rust: utils: Add 'gethostname()' function

Add 'gethostname' function to retrieve the system hostname using libc
gethostname.

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Marc Hartmayer <marc@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/utils/src/hostname.rs

@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: MIT
+//
+// Copyright IBM Corp. 2026
+
+use std::{ffi::CStr, io};
+
+/// Returns the maximum hostname length supported by the system.
+///
+/// # Returns
+///
+/// The maximum hostname length in bytes, excluding the NUL terminator.
+fn max_hostname_len() -> usize {
+    const _POSIX_HOST_NAME_MAX: usize = 255;
+
+    // SAFETY: sysconf is safe to call with _SC_HOST_NAME_MAX and only reads system configuration without side effects.
+    let n = unsafe { libc::sysconf(libc::_SC_HOST_NAME_MAX) };
+    if n < 0 {
+        _POSIX_HOST_NAME_MAX
+    } else {
+        n.try_into().unwrap()
+    }
+}
+
+/// Retrieves the system hostname using libc gethostname.
+///
+/// # Returns
+///
+/// Returns `Ok(String)` containing the hostname on success, or an `Err(io::Error)` otherwise.
+///
+/// # Examples
+///
+/// ```rust,no_run
+/// use utils::gethostname;
+///
+/// let hostname = gethostname().expect("Failed to get hostname");
+/// println!("Hostname: {}", hostname);
+/// ```
+pub fn gethostname() -> io::Result<String> {
+    // Add space for NUL terminator
+    let buf_len = max_hostname_len().checked_add(1).unwrap();
+    let mut buf = vec![0u8; buf_len];
+
+    // SAFETY: `buf` is a byte array large enough for storing the result of
+    // `gethostname` as the max length was just checked before.
+    let result = unsafe { libc::gethostname(buf.as_mut_ptr() as *mut libc::c_char, buf.len()) };
+    if result != 0 {
+        // libc::gethostname returns -1 on error and sets errno
+        return Err(io::Error::last_os_error());
+    }
+
+    // If it is not NUL-terminated, then add the NUL-termination at the end
+    if !buf.contains(&0) {
+        if let Some(last) = buf.last_mut() {
+            *last = 0;
+        }
+    }
+
+    assert!(isize::try_from(buf_len).unwrap() <= isize::MAX);
+
+    // SAFETY: We made sure that `buf` is:
+    // 1. NUL-terminated
+    // 2. A single allocation (vec![...] was used for the allocation)
+    // 3. `buf_len` is <= isize::MAX (verified by assertion above)
+    // Therefore, it's safe to construct a CStr from the buffer pointer.
+    let cstr = unsafe { CStr::from_ptr(buf.as_ptr() as *const libc::c_char) };
+    Ok(cstr.to_string_lossy().into_owned())
+}

rust/utils/src/lib.rs

@@ -7,6 +7,7 @@ mod cli;
 mod exit_code;
 mod file;
 mod hexslice;
+mod hostname;
 mod log;
 mod tmpfile;
 
@@ -20,6 +21,7 @@ pub use crate::{
     exit_code::{docstring, ExitCodeDoc, ExitCodeTrait, ExitCodeVariantDoc},
     file::{AtomicFile, AtomicFileOperation},
     hexslice::HexSlice,
+    hostname::gethostname,
     log::PvLogger,
     tmpfile::TemporaryDirectory,
 };