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use crate::guards::DeferredAddWithLabels;
use prometheus::{
register_histogram_vec, register_int_counter_vec, register_int_gauge_vec, HistogramTimer,
HistogramVec, IntCounterVec, IntGaugeVec,
};
use std::marker::PhantomData;
/// A sequence of values for Prometheus labels
pub type LabelValues<'a> = Vec<&'a str>;
/// The `Labels` trait applies to values intended to generate Prometheus labels for a metric.
///
/// A metric in Prometheus can include any number of labels. Each label has a fixed name,
/// and when events are emitted for the metric, those events must include values for each
/// of the labels. Using labels makes it possible to easily see a metric in aggregate (i.e.,
/// to see totals regardless of label values), or to query specific kinds of events by
/// filtering label values.
///
/// Thus, for example, rather than having a separate metric for each kind of error that
/// arises, we can produce one metric with an "err" label, whose value will reflect which
/// error has occurred. That simplifies the top-level list of metrics, and makes it easier
/// to build queries to aggregate specific kinds of error events.
///
/// This trait adds some extra guard rails on top of the prometheus-rs crate, so that when
/// we emit a labeled metric we can use a custom type to represent the labels, rather than
/// working directly with slices of string slices. When defining a labeled metric, you should
/// also define a new type representing its labels that implements the `Labels` trait.
/// Then, when emitting events for the metric, labels are passed in using this custom type,
/// which rules out several kinds of bugs (like missing or incorrectly ordered label values).
///
/// You can define labeled metrics using types like [`IntCounterWithLabels`], which are
/// parameterized by a type that implements `Labels`.
///
/// [`IntCounterWithLabels`]: struct.IntCounterWithLabels.html
pub trait Labels {
/// The names of the labels that will be defined for the corresponding metric.
fn label_names() -> Vec<&'static str>;
/// Labels values to seed the metric with initially.
///
/// Since Prometheus doesn't know the possible values a label will take on, when we set
/// up a labeled metric by default no values will appear until events are emitted. But
/// for discoverability, it's helpful to initialize a labeled metric with some possible
/// label values (at count 0) even if no events for the metric have occurred.
///
/// The label values provided by this function are used to pre-populate the metric at
/// count 0. **The values do _not_ need to be exhaustive**; it's fine for events to emit
/// label values that are not included here.
fn possible_label_values() -> Vec<LabelValues<'static>>;
/// The actual label values to provide when emitting an event to Prometheus.
///
/// The sequence of values should correspond to the names provided in `label_names`,
/// in order.
fn label_values(&self) -> LabelValues;
}
/// A Prometheus integer counter metric, with labels described by the type `L`.
///
/// The type `L` must implement the [`Labels`] trait; see the documentation for that trait
/// for an overview of Prometheus metric labels.
///
/// [`Labels`]: trait.Labels.html
pub struct IntCounterWithLabels<L: Labels> {
metric: IntCounterVec,
_labels: PhantomData<L>,
}
impl<L: Labels> IntCounterWithLabels<L> {
/// Construct and immediately register a new `IntCounterWithLabels` instance.
pub fn register_new(name: &str, help: &str) -> IntCounterWithLabels<L> {
let metric = register_int_counter_vec!(name, help, &L::label_names()).unwrap();
for vals in L::possible_label_values() {
metric.with_label_values(&vals).inc_by(0);
}
Self {
metric,
_labels: PhantomData,
}
}
/// Get the value of the counter with the provided `labels`.
pub fn get(&self, labels: &L) -> u64 {
self.metric.with_label_values(&labels.label_values()).get()
}
/// Increment the metric by `1`, using the provided `labels` for the event.
pub fn inc(&self, labels: &L) {
self.metric.with_label_values(&labels.label_values()).inc();
}
/// Increment the metric by `v`, using the provided `labels` for the event.
pub fn add(&self, v: u64, labels: &L) {
self.metric
.with_label_values(&labels.label_values())
.inc_by(v);
}
/// Creates a guard value that will increment the metric by `1`, using the provided `labels`,
/// once dropped.
///
/// Prior to dropping, the labels can be altered using [`DeferredAddWithLabels::with_labels`].
#[must_use]
pub fn deferred_inc<'a>(&'a self, labels: L) -> DeferredAddWithLabels<'a, L> {
DeferredAddWithLabels::new(self, 1, labels)
}
/// Creates a guard value that will increment the metric by `v`, using the provided `labels`,
/// once dropped.
///
/// Prior to dropping, the labels can be altered using [`DeferredAddWithLabels::with_labels`].
#[must_use]
pub fn deferred_add<'a>(&'a self, v: u64, labels: L) -> DeferredAddWithLabels<'a, L> {
DeferredAddWithLabels::new(self, v, labels)
}
}
/// A Prometheus integer gauge metric, with labels described by the type `L`.
///
/// The type `L` must implement the [`Labels`] trait; see the documentation for that trait
/// for an overview of Prometheus metric labels.
///
/// [`Labels`]: trait.Labels.html
pub struct IntGaugeWithLabels<L: Labels> {
metric: IntGaugeVec,
_labels: PhantomData<L>,
}
impl<L: Labels> IntGaugeWithLabels<L> {
/// Construct and immediately register a new `IntGaugeWithLabels` instance.
pub fn register_new(name: &str, help: &str) -> IntGaugeWithLabels<L> {
let metric = register_int_gauge_vec!(name, help, &L::label_names()).unwrap();
// Note: for gauges, unlike counters, we don't need to -- and should not! -- prepopulate
// the metric with the possible labels. Unlike counters, which are only updated when an
// event occurs, gauges _always_ have a value. Moreover, we cannot make assumptions about
// an initial gauge value (unlike an initial 0 value for counters).
Self {
metric,
_labels: PhantomData,
}
}
/// Get the value of the gauge with the provided `labels`.
pub fn get(&self, labels: &L) -> i64 {
self.metric.with_label_values(&labels.label_values()).get()
}
/// Set the value of the gauge with the provided `labels`.
pub fn set(&self, labels: &L, value: i64) {
self.metric
.with_label_values(&labels.label_values())
.set(value);
}
/// Add `value` to the gauge with the provided `labels`.
pub fn add(&self, labels: &L, value: i64) {
self.metric
.with_label_values(&labels.label_values())
.add(value);
}
/// Subtract `value` from the gauge with the provided `labels`.
pub fn sub(&self, labels: &L, value: i64) {
self.metric
.with_label_values(&labels.label_values())
.sub(value);
}
/// Increment the gauge by `1`, using the provided `labels` for the event.
pub fn inc(&self, labels: &L) {
self.metric.with_label_values(&labels.label_values()).inc();
}
/// Decrement the gauge by `1`, using the provided `labels` for the event.
pub fn dec(&self, labels: &L) {
self.metric.with_label_values(&labels.label_values()).dec();
}
}
/// A Prometheus histogram metric, with labels described by the type `L`.
///
/// The type `L` must implement the [`Labels`] trait; see the documentation for that trait
/// for an overview of Prometheus metric labels.
///
/// [`Labels`]: trait.Labels.html
pub struct HistogramWithLabels<L: Labels> {
metric: HistogramVec,
_labels: PhantomData<L>,
}
impl<L: Labels> HistogramWithLabels<L> {
/// Construct and immediately register a new `HistogramWithLabels` instance.
pub fn register_new(name: &str, help: &str) -> Self {
let metric = register_histogram_vec!(name, help, &L::label_names()).unwrap();
// Note: for histograms, like gauges, we don't need to -- and should not! -- prepopulate
// the metric with the possible labels.
Self {
metric,
_labels: PhantomData,
}
}
/// Construct and immediately register a new `HistogramWithLabels` instance.
///
/// This will use the provided `buckets` when registering the underlying [`HistogramVec`].
pub fn register_new_with_buckets(name: &str, help: &str, buckets: Vec<f64>) -> Self {
let metric = register_histogram_vec!(name, help, &L::label_names(), buckets).unwrap();
// Note: for histograms, like gauges, we don't need to -- and should not! -- prepopulate
// the metric with the possible labels.
Self {
metric,
_labels: PhantomData,
}
}
/// Add a single observation to the histogram with the provided `labels`.
pub fn observe(&self, labels: &L, value: f64) {
self.metric
.with_label_values(&labels.label_values())
.observe(value);
}
/// Return a [`HistogramTimer`] to track a duration, using the provided `labels`.
pub fn start_timer(&self, labels: &L) -> HistogramTimer {
self.metric
.with_label_values(&labels.label_values())
.start_timer()
}
/// Observe execution time of a closure, in seconds.
pub fn observe_closure_duration<F, T>(&self, labels: &L, f: F) -> T
where
F: FnOnce() -> T,
{
self.metric
.with_label_values(&labels.label_values())
.observe_closure_duration(f)
}
/// Return accumulated sum of all samples, using the provided `labels`.
pub fn get_sample_sum(&self, labels: &L) -> f64 {
self.metric
.with_label_values(&labels.label_values())
.get_sample_sum()
}
/// Return count of all samples, using the provided `labels`.
pub fn get_sample_count(&self, labels: &L) -> u64 {
self.metric
.with_label_values(&labels.label_values())
.get_sample_count()
}
}
#[cfg(test)]
mod tests {
use super::*;
use lazy_static::lazy_static;
use test_labels::*;
#[allow(dead_code)]
mod test_labels {
use crate::label_enum;
label_enum! {
pub enum Animal {
Bird,
Cat,
Dog,
}
}
label_enum! {
pub enum Size {
Small,
Large,
}
}
}
struct TestLabels {
animal: Animal,
size: Size,
}
impl Labels for TestLabels {
fn label_names() -> Vec<&'static str> {
vec!["animal", "size"]
}
fn possible_label_values() -> Vec<LabelValues<'static>> {
Default::default() // elide this for brevity.
}
fn label_values(&self) -> LabelValues {
let Self { animal, size } = self;
vec![animal.as_str(), size.as_str()]
}
}
/// Show that an [`IntCounterWithLabels`] can have its value accessed.
#[test]
fn int_counter_with_labels_get_works() {
lazy_static! {
static ref COUNTER: IntCounterWithLabels<TestLabels> =
IntCounterWithLabels::register_new(
"test_label_counter",
"a labeled counter for tests"
);
}
// Increment the counter for some various combinations of label values.
COUNTER.inc(&TestLabels {
animal: Animal::Bird,
size: Size::Large,
});
COUNTER.inc(&TestLabels {
animal: Animal::Bird,
size: Size::Small,
});
COUNTER.inc(&TestLabels {
animal: Animal::Cat,
size: Size::Large,
});
assert_eq!(
COUNTER.get(&TestLabels {
animal: Animal::Bird,
size: Size::Large,
}),
1
);
assert_eq!(
COUNTER.get(&TestLabels {
animal: Animal::Cat,
size: Size::Small,
}),
0
);
}
/// Show that an [`IntGaugeWithLabels`] can have its value accessed.
#[test]
fn int_gauge_with_labels_get_works() {
lazy_static! {
static ref GAUGE: IntGaugeWithLabels<TestLabels> =
IntGaugeWithLabels::register_new("test_label_gauge", "a labeled gauge for tests");
}
// Increment the gauge for some various combinations of label values.
GAUGE.inc(&TestLabels {
animal: Animal::Bird,
size: Size::Large,
});
GAUGE.inc(&TestLabels {
animal: Animal::Bird,
size: Size::Small,
});
GAUGE.inc(&TestLabels {
animal: Animal::Cat,
size: Size::Large,
});
assert_eq!(
GAUGE.get(&TestLabels {
animal: Animal::Bird,
size: Size::Large,
}),
1
);
assert_eq!(
GAUGE.get(&TestLabels {
animal: Animal::Cat,
size: Size::Small,
}),
0
);
}
}