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use std::fs::{read_link, read_to_string};
pub(crate) fn get_timezone_inner() -> Result<String, crate::GetTimezoneError> {
etc_localtime().or_else(|_| etc_timezone())
}
fn etc_timezone() -> Result<String, crate::GetTimezoneError> {
// see https://stackoverflow.com/a/12523283
let mut contents = read_to_string("/etc/timezone")?;
// Trim to the correct length without allocating.
contents.truncate(contents.trim_end().len());
Ok(contents)
}
fn etc_localtime() -> Result<String, crate::GetTimezoneError> {
// Per <https://www.man7.org/linux/man-pages/man5/localtime.5.html>:
// “ The /etc/localtime file configures the system-wide timezone of the local system that is
// used by applications for presentation to the user. It should be an absolute or relative
// symbolic link pointing to /usr/share/zoneinfo/, followed by a timezone identifier such as
// "Europe/Berlin" or "Etc/UTC". The resulting link should lead to the corresponding binary
// tzfile(5) timezone data for the configured timezone. ”
// Systemd does not canonicalize the link, but only checks if it is prefixed by
// "/usr/share/zoneinfo/" or "../usr/share/zoneinfo/". So we do the same.
// <https://github.com/systemd/systemd/blob/9102c625a673a3246d7e73d8737f3494446bad4e/src/basic/time-util.c#L1493>
const PREFIXES: &[&str] = &[
"/usr/share/zoneinfo/", // absolute path
"../usr/share/zoneinfo/", // relative path
"/etc/zoneinfo/", // absolute path for NixOS
"../etc/zoneinfo/", // relative path for NixOS
];
let mut s = read_link("/etc/localtime")?
.into_os_string()
.into_string()
.map_err(|_| crate::GetTimezoneError::FailedParsingString)?;
for &prefix in PREFIXES {
if s.starts_with(prefix) {
// Trim to the correct length without allocating.
s.replace_range(..prefix.len(), "");
return Ok(s);
}
}
Err(crate::GetTimezoneError::FailedParsingString)
}
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