tracing_tree/
time.rs

1/// A type that can measure and format the current time.
2///
3/// This trait is used by [HierarchicalLayer] to include a timestamp with each
4/// [Event] when it is logged.
5///
6/// Notable default implementations of this trait are [LocalDateTime] and `()`.
7/// The former prints the current time as reported by [time's OffsetDateTime]
8/// (note that it requires a `time` feature to be enabled and may panic!
9/// make sure to check out the docs for the [LocalDateTime]),
10/// and the latter does not print the current time at all.
11///
12/// Inspired by the [FormatTime] trait from [tracing-subscriber].
13///
14/// [HierarchicalLayer]: crate::HierarchicalLayer
15/// [Event]: tracing_core::Event
16/// [time's OffsetDateTime]: time::OffsetDateTime
17/// [FormatTime]: tracing_subscriber::fmt::time::FormatTime
18/// [tracing-subscriber]: tracing_subscriber
19// NB:
20//   We can't use `tracing_subscriber::fmt::format::Writer`
21//   since it doesn't have a public constructor.
22pub trait FormatTime {
23    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result;
24}
25
26////////////////////////////////////////////////////////////////////////////////////////////////////
27
28/// Default do-nothing time formatter.
29impl FormatTime for () {
30    fn format_time(&self, _w: &mut impl std::fmt::Write) -> std::fmt::Result {
31        Ok(())
32    }
33}
34
35////////////////////////////////////////////////////////////////////////////////////////////////////
36
37/// Retrieve and print the current wall-clock time in UTC timezone.
38#[cfg(feature = "time")]
39#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
40pub struct UtcDateTime;
41
42#[cfg(feature = "time")]
43impl FormatTime for UtcDateTime {
44    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result {
45        let time = time::OffsetDateTime::now_utc();
46        write!(w, "{} {}", time.date(), time.time())
47    }
48}
49
50////////////////////////////////////////////////////////////////////////////////////////////////////
51
52/// Retrieve and print the current wall-clock time.
53///
54/// # Panics
55///
56/// Panics if [time crate] cannot determine the local UTC offset.
57///
58/// [time crate]: time
59// NB:
60//   Can't use `tracing_subscriber::fmt::time::SystemTime` since it uses
61//   private `datetime` module to format the actual time.
62#[cfg(feature = "time")]
63#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
64pub struct LocalDateTime;
65
66#[cfg(feature = "time")]
67impl FormatTime for LocalDateTime {
68    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result {
69        let time = time::OffsetDateTime::now_local().expect("time offset cannot be determined");
70        write!(w, "{}", time)
71    }
72}
73
74////////////////////////////////////////////////////////////////////////////////////////////////////
75
76/// Retrieve and print the relative elapsed wall-clock time since an epoch.
77///
78/// The `Default` implementation for `Uptime` makes the epoch the current time.
79// NB: Copy-pasted from `tracing-subscriber::fmt::time::Uptime`.
80#[derive(Debug, Clone, Copy, Eq, PartialEq)]
81pub struct Uptime {
82    epoch: std::time::Instant,
83}
84
85impl Default for Uptime {
86    fn default() -> Self {
87        Uptime {
88            epoch: std::time::Instant::now(),
89        }
90    }
91}
92
93impl From<std::time::Instant> for Uptime {
94    fn from(epoch: std::time::Instant) -> Self {
95        Uptime { epoch }
96    }
97}
98
99impl FormatTime for Uptime {
100    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result {
101        let e = self.epoch.elapsed();
102        write!(w, "{:4}.{:06}s", e.as_secs(), e.subsec_micros())
103    }
104}
105
106////////////////////////////////////////////////////////////////////////////////////////////////////
107
108impl<'a, F> FormatTime for &'a F
109where
110    F: FormatTime,
111{
112    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result {
113        (*self).format_time(w)
114    }
115}
116
117// NB:
118//   Can't impl for `fn(&mut impl std::fmt::Write)` since impl trait is not allowed
119//   outside of function and inherent method return types for now.
tracing_tree/time.rs

tracing_tree/
time.rs
