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Use thread safe libtz instead of libc to get local timezone offset.
Fixes #293 without needing to disable the feature.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,135 +1,13 @@ | ||
| //! Get the system's UTC offset on Unix. | ||
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| use core::mem::MaybeUninit; | ||
| use libtz::Timezone; | ||
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| use crate::util::local_offset::{self, Soundness}; | ||
| use crate::{OffsetDateTime, UtcOffset}; | ||
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| /// Convert the given Unix timestamp to a `libc::tm`. Returns `None` on any error. | ||
| /// | ||
| /// # Safety | ||
| /// | ||
| /// This method must only be called when the process is single-threaded. | ||
| /// | ||
| /// This method will remain `unsafe` until `std::env::set_var` is deprecated or has its behavior | ||
| /// altered. This method is, on its own, safe. It is the presence of a safe, unsound way to set | ||
| /// environment variables that makes it unsafe. | ||
| unsafe fn timestamp_to_tm(timestamp: i64) -> Option<libc::tm> { | ||
| extern "C" { | ||
| #[cfg_attr(target_os = "netbsd", link_name = "__tzset50")] | ||
| fn tzset(); | ||
| } | ||
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| // The exact type of `timestamp` beforehand can vary, so this conversion is necessary. | ||
| #[allow(clippy::useless_conversion)] | ||
| let timestamp = timestamp.try_into().ok()?; | ||
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| let mut tm = MaybeUninit::uninit(); | ||
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| // Update timezone information from system. `localtime_r` does not do this for us. | ||
| // | ||
| // Safety: tzset is thread-safe. | ||
| unsafe { tzset() }; | ||
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| // Safety: We are calling a system API, which mutates the `tm` variable. If a null | ||
| // pointer is returned, an error occurred. | ||
| let tm_ptr = unsafe { libc::localtime_r(×tamp, tm.as_mut_ptr()) }; | ||
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| if tm_ptr.is_null() { | ||
| None | ||
| } else { | ||
| // Safety: The value was initialized, as we no longer have a null pointer. | ||
| Some(unsafe { tm.assume_init() }) | ||
| } | ||
| } | ||
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| /// Convert a `libc::tm` to a `UtcOffset`. Returns `None` on any error. | ||
| // This is available to any target known to have the `tm_gmtoff` extension. | ||
| #[cfg(any( | ||
| target_os = "redox", | ||
| target_os = "linux", | ||
| target_os = "l4re", | ||
| target_os = "android", | ||
| target_os = "emscripten", | ||
| target_os = "macos", | ||
| target_os = "ios", | ||
| target_os = "watchos", | ||
| target_os = "freebsd", | ||
| target_os = "dragonfly", | ||
| target_os = "openbsd", | ||
| target_os = "netbsd", | ||
| target_os = "haiku", | ||
| ))] | ||
| fn tm_to_offset(_unix_timestamp: i64, tm: libc::tm) -> Option<UtcOffset> { | ||
| let seconds = tm.tm_gmtoff.try_into().ok()?; | ||
| UtcOffset::from_whole_seconds(seconds).ok() | ||
| } | ||
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| /// Convert a `libc::tm` to a `UtcOffset`. Returns `None` on any error. | ||
| /// | ||
| /// This method can return an incorrect value, as it only approximates the `tm_gmtoff` field. The | ||
| /// reason for this is that daylight saving time does not start on the same date every year, nor are | ||
| /// the rules for daylight saving time the same for every year. This implementation assumes 1970 is | ||
| /// equivalent to every other year, which is not always the case. | ||
| #[cfg(not(any( | ||
| target_os = "redox", | ||
| target_os = "linux", | ||
| target_os = "l4re", | ||
| target_os = "android", | ||
| target_os = "emscripten", | ||
| target_os = "macos", | ||
| target_os = "ios", | ||
| target_os = "watchos", | ||
| target_os = "freebsd", | ||
| target_os = "dragonfly", | ||
| target_os = "openbsd", | ||
| target_os = "netbsd", | ||
| target_os = "haiku", | ||
| )))] | ||
| fn tm_to_offset(unix_timestamp: i64, tm: libc::tm) -> Option<UtcOffset> { | ||
| use crate::Date; | ||
|
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| let mut tm = tm; | ||
| if tm.tm_sec == 60 { | ||
| // Leap seconds are not currently supported. | ||
| tm.tm_sec = 59; | ||
| } | ||
|
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| let local_timestamp = | ||
| Date::from_ordinal_date(1900 + tm.tm_year, u16::try_from(tm.tm_yday).ok()? + 1) | ||
| .ok()? | ||
| .with_hms( | ||
| tm.tm_hour.try_into().ok()?, | ||
| tm.tm_min.try_into().ok()?, | ||
| tm.tm_sec.try_into().ok()?, | ||
| ) | ||
| .ok()? | ||
| .assume_utc() | ||
| .unix_timestamp(); | ||
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| let diff_secs = (local_timestamp - unix_timestamp).try_into().ok()?; | ||
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| UtcOffset::from_whole_seconds(diff_secs).ok() | ||
| } | ||
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| /// Obtain the system's UTC offset. | ||
| pub(super) fn local_offset_at(datetime: OffsetDateTime) -> Option<UtcOffset> { | ||
| // Ensure that the process is single-threaded unless the user has explicitly opted out of this | ||
| // check. This is to prevent issues with the environment being mutated by a different thread in | ||
| // the process while execution of this function is taking place, which can cause a segmentation | ||
| // fault by dereferencing a dangling pointer. | ||
| // If the `num_threads` crate is incapable of determining the number of running threads, then | ||
| // we conservatively return `None` to avoid a soundness bug. | ||
|
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| if local_offset::get_soundness() == Soundness::Unsound | ||
| || num_threads::is_single_threaded() == Some(true) | ||
| { | ||
| let unix_timestamp = datetime.unix_timestamp(); | ||
| // Safety: We have just confirmed that the process is single-threaded or the user has | ||
| // explicitly opted out of soundness. | ||
| let tm = unsafe { timestamp_to_tm(unix_timestamp) }?; | ||
| tm_to_offset(unix_timestamp, tm) | ||
| } else { | ||
| None | ||
| } | ||
| let tz = Timezone::default().ok()?; | ||
| let tm = tz.localtime(datetime.unix_timestamp()).ok()?; | ||
| let seconds = tm.tm_gmtoff.try_into().ok()?; | ||
| UtcOffset::from_whole_seconds(seconds).ok() | ||
| } |