From a8ece1190bf6b340175bc5b688e52bd29924f483 Mon Sep 17 00:00:00 2001 From: Sebastian Thiel Date: Tue, 31 Oct 2023 15:05:06 +0100 Subject: [PATCH] Add support for pre-unix-epoch file dates on Apple platforms (#108277) Time in UNIX system calls counts from the epoch, 1970-01-01. The timespec struct used in various system calls represents this as a number of seconds and a number of nanoseconds. Nanoseconds are required to be between 0 and 999_999_999, because the portion outside that range should be represented in the seconds field; if nanoseconds were larger than 999_999_999, the seconds field should go up instead. Suppose you ask for the time 1969-12-31, what time is that? On UNIX systems that support times before the epoch, that's seconds=-86400, one day before the epoch. But now, suppose you ask for the time 1969-12-31 23:59:00.1. In other words, a tenth of a second after one minute before the epoch. On most UNIX systems, that's represented as seconds=-60, nanoseconds=100_000_000. The macOS bug is that it returns seconds=-59, nanoseconds=-900_000_000. While that's in some sense an accurate description of the time (59.9 seconds before the epoch), that violates the invariant of the timespec data structure: nanoseconds must be between 0 and 999999999. This causes this assertion in the Rust standard library. So, on macOS, if we get a Timespec value with seconds less than or equal to zero, and nanoseconds between -999_999_999 and -1 (inclusive), we can add 1_000_000_000 to the nanoseconds and subtract 1 from the seconds, and then convert. The resulting timespec value is still accepted by macOS, and when fed back into the OS, produces the same results. (If you set a file's mtime with that timestamp, then read it back, you get back the one with negative nanoseconds again.) Co-authored-by: Josh Triplett --- library/std/src/fs/tests.rs | 42 ++++++++++++++++++++++++++++++++ library/std/src/sys/unix/time.rs | 24 ++++++++++++++++++ 2 files changed, 66 insertions(+) diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs index 736b495343e91..547a7b7052f43 100644 --- a/library/std/src/fs/tests.rs +++ b/library/std/src/fs/tests.rs @@ -1708,6 +1708,48 @@ fn test_file_times() { } } +#[test] +#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))] +fn test_file_times_pre_epoch_with_nanos() { + #[cfg(target_os = "ios")] + use crate::os::ios::fs::FileTimesExt; + #[cfg(target_os = "macos")] + use crate::os::macos::fs::FileTimesExt; + #[cfg(target_os = "tvos")] + use crate::os::tvos::fs::FileTimesExt; + #[cfg(target_os = "watchos")] + use crate::os::watchos::fs::FileTimesExt; + + let tmp = tmpdir(); + let file = File::create(tmp.join("foo")).unwrap(); + + for (accessed, modified, created) in [ + // The first round is to set filetimes to something we know works, but this time + // it's validated with nanoseconds as well which probe the numeric boundary. + ( + SystemTime::UNIX_EPOCH + Duration::new(12345, 1), + SystemTime::UNIX_EPOCH + Duration::new(54321, 100_000_000), + SystemTime::UNIX_EPOCH + Duration::new(32123, 999_999_999), + ), + // The second rounds uses pre-epoch dates along with nanoseconds that probe + // the numeric boundary. + ( + SystemTime::UNIX_EPOCH - Duration::new(1, 1), + SystemTime::UNIX_EPOCH - Duration::new(60, 100_000_000), + SystemTime::UNIX_EPOCH - Duration::new(3600, 999_999_999), + ), + ] { + let mut times = FileTimes::new(); + times = times.set_accessed(accessed).set_modified(modified).set_created(created); + file.set_times(times).unwrap(); + + let metadata = file.metadata().unwrap(); + assert_eq!(metadata.accessed().unwrap(), accessed); + assert_eq!(metadata.modified().unwrap(), modified); + assert_eq!(metadata.created().unwrap(), created); + } +} + #[test] #[cfg(windows)] fn windows_unix_socket_exists() { diff --git a/library/std/src/sys/unix/time.rs b/library/std/src/sys/unix/time.rs index e4540b99413bf..f2e86a4fb2b1b 100644 --- a/library/std/src/sys/unix/time.rs +++ b/library/std/src/sys/unix/time.rs @@ -76,6 +76,30 @@ impl Timespec { } const fn new(tv_sec: i64, tv_nsec: i64) -> Timespec { + // On Apple OS, dates before epoch are represented differently than on other + // Unix platforms: e.g. 1/10th of a second before epoch is represented as `seconds=-1` + // and `nanoseconds=100_000_000` on other platforms, but is `seconds=0` and + // `nanoseconds=-900_000_000` on Apple OS. + // + // To compensate, we first detect this special case by checking if both + // seconds and nanoseconds are in range, and then correct the value for seconds + // and nanoseconds to match the common unix representation. + // + // Please note that Apple OS nonetheless accepts the standard unix format when + // setting file times, which makes this compensation round-trippable and generally + // transparent. + #[cfg(any( + target_os = "macos", + target_os = "ios", + target_os = "tvos", + target_os = "watchos" + ))] + let (tv_sec, tv_nsec) = + if (tv_sec <= 0 && tv_sec > i64::MIN) && (tv_nsec < 0 && tv_nsec > -1_000_000_000) { + (tv_sec - 1, tv_nsec + 1_000_000_000) + } else { + (tv_sec, tv_nsec) + }; assert!(tv_nsec >= 0 && tv_nsec < NSEC_PER_SEC as i64); // SAFETY: The assert above checks tv_nsec is within the valid range Timespec { tv_sec, tv_nsec: unsafe { Nanoseconds(tv_nsec as u32) } }