tor_hscrypto/
time.rs

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1//! Manipulate time periods (as used in the onion service system)
2
3use std::{
4    fmt::Display,
5    time::{Duration, SystemTime},
6};
7
8use humantime::format_rfc3339_seconds;
9use tor_units::IntegerMinutes;
10
11/// A period of time, as used in the onion service system.
12///
13/// A `TimePeriod` is defined as a duration (in seconds), and the number of such
14/// durations that have elapsed since a given offset from the Unix epoch.  So
15/// for example, the interval "(86400 seconds length, 15 intervals, 12 hours
16/// offset)", covers `1970-01-16T12:00:00` up to but not including
17/// `1970-01-17T12:00:00`.
18///
19/// These time periods are used to derive a different `BlindedOnionIdKey` during
20/// each period from each `OnionIdKey`.
21#[derive(Copy, Clone, Debug, Eq, PartialEq)]
22pub struct TimePeriod {
23    /// Index of the time periods that have passed since the unix epoch.
24    pub(crate) interval_num: u64,
25    /// The length of a time period, in **minutes**.
26    ///
27    /// The spec admits only periods which are a whole number of minutes.
28    pub(crate) length: IntegerMinutes<u32>,
29    /// Our offset from the epoch, in seconds.
30    ///
31    /// This is the amount of time after the Unix epoch when our epoch begins,
32    /// rounded down to the nearest second.
33    pub(crate) epoch_offset_in_sec: u32,
34}
35
36/// Two [`TimePeriod`]s are ordered with respect to one another if they have the
37/// same interval length and offset.
38impl PartialOrd for TimePeriod {
39    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
40        if self.length == other.length && self.epoch_offset_in_sec == other.epoch_offset_in_sec {
41            Some(self.interval_num.cmp(&other.interval_num))
42        } else {
43            None
44        }
45    }
46}
47
48impl Display for TimePeriod {
49    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
50        write!(f, "#{} ", self.interval_num())?;
51        match self.range() {
52            Ok(r) => {
53                let mins = self.length().as_minutes();
54                write!(
55                    f,
56                    "{}..+{}:{:02}",
57                    format_rfc3339_seconds(r.start),
58                    mins / 60,
59                    mins % 60
60                )
61            }
62            Err(_) => write!(f, "overflow! {self:?}"),
63        }
64    }
65}
66
67impl TimePeriod {
68    /// Construct a time period of a given `length` that contains `when`.
69    ///
70    /// The `length` value is rounded down to the nearest second,
71    /// and must then be a whole number of minutes.
72    ///
73    /// The `epoch_offset` value is the amount of time after the Unix epoch when
74    /// our epoch begins.  It is also rounded down to the nearest second.
75    ///
76    /// Return None if the Duration is too large or too small, or if `when`
77    /// cannot be represented as a time period.
78    pub fn new(
79        length: Duration,
80        when: SystemTime,
81        epoch_offset: Duration,
82    ) -> Result<Self, TimePeriodError> {
83        // The algorithm here is specified in rend-spec-v3 section 2.2.1
84        let length_in_sec =
85            u32::try_from(length.as_secs()).map_err(|_| TimePeriodError::IntervalInvalid)?;
86        if length_in_sec % 60 != 0 || length.subsec_nanos() != 0 {
87            return Err(TimePeriodError::IntervalInvalid);
88        }
89        let length_in_minutes = length_in_sec / 60;
90        let length = IntegerMinutes::new(length_in_minutes);
91        let epoch_offset_in_sec =
92            u32::try_from(epoch_offset.as_secs()).map_err(|_| TimePeriodError::OffsetInvalid)?;
93        let interval_num = when
94            .duration_since(SystemTime::UNIX_EPOCH + epoch_offset)
95            .map_err(|_| TimePeriodError::OutOfRange)?
96            .as_secs()
97            / u64::from(length_in_sec);
98        Ok(TimePeriod {
99            interval_num,
100            length,
101            epoch_offset_in_sec,
102        })
103    }
104
105    /// Compute the `TimePeriod`, given its length (in **minutes**), index (the number of time
106    /// periods that have passed since the unix epoch), and offset from the epoch (in seconds).
107    ///
108    /// The `epoch_offset_in_sec` value is the number of seconds after the Unix epoch when our
109    /// epoch begins, rounded down to the nearest second.
110    /// Note that this is *not* the time_t at which this *Time Period* begins.
111    ///
112    /// The returned TP begins at the time_t `interval_num * length * 60 + epoch_offset_in_sec`
113    /// and ends `length * 60` seconds later.
114    pub fn from_parts(length: u32, interval_num: u64, epoch_offset_in_sec: u32) -> Self {
115        let length_in_sec = length * 60;
116
117        Self {
118            interval_num,
119            length: length.into(),
120            epoch_offset_in_sec,
121        }
122    }
123
124    /// Return the time period after this one.
125    ///
126    /// Return None if this is the last representable time period.
127    pub fn next(&self) -> Option<Self> {
128        Some(TimePeriod {
129            interval_num: self.interval_num.checked_add(1)?,
130            ..*self
131        })
132    }
133    /// Return the time period before this one.
134    ///
135    /// Return None if this is the first representable time period.
136    pub fn prev(&self) -> Option<Self> {
137        Some(TimePeriod {
138            interval_num: self.interval_num.checked_sub(1)?,
139            ..*self
140        })
141    }
142    /// Return true if this time period contains `when`.
143    ///
144    /// # Limitations
145    ///
146    /// This function always returns false if the time period contains any times
147    /// that cannot be represented as a `SystemTime`.
148    pub fn contains(&self, when: SystemTime) -> bool {
149        match self.range() {
150            Ok(r) => r.contains(&when),
151            Err(_) => false,
152        }
153    }
154    /// Return a range representing the [`SystemTime`] values contained within
155    /// this time period.
156    ///
157    /// Return None if this time period contains any times that can be
158    /// represented as a `SystemTime`.
159    pub fn range(&self) -> Result<std::ops::Range<SystemTime>, TimePeriodError> {
160        (|| {
161            let length_in_sec = u64::from(self.length.as_minutes()) * 60;
162            let start_sec = length_in_sec.checked_mul(self.interval_num)?;
163            let end_sec = start_sec.checked_add(length_in_sec)?;
164            let epoch_offset = Duration::new(self.epoch_offset_in_sec.into(), 0);
165            let start = (SystemTime::UNIX_EPOCH + epoch_offset)
166                .checked_add(Duration::from_secs(start_sec))?;
167            let end = (SystemTime::UNIX_EPOCH + epoch_offset)
168                .checked_add(Duration::from_secs(end_sec))?;
169            Some(start..end)
170        })()
171        .ok_or(TimePeriodError::OutOfRange)
172    }
173
174    /// Return the numeric index of this time period.
175    ///
176    /// This function should only be used when encoding the time period for
177    /// cryptographic purposes.
178    pub fn interval_num(&self) -> u64 {
179        self.interval_num
180    }
181
182    /// Return the length of this time period as a number of seconds.
183    ///
184    /// This function should only be used when encoding the time period for
185    /// cryptographic purposes.
186    pub fn length(&self) -> IntegerMinutes<u32> {
187        self.length
188    }
189
190    /// Return our offset from the epoch, in seconds.
191    ///
192    /// Note that this is *not* the start of the TP.
193    /// See `TimePeriod::from_parts`.
194    pub fn epoch_offset_in_sec(&self) -> u32 {
195        self.epoch_offset_in_sec
196    }
197}
198
199/// An error that occurs when creating or manipulating a [`TimePeriod`]
200#[derive(Clone, Debug, thiserror::Error)]
201#[non_exhaustive]
202pub enum TimePeriodError {
203    /// We couldn't represent the time period in the way we were trying to
204    /// represent it, since it outside of the range supported by the data type.
205    #[error("Time period out was out of range")]
206    OutOfRange,
207
208    /// The time period couldn't be constructed because its interval was
209    /// invalid.
210    ///
211    /// (We require that intervals are a multiple of 60 seconds, and that they
212    /// can be represented in a `u32`.)
213    #[error("Invalid time period interval")]
214    IntervalInvalid,
215
216    /// The time period couldn't be constructed because its offset was invalid.
217    ///
218    /// (We require that offsets can be represented in a `u32`.)
219    #[error("Invalid time period offset")]
220    OffsetInvalid,
221}
222
223#[cfg(test)]
224mod test {
225    // @@ begin test lint list maintained by maint/add_warning @@
226    #![allow(clippy::bool_assert_comparison)]
227    #![allow(clippy::clone_on_copy)]
228    #![allow(clippy::dbg_macro)]
229    #![allow(clippy::mixed_attributes_style)]
230    #![allow(clippy::print_stderr)]
231    #![allow(clippy::print_stdout)]
232    #![allow(clippy::single_char_pattern)]
233    #![allow(clippy::unwrap_used)]
234    #![allow(clippy::unchecked_duration_subtraction)]
235    #![allow(clippy::useless_vec)]
236    #![allow(clippy::needless_pass_by_value)]
237    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
238
239    use super::*;
240    use humantime::{parse_duration, parse_rfc3339};
241
242    /// Check reconstructing `period` from parts produces an identical `TimePeriod`.
243    fn assert_eq_from_parts(period: TimePeriod) {
244        assert_eq!(
245            period,
246            TimePeriod::from_parts(
247                period.length().as_minutes(),
248                period.interval_num(),
249                period.epoch_offset_in_sec()
250            )
251        );
252    }
253
254    #[test]
255    fn check_testvec() {
256        // Test case from C tor, taken from rend-spec.
257        let offset = Duration::new(12 * 60 * 60, 0);
258        let time = parse_rfc3339("2016-04-13T11:00:00Z").unwrap();
259        let one_day = parse_duration("1day").unwrap();
260        let period = TimePeriod::new(one_day, time, offset).unwrap();
261        assert_eq!(period.interval_num, 16903);
262        assert!(period.contains(time));
263        assert_eq_from_parts(period);
264
265        let time = parse_rfc3339("2016-04-13T11:59:59Z").unwrap();
266        let period = TimePeriod::new(one_day, time, offset).unwrap();
267        assert_eq!(period.interval_num, 16903); // still the same.
268        assert!(period.contains(time));
269        assert_eq_from_parts(period);
270
271        assert_eq!(period.prev().unwrap().interval_num, 16902);
272        assert_eq!(period.next().unwrap().interval_num, 16904);
273
274        let time2 = parse_rfc3339("2016-04-13T12:00:00Z").unwrap();
275        let period2 = TimePeriod::new(one_day, time2, offset).unwrap();
276        assert_eq!(period2.interval_num, 16904);
277        assert!(period < period2);
278        assert!(period2 > period);
279        assert_eq!(period.next().unwrap(), period2);
280        assert_eq!(period2.prev().unwrap(), period);
281        assert!(period2.contains(time2));
282        assert!(!period2.contains(time));
283        assert!(!period.contains(time2));
284
285        assert_eq!(
286            period.range().unwrap(),
287            parse_rfc3339("2016-04-12T12:00:00Z").unwrap()
288                ..parse_rfc3339("2016-04-13T12:00:00Z").unwrap()
289        );
290        assert_eq!(
291            period2.range().unwrap(),
292            parse_rfc3339("2016-04-13T12:00:00Z").unwrap()
293                ..parse_rfc3339("2016-04-14T12:00:00Z").unwrap()
294        );
295        assert_eq_from_parts(period2);
296    }
297}
tor_hscrypto/time.rs

tor_hscrypto/
time.rs
