Do not panic on unsupported Go runtime metrics

Log the unsupported Go runtime metrics on startup instead, so the user is aware of unsupported metrics.
The solution for removing the log lines is to upgrade Go builder.

Reduce the minimum supported Go version at go.mod from Go1.20 to Go1.16, where the runtime/metrics package has been added.
See https://tip.golang.org/doc/go1.16#runtime

Updates #59
Updates #60

go.mod

@@ -5,6 +5,4 @@ require (
 	golang.org/x/sys v0.15.0
 )
 
-require github.com/valyala/fastrand v1.1.0 // indirect
-
-go 1.20
+go 1.16

go_metrics.go

@@ -3,6 +3,7 @@ package metrics
 import (
 	"fmt"
 	"io"
+	"log"
 	"math"
 	"runtime"
 	runtimemetrics "runtime/metrics"
@@ -22,6 +23,25 @@ var runtimeMetrics = [][2]string{
 	{"/gc/gomemlimit:bytes", "go_memlimit_bytes"},
 }
 
+var supportedRuntimeMetrics = initSupportedRuntimeMetrics(runtimeMetrics)
+
+func initSupportedRuntimeMetrics(rms [][2]string) [][2]string {
+	exposedMetrics := make(map[string]struct{})
+	for _, d := range runtimemetrics.All() {
+		exposedMetrics[d.Name] = struct{}{}
+	}
+	var supportedMetrics [][2]string
+	for _, rm := range rms {
+		metricName := rm[0]
+		if _, ok := exposedMetrics[metricName]; ok {
+			supportedMetrics = append(supportedMetrics, rm)
+		} else {
+			log.Printf("github.com/VictoriaMetrics/metrics: do not expose %s metric, since the corresponding metric %s isn't supported in the current Go runtime", rm[1], metricName)
+		}
+	}
+	return supportedMetrics
+}
+
 func writeGoMetrics(w io.Writer) {
 	writeRuntimeMetrics(w)
 
@@ -81,18 +101,19 @@ func writeGoMetrics(w io.Writer) {
 }
 
 func writeRuntimeMetrics(w io.Writer) {
-	samples := make([]runtimemetrics.Sample, len(runtimeMetrics))
-	for i, rm := range runtimeMetrics {
+	samples := make([]runtimemetrics.Sample, len(supportedRuntimeMetrics))
+	for i, rm := range supportedRuntimeMetrics {
 		samples[i].Name = rm[0]
 	}
 	runtimemetrics.Read(samples)
-	for i, rm := range runtimeMetrics {
+	for i, rm := range supportedRuntimeMetrics {
 		writeRuntimeMetric(w, rm[1], &samples[i])
 	}
 }
 
 func writeRuntimeMetric(w io.Writer, name string, sample *runtimemetrics.Sample) {
-	switch sample.Value.Kind() {
+	kind := sample.Value.Kind()
+	switch kind {
 	case runtimemetrics.KindBad:
 		panic(fmt.Errorf("BUG: unexpected runtimemetrics.KindBad for sample.Name=%q", sample.Name))
 	case runtimemetrics.KindUint64:
@@ -101,6 +122,8 @@ func writeRuntimeMetric(w io.Writer, name string, sample *runtimemetrics.Sample)
 		fmt.Fprintf(w, "%s %g\n", name, sample.Value.Float64())
 	case runtimemetrics.KindFloat64Histogram:
 		writeRuntimeHistogramMetric(w, name, sample.Value.Float64Histogram())
+	default:
+		panic(fmt.Errorf("unexpected metric kind=%d", kind))
 	}
 }
 

go_metrics_test.go

@@ -1,12 +1,21 @@
 package metrics
 
 import (
+	"bytes"
 	"math"
 	runtimemetrics "runtime/metrics"
 	"strings"
 	"testing"
 )
 
+func TestWriteRuntimeMetrics(t *testing.T) {
+	var bb bytes.Buffer
+	writeRuntimeMetrics(&bb)
+	if n := bb.Len(); n == 0 {
+		t.Fatalf("unexpected empty runtime metrics")
+	}
+}
+
 func TestWriteRuntimeHistogramMetricOk(t *testing.T) {
 	f := func(h *runtimemetrics.Float64Histogram, resultExpected string) {
 		t.Helper()

vendor/modules.txt

@@ -1,9 +1,8 @@
 # github.com/valyala/fastrand v1.1.0
-## explicit
 github.com/valyala/fastrand
 # github.com/valyala/histogram v1.2.0
-## explicit; go 1.12
+## explicit
 github.com/valyala/histogram
 # golang.org/x/sys v0.15.0
-## explicit; go 1.18
+## explicit
 golang.org/x/sys/windows