feat(nix-rust#1384): change timestamps args of utimensat and futimens…

… to be optional

README.md

@@ -17,7 +17,7 @@ usage.
 
 As an example of what Nix provides, examine the differences between what is
 exposed by libc and nix for the
-[gethostname](https://man7.org/linux/man-pages/man2/gethostname.2.html) system
+[gethostname](https://pubs.opengroup.org/onlinepubs/9699919799/functions/gethostname.html) system
 call:
 
 ```rust,ignore

src/sys/stat.rs

@@ -7,6 +7,7 @@ pub use libc::c_uint;
 ))]
 pub use libc::c_ulong;
 pub use libc::stat as FileStat;
+pub use libc::UTIME_NOW;
 pub use libc::{dev_t, mode_t};
 
 #[cfg(not(target_os = "redox"))]
@@ -402,14 +403,51 @@ pub fn lutimes<P: ?Sized + NixPath>(
     Errno::result(res).map(drop)
 }
 
-/// Change the access and modification times of the file specified by a file descriptor.
+/// A helper function to convert `atime: Option<&TimeSpec>, mtime: Option<&TimeSpec>`
+/// to `[libc::timespec; 2], used in the implementation of [`utimnsat(3)`]
+/// and [`futimens(3)`]
+fn time_convert(
+    atime: Option<&TimeSpec>,
+    mtime: Option<&TimeSpec>,
+) -> [libc::timespec; 2] {
+    let mut times = [
+        libc::timespec {
+            tv_sec: 0,
+            tv_nsec: libc::UTIME_OMIT,
+        },
+        libc::timespec {
+            tv_sec: 0,
+            tv_nsec: libc::UTIME_OMIT,
+        },
+    ];
+    if let Some(atime) = atime {
+        times[0].tv_sec = atime.tv_sec();
+        times[0].tv_nsec = atime.tv_nsec();
+    }
+    if let Some(mtime) = mtime {
+        times[1].tv_sec = mtime.tv_sec();
+        times[1].tv_nsec = mtime.tv_nsec();
+    }
+    times
+}
+
+/// Change the access and modification times of the file specified by a file
+/// descriptor.
+///
+/// When a timestamp argument is set to `None`, it remains unchanged. If you
+/// would like to change a timestamp to the special value `Now`, set the `st_nsec`
+/// field of that timestamp to [`UTIME_NOW`].
 ///
 /// # References
 ///
 /// [futimens(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/futimens.html).
 #[inline]
-pub fn futimens(fd: RawFd, atime: &TimeSpec, mtime: &TimeSpec) -> Result<()> {
-    let times: [libc::timespec; 2] = [*atime.as_ref(), *mtime.as_ref()];
+pub fn futimens(
+    fd: RawFd,
+    atime: Option<&TimeSpec>,
+    mtime: Option<&TimeSpec>,
+) -> Result<()> {
+    let times = time_convert(atime, mtime);
     let res = unsafe { libc::futimens(fd, &times[0]) };
 
     Errno::result(res).map(drop)
@@ -429,6 +467,10 @@ pub enum UtimensatFlags {
 /// with the file descriptor `dirfd` or the current working directory
 /// if `dirfd` is `None`.
 ///
+/// When a timestamp argument is set to `None`, it remains unchanged. If you
+/// would like to change a timestamp to the special value `Now`, set the `st_nsec`
+/// field of that timestamp to [`UTIME_NOW`].
+///
 /// If `flag` is `UtimensatFlags::NoFollowSymlink` and `path` names a symbolic link,
 /// then the mode of the symbolic link is changed.
 ///
@@ -444,15 +486,15 @@ pub enum UtimensatFlags {
 pub fn utimensat<P: ?Sized + NixPath>(
     dirfd: Option<RawFd>,
     path: &P,
-    atime: &TimeSpec,
-    mtime: &TimeSpec,
+    atime: Option<&TimeSpec>,
+    mtime: Option<&TimeSpec>,
     flag: UtimensatFlags,
 ) -> Result<()> {
     let atflag = match flag {
         UtimensatFlags::FollowSymlink => AtFlags::empty(),
         UtimensatFlags::NoFollowSymlink => AtFlags::AT_SYMLINK_NOFOLLOW,
     };
-    let times: [libc::timespec; 2] = [*atime.as_ref(), *mtime.as_ref()];
+    let times = time_convert(atime, mtime);
     let res = path.with_nix_path(|cstr| unsafe {
         libc::utimensat(
             at_rawfd(dirfd),

test/test_stat.rs

@@ -275,10 +275,47 @@ fn test_futimens() {
     let fd = fcntl::open(&fullpath, fcntl::OFlag::empty(), stat::Mode::empty())
         .unwrap();
 
-    futimens(fd, &TimeSpec::seconds(10), &TimeSpec::seconds(20)).unwrap();
+    futimens(
+        fd,
+        Some(&TimeSpec::seconds(10)),
+        Some(&TimeSpec::seconds(20)),
+    )
+    .unwrap();
     assert_times_eq(10, 20, &fs::metadata(&fullpath).unwrap());
 }
 
+#[test]
+#[cfg(not(any(target_os = "redox", target_os = "haiku")))]
+fn test_futimens_unchanged() {
+    let tempdir = tempfile::tempdir().unwrap();
+    let fullpath = tempdir.path().join("file");
+    drop(File::create(&fullpath).unwrap());
+    let fd = fcntl::open(&fullpath, fcntl::OFlag::empty(), stat::Mode::empty())
+        .unwrap();
+
+    let old_atime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .accessed()
+        .unwrap();
+    let old_mtime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .modified()
+        .unwrap();
+
+    futimens(fd, None, None).unwrap();
+
+    let new_atime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .accessed()
+        .unwrap();
+    let new_mtime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .modified()
+        .unwrap();
+    assert_eq!(old_atime, new_atime);
+    assert_eq!(old_mtime, new_mtime);
+}
+
 #[test]
 #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
 fn test_utimensat() {
@@ -295,8 +332,8 @@ fn test_utimensat() {
     utimensat(
         Some(dirfd),
         filename,
-        &TimeSpec::seconds(12345),
-        &TimeSpec::seconds(678),
+        Some(&TimeSpec::seconds(12345)),
+        Some(&TimeSpec::seconds(678)),
         UtimensatFlags::FollowSymlink,
     )
     .unwrap();
@@ -307,14 +344,54 @@ fn test_utimensat() {
     utimensat(
         None,
         filename,
-        &TimeSpec::seconds(500),
-        &TimeSpec::seconds(800),
+        Some(&TimeSpec::seconds(500)),
+        Some(&TimeSpec::seconds(800)),
         UtimensatFlags::FollowSymlink,
     )
     .unwrap();
     assert_times_eq(500, 800, &fs::metadata(&fullpath).unwrap());
 }
 
+#[test]
+#[cfg(not(any(target_os = "redox", target_os = "haiku")))]
+fn test_utimensat_unchanged() {
+    let _dr = crate::DirRestore::new();
+    let tempdir = tempfile::tempdir().unwrap();
+    let filename = "foo.txt";
+    let fullpath = tempdir.path().join(filename);
+    drop(File::create(&fullpath).unwrap());
+    let dirfd =
+        fcntl::open(tempdir.path(), fcntl::OFlag::empty(), stat::Mode::empty())
+            .unwrap();
+
+    let old_atime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .accessed()
+        .unwrap();
+    let old_mtime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .modified()
+        .unwrap();
+    utimensat(
+        Some(dirfd),
+        filename,
+        None,
+        None,
+        UtimensatFlags::NoFollowSymlink,
+    )
+    .unwrap();
+    let new_atime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .accessed()
+        .unwrap();
+    let new_mtime = fs::metadata(fullpath.as_path())
+        .unwrap()
+        .modified()
+        .unwrap();
+    assert_eq!(old_atime, new_atime);
+    assert_eq!(old_mtime, new_mtime);
+}
+
 #[test]
 #[cfg(not(target_os = "redox"))]
 fn test_mkdirat_success_path() {