touch: do not hang on a reader-less FIFO

src/uu/touch/src/touch.rs

@@ -4,13 +4,15 @@
 // file that was distributed with this source code.
 
 // spell-checker:ignore (ToDO) datelike datetime filetime lpszfilepath mktime strtime timelike utime DATETIME UTIME futimens
-// spell-checker:ignore (FORMATS) MMDDhhmm YYYYMMDDHHMM YYMMDDHHMM YYYYMMDDHHMMS CREAT
+// spell-checker:ignore (FORMATS) MMDDhhmm YYYYMMDDHHMM YYMMDDHHMM YYYYMMDDHHMMS CREAT ENXIO RDONLY utimensat
 
 pub mod error;
 
 use clap::builder::{PossibleValue, ValueParser};
 use clap::{Arg, ArgAction, ArgGroup, ArgMatches, Command};
-use filetime::{FileTime, set_file_times, set_symlink_file_times};
+#[cfg(not(unix))]
+use filetime::set_file_times;
+use filetime::{FileTime, set_symlink_file_times};
 use jiff::civil::Time;
 use jiff::fmt::strtime;
 use jiff::tz::TimeZone;
@@ -607,14 +609,71 @@ fn update_times(
 
     #[cfg(unix)]
     {
+        if is_stdout {
+            // `touch -` operates on whatever file is open as stdout (fd 1),
+            // even when it was opened read-only. Use futimens on the fd
+            // directly: it preserves the UTIME_NOW sentinel, while
+            // filetime::set_file_times would normalize it into a literal
+            // 1970 timestamp.
+            let timestamps = build_timestamps(atime, mtime);
+            return futimens(std::io::stdout(), &timestamps)
+                .map_err(|e| Error::from_raw_os_error(e.raw_os_error()))
+                .map_err_context(
+                    || translate!("touch-error-setting-times-of-path", "path" => path.quote()),
+                );
+        }
+
         // Open write-only and use futimens to trigger IN_CLOSE_WRITE on Linux.
-        if !is_stdout && try_futimens_via_write_fd(path, atime, mtime).is_ok() {
+        if try_futimens_via_write_fd(path, atime, mtime).is_ok() {
             return Ok(());
         }
+        // The write-FD approach fails on special files such as FIFOs (the
+        // write-only open returns ENXIO when there is no reader). Set the times
+        // by path with utimensat, which never opens the file and so never
+        // blocks — unlike filetime::set_file_times, which opens O_RDONLY and
+        // would hang on a reader-less FIFO.
+        set_times_by_path(path, atime, mtime)
+    }
+
+    #[cfg(not(unix))]
+    {
+        set_file_times(path, atime, mtime).map_err_context(
+            || translate!("touch-error-setting-times-of-path", "path" => path.quote()),
+        )
     }
+}
 
-    set_file_times(path, atime, mtime)
-        .map_err_context(|| translate!("touch-error-setting-times-of-path", "path" => path.quote()))
+#[cfg(unix)]
+/// Build a rustix `Timestamps` from the access and modification `FileTime`s,
+/// preserving the `UTIME_NOW`/`UTIME_OMIT` sentinels in the nanoseconds field.
+fn build_timestamps(atime: FileTime, mtime: FileTime) -> Timestamps {
+    Timestamps {
+        last_access: rustix::fs::Timespec {
+            tv_sec: atime.unix_seconds(),
+            tv_nsec: atime.nanoseconds() as _,
+        },
+        last_modification: rustix::fs::Timespec {
+            tv_sec: mtime.unix_seconds(),
+            tv_nsec: mtime.nanoseconds() as _,
+        },
+    }
+}
+
+#[cfg(unix)]
+/// Set file times by path using `utimensat`, following symlinks.
+///
+/// This never opens the file, so it does not block on special files such as
+/// FIFOs.
+fn set_times_by_path(path: &Path, atime: FileTime, mtime: FileTime) -> UResult<()> {
+    let timestamps = build_timestamps(atime, mtime);
+    rustix::fs::utimensat(
+        rustix::fs::CWD,
+        path,
+        &timestamps,
+        rustix::fs::AtFlags::empty(),
+    )
+    .map_err(|e| Error::from_raw_os_error(e.raw_os_error()))
+    .map_err_context(|| translate!("touch-error-setting-times-of-path", "path" => path.quote()))
 }
 
 #[cfg(unix)]

tests/by-util/test_touch.rs

@@ -789,6 +789,42 @@ fn test_touch_system_fails() {
         .stderr_contains("setting times of '/'");
 }
 
+#[test]
+#[cfg(unix)]
+#[cfg_attr(wasi_runner, ignore = "WASI: no FIFO support")]
+fn test_touch_fifo() {
+    // touch must not hang on a reader-less FIFO and must update its times.
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.mkfifo("fifo");
+    ucmd.args(&["-d", "2020-01-01 00:00:00", "fifo"])
+        .succeeds()
+        .no_output();
+    assert!(at.is_fifo("fifo"));
+}
+
+#[test]
+#[cfg(unix)]
+#[cfg_attr(wasi_runner, ignore = "WASI: no stdout-to-file redirection")]
+fn test_touch_dash_updates_stdout_file() {
+    // `touch -` must update the times of the file open as stdout (fd 1), even
+    // when it is read-only, and set them to "now" rather than a 1970 sentinel.
+    use std::fs::File;
+    use std::time::SystemTime;
+
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.touch("c");
+    // Age the file so the update to "now" is detectable.
+    let old = FileTime::from_unix_time(1_000_000, 0);
+    filetime::set_file_times(at.plus("c"), old, old).unwrap();
+
+    let file = File::open(at.plus("c")).unwrap();
+    ucmd.set_stdout(file).arg("-").succeeds();
+
+    let mtime = at.metadata("c").modified().unwrap();
+    let age = SystemTime::now().duration_since(mtime).unwrap();
+    assert!(age.as_secs() < 60, "touch - left mtime stale: {age:?}");
+}
+
 #[test]
 #[cfg(not(target_os = "windows"))]
 fn test_touch_trailing_slash() {