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subscriber: Add with_buf_capacity_limit to fmt Layer #3489

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subscriber: Add with_buf_capacity_limit to fmt Layer #3489

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64 changes: 64 additions & 0 deletions tracing-subscriber/src/fmt/fmt_layer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,7 @@ pub struct Layer<
fmt_span: format::FmtSpanConfig,
is_ansi: bool,
log_internal_errors: bool,
max_buf_capacity: Option<usize>,
_inner: PhantomData<fn(S)>,
}

Expand Down Expand Up @@ -123,6 +124,7 @@ where
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand Down Expand Up @@ -153,6 +155,7 @@ where
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand Down Expand Up @@ -186,6 +189,7 @@ impl<S, N, E, W> Layer<S, N, E, W> {
fmt_span: self.fmt_span,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
make_writer,
_inner: self._inner,
}
Expand Down Expand Up @@ -291,6 +295,7 @@ impl<S, N, E, W> Layer<S, N, E, W> {
fmt_span: self.fmt_span,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
make_writer: TestWriter::default(),
_inner: self._inner,
}
Expand Down Expand Up @@ -358,6 +363,17 @@ impl<S, N, E, W> Layer<S, N, E, W> {
}
}

/// Sets the maximum capacity (in bytes) retained by the thread-local
/// formatting buffer between events. After formatting, if the buffer
/// capacity exceeds `max_capacity` it is shrunk back. By default there
/// is no limit and the buffer retains whatever capacity it grew to.
pub fn with_buf_capacity_limit(self, max_capacity: usize) -> Self {
Self {
max_buf_capacity: Some(max_capacity),
..self
}
}

/// Updates the [`MakeWriter`] by applying a function to the existing [`MakeWriter`].
///
/// This sets the [`MakeWriter`] that the layer being built will use to write events.
Expand Down Expand Up @@ -387,6 +403,7 @@ impl<S, N, E, W> Layer<S, N, E, W> {
fmt_span: self.fmt_span,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
make_writer: f(self.make_writer),
_inner: self._inner,
}
Expand Down Expand Up @@ -419,6 +436,7 @@ where
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand All @@ -432,6 +450,7 @@ where
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand Down Expand Up @@ -561,6 +580,7 @@ where
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand All @@ -576,6 +596,7 @@ where
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand Down Expand Up @@ -607,6 +628,7 @@ where
// always disable ANSI escapes in JSON mode!
is_ansi: false,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand Down Expand Up @@ -674,6 +696,7 @@ impl<S, N, E, W> Layer<S, N, E, W> {
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand Down Expand Up @@ -705,6 +728,7 @@ impl<S, N, E, W> Layer<S, N, E, W> {
make_writer: self.make_writer,
is_ansi: self.is_ansi,
log_internal_errors: self.log_internal_errors,
max_buf_capacity: self.max_buf_capacity,
_inner: self._inner,
}
}
Expand All @@ -723,6 +747,7 @@ impl<S> Default for Layer<S> {
make_writer: io::stdout,
is_ansi: ansi,
log_internal_errors: false,
max_buf_capacity: None,
_inner: PhantomData,
}
}
Expand Down Expand Up @@ -1018,6 +1043,9 @@ where
}

buf.clear();
if let Some(max_cap) = self.max_buf_capacity {
buf.shrink_to(max_cap);
}
});
}

Expand Down Expand Up @@ -1666,4 +1694,40 @@ mod test {
actual.as_str()
);
}

#[test]
fn buf_capacity_limit_does_not_break_formatting() {
// Verify that setting a buf capacity limit still produces correct output
// for both small and large events.
let make_writer = MockMakeWriter::default();
let subscriber = crate::fmt::Subscriber::builder()
.with_writer(make_writer.clone())
.with_level(false)
.with_ansi(false)
.with_timer(MockTime)
.with_buf_capacity_limit(256)
.finish();

with_default(subscriber, || {
// A large event that exceeds the 256-byte limit
let big = "x".repeat(1024);
tracing::info!(big_field = big.as_str(), "large event");

// A small event afterwards -- this verifies that the buffer was
// usable after being shrunk.
tracing::info!("small event");
});

let actual = make_writer.get_string();
assert!(
actual.contains("large event"),
"large event should have been written, got: {}",
actual
);
assert!(
actual.contains("small event"),
"small event should have been written after buf shrink, got: {}",
actual
);
}
}
14 changes: 14 additions & 0 deletions tracing-subscriber/src/fmt/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -658,6 +658,20 @@ where
}
}

/// Sets the maximum capacity (in bytes) retained by the thread-local
/// formatting buffer between events.
///
/// See [`Layer::with_buf_capacity_limit`] for details.
pub fn with_buf_capacity_limit(
self,
max_capacity: usize,
) -> SubscriberBuilder<N, format::Format<L, T>, F, W> {
SubscriberBuilder {
inner: self.inner.with_buf_capacity_limit(max_capacity),
..self
}
}

/// Sets whether or not an event's target is displayed.
pub fn with_target(
self,
Expand Down