tracing capture interface

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/log/capture/layer.rs

@@ -0,0 +1,82 @@
+use std::{fmt, sync::Arc};
+
+use tracing::field::{Field, Visit};
+use tracing_core::{Event, Subscriber};
+use tracing_subscriber::{layer::Context, registry::LookupSpan};
+
+use super::{Capture, Data, State};
+
+pub type Value = (&'static str, String);
+
+pub struct Layer {
+	state: Arc<State>,
+}
+
+struct Visitor {
+	values: Vec<Value>,
+}
+
+impl Layer {
+	pub fn new(state: &Arc<State>) -> Self {
+		Self {
+			state: state.clone(),
+		}
+	}
+}
+
+impl fmt::Debug for Layer {
+	fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+		formatter.debug_struct("capture::Layer").finish()
+	}
+}
+
+impl<S> tracing_subscriber::Layer<S> for Layer
+where
+	S: Subscriber + for<'a> LookupSpan<'a>,
+{
+	fn on_event(&self, event: &Event<'_>, ctx: Context<'_, S>) {
+		self.state
+			.active
+			.read()
+			.expect("shared lock")
+			.iter()
+			.filter(|capture| filter(capture, event, &ctx))
+			.for_each(|capture| handle(capture, event, &ctx));
+	}
+}
+
+fn handle<S>(capture: &Capture, event: &Event<'_>, ctx: &Context<'_, S>)
+where
+	S: Subscriber + for<'a> LookupSpan<'a>,
+{
+	let mut visitor = Visitor {
+		values: Vec::new(),
+	};
+	event.record(&mut visitor);
+
+	let mut closure = capture.closure.lock().expect("exclusive lock");
+	closure(Data {
+		event,
+		current: &ctx.current_span(),
+		values: Some(&mut visitor.values),
+	});
+}
+
+fn filter<S>(capture: &Capture, event: &Event<'_>, ctx: &Context<'_, S>) -> bool
+where
+	S: Subscriber + for<'a> LookupSpan<'a>,
+{
+	capture.filter.as_ref().map_or(true, |filter| {
+		filter(Data {
+			event,
+			current: &ctx.current_span(),
+			values: None,
+		})
+	})
+}
+
+impl Visit for Visitor {
+	fn record_debug(&mut self, f: &Field, v: &dyn fmt::Debug) { self.values.push((f.name(), format!("{v:?}"))); }
+
+	fn record_str(&mut self, f: &Field, v: &str) { self.values.push((f.name(), v.to_owned())); }
+}