feat: Format and print time in which event has occurred

Author: TmLev

Cargo.toml

@@ -14,6 +14,7 @@ tracing-subscriber = { version = "0.3", default-features = false, features = ["r
 nu-ansi-term = "0.46.0"
 atty = "0.2"
 tracing-log = { version = "0.1", optional = true }
+time = { version = "0.3.20", features = ["formatting", "local-offset"] }
 
 [features]
 default = ["tracing-log"]

src/lib.rs

@@ -1,6 +1,9 @@
 pub(crate) mod format;
+pub mod time;
 
+use crate::time::FormatTime;
 use format::{Buffers, ColorLevel, Config, FmtEvent, SpanMode};
+
 use nu_ansi_term::{Color, Style};
 use std::{
     fmt::{self, Write as _},
@@ -43,13 +46,15 @@ impl Visit for Data {
     }
 }
 #[derive(Debug)]
-pub struct HierarchicalLayer<W = fn() -> io::Stderr>
+pub struct HierarchicalLayer<W = fn() -> io::Stderr, FT = ()>
 where
     W: for<'writer> MakeWriter<'writer> + 'static,
+    FT: FormatTime,
 {
     make_writer: W,
     bufs: Mutex<Buffers>,
     config: Config,
+    timer: FT,
 }
 
 impl Default for HierarchicalLayer {
@@ -70,13 +75,15 @@ impl HierarchicalLayer<fn() -> io::Stderr> {
             make_writer: io::stderr,
             bufs: Mutex::new(Buffers::new()),
             config,
+            timer: (),
         }
     }
 }
 
-impl<W> HierarchicalLayer<W>
+impl<W, FT> HierarchicalLayer<W, FT>
 where
     W: for<'writer> MakeWriter<'writer> + 'static,
+    FT: FormatTime,
 {
     /// Enables terminal colors, boldness and italics.
     pub fn with_ansi(self, ansi: bool) -> Self {
@@ -86,14 +93,15 @@ where
         }
     }
 
-    pub fn with_writer<W2>(self, make_writer: W2) -> HierarchicalLayer<W2>
+    pub fn with_writer<W2>(self, make_writer: W2) -> HierarchicalLayer<W2, FT>
     where
         W2: for<'writer> MakeWriter<'writer>,
     {
         HierarchicalLayer {
             make_writer,
             config: self.config,
             bufs: self.bufs,
+            timer: self.timer,
         }
     }
 
@@ -113,6 +121,16 @@ where
         }
     }
 
+    /// Specifies how to measure and format time at which event has occurred.
+    pub fn with_timer<FT2: FormatTime>(self, timer: FT2) -> HierarchicalLayer<W, FT2> {
+        HierarchicalLayer {
+            make_writer: self.make_writer,
+            config: self.config,
+            bufs: self.bufs,
+            timer,
+        }
+    }
+
     /// Whether to render the event and span targets. Usually targets are the module path to the
     /// event/span macro invocation.
     pub fn with_targets(self, targets: bool) -> Self {
@@ -274,10 +292,11 @@ where
     }
 }
 
-impl<S, W> Layer<S> for HierarchicalLayer<W>
+impl<S, W, FT> Layer<S> for HierarchicalLayer<W, FT>
 where
     S: Subscriber + for<'span> LookupSpan<'span>,
     W: for<'writer> MakeWriter<'writer> + 'static,
+    FT: FormatTime + 'static, // TODO(TmLev): Maybe it doesn't have to be static?
 {
     fn on_new_span(&self, attrs: &Attributes, id: &Id, ctx: Context<S>) {
         let span = ctx.span(id).expect("in new_span but span does not exist");
@@ -306,6 +325,13 @@ where
         let bufs = &mut *guard;
         let mut event_buf = &mut bufs.current_buf;
 
+        // Time.
+
+        // TODO(TmLev): Error handling?
+        self.timer
+            .format_time(&mut event_buf)
+            .expect("Unable to write time to buffer");
+
         // printing the indentation
         let indent = ctx
             .event_scope(event)

src/time.rs

@@ -0,0 +1,101 @@
+/// A type that can measure and format the current time.
+///
+/// This trait is used by [HierarchicalLayer] to include a timestamp with each
+/// [Event] when it is logged.
+///
+/// Notable default implementations of this trait are [OffsetDateTime] and `()`.
+/// The former prints the current time as reported by [time's OffsetDateTime]
+/// (note that it may panic! make sure to check out the docs for the [OffsetDateTime]),
+/// and the latter does not print the current time at all.
+///
+/// Inspired by the [FormatTime] trait from [tracing-subscriber].
+///
+/// [HierarchicalLayer]: crate::HierarchicalLayer
+/// [Event]: tracing_core::Event
+/// [time's OffsetDateTime]: time::OffsetDateTime
+/// [FormatTime]: tracing_subscriber::fmt::time::FormatTime
+/// [tracing-subscriber]: tracing_subscriber
+// NB:
+//   We can't use `tracing_subscriber::fmt::format::Writer`
+//   since it doesn't have a public constructor.
+pub trait FormatTime {
+    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+/// Default do-nothing time formatter.
+impl FormatTime for () {
+    fn format_time(&self, _w: &mut impl std::fmt::Write) -> std::fmt::Result {
+        Ok(())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+/// Retrieve and print the current wall-clock time.
+///
+/// # Panics
+///
+/// Panics if [time crate] cannot determine the local UTC offset.
+///
+/// [time crate]: time
+// NB:
+//   Can't use `tracing_subscriber::fmt::time::SystemTime` since it uses
+//   private `datetime` module to format the actual time.
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
+pub struct OffsetDateTime;
+
+impl FormatTime for OffsetDateTime {
+    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result {
+        let time = time::OffsetDateTime::now_local().expect("time offset cannot be determined");
+        write!(w, "{}", time)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+/// Retrieve and print the relative elapsed wall-clock time since an epoch.
+///
+/// The `Default` implementation for `Uptime` makes the epoch the current time.
+// NB: Copy-pasted from `tracing-subscriber::fmt::time::Uptime`.
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+pub struct Uptime {
+    epoch: std::time::Instant,
+}
+
+impl Default for Uptime {
+    fn default() -> Self {
+        Uptime {
+            epoch: std::time::Instant::now(),
+        }
+    }
+}
+
+impl From<std::time::Instant> for Uptime {
+    fn from(epoch: std::time::Instant) -> Self {
+        Uptime { epoch }
+    }
+}
+
+impl FormatTime for Uptime {
+    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result {
+        let e = self.epoch.elapsed();
+        write!(w, "{:4}.{:09}s", e.as_secs(), e.subsec_nanos())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+impl<'a, F> FormatTime for &'a F
+where
+    F: FormatTime,
+{
+    fn format_time(&self, w: &mut impl std::fmt::Write) -> std::fmt::Result {
+        (*self).format_time(w)
+    }
+}
+
+// NB:
+//   Can't impl for `fn(&mut impl std::fmt::Write)` since impl trait is not allowed
+//   outside of function and inherent method return types for now.