feat: [#1446] add aggregate function sum to metric collection

It allows sum metric samples matching a given criteria. The criteria is
a label set. Sample values are added if they contain all the label
name/value pairs specified in the criteria.

For example, given these metric's samples in Prometheus export text format:

```
udp_tracker_server_requests_accepted_total{request_kind="scrape",server_binding_address_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6969",server_binding_protocol="udp"} 213118
udp_tracker_server_requests_accepted_total{request_kind="announce",server_binding_address_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6969",server_binding_protocol="udp"} 16460553
udp_tracker_server_requests_accepted_total{request_kind="connect",server_binding_address_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6868",server_binding_protocol="udp"} 617
udp_tracker_server_requests_accepted_total{request_kind="connect",server_binding_address_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6969",server_binding_protocol="udp"} 17148137
```

And the criteria: it should contain the label `request_kind` with the value `connect`.

It should return: 617 + 17148137 = 17148754

Author: josecelano

packages/http-tracker-core/src/statistics/metrics.rs

@@ -33,7 +33,7 @@ impl Metrics {
         labels: &LabelSet,
         now: DurationSinceUnixEpoch,
     ) -> Result<(), Error> {
-        self.metric_collection.increase_counter(metric_name, labels, now)
+        self.metric_collection.increment_counter(metric_name, labels, now)
     }
 
     /// # Errors

packages/metrics/src/aggregate.rs

@@ -0,0 +1,28 @@
+use derive_more::Display;
+
+#[derive(Debug, Display, Clone, Copy, PartialEq)]
+pub struct AggregateValue(f64);
+
+impl AggregateValue {
+    #[must_use]
+    pub fn new(value: f64) -> Self {
+        Self(value)
+    }
+
+    #[must_use]
+    pub fn value(&self) -> f64 {
+        self.0
+    }
+}
+
+impl From<f64> for AggregateValue {
+    fn from(value: f64) -> Self {
+        Self(value)
+    }
+}
+
+impl From<AggregateValue> for f64 {
+    fn from(value: AggregateValue) -> Self {
+        value.0
+    }
+}

packages/metrics/src/counter.rs

@@ -17,6 +17,11 @@ impl Counter {
         self.0
     }
 
+    #[must_use]
+    pub fn primitive(&self) -> u64 {
+        self.value()
+    }
+
     pub fn increment(&mut self, value: u64) {
         self.0 += value;
     }
@@ -26,12 +31,25 @@ impl Counter {
     }
 }
 
+impl From<u32> for Counter {
+    fn from(value: u32) -> Self {
+        Self(u64::from(value))
+    }
+}
+
 impl From<u64> for Counter {
     fn from(value: u64) -> Self {
         Self(value)
     }
 }
 
+impl From<i32> for Counter {
+    fn from(value: i32) -> Self {
+        #[allow(clippy::cast_sign_loss)]
+        Self(value as u64)
+    }
+}
+
 impl From<Counter> for u64 {
     fn from(counter: Counter) -> Self {
         counter.value()

packages/metrics/src/gauge.rs

@@ -17,6 +17,11 @@ impl Gauge {
         self.0
     }
 
+    #[must_use]
+    pub fn primitive(&self) -> f64 {
+        self.value()
+    }
+
     pub fn set(&mut self, value: f64) {
         self.0 = value;
     }
@@ -30,6 +35,12 @@ impl Gauge {
     }
 }
 
+impl From<f32> for Gauge {
+    fn from(value: f32) -> Self {
+        Self(f64::from(value))
+    }
+}
+
 impl From<f64> for Gauge {
     fn from(value: f64) -> Self {
         Self(value)

packages/metrics/src/label/set.rs

@@ -1,3 +1,4 @@
+use std::collections::btree_map::Iter;
 use std::collections::BTreeMap;
 use std::fmt::Display;
 
@@ -12,6 +13,11 @@ pub struct LabelSet {
 }
 
 impl LabelSet {
+    #[must_use]
+    pub fn empty() -> Self {
+        Self { items: BTreeMap::new() }
+    }
+
     /// Insert a new label pair or update the value of an existing label.
     pub fn upsert(&mut self, key: LabelName, value: LabelValue) {
         self.items.insert(key, value);
@@ -20,6 +26,21 @@ impl LabelSet {
     pub fn is_empty(&self) -> bool {
         self.items.is_empty()
     }
+
+    pub fn contains_pair(&self, name: &LabelName, value: &LabelValue) -> bool {
+        match self.items.get(name) {
+            Some(existing_value) => existing_value == value,
+            None => false,
+        }
+    }
+
+    pub fn matches(&self, criteria: &LabelSet) -> bool {
+        criteria.iter().all(|(key, value)| self.contains_pair(key, value))
+    }
+
+    pub fn iter(&self) -> Iter<'_, LabelName, LabelValue> {
+        self.items.iter()
+    }
 }
 
 impl Display for LabelSet {

packages/metrics/src/lib.rs

@@ -1,3 +1,4 @@
+pub mod aggregate;
 pub mod counter;
 pub mod gauge;
 pub mod label;

packages/metrics/src/metric/aggregate/mod.rs

@@ -0,0 +1 @@
+pub mod sum;