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use metrics::Label;
use std::{any::TypeId, marker::PhantomData};
use tracing_core::span::{Attributes, Id, Record};
use tracing_core::{field::Visit, Dispatch, Field, Subscriber};
use tracing_subscriber::{layer::Context, registry::LookupSpan, Layer};
#[doc(hidden)]
pub struct Labels(pub Vec<Label>);
impl Visit for Labels {
fn record_str(&mut self, field: &Field, value: &str) {
let label = Label::new(field.name(), value.to_owned());
self.0.push(label);
}
fn record_bool(&mut self, field: &Field, value: bool) {
let label = Label::from_static_parts(field.name(), if value { "true" } else { "false" });
self.0.push(label);
}
fn record_i64(&mut self, field: &Field, value: i64) {
let mut s = String::with_capacity(32);
itoa::fmt(&mut s, value).expect("failed to format/write i64");
let label = Label::new(field.name(), s);
self.0.push(label);
}
fn record_u64(&mut self, field: &Field, value: u64) {
let mut s = String::with_capacity(32);
itoa::fmt(&mut s, value).expect("failed to format/write u64");
let label = Label::new(field.name(), s);
self.0.push(label);
}
fn record_debug(&mut self, field: &Field, value: &dyn std::fmt::Debug) {
let value_string = format!("{:?}", value);
let label = Label::new(field.name(), value_string);
self.0.push(label);
}
}
impl Labels {
fn from_attributes(attrs: &Attributes<'_>) -> Self {
let mut labels = Self(Vec::new());
let record = Record::new(attrs.values());
record.record(&mut labels);
labels
}
}
impl AsRef<Vec<Label>> for Labels {
fn as_ref(&self) -> &Vec<Label> {
&self.0
}
}
pub struct WithContext {
with_labels: fn(&Dispatch, &Id, f: &mut dyn FnMut(&Labels)),
}
impl WithContext {
pub fn with_labels<'a>(&self, dispatch: &'a Dispatch, id: &Id, f: &mut dyn FnMut(&Vec<Label>)) {
let mut ff = |labels: &Labels| f(labels.as_ref());
(self.with_labels)(dispatch, id, &mut ff)
}
}
pub struct MetricsLayer<S> {
ctx: WithContext,
_subscriber: PhantomData<fn(S)>,
_priv: (),
}
impl<S> MetricsLayer<S>
where
S: Subscriber + for<'span> LookupSpan<'span>,
{
pub fn new() -> Self {
let ctx = WithContext {
with_labels: Self::with_labels,
};
Self {
ctx,
_subscriber: PhantomData,
_priv: (),
}
}
fn with_labels(dispatch: &Dispatch, id: &Id, f: &mut dyn FnMut(&Labels)) {
let span = {
let subscriber = dispatch
.downcast_ref::<S>()
.expect("subscriber should downcast to expected type; this is a bug!");
subscriber
.span(id)
.expect("registry should have a span for the current ID")
};
let parents = span.parents();
for span in std::iter::once(span).chain(parents) {
let extensions = span.extensions();
if let Some(value) = extensions.get::<Labels>() {
f(value);
}
}
}
}
impl<S> Layer<S> for MetricsLayer<S>
where
S: Subscriber + for<'a> LookupSpan<'a>,
{
fn new_span(&self, attrs: &Attributes<'_>, id: &Id, cx: Context<'_, S>) {
let span = cx.span(id).expect("span must already exist!");
let labels = Labels::from_attributes(attrs);
span.extensions_mut().insert(labels);
}
unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> {
match id {
id if id == TypeId::of::<Self>() => Some(self as *const _ as *const ()),
id if id == TypeId::of::<WithContext>() => Some(&self.ctx as *const _ as *const ()),
_ => None,
}
}
}
impl<S> Default for MetricsLayer<S>
where
S: Subscriber + for<'span> LookupSpan<'span>,
{
fn default() -> Self {
MetricsLayer::new()
}
}
pub trait SpanExt {
fn with_labels<F>(&self, f: F)
where
F: FnMut(&Vec<Label>);
}
impl SpanExt for tracing::Span {
fn with_labels<F>(&self, mut f: F)
where
F: FnMut(&Vec<Label>),
{
self.with_subscriber(|(id, subscriber)| {
if let Some(ctx) = subscriber.downcast_ref::<WithContext>() {
ctx.with_labels(subscriber, id, &mut f)
}
});
}
}