proxy: Implement a From converter for latency::Ms (#872)

This reduces callsite verbosity for latency measurements at the expense of a fn-level
generic.

proxy/src/telemetry/metrics/histogram.rs

@@ -65,8 +65,9 @@ impl<V: Into<u64>> Histogram<V> {
         }
     }
 
-    pub fn add(&mut self, v: V) {
-        let value = v.into();
+    pub fn add<U: Into<V>>(&mut self, u: U) {
+        let v: V = u.into();
+        let value: u64 = v.into();
 
         let idx = self.bounds.0.iter()
             .position(|b| match *b {
@@ -184,7 +185,7 @@ mod tests {
 
     quickcheck! {
         fn bucket_incremented(obs: u64) -> bool {
-            let mut hist = Histogram::new(&BOUNDS);
+            let mut hist = Histogram::<u64>::new(&BOUNDS);
             hist.add(obs);
             let incremented_bucket = &BOUNDS.0.iter()
                 .position(|bucket| match *bucket {
@@ -201,7 +202,7 @@ mod tests {
         }
 
         fn sum_equals_total_of_observations(observations: Vec<u64>) -> bool {
-            let mut hist = Histogram::new(&BOUNDS);
+            let mut hist = Histogram::<u64>::new(&BOUNDS);
 
             let mut expected_sum = Wrapping(0u64);
             for obs in observations {
@@ -213,7 +214,7 @@ mod tests {
         }
 
         fn count_equals_number_of_observations(observations: Vec<u64>) -> bool {
-            let mut hist = Histogram::new(&BOUNDS);
+            let mut hist = Histogram::<u64>::new(&BOUNDS);
 
             for obs in &observations {
                 hist.add(*obs);
@@ -228,7 +229,7 @@ mod tests {
 
         fn multiple_observations_increment_buckets(observations: Vec<u64>) -> bool {
             let mut buckets_and_counts: HashMap<usize, u64> = HashMap::new();
-            let mut hist = Histogram::new(&BOUNDS);
+            let mut hist = Histogram::<u64>::new(&BOUNDS);
 
             for obs in observations {
                 let incremented_bucket = &BOUNDS.0.iter()

proxy/src/telemetry/metrics/latency.rs

@@ -43,7 +43,7 @@ pub const BOUNDS: &Bounds = &Bounds(&[
 
 /// A duration in milliseconds.
 #[derive(Debug, Default, Clone)]
-pub struct Ms(pub Duration);
+pub struct Ms(Duration);
 
 // /// A duration in microseconds.
 // #[derive(Debug, Default, Clone)]
@@ -56,6 +56,12 @@ impl Into<u64> for Ms {
     }
 }
 
+impl From<Duration> for Ms {
+    fn from(d: Duration) -> Self {
+        Ms(d)
+    }
+}
+
 impl Default for Histogram<Ms> {
     fn default() -> Self {
         Histogram::new(BOUNDS)

proxy/src/telemetry/metrics/mod.rs

@@ -447,7 +447,7 @@ impl Aggregate {
                 ));
                 self.update(|metrics| {
                     metrics.response_total(&labels).incr();
-                    metrics.response_latency(&labels).add(latency::Ms(end.since_request_open));
+                    metrics.response_latency(&labels).add(end.since_request_open);
                 });
             },
 
@@ -456,7 +456,7 @@ impl Aggregate {
                 let labels = Arc::new(ResponseLabels::fail(res));
                 self.update(|metrics| {
                     metrics.response_total(&labels).incr();
-                    metrics.response_latency(&labels).add(latency::Ms(fail.since_request_open));
+                    metrics.response_latency(&labels).add(fail.since_request_open);
                 });
             },
 
@@ -475,8 +475,7 @@ impl Aggregate {
                     *metrics.tcp().write_bytes_total(&labels) += close.tx_bytes as u64;
                     *metrics.tcp().read_bytes_total(&labels) += close.rx_bytes as u64;
 
-                    metrics.tcp().connection_duration(&close_labels)
-                        .add(latency::Ms(close.duration));
+                    metrics.tcp().connection_duration(&close_labels).add(close.duration);
                     metrics.tcp().close_total(&close_labels).incr();
 
                     let metrics = metrics.tcp().open_connections.values.get_mut(&labels);