metrics: return histograms for time metrics

create local type MetricsMap
implement receive_metric function for local types
add error management

command/src/command.proto

@@ -572,13 +572,15 @@ message BackendMetrics {
     map<string, FilteredMetrics> metrics = 2;
 }
 
+// A metric, in a "filtered" format, which means: sendable to outside programs.
 message FilteredMetrics {
     oneof inner {
         uint64 gauge = 1;
         int64 count = 2;
         uint64 time = 3;
         Percentiles percentiles = 4;
         FilteredTimeSerie time_serie = 5;
+        FilteredHistogram histogram = 6;
     }
 }
 
@@ -588,7 +590,6 @@ message FilteredTimeSerie {
     repeated uint32 last_hour = 3;
 }
 
-
 message Percentiles {
     required uint64 samples = 1;
     required uint64 p_50 = 2;
@@ -600,6 +601,20 @@ message Percentiles {
     required uint64 p_100 = 8;
 }
 
+// a histogram meant to be translated to prometheus
+message FilteredHistogram {
+    required uint64 sum = 1;
+    required uint64 count = 2;
+    repeated Bucket buckets = 3;
+}
+
+// a prometheus histogram bucket
+message Bucket {
+    required uint64 count = 1;
+    // upper range of the bucket (le = less or equal)
+    required uint64 le = 2;
+}
+
 message RequestCounts {
     map<string, int32> map = 1;
-}
+}

command/src/proto/display.rs

@@ -18,6 +18,8 @@ use crate::proto::{
     DisplayError,
 };
 
+use super::command::FilteredHistogram;
+
 impl Display for CertificateAndKey {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         let versions = self.versions.iter().fold(String::new(), |acc, tls_v| {
@@ -232,6 +234,7 @@ fn print_proxy_metrics(proxy_metrics: &BTreeMap<String, FilteredMetrics>) {
     let filtered = filter_metrics(proxy_metrics);
     print_gauges_and_counts(&filtered);
     print_percentiles(&filtered);
+    print_histograms(&filtered);
 }
 
 fn print_worker_metrics(worker_metrics: &WorkerMetrics) -> Result<(), DisplayError> {
@@ -372,6 +375,37 @@ fn print_percentiles(filtered_metrics: &BTreeMap<String, FilteredMetrics>) {
     percentile_table.printstd();
 }
 
+fn print_histograms(filtered_metrics: &BTreeMap<String, FilteredMetrics>) {
+    let histograms: BTreeMap<String, FilteredHistogram> = filtered_metrics
+        .iter()
+        .filter_map(|(name, metric)| match metric.inner.clone() {
+            Some(filtered_metrics::Inner::Histogram(hist)) => Some((name.to_owned(), hist)),
+            _ => None,
+        })
+        .collect();
+
+    for (name, histogram) in histograms {
+        print_histogram(&name, &histogram);
+    }
+}
+
+fn print_histogram(metric_name: &str, hist: &FilteredHistogram) {
+    println!("{}", metric_name);
+    let mut first_row = Row::new(vec![cell!("sum"), cell!("count")]);
+    let mut value_row = Row::new(vec![cell!(hist.sum), cell!(hist.count)]);
+
+    for bucket in &hist.buckets {
+        first_row.add_cell(cell!(bucket.le));
+        value_row.add_cell(cell!(bucket.count));
+    }
+
+    let mut table = Table::new();
+    table.set_format(*prettytable::format::consts::FORMAT_BOX_CHARS);
+    table.add_row(first_row);
+    table.add_row(value_row);
+    table.printstd();
+}
+
 fn print_available_metrics(available_metrics: &AvailableMetrics) -> Result<(), DisplayError> {
     println!("Available metrics on the proxy level:");
     for metric_name in &available_metrics.proxy_metrics {