feat: exporter name prefix & custom metric serialisation

metrics.v

@@ -4,21 +4,13 @@ import io
 
 [params]
 pub struct Metric {
+pub:
 	name   string      [required]
 	labels [][2]string
 }
 
-[inline]
-fn join_two_array(arr [2]string) string {
-	return '${arr[0]}="${arr[1]}"'
-}
-
 pub fn (m &Metric) str() string {
-	if m.labels.len == 0 {
-		return m.name
-	}
-
-	return '$m.name{${m.labels.map(join_two_array(it)).join(',')}}'
+	return '$m.name $m.labels'
 }
 
 pub interface MetricsCollector {
@@ -38,7 +30,8 @@ mut:
 }
 
 pub interface MetricsExporter {
-	load(collector MetricsCollector)
+	load(prefix string, collector MetricsCollector)
 	export_to_writer(writer io.Writer) !
 	export_to_string() !string
+	serialize_metric(metric Metric) string
 }

prometheus.v

@@ -7,6 +7,7 @@ import arrays
 pub struct PrometheusExporter {
 	buckets []f64
 mut:
+	prefix    string
 	collector &MetricsCollector = unsafe { nil }
 }
 
@@ -16,10 +17,24 @@ pub fn new_prometheus_exporter(buckets []f64) PrometheusExporter {
 	}
 }
 
-pub fn (mut e PrometheusExporter) load(collector &MetricsCollector) {
+pub fn (mut e PrometheusExporter) load(prefix string, collector &MetricsCollector) {
 	unsafe {
 		e.collector = collector
 	}
+	e.prefix = prefix
+}
+
+[inline]
+fn join_two_array(arr [2]string) string {
+	return '${arr[0]}="${arr[1]}"'
+}
+
+pub fn (e &PrometheusExporter) serialize_metric(metric Metric) string {
+	if metric.labels.len == 0 {
+		return '$e.prefix$metric.name'
+	}
+
+	return '$e.prefix$metric.name{${metric.labels.map(join_two_array(it)).join(',')}}'
 }
 
 pub fn (mut e PrometheusExporter) export_to_string() !string {
@@ -33,14 +48,14 @@ pub fn (mut e PrometheusExporter) export_to_string() !string {
 pub fn (mut e PrometheusExporter) export_to_writer(mut writer io.Writer) ! {
 	for counter in e.collector.counters() {
 		val := e.collector.counter_get(counter) or { return error("This can't happen.") }
-		line := '$counter $val\n'
+		line := '${e.serialize_metric(counter)} $val\n'
 
 		writer.write(line.bytes())!
 	}
 
 	for gauge in e.collector.gauges() {
 		val := e.collector.gauge_get(gauge) or { return error("This can't happen.") }
-		line := '$gauge $val\n'
+		line := '${e.serialize_metric(gauge)} $val\n'
 
 		writer.write(line.bytes())!
 	}
@@ -72,13 +87,13 @@ pub fn (mut e PrometheusExporter) export_to_writer(mut writer io.Writer) ! {
 			...hist
 			name: '${hist.name}_count'
 		}
-		writer.write('$m $total_count\n'.bytes())!
+		writer.write('${e.serialize_metric(m)} $total_count\n'.bytes())!
 
 		m = Metric{
 			...hist
 			name: '${hist.name}_sum'
 		}
-		writer.write('$m $sum\n'.bytes())!
+		writer.write('${e.serialize_metric(m)} $sum\n'.bytes())!
 
 		mut le_labels := [][2]string{}
 		le_labels.prepend(hist.labels)
@@ -92,7 +107,7 @@ pub fn (mut e PrometheusExporter) export_to_writer(mut writer io.Writer) ! {
 				labels: le_labels
 			}
 
-			writer.write('$m ${bucket_counts[j]}\n'.bytes())!
+			writer.write('${e.serialize_metric(m)} ${bucket_counts[j]}\n'.bytes())!
 		}
 	}
 }

prometheus_test.v

@@ -5,9 +5,9 @@ fn test_only_counters() {
 	m.counter_increment(name: 'test')
 
 	mut e := new_prometheus_exporter([])
-	e.load(m)
+	e.load('hi_', m)
 
-	assert e.export_to_string()! == 'test 1\n'
+	assert e.export_to_string()! == 'hi_test 1\n'
 
 	metric := Metric{
 		name: 'test2'
@@ -16,7 +16,7 @@ fn test_only_counters() {
 	m.counter_increment(metric)
 	m.counter_increment(metric)
 
-	assert e.export_to_string()! == 'test 1\ntest2{hi="label",hi2="label2"} 2\n'
+	assert e.export_to_string()! == 'hi_test 1\nhi_test2{hi="label",hi2="label2"} 2\n'
 }
 
 fn test_only_gauges() {
@@ -24,9 +24,9 @@ fn test_only_gauges() {
 	m.gauge_set(3.25, name: 'test')
 
 	mut e := new_prometheus_exporter([])
-	e.load(m)
+	e.load('hi_', m)
 
-	assert e.export_to_string()! == 'test 3.25\n'
+	assert e.export_to_string()! == 'hi_test 3.25\n'
 
 	metric := Metric{
 		name: 'test2'
@@ -34,7 +34,7 @@ fn test_only_gauges() {
 	}
 	m.gauge_add(2.5, metric)
 
-	assert e.export_to_string()! == 'test 3.25\ntest2{hi="label",hi2="label2"} 2.5\n'
+	assert e.export_to_string()! == 'hi_test 3.25\nhi_test2{hi="label",hi2="label2"} 2.5\n'
 }
 
 fn test_single_histogram() {
@@ -43,7 +43,7 @@ fn test_single_histogram() {
 	m.histogram_record(5.0, name: 'test')
 
 	mut e := new_prometheus_exporter([0.5, 5.0])
-	e.load(m)
+	e.load('hi_', m)
 
-	assert e.export_to_string()! == 'test_count 1\ntest_sum 5.0\ntest_bucket{le="0.5"} 0\ntest_bucket{le="5.0"} 1\n'
+	assert e.export_to_string()! == 'hi_test_count 1\nhi_test_sum 5.0\nhi_test_bucket{le="0.5"} 0\nhi_test_bucket{le="5.0"} 1\n'
 }