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[tracing-subscriber]: add chrono crate implementations of FormatTime (#…
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…2690)

Issue #2080 explains that it's not
possible to soundly use
[`tracing_subscriber::fmt::time::LocalTime`](https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/time/struct.LocalTime.html)
in a multithreaded context. It proposes adding alternative time formatters that
use the [chrono crate](https://docs.rs/chrono/latest/chrono/) to workaround
which is what this PR offers.

A new source file 'chrono_crate.rs' is added to the 'tracing-subscriber'
package implementing `mod chrono_crate` providing two new tag types `LocalTime`
and `Utc` with associated `time::FormatTime` trait implementations that call
`chrono::Local::now().to_rfc3339()` and `chrono::Utc::now().to_rfc3339()`
respectively. Simple unit-tests of the new functionality accompany the
additions.
---------

Co-authored-by: David Barsky <[email protected]>
Co-authored-by: Shayne Fletcher <[email protected]>
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3 people committed Sep 27, 2023
1 parent 77adbb3 commit 7a5e7d3
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1 change: 1 addition & 0 deletions tracing-subscriber/Cargo.toml
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Expand Up @@ -59,6 +59,7 @@ tracing-serde = { path = "../tracing-serde", version = "0.1.3", optional = true

# opt-in deps
parking_lot = { version = "0.12.1", optional = true }
chrono = { version = "0.4.26", default-features = false, features = ["clock", "std"], optional = true }

# registry
sharded-slab = { version = "0.1.4", optional = true }
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177 changes: 177 additions & 0 deletions tracing-subscriber/src/fmt/time/chrono_crate.rs
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@@ -0,0 +1,177 @@
use crate::fmt::format::Writer;
use crate::fmt::time::FormatTime;

use std::sync::Arc;

/// Formats [local time]s and [UTC time]s with `FormatTime` implementations
/// that use the [`chrono` crate].
///
/// [local time]: [`chrono::offset::Local`]
/// [UTC time]: [`chrono::offset::Utc`]
/// [`chrono` crate]: [`chrono`]

/// Formats the current [local time] using a [formatter] from the [`chrono`] crate.
///
/// [local time]: chrono::Local::now()
/// [formatter]: chrono::format
#[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
#[derive(Debug, Clone, Eq, PartialEq, Default)]
pub struct ChronoLocal {
format: Arc<ChronoFmtType>,
}

impl ChronoLocal {
/// Format the time using the [`RFC 3339`] format
/// (a subset of [`ISO 8601`]).
///
/// [`RFC 3339`]: https://tools.ietf.org/html/rfc3339
/// [`ISO 8601`]: https://en.wikipedia.org/wiki/ISO_8601
pub fn rfc_3339() -> Self {
Self {
format: Arc::new(ChronoFmtType::Rfc3339),
}
}

/// Format the time using the given format string.
///
/// See [`chrono::format::strftime`] for details on the supported syntax.
pub fn new(format_string: String) -> Self {
Self {
format: Arc::new(ChronoFmtType::Custom(format_string)),
}
}
}

impl FormatTime for ChronoLocal {
fn format_time(&self, w: &mut Writer<'_>) -> alloc::fmt::Result {
let t = chrono::Local::now();
match self.format.as_ref() {
ChronoFmtType::Rfc3339 => {
use chrono::format::{Fixed, Item};
write!(
w,
"{}",
t.format_with_items(core::iter::once(Item::Fixed(Fixed::RFC3339)))
)
}
ChronoFmtType::Custom(fmt) => {
write!(w, "{}", t.format(fmt))
}
}
}
}

/// Formats the current [UTC time] using a [formatter] from the [`chrono`] crate.
///
/// [UTC time]: chrono::Utc::now()
/// [formatter]: chrono::format
#[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
#[derive(Debug, Clone, Eq, PartialEq, Default)]
pub struct ChronoUtc {
format: Arc<ChronoFmtType>,
}

impl ChronoUtc {
/// Format the time using the [`RFC 3339`] format
/// (a subset of [`ISO 8601`]).
///
/// [`RFC 3339`]: https://tools.ietf.org/html/rfc3339
/// [`ISO 8601`]: https://en.wikipedia.org/wiki/ISO_8601
pub fn rfc_3339() -> Self {
Self {
format: Arc::new(ChronoFmtType::Rfc3339),
}
}

/// Format the time using the given format string.
///
/// See [`chrono::format::strftime`] for details on the supported syntax.
pub fn new(format_string: String) -> Self {
Self {
format: Arc::new(ChronoFmtType::Custom(format_string)),
}
}
}

impl FormatTime for ChronoUtc {
fn format_time(&self, w: &mut Writer<'_>) -> alloc::fmt::Result {
let t = chrono::Utc::now();
match self.format.as_ref() {
ChronoFmtType::Rfc3339 => w.write_str(&t.to_rfc3339()),
ChronoFmtType::Custom(fmt) => w.write_str(&format!("{}", t.format(fmt))),
}
}
}

/// The RFC 3339 format is used by default but a custom format string
/// can be used. See [`chrono::format::strftime`]for details on
/// the supported syntax.
///
/// [`chrono::format::strftime`]: https://docs.rs/chrono/0.4.9/chrono/format/strftime/index.html
#[derive(Debug, Clone, Eq, PartialEq)]
enum ChronoFmtType {
/// Format according to the RFC 3339 convention.
Rfc3339,
/// Format according to a custom format string.
Custom(String),
}

impl Default for ChronoFmtType {
fn default() -> Self {
ChronoFmtType::Rfc3339
}
}

#[cfg(test)]
mod tests {
use crate::fmt::format::Writer;
use crate::fmt::time::FormatTime;

use std::sync::Arc;

use super::ChronoFmtType;
use super::ChronoLocal;
use super::ChronoUtc;

#[test]
fn test_chrono_format_time_utc_default() {
let mut buf = String::new();
let mut dst: Writer<'_> = Writer::new(&mut buf);
assert!(FormatTime::format_time(&ChronoUtc::default(), &mut dst).is_ok());
// e.g. `buf` contains "2023-08-18T19:05:08.662499+00:00"
assert!(chrono::DateTime::parse_from_str(&buf, "%FT%H:%M:%S%.6f%z").is_ok());
}

#[test]
fn test_chrono_format_time_utc_custom() {
let fmt = ChronoUtc {
format: Arc::new(ChronoFmtType::Custom("%a %b %e %T %Y".to_owned())),
};
let mut buf = String::new();
let mut dst: Writer<'_> = Writer::new(&mut buf);
assert!(FormatTime::format_time(&fmt, &mut dst).is_ok());
// e.g. `buf` contains "Wed Aug 23 15:53:23 2023"
assert!(chrono::NaiveDateTime::parse_from_str(&buf, "%a %b %e %T %Y").is_ok());
}

#[test]
fn test_chrono_format_time_local_default() {
let mut buf = String::new();
let mut dst: Writer<'_> = Writer::new(&mut buf);
assert!(FormatTime::format_time(&ChronoLocal::default(), &mut dst).is_ok());
// e.g. `buf` contains "2023-08-18T14:59:08.662499-04:00".
assert!(chrono::DateTime::parse_from_str(&buf, "%FT%H:%M:%S%.6f%z").is_ok());
}

#[test]
fn test_chrono_format_time_local_custom() {
let fmt = ChronoLocal {
format: Arc::new(ChronoFmtType::Custom("%a %b %e %T %Y".to_owned())),
};
let mut buf = String::new();
let mut dst: Writer<'_> = Writer::new(&mut buf);
assert!(FormatTime::format_time(&fmt, &mut dst).is_ok());
// e.g. `buf` contains "Wed Aug 23 15:55:46 2023".
assert!(chrono::NaiveDateTime::parse_from_str(&buf, "%a %b %e %T %Y").is_ok());
}
}
13 changes: 13 additions & 0 deletions tracing-subscriber/src/fmt/time/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ mod datetime;

#[cfg(feature = "time")]
mod time_crate;

#[cfg(feature = "time")]
#[cfg_attr(docsrs, doc(cfg(feature = "time")))]
pub use time_crate::UtcTime;
Expand All @@ -19,6 +20,18 @@ pub use time_crate::LocalTime;
#[cfg_attr(docsrs, doc(cfg(feature = "time")))]
pub use time_crate::OffsetTime;

/// [`chrono`]-based implementation for [`FormatTime`].
#[cfg(feature = "chrono")]
mod chrono_crate;

#[cfg(feature = "chrono")]
#[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
pub use chrono_crate::ChronoLocal;

#[cfg(feature = "chrono")]
#[cfg_attr(docsrs, doc(cfg(feature = "chrono")))]
pub use chrono_crate::ChronoUtc;

/// A type that can measure and format the current time.
///
/// This trait is used by `Format` to include a timestamp with each `Event` when it is logged.
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