iana_time_zone/
tz_linux.rs

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1use std::fs::{read_link, read_to_string};
2
3pub(crate) fn get_timezone_inner() -> Result<String, crate::GetTimezoneError> {
4    etc_localtime()
5        .or_else(|_| etc_timezone())
6        .or_else(|_| openwrt::etc_config_system())
7}
8
9fn etc_timezone() -> Result<String, crate::GetTimezoneError> {
10    // see https://stackoverflow.com/a/12523283
11    let mut contents = read_to_string("/etc/timezone")?;
12    // Trim to the correct length without allocating.
13    contents.truncate(contents.trim_end().len());
14    Ok(contents)
15}
16
17fn etc_localtime() -> Result<String, crate::GetTimezoneError> {
18    // Per <https://www.man7.org/linux/man-pages/man5/localtime.5.html>:
19    // “ The /etc/localtime file configures the system-wide timezone of the local system that is
20    //   used by applications for presentation to the user. It should be an absolute or relative
21    //   symbolic link pointing to /usr/share/zoneinfo/, followed by a timezone identifier such as
22    //   "Europe/Berlin" or "Etc/UTC". The resulting link should lead to the corresponding binary
23    //   tzfile(5) timezone data for the configured timezone. ”
24
25    // Systemd does not canonicalize the link, but only checks if it is prefixed by
26    // "/usr/share/zoneinfo/" or "../usr/share/zoneinfo/". So we do the same.
27    // <https://github.com/systemd/systemd/blob/9102c625a673a3246d7e73d8737f3494446bad4e/src/basic/time-util.c#L1493>
28
29    const PREFIXES: &[&str] = &[
30        "/usr/share/zoneinfo/",   // absolute path
31        "../usr/share/zoneinfo/", // relative path
32        "/etc/zoneinfo/",         // absolute path for NixOS
33        "../etc/zoneinfo/",       // relative path for NixOS
34    ];
35    let mut s = read_link("/etc/localtime")?
36        .into_os_string()
37        .into_string()
38        .map_err(|_| crate::GetTimezoneError::FailedParsingString)?;
39    for &prefix in PREFIXES {
40        if s.starts_with(prefix) {
41            // Trim to the correct length without allocating.
42            s.replace_range(..prefix.len(), "");
43            return Ok(s);
44        }
45    }
46    Err(crate::GetTimezoneError::FailedParsingString)
47}
48
49mod openwrt {
50    use std::io::BufRead;
51    use std::{fs, io, iter};
52
53    pub(crate) fn etc_config_system() -> Result<String, crate::GetTimezoneError> {
54        let f = fs::OpenOptions::new()
55            .read(true)
56            .open("/etc/config/system")?;
57        let mut f = io::BufReader::new(f);
58        let mut in_system_section = false;
59        let mut line = String::with_capacity(80);
60
61        // prefer option "zonename" (IANA time zone) over option "timezone" (POSIX time zone)
62        let mut timezone = None;
63        loop {
64            line.clear();
65            f.read_line(&mut line)?;
66            if line.is_empty() {
67                break;
68            }
69
70            let mut iter = IterWords(&line);
71            let mut next = || iter.next().transpose();
72
73            if let Some(keyword) = next()? {
74                if keyword == "config" {
75                    in_system_section = next()? == Some("system") && next()?.is_none();
76                } else if in_system_section && keyword == "option" {
77                    if let Some(key) = next()? {
78                        if key == "zonename" {
79                            if let (Some(zonename), None) = (next()?, next()?) {
80                                return Ok(zonename.to_owned());
81                            }
82                        } else if key == "timezone" {
83                            if let (Some(value), None) = (next()?, next()?) {
84                                timezone = Some(value.to_owned());
85                            }
86                        }
87                    }
88                }
89            }
90        }
91
92        timezone.ok_or_else(|| crate::GetTimezoneError::OsError)
93    }
94
95    #[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
96    struct BrokenQuote;
97
98    impl From<BrokenQuote> for crate::GetTimezoneError {
99        fn from(_: BrokenQuote) -> Self {
100            crate::GetTimezoneError::FailedParsingString
101        }
102    }
103
104    /// Iterated over all words in a OpenWRT config line.
105    struct IterWords<'a>(&'a str);
106
107    impl<'a> Iterator for IterWords<'a> {
108        type Item = Result<&'a str, BrokenQuote>;
109
110        fn next(&mut self) -> Option<Self::Item> {
111            match read_word(self.0) {
112                Ok(Some((item, tail))) => {
113                    self.0 = tail;
114                    Some(Ok(item))
115                }
116                Ok(None) => {
117                    self.0 = "";
118                    None
119                }
120                Err(err) => {
121                    self.0 = "";
122                    Some(Err(err))
123                }
124            }
125        }
126    }
127
128    impl iter::FusedIterator for IterWords<'_> {}
129
130    /// Read the next word in a OpenWRT config line. Strip any surrounding quotation marks.
131    ///
132    /// Returns
133    ///
134    ///  * a tuple `Some((word, remaining_line))` if found,
135    ///  * `None` if the line is exhausted, or
136    ///  * `Err(BrokenQuote)` if the line could not be parsed.
137    #[allow(clippy::manual_strip)] // needs to be compatile to 1.36
138    fn read_word(s: &str) -> Result<Option<(&str, &str)>, BrokenQuote> {
139        let s = s.trim_start();
140        if s.is_empty() || s.starts_with('#') {
141            Ok(None)
142        } else if s.starts_with('\'') {
143            let mut iter = s[1..].splitn(2, '\'');
144            match (iter.next(), iter.next()) {
145                (Some(item), Some(tail)) => Ok(Some((item, tail))),
146                _ => Err(BrokenQuote),
147            }
148        } else if s.starts_with('"') {
149            let mut iter = s[1..].splitn(2, '"');
150            match (iter.next(), iter.next()) {
151                (Some(item), Some(tail)) => Ok(Some((item, tail))),
152                _ => Err(BrokenQuote),
153            }
154        } else {
155            let mut iter = s.splitn(2, |c: char| c.is_whitespace());
156            match (iter.next(), iter.next()) {
157                (Some(item), Some(tail)) => Ok(Some((item, tail))),
158                _ => Ok(Some((s, ""))),
159            }
160        }
161    }
162
163    #[cfg(test)]
164    #[test]
165    fn test_read_word() {
166        assert_eq!(
167            read_word("       option timezone 'CST-8'\n").unwrap(),
168            Some(("option", "timezone 'CST-8'\n")),
169        );
170        assert_eq!(
171            read_word("timezone 'CST-8'\n").unwrap(),
172            Some(("timezone", "'CST-8'\n")),
173        );
174        assert_eq!(read_word("'CST-8'\n").unwrap(), Some(("CST-8", "\n")));
175        assert_eq!(read_word("\n").unwrap(), None);
176
177        assert_eq!(
178            read_word(r#""time 'Zone'""#).unwrap(),
179            Some(("time 'Zone'", "")),
180        );
181
182        assert_eq!(read_word("'CST-8").unwrap_err(), BrokenQuote);
183    }
184}
iana_time_zone/tz_linux.rs

iana_time_zone/
tz_linux.rs
