Allow incrementing/decrementing gauge metrics.

packages/metrics/src/gauge.rs

@@ -20,6 +20,14 @@ impl Gauge {
     pub fn set(&mut self, value: f64) {
         self.0 = value;
     }
+
+    pub fn increment(&mut self, value: f64) {
+        self.0 += value;
+    }
+
+    pub fn decrement(&mut self, value: f64) {
+        self.0 -= value;
+    }
 }
 
 impl From<f64> for Gauge {
@@ -72,6 +80,20 @@ mod tests {
         assert_relative_eq!(gauge.value(), 1.0);
     }
 
+    #[test]
+    fn it_could_be_incremented() {
+        let mut gauge = Gauge::new(0.0);
+        gauge.increment(1.0);
+        assert_relative_eq!(gauge.value(), 1.0);
+    }
+
+    #[test]
+    fn it_could_be_decremented() {
+        let mut gauge = Gauge::new(1.0);
+        gauge.decrement(1.0);
+        assert_relative_eq!(gauge.value(), 0.0);
+    }
+
     #[test]
     fn it_serializes_to_prometheus() {
         let counter = Gauge::new(42.0);

packages/metrics/src/metric/mod.rs

@@ -61,6 +61,14 @@ impl Metric<Gauge> {
     pub fn set(&mut self, label_set: &LabelSet, value: f64, time: DurationSinceUnixEpoch) {
         self.sample_collection.set(label_set, value, time);
     }
+
+    pub fn increment(&mut self, label_set: &LabelSet, time: DurationSinceUnixEpoch) {
+        self.sample_collection.increment(label_set, time);
+    }
+
+    pub fn decrement(&mut self, label_set: &LabelSet, time: DurationSinceUnixEpoch) {
+        self.sample_collection.decrement(label_set, time);
+    }
 }
 
 impl<T: PrometheusSerializable> PrometheusSerializable for Metric<T> {

packages/metrics/src/metric_collection.rs

@@ -136,6 +136,38 @@ impl MetricCollection {
         Ok(())
     }
 
+    /// # Errors
+    ///
+    /// Return an error if a metrics of a different type with the same name
+    /// already exists.
+    pub fn increase_gauge(&mut self, name: &MetricName, label_set: &LabelSet, time: DurationSinceUnixEpoch) -> Result<(), Error> {
+        if self.counters.metrics.contains_key(name) {
+            return Err(Error::MetricNameCollisionAdding {
+                metric_name: name.clone(),
+            });
+        }
+
+        self.gauges.increment(name, label_set, time);
+
+        Ok(())
+    }
+
+    /// # Errors
+    ///
+    /// Return an error if a metrics of a different type with the same name
+    /// already exists.
+    pub fn decrease_gauge(&mut self, name: &MetricName, label_set: &LabelSet, time: DurationSinceUnixEpoch) -> Result<(), Error> {
+        if self.counters.metrics.contains_key(name) {
+            return Err(Error::MetricNameCollisionAdding {
+                metric_name: name.clone(),
+            });
+        }
+
+        self.gauges.decrement(name, label_set, time);
+
+        Ok(())
+    }
+
     pub fn ensure_gauge_exists(&mut self, name: &MetricName) {
         self.gauges.ensure_metric_exists(name);
     }
@@ -353,6 +385,36 @@ impl MetricKindCollection<Gauge> {
         metric.set(label_set, value, time);
     }
 
+    /// Increments the gauge for the given metric name and labels.
+    ///
+    /// If the metric name does not exist, it will be created.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the metric does not exist and it could not be created.
+    pub fn increment(&mut self, name: &MetricName, label_set: &LabelSet, time: DurationSinceUnixEpoch) {
+        self.ensure_metric_exists(name);
+
+        let metric = self.metrics.get_mut(name).expect("Gauge metric should exist");
+
+        metric.increment(label_set, time);
+    }
+
+    /// Decrements the gauge for the given metric name and labels.
+    ///
+    /// If the metric name does not exist, it will be created.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the metric does not exist and it could not be created.
+    pub fn decrement(&mut self, name: &MetricName, label_set: &LabelSet, time: DurationSinceUnixEpoch) {
+        self.ensure_metric_exists(name);
+
+        let metric = self.metrics.get_mut(name).expect("Gauge metric should exist");
+
+        metric.decrement(label_set, time);
+    }
+
     #[must_use]
     pub fn get_value(&self, name: &MetricName, label_set: &LabelSet) -> Option<Gauge> {
         self.metrics

packages/metrics/src/sample.rs

@@ -64,6 +64,14 @@ impl Sample<Gauge> {
     pub fn set(&mut self, value: f64, time: DurationSinceUnixEpoch) {
         self.measurement.set(value, time);
     }
+
+    pub fn increment(&mut self, time: DurationSinceUnixEpoch) {
+        self.measurement.increment(time);
+    }
+
+    pub fn decrement(&mut self, time: DurationSinceUnixEpoch) {
+        self.measurement.decrement(time);
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -121,6 +129,16 @@ impl Measurement<Gauge> {
         self.value.set(value);
         self.set_recorded_at(time);
     }
+
+    pub fn increment(&mut self, time: DurationSinceUnixEpoch) {
+        self.value.increment(1.0);
+        self.set_recorded_at(time);
+    }
+
+    pub fn decrement(&mut self, time: DurationSinceUnixEpoch) {
+        self.value.decrement(1.0);
+        self.set_recorded_at(time);
+    }
 }
 
 /// Serializes the `recorded_at` field as a string in ISO 8601 format (RFC 3339).
@@ -273,14 +291,32 @@ mod tests {
         }
 
         #[test]
-        fn it_should_allow_incrementing_the_counter() {
+        fn it_should_allow_setting_a_value() {
             let mut sample = Sample::new(Gauge::default(), DurationSinceUnixEpoch::default(), LabelSet::default());
 
             sample.set(1.0, updated_at_time());
 
             assert_eq!(sample.value(), &Gauge::new(1.0));
         }
 
+        #[test]
+        fn it_should_allow_incrementing_the_value() {
+            let mut sample = Sample::new(Gauge::new(0.0), DurationSinceUnixEpoch::default(), LabelSet::default());
+
+            sample.increment(updated_at_time());
+
+            assert_eq!(sample.value(), &Gauge::new(1.0));
+        }
+
+        #[test]
+        fn it_should_allow_decrementing_the_value() {
+            let mut sample = Sample::new(Gauge::new(1.0), DurationSinceUnixEpoch::default(), LabelSet::default());
+
+            sample.decrement(updated_at_time());
+
+            assert_eq!(sample.value(), &Gauge::new(0.0));
+        }
+
         #[test]
         fn it_should_record_the_latest_update_time_when_the_counter_is_incremented() {
             let mut sample = Sample::new(Gauge::default(), DurationSinceUnixEpoch::default(), LabelSet::default());

packages/metrics/src/sample_collection.rs

@@ -90,6 +90,24 @@ impl SampleCollection<Gauge> {
 
         sample.set(value, time);
     }
+
+    pub fn increment(&mut self, label_set: &LabelSet, time: DurationSinceUnixEpoch) {
+        let sample = self
+            .samples
+            .entry(label_set.clone())
+            .or_insert_with(|| Measurement::new(Gauge::default(), time));
+
+        sample.increment(time);
+    }
+
+    pub fn decrement(&mut self, label_set: &LabelSet, time: DurationSinceUnixEpoch) {
+        let sample = self
+            .samples
+            .entry(label_set.clone())
+            .or_insert_with(|| Measurement::new(Gauge::default(), time));
+
+        sample.decrement(time);
+    }
 }
 
 impl<T: Serialize> Serialize for SampleCollection<T> {
@@ -278,7 +296,7 @@ mod tests {
         #[test]
         fn it_should_increment_the_counter_for_a_preexisting_label_set() {
             let label_set = LabelSet::default();
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Counter>::default();
 
             // Initialize the sample
             collection.increment(&label_set, sample_update_time());
@@ -296,7 +314,7 @@ mod tests {
         #[test]
         fn it_should_allow_increment_the_counter_for_a_non_existent_label_set() {
             let label_set = LabelSet::default();
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Counter>::default();
 
             // Increment a non-existent label
             collection.increment(&label_set, sample_update_time());
@@ -312,7 +330,7 @@ mod tests {
             let label_set = LabelSet::default();
             let initial_time = sample_update_time();
 
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Counter>::default();
             collection.increment(&label_set, initial_time);
 
             // Increment with a new time
@@ -330,7 +348,7 @@ mod tests {
             let label2 = LabelSet::from([("name", "value2")]);
             let now = sample_update_time();
 
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Counter>::default();
 
             collection.increment(&label1, now);
             collection.increment(&label2, now);
@@ -351,9 +369,9 @@ mod tests {
         use crate::gauge::Gauge;
 
         #[test]
-        fn it_should_increment_the_gauge_for_a_preexisting_label_set() {
+        fn it_should_allow_setting_the_gauge_for_a_preexisting_label_set() {
             let label_set = LabelSet::default();
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Gauge>::default();
 
             // Initialize the sample
             collection.set(&label_set, 1.0, sample_update_time());
@@ -369,9 +387,9 @@ mod tests {
         }
 
         #[test]
-        fn it_should_allow_increment_the_gauge_for_a_non_existent_label_set() {
+        fn it_should_allow_setting_the_gauge_for_a_non_existent_label_set() {
             let label_set = LabelSet::default();
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Gauge>::default();
 
             // Set a non-existent label
             collection.set(&label_set, 1.0, sample_update_time());
@@ -383,11 +401,11 @@ mod tests {
         }
 
         #[test]
-        fn it_should_update_the_latest_update_time_when_incremented() {
+        fn it_should_update_the_latest_update_time_when_setting() {
             let label_set = LabelSet::default();
             let initial_time = sample_update_time();
 
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Gauge>::default();
             collection.set(&label_set, 1.0, initial_time);
 
             // Set with a new time
@@ -400,12 +418,12 @@ mod tests {
         }
 
         #[test]
-        fn it_should_increment_the_gauge_for_multiple_labels() {
+        fn it_should_allow_setting_the_gauge_for_multiple_labels() {
             let label1 = LabelSet::from([("name", "value1")]);
             let label2 = LabelSet::from([("name", "value2")]);
             let now = sample_update_time();
 
-            let mut collection = SampleCollection::default();
+            let mut collection = SampleCollection::<Gauge>::default();
 
             collection.set(&label1, 1.0, now);
             collection.set(&label2, 2.0, now);
@@ -414,5 +432,33 @@ mod tests {
             assert_eq!(collection.get(&label2).unwrap().value(), &Gauge::new(2.0));
             assert_eq!(collection.len(), 2);
         }
+
+        #[test]
+        fn it_should_allow_incrementing_the_gauge() {
+            let label_set = LabelSet::default();
+            let mut collection = SampleCollection::<Gauge>::default();
+
+            // Initialize the sample
+            collection.set(&label_set, 1.0, sample_update_time());
+
+            // Increment
+            collection.increment(&label_set, sample_update_time());
+            let sample = collection.get(&label_set).unwrap();
+            assert_eq!(*sample.value(), Gauge::new(2.0));
+        }
+
+        #[test]
+        fn it_should_allow_decrementing_the_gauge() {
+            let label_set = LabelSet::default();
+            let mut collection = SampleCollection::<Gauge>::default();
+
+            // Initialize the sample
+            collection.set(&label_set, 1.0, sample_update_time());
+
+            // Increment
+            collection.decrement(&label_set, sample_update_time());
+            let sample = collection.get(&label_set).unwrap();
+            assert_eq!(*sample.value(), Gauge::new(0.0));
+        }
     }
 }