "logname",
   "nohup",
   "nproc",
   "more",
@@ -636,7 +637,6 @@ feat_require_unix_core = [
   "groups",
   "id",
   "install",
-  "logname",
   "mkfifo",
   "mknod",
   "stat",

src/uu/logname/Cargo.toml

@@ -19,9 +19,17 @@ doctest = false
 [dependencies]
 clap = { workspace = true }
 fluent = { workspace = true }
-libc = { workspace = true }
 uucore = { workspace = true }
 
+[target.'cfg(unix)'.dependencies]
+libc = { workspace = true }
+
+[target.'cfg(windows)'.dependencies]
+windows-sys = { workspace = true, features = [
+  "Win32_Foundation",
+  "Win32_System_RemoteDesktop",
+] }
+
 [lints]
 workspace = true
 

src/uu/logname/src/logname.rs

@@ -3,15 +3,16 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// spell-checker:ignore (ToDO) getlogin userlogin
+// spell-checker:ignore (ToDO) getlogin userlogin runas
 
 use clap::Command;
-use core::ffi::CStr;
 use std::io::{Write, stdout};
 use uucore::translate;
 use uucore::{error::UResult, show_error};
 
+#[cfg(unix)]
 fn get_userlogin() -> Option<String> {
+    use core::ffi::CStr;
     let login_ptr = unsafe { libc::getlogin() };
     if login_ptr.is_null() {
         None
@@ -20,6 +21,43 @@ fn get_userlogin() -> Option<String> {
     }
 }
 
+#[cfg(windows)]
+fn get_userlogin() -> Option<String> {
+    use std::ffi::OsString;
+    use std::os::windows::ffi::OsStringExt;
+    use windows_sys::Win32::System::RemoteDesktop::{
+        WTS_CURRENT_SERVER_HANDLE, WTS_CURRENT_SESSION, WTSFreeMemory, WTSQuerySessionInformationW,
+        WTSUserName,
+    };
+    // Ask for the user logged on to this session rather than the process token's user
+    // (`GetUserNameW`, as `whoami` does), so `runas` or a service account still reports
+    // the person who logged in, like `getlogin` does on Unix.
+    let mut buffer = std::ptr::null_mut();
+    let mut bytes = 0_u32;
+    // SAFETY: on success the buffer holds `bytes` bytes, a NUL-terminated UTF-16 string.
+    let ok = unsafe {
+        WTSQuerySessionInformationW(
+            WTS_CURRENT_SERVER_HANDLE,
+            WTS_CURRENT_SESSION,
+            WTSUserName,
+            &raw mut buffer,
+            &raw mut bytes,
+        )
+    };
+    if ok == 0 || buffer.is_null() {
+        return None;
+    }
+    // `bytes` includes the terminating NUL
+    let len = (bytes as usize / 2).saturating_sub(1);
+    // SAFETY: `buffer` is valid for `len` u16s and is freed right after copying.
+    let name = OsString::from_wide(unsafe { std::slice::from_raw_parts(buffer, len) });
+    // SAFETY: `buffer` was allocated by `WTSQuerySessionInformationW`, is freed exactly once
+    // and is not used afterwards; `name` owns its own copy.
+    unsafe { WTSFreeMemory(buffer.cast()) };
+    // Session 0 (services) has no logged-on user and returns an empty name.
+    (!name.is_empty()).then(|| name.to_string_lossy().into_owned())
+}
+
 #[uucore::main(no_signals)]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let _ = uucore::clap_localization::handle_clap_result(uu_app(), args)?;

tests/by-util/test_logname.rs

@@ -48,7 +48,7 @@ fn test_output_format() {
     }
     result.success();
     assert!(
-        Regex::new(r"^\w+\n$")
+        Regex::new(r"^[^\r\n]+\n$")
             .unwrap()
             .is_match(result.stdout_str()),
         "unexpected logname output: {:?}",