allow exposing meta information for registered metrics (#61)

* allow exposing meta information for registered metrics

New public method `ExposeMetadata` allows enabling exposition
of dummy meta-info for all exposed metrics across all Sets.

This feature is needed to improve compatibility
with 3rd-party scrapers that require meta information to be present.

This commit doesn't update exposition of default system/process
metrics to keep the list of changes small. This change should
be added in a follow-up commit.

https://github.com/VictoriaMetrics/metrics/issues/48

* cleanup

* wip

* wip

* wip

* wip

---------

Co-authored-by: Aliaksandr Valialkin <valyala@victoriametrics.com>

README.md

@@ -73,8 +73,11 @@ http.HandleFunc("/metrics", func(w http.ResponseWriter, req *http.Request) {
 metrics.InitPush("http://victoria-metrics:8428/api/v1/import/prometheus", 10*time.Second, `instance="foobar"`, true)
 ```
 
-See [docs](http://godoc.org/github.com/VictoriaMetrics/metrics) for more info.
+By default, exposed metrics [do not have](https://github.com/VictoriaMetrics/metrics/issues/48#issuecomment-1620765811)
+`TYPE` or `HELP` meta information. Call [`ExposeMetadata(true)`](https://pkg.go.dev/github.com/VictoriaMetrics/metrics#ExposeMetadata)
+in order to generate `TYPE` and `HELP` meta information per each metric.
 
+See [docs](https://pkg.go.dev/github.com/VictoriaMetrics/metrics) for more info.
 
 ### Users
 

counter.go

@@ -58,6 +58,10 @@ func (c *Counter) marshalTo(prefix string, w io.Writer) {
 	fmt.Fprintf(w, "%s %d\n", prefix, v)
 }
 
+func (c *Counter) metricType() string {
+	return "counter"
+}
+
 // GetOrCreateCounter returns registered counter with the given name
 // or creates new counter if the registry doesn't contain counter with
 // the given name.

floatcounter.go

@@ -63,6 +63,10 @@ func (fc *FloatCounter) marshalTo(prefix string, w io.Writer) {
 	fmt.Fprintf(w, "%s %g\n", prefix, v)
 }
 
+func (fc *FloatCounter) metricType() string {
+	return "counter"
+}
+
 // GetOrCreateFloatCounter returns registered FloatCounter with the given name
 // or creates new FloatCounter if the registry doesn't contain FloatCounter with
 // the given name.

gauge.go

@@ -46,6 +46,10 @@ func (g *Gauge) marshalTo(prefix string, w io.Writer) {
 	}
 }
 
+func (g *Gauge) metricType() string {
+	return "gauge"
+}
+
 // GetOrCreateGauge returns registered gauge with the given name
 // or creates new gauge if the registry doesn't contain gauge with
 // the given name.

go.mod

@@ -5,4 +5,6 @@ require (
 	golang.org/x/sys v0.15.0
 )
 
-go 1.16
+require github.com/valyala/fastrand v1.1.0 // indirect
+
+go 1.17

go_metrics.go

@@ -47,34 +47,34 @@ func writeGoMetrics(w io.Writer) {
 
 	var ms runtime.MemStats
 	runtime.ReadMemStats(&ms)
-	fmt.Fprintf(w, "go_memstats_alloc_bytes %d\n", ms.Alloc)
-	fmt.Fprintf(w, "go_memstats_alloc_bytes_total %d\n", ms.TotalAlloc)
-	fmt.Fprintf(w, "go_memstats_buck_hash_sys_bytes %d\n", ms.BuckHashSys)
-	fmt.Fprintf(w, "go_memstats_frees_total %d\n", ms.Frees)
-	fmt.Fprintf(w, "go_memstats_gc_cpu_fraction %g\n", ms.GCCPUFraction)
-	fmt.Fprintf(w, "go_memstats_gc_sys_bytes %d\n", ms.GCSys)
+	WriteGaugeUint64(w, "go_memstats_alloc_bytes", ms.Alloc)
+	WriteCounterUint64(w, "go_memstats_alloc_bytes_total", ms.TotalAlloc)
+	WriteGaugeUint64(w, "go_memstats_buck_hash_sys_bytes", ms.BuckHashSys)
+	WriteCounterUint64(w, "go_memstats_frees_total", ms.Frees)
+	WriteGaugeFloat64(w, "go_memstats_gc_cpu_fraction", ms.GCCPUFraction)
+	WriteGaugeUint64(w, "go_memstats_gc_sys_bytes", ms.GCSys)
 
-	fmt.Fprintf(w, "go_memstats_heap_alloc_bytes %d\n", ms.HeapAlloc)
-	fmt.Fprintf(w, "go_memstats_heap_idle_bytes %d\n", ms.HeapIdle)
-	fmt.Fprintf(w, "go_memstats_heap_inuse_bytes %d\n", ms.HeapInuse)
-	fmt.Fprintf(w, "go_memstats_heap_objects %d\n", ms.HeapObjects)
-	fmt.Fprintf(w, "go_memstats_heap_released_bytes %d\n", ms.HeapReleased)
-	fmt.Fprintf(w, "go_memstats_heap_sys_bytes %d\n", ms.HeapSys)
-	fmt.Fprintf(w, "go_memstats_last_gc_time_seconds %g\n", float64(ms.LastGC)/1e9)
-	fmt.Fprintf(w, "go_memstats_lookups_total %d\n", ms.Lookups)
-	fmt.Fprintf(w, "go_memstats_mallocs_total %d\n", ms.Mallocs)
-	fmt.Fprintf(w, "go_memstats_mcache_inuse_bytes %d\n", ms.MCacheInuse)
-	fmt.Fprintf(w, "go_memstats_mcache_sys_bytes %d\n", ms.MCacheSys)
-	fmt.Fprintf(w, "go_memstats_mspan_inuse_bytes %d\n", ms.MSpanInuse)
-	fmt.Fprintf(w, "go_memstats_mspan_sys_bytes %d\n", ms.MSpanSys)
-	fmt.Fprintf(w, "go_memstats_next_gc_bytes %d\n", ms.NextGC)
-	fmt.Fprintf(w, "go_memstats_other_sys_bytes %d\n", ms.OtherSys)
-	fmt.Fprintf(w, "go_memstats_stack_inuse_bytes %d\n", ms.StackInuse)
-	fmt.Fprintf(w, "go_memstats_stack_sys_bytes %d\n", ms.StackSys)
-	fmt.Fprintf(w, "go_memstats_sys_bytes %d\n", ms.Sys)
+	WriteGaugeUint64(w, "go_memstats_heap_alloc_bytes", ms.HeapAlloc)
+	WriteGaugeUint64(w, "go_memstats_heap_idle_bytes", ms.HeapIdle)
+	WriteGaugeUint64(w, "go_memstats_heap_inuse_bytes", ms.HeapInuse)
+	WriteGaugeUint64(w, "go_memstats_heap_objects", ms.HeapObjects)
+	WriteGaugeUint64(w, "go_memstats_heap_released_bytes", ms.HeapReleased)
+	WriteGaugeUint64(w, "go_memstats_heap_sys_bytes", ms.HeapSys)
+	WriteGaugeFloat64(w, "go_memstats_last_gc_time_seconds", float64(ms.LastGC)/1e9)
+	WriteCounterUint64(w, "go_memstats_lookups_total", ms.Lookups)
+	WriteCounterUint64(w, "go_memstats_mallocs_total", ms.Mallocs)
+	WriteGaugeUint64(w, "go_memstats_mcache_inuse_bytes", ms.MCacheInuse)
+	WriteGaugeUint64(w, "go_memstats_mcache_sys_bytes", ms.MCacheSys)
+	WriteGaugeUint64(w, "go_memstats_mspan_inuse_bytes", ms.MSpanInuse)
+	WriteGaugeUint64(w, "go_memstats_mspan_sys_bytes", ms.MSpanSys)
+	WriteGaugeUint64(w, "go_memstats_next_gc_bytes", ms.NextGC)
+	WriteGaugeUint64(w, "go_memstats_other_sys_bytes", ms.OtherSys)
+	WriteGaugeUint64(w, "go_memstats_stack_inuse_bytes", ms.StackInuse)
+	WriteGaugeUint64(w, "go_memstats_stack_sys_bytes", ms.StackSys)
+	WriteGaugeUint64(w, "go_memstats_sys_bytes", ms.Sys)
 
-	fmt.Fprintf(w, "go_cgo_calls_count %d\n", runtime.NumCgoCall())
-	fmt.Fprintf(w, "go_cpu_count %d\n", runtime.NumCPU())
+	WriteCounterUint64(w, "go_cgo_calls_count", uint64(runtime.NumCgoCall()))
+	WriteGaugeUint64(w, "go_cpu_count", uint64(runtime.NumCPU()))
 
 	gcPauses := histogram.NewFast()
 	for _, pauseNs := range ms.PauseNs[:] {
@@ -82,20 +82,25 @@ func writeGoMetrics(w io.Writer) {
 	}
 	phis := []float64{0, 0.25, 0.5, 0.75, 1}
 	quantiles := make([]float64, 0, len(phis))
+	writeMetadataIfNeeded(w, "go_gc_duration_seconds", "summary")
 	for i, q := range gcPauses.Quantiles(quantiles[:0], phis) {
 		fmt.Fprintf(w, `go_gc_duration_seconds{quantile="%g"} %g`+"\n", phis[i], q)
 	}
-	fmt.Fprintf(w, `go_gc_duration_seconds_sum %g`+"\n", float64(ms.PauseTotalNs)/1e9)
-	fmt.Fprintf(w, `go_gc_duration_seconds_count %d`+"\n", ms.NumGC)
-	fmt.Fprintf(w, `go_gc_forced_count %d`+"\n", ms.NumForcedGC)
+	fmt.Fprintf(w, "go_gc_duration_seconds_sum %g\n", float64(ms.PauseTotalNs)/1e9)
+	fmt.Fprintf(w, "go_gc_duration_seconds_count %d\n", ms.NumGC)
 
-	fmt.Fprintf(w, `go_gomaxprocs %d`+"\n", runtime.GOMAXPROCS(0))
-	fmt.Fprintf(w, `go_goroutines %d`+"\n", runtime.NumGoroutine())
+	WriteCounterUint64(w, "go_gc_forced_count", uint64(ms.NumForcedGC))
+
+	WriteGaugeUint64(w, "go_gomaxprocs", uint64(runtime.GOMAXPROCS(0)))
+	WriteGaugeUint64(w, "go_goroutines", uint64(runtime.NumGoroutine()))
 	numThread, _ := runtime.ThreadCreateProfile(nil)
-	fmt.Fprintf(w, `go_threads %d`+"\n", numThread)
+	WriteGaugeUint64(w, "go_threads", uint64(numThread))
 
 	// Export build details.
+	writeMetadataIfNeeded(w, "go_info", "gauge")
 	fmt.Fprintf(w, "go_info{version=%q} 1\n", runtime.Version())
+
+	writeMetadataIfNeeded(w, "go_info_ext", "gauge")
 	fmt.Fprintf(w, "go_info_ext{compiler=%q, GOARCH=%q, GOOS=%q, GOROOT=%q} 1\n",
 		runtime.Compiler, runtime.GOARCH, runtime.GOOS, runtime.GOROOT())
 }
@@ -117,11 +122,22 @@ func writeRuntimeMetric(w io.Writer, name string, sample *runtimemetrics.Sample)
 	case runtimemetrics.KindBad:
 		panic(fmt.Errorf("BUG: unexpected runtimemetrics.KindBad for sample.Name=%q", sample.Name))
 	case runtimemetrics.KindUint64:
-		fmt.Fprintf(w, "%s %d\n", name, sample.Value.Uint64())
+		v := sample.Value.Uint64()
+		if strings.HasSuffix(name, "_total") {
+			WriteCounterUint64(w, name, v)
+		} else {
+			WriteGaugeUint64(w, name, v)
+		}
 	case runtimemetrics.KindFloat64:
-		fmt.Fprintf(w, "%s %g\n", name, sample.Value.Float64())
+		v := sample.Value.Float64()
+		if isCounterName(name) {
+			WriteCounterFloat64(w, name, v)
+		} else {
+			WriteGaugeFloat64(w, name, v)
+		}
 	case runtimemetrics.KindFloat64Histogram:
-		writeRuntimeHistogramMetric(w, name, sample.Value.Float64Histogram())
+		h := sample.Value.Float64Histogram()
+		writeRuntimeHistogramMetric(w, name, h)
 	default:
 		panic(fmt.Errorf("unexpected metric kind=%d", kind))
 	}
@@ -149,6 +165,7 @@ func writeRuntimeHistogramMetric(w io.Writer, name string, h *runtimemetrics.Flo
 
 	totalCount := uint64(0)
 	iNext := 0.0
+	writeMetadataIfNeeded(w, name, "histogram")
 	for i, count := range counts {
 		totalCount += count
 		if float64(i) >= iNext {

histogram.go

@@ -228,3 +228,7 @@ func (h *Histogram) getSum() float64 {
 	h.mu.Unlock()
 	return sum
 }
+
+func (h *Histogram) metricType() string {
+	return "histogram"
+}

metrics.go

@@ -13,9 +13,12 @@
 package metrics
 
 import (
+	"fmt"
 	"io"
 	"sort"
+	"strings"
 	"sync"
+	"sync/atomic"
 	"unsafe"
 )
 
@@ -25,8 +28,17 @@ type namedMetric struct {
 	isAux  bool
 }
 
+func (nm *namedMetric) family() string {
+	n := strings.IndexByte(nm.name, '{')
+	if n < 0 {
+		return nm.name
+	}
+	return nm.name[:n]
+}
+
 type metric interface {
 	marshalTo(prefix string, w io.Writer)
+	metricType() string
 }
 
 var defaultSet = NewSet()
@@ -241,3 +253,56 @@ func ListMetricNames() []string {
 func GetDefaultSet() *Set {
 	return defaultSet
 }
+
+// ExposeMetadata allows enabling adding TYPE and HELP metadata to the exposed metrics globally.
+//
+// It is safe to call this method multiple times. It is allowed to change it in runtime.
+// ExposeMetadata is set to false by default.
+func ExposeMetadata(v bool) {
+	n := 0
+	if v {
+		n = 1
+	}
+	atomic.StoreUint32(&exposeMetadata, uint32(n))
+}
+
+func isMetadataEnabled() bool {
+	n := atomic.LoadUint32(&exposeMetadata)
+	return n != 0
+}
+
+var exposeMetadata uint32
+
+func isCounterName(name string) bool {
+	return strings.HasSuffix(name, "_total")
+}
+
+// WriteGaugeUint64 writes gauge metric with the given name and value to w in Prometheus text exposition format.
+func WriteGaugeUint64(w io.Writer, name string, value uint64) {
+	writeMetricUint64(w, name, "gauge", value)
+}
+
+// WriteGaugeFloat64 writes gauge metric with the given name and value to w in Prometheus text exposition format.
+func WriteGaugeFloat64(w io.Writer, name string, value float64) {
+	writeMetricFloat64(w, name, "gauge", value)
+}
+
+// WriteCounterUint64 writes counter metric with the given name and value to w in Prometheus text exposition format.
+func WriteCounterUint64(w io.Writer, name string, value uint64) {
+	writeMetricUint64(w, name, "counter", value)
+}
+
+// WriteCounterFloat64 writes counter metric with the given name and value to w in Prometheus text exposition format.
+func WriteCounterFloat64(w io.Writer, name string, value float64) {
+	writeMetricFloat64(w, name, "counter", value)
+}
+
+func writeMetricUint64(w io.Writer, metricName, metricType string, value uint64) {
+	writeMetadataIfNeeded(w, metricName, metricType)
+	fmt.Fprintf(w, "%s %d\n", metricName, value)
+}
+
+func writeMetricFloat64(w io.Writer, metricName, metricType string, value float64) {
+	writeMetadataIfNeeded(w, metricName, metricType)
+	fmt.Fprintf(w, "%s %g\n", metricName, value)
+}

metrics_test.go

@@ -8,6 +8,81 @@ import (
 	"time"
 )
 
+func TestWriteMetrics(t *testing.T) {
+	t.Run("gauge_uint64", func(t *testing.T) {
+		var bb bytes.Buffer
+
+		WriteGaugeUint64(&bb, "foo", 123)
+		sExpected := "foo 123\n"
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+
+		ExposeMetadata(true)
+		bb.Reset()
+		WriteGaugeUint64(&bb, "foo", 123)
+		sExpected = "# HELP foo\n# TYPE foo gauge\nfoo 123\n"
+		ExposeMetadata(false)
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+	})
+	t.Run("gauge_float64", func(t *testing.T) {
+		var bb bytes.Buffer
+
+		WriteGaugeFloat64(&bb, "foo", 1.23)
+		sExpected := "foo 1.23\n"
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+
+		ExposeMetadata(true)
+		bb.Reset()
+		WriteGaugeFloat64(&bb, "foo", 1.23)
+		sExpected = "# HELP foo\n# TYPE foo gauge\nfoo 1.23\n"
+		ExposeMetadata(false)
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+	})
+	t.Run("counter_uint64", func(t *testing.T) {
+		var bb bytes.Buffer
+
+		WriteCounterUint64(&bb, "foo_total", 123)
+		sExpected := "foo_total 123\n"
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+
+		ExposeMetadata(true)
+		bb.Reset()
+		WriteCounterUint64(&bb, "foo_total", 123)
+		sExpected = "# HELP foo_total\n# TYPE foo_total counter\nfoo_total 123\n"
+		ExposeMetadata(false)
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+	})
+	t.Run("counter_float64", func(t *testing.T) {
+		var bb bytes.Buffer
+
+		WriteCounterFloat64(&bb, "foo_total", 1.23)
+		sExpected := "foo_total 1.23\n"
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+
+		ExposeMetadata(true)
+		bb.Reset()
+		WriteCounterFloat64(&bb, "foo_total", 1.23)
+		sExpected = "# HELP foo_total\n# TYPE foo_total counter\nfoo_total 1.23\n"
+		ExposeMetadata(false)
+		if s := bb.String(); s != sExpected {
+			t.Fatalf("unexpected value; got\n%s\nwant\n%s", s, sExpected)
+		}
+	})
+}
+
 func TestGetDefaultSet(t *testing.T) {
 	s := GetDefaultSet()
 	if s != defaultSet {

process_metrics_linux.go

@@ -74,15 +74,15 @@ func writeProcessMetrics(w io.Writer) {
 
 	utime := float64(p.Utime) / userHZ
 	stime := float64(p.Stime) / userHZ
-	fmt.Fprintf(w, "process_cpu_seconds_system_total %g\n", stime)
-	fmt.Fprintf(w, "process_cpu_seconds_total %g\n", utime+stime)
-	fmt.Fprintf(w, "process_cpu_seconds_user_total %g\n", utime)
-	fmt.Fprintf(w, "process_major_pagefaults_total %d\n", p.Majflt)
-	fmt.Fprintf(w, "process_minor_pagefaults_total %d\n", p.Minflt)
-	fmt.Fprintf(w, "process_num_threads %d\n", p.NumThreads)
-	fmt.Fprintf(w, "process_resident_memory_bytes %d\n", p.Rss*4096)
-	fmt.Fprintf(w, "process_start_time_seconds %d\n", startTimeSeconds)
-	fmt.Fprintf(w, "process_virtual_memory_bytes %d\n", p.Vsize)
+	WriteCounterFloat64(w, "process_cpu_seconds_system_total", stime)
+	WriteCounterFloat64(w, "process_cpu_seconds_total", utime+stime)
+	WriteCounterFloat64(w, "process_cpu_seconds_user_total", utime)
+	WriteCounterUint64(w, "process_major_pagefaults_total", uint64(p.Majflt))
+	WriteCounterUint64(w, "process_minor_pagefaults_total", uint64(p.Minflt))
+	WriteGaugeUint64(w, "process_num_threads", uint64(p.NumThreads))
+	WriteGaugeUint64(w, "process_resident_memory_bytes", uint64(p.Rss)*4096)
+	WriteGaugeUint64(w, "process_start_time_seconds", uint64(startTimeSeconds))
+	WriteGaugeUint64(w, "process_virtual_memory_bytes", uint64(p.Vsize))
 	writeProcessMemMetrics(w)
 	writeIOMetrics(w)
 }
@@ -133,12 +133,12 @@ func writeIOMetrics(w io.Writer) {
 			writeBytes = getInt(s)
 		}
 	}
-	fmt.Fprintf(w, "process_io_read_bytes_total %d\n", rchar)
-	fmt.Fprintf(w, "process_io_written_bytes_total %d\n", wchar)
-	fmt.Fprintf(w, "process_io_read_syscalls_total %d\n", syscr)
-	fmt.Fprintf(w, "process_io_write_syscalls_total %d\n", syscw)
-	fmt.Fprintf(w, "process_io_storage_read_bytes_total %d\n", readBytes)
-	fmt.Fprintf(w, "process_io_storage_written_bytes_total %d\n", writeBytes)
+	WriteGaugeUint64(w, "process_io_read_bytes_total", uint64(rchar))
+	WriteGaugeUint64(w, "process_io_written_bytes_total", uint64(wchar))
+	WriteGaugeUint64(w, "process_io_read_syscalls_total", uint64(syscr))
+	WriteGaugeUint64(w, "process_io_write_syscalls_total", uint64(syscw))
+	WriteGaugeUint64(w, "process_io_storage_read_bytes_total", uint64(readBytes))
+	WriteGaugeUint64(w, "process_io_storage_written_bytes_total", uint64(writeBytes))
 }
 
 var startTimeSeconds = time.Now().Unix()
@@ -155,8 +155,8 @@ func writeFDMetrics(w io.Writer) {
 		log.Printf("ERROR: metrics: cannot determine the limit on open file descritors: %s", err)
 		return
 	}
-	fmt.Fprintf(w, "process_max_fds %d\n", maxOpenFDs)
-	fmt.Fprintf(w, "process_open_fds %d\n", totalOpenFDs)
+	WriteGaugeUint64(w, "process_max_fds", maxOpenFDs)
+	WriteGaugeUint64(w, "process_open_fds", totalOpenFDs)
 }
 
 func getOpenFDsCount(path string) (uint64, error) {
@@ -224,11 +224,11 @@ func writeProcessMemMetrics(w io.Writer) {
 		log.Printf("ERROR: metrics: cannot determine memory status: %s", err)
 		return
 	}
-	fmt.Fprintf(w, "process_virtual_memory_peak_bytes %d\n", ms.vmPeak)
-	fmt.Fprintf(w, "process_resident_memory_peak_bytes %d\n", ms.rssPeak)
-	fmt.Fprintf(w, "process_resident_memory_anon_bytes %d\n", ms.rssAnon)
-	fmt.Fprintf(w, "process_resident_memory_file_bytes %d\n", ms.rssFile)
-	fmt.Fprintf(w, "process_resident_memory_shared_bytes %d\n", ms.rssShmem)
+	WriteGaugeUint64(w, "process_virtual_memory_peak_bytes", ms.vmPeak)
+	WriteGaugeUint64(w, "process_resident_memory_peak_bytes", ms.rssPeak)
+	WriteGaugeUint64(w, "process_resident_memory_anon_bytes", ms.rssAnon)
+	WriteGaugeUint64(w, "process_resident_memory_file_bytes", ms.rssFile)
+	WriteGaugeUint64(w, "process_resident_memory_shared_bytes", ms.rssShmem)
 
 }
 

process_metrics_windows.go

@@ -4,7 +4,6 @@
 package metrics
 
 import (
-	"fmt"
 	"io"
 	"log"
 	"syscall"
@@ -55,16 +54,16 @@ func writeProcessMetrics(w io.Writer) {
 		log.Printf("ERROR: metrics: cannot read process memory information: %s", err)
 		return
 	}
-	stimeSeconds := (uint64(stime.HighDateTime)<<32 + uint64(stime.LowDateTime)) / 1e7
-	utimeSeconds := (uint64(utime.HighDateTime)<<32 + uint64(utime.LowDateTime)) / 1e7
-	fmt.Fprintf(w, "process_cpu_seconds_system_total %d\n", stimeSeconds)
-	fmt.Fprintf(w, "process_cpu_seconds_total %d\n", stimeSeconds+utimeSeconds)
-	fmt.Fprintf(w, "process_cpu_seconds_user_total %d\n", stimeSeconds)
-	fmt.Fprintf(w, "process_pagefaults_total %d\n", mc.PageFaultCount)
-	fmt.Fprintf(w, "process_start_time_seconds %d\n", startTime.Nanoseconds()/1e9)
-	fmt.Fprintf(w, "process_virtual_memory_bytes %d\n", mc.PrivateUsage)
-	fmt.Fprintf(w, "process_resident_memory_peak_bytes %d\n", mc.PeakWorkingSetSize)
-	fmt.Fprintf(w, "process_resident_memory_bytes %d\n", mc.WorkingSetSize)
+	stimeSeconds := float64(uint64(stime.HighDateTime)<<32+uint64(stime.LowDateTime)) / 1e7
+	utimeSeconds := float64(uint64(utime.HighDateTime)<<32+uint64(utime.LowDateTime)) / 1e7
+	WriteCounterFloat64(w, "process_cpu_seconds_system_total", stimeSeconds)
+	WriteCounterFloat64(w, "process_cpu_seconds_total", stimeSeconds+utimeSeconds)
+	WriteCounterFloat64(w, "process_cpu_seconds_user_total", stimeSeconds)
+	WriteCounterUint64(w, "process_pagefaults_total", uint64(mc.PageFaultCount))
+	WriteGaugeUint64(w, "process_start_time_seconds", uint64(startTime.Nanoseconds())/1e9)
+	WriteGaugeUint64(w, "process_virtual_memory_bytes", uint64(mc.PrivateUsage))
+	WriteGaugeUint64(w, "process_resident_memory_peak_bytes", uint64(mc.PeakWorkingSetSize))
+	WriteGaugeUint64(w, "process_resident_memory_bytes", uint64(mc.WorkingSetSize))
 }
 
 func writeFDMetrics(w io.Writer) {
@@ -80,6 +79,6 @@ func writeFDMetrics(w io.Writer) {
 	}
 	// it seems to be hard-coded limit for 64-bit systems
 	// https://learn.microsoft.com/en-us/archive/blogs/markrussinovich/pushing-the-limits-of-windows-handles#maximum-number-of-handles
-	fmt.Fprintf(w, "process_max_fds %d\n", 16777216)
-	fmt.Fprintf(w, "process_open_fds %d\n", count)
+	WriteGaugeUint64(w, "process_max_fds", 16777216)
+	WriteGaugeUint64(w, "process_open_fds", uint64(count))
 }

set.go

@@ -47,14 +47,30 @@ func (s *Set) WritePrometheus(w io.Writer) {
 	sa := append([]*namedMetric(nil), s.a...)
 	s.mu.Unlock()
 
-	// Call marshalTo without the global lock, since certain metric types such as Gauge
-	// can call a callback, which, in turn, can try calling s.mu.Lock again.
+	prevMetricFamily := ""
 	for _, nm := range sa {
+		metricFamily := nm.family()
+		if metricFamily != prevMetricFamily {
+			// write meta info only once per metric family
+			metricType := nm.metric.metricType()
+			writeMetadataIfNeeded(&bb, metricFamily, metricType)
+			prevMetricFamily = metricFamily
+		}
+		// Call marshalTo without the global lock, since certain metric types such as Gauge
+		// can call a callback, which, in turn, can try calling s.mu.Lock again.
 		nm.metric.marshalTo(nm.name, &bb)
 	}
 	w.Write(bb.Bytes())
 }
 
+func writeMetadataIfNeeded(w io.Writer, metricFamily, metricType string) {
+	if !isMetadataEnabled() {
+		return
+	}
+	fmt.Fprintf(w, "# HELP %s\n", metricFamily)
+	fmt.Fprintf(w, "# TYPE %s %s\n", metricFamily, metricType)
+}
+
 // NewHistogram creates and returns new histogram in s with the given name.
 //
 // name must be valid Prometheus-compatible metric with possible labels.

set_example_test.go

@@ -23,3 +23,56 @@ func ExampleSet() {
 	// set_counter 1
 	// set_gauge{foo="bar"} 42
 }
+
+func ExampleExposeMetadata() {
+	metrics.ExposeMetadata(true)
+	defer metrics.ExposeMetadata(false)
+
+	s := metrics.NewSet()
+
+	sc := s.NewCounter("set_counter")
+	sc.Inc()
+
+	s.NewGauge(`unused_bytes{foo="bar"}`, func() float64 { return 58 })
+	s.NewGauge(`used_bytes{foo="bar"}`, func() float64 { return 42 })
+	s.NewGauge(`used_bytes{foo="baz"}`, func() float64 { return 43 })
+
+	h := s.NewHistogram(`request_duration_seconds{path="/foo/bar"}`)
+	h.Update(1)
+	h.Update(2)
+
+	s.NewSummary("response_size_bytes").Update(1)
+
+	// Dump metrics from s.
+	var bb bytes.Buffer
+	s.WritePrometheus(&bb)
+	fmt.Printf("set metrics:\n%s\n", bb.String())
+
+	// Output:
+	// set metrics:
+	// # HELP request_duration_seconds
+	// # TYPE request_duration_seconds histogram
+	// request_duration_seconds_bucket{path="/foo/bar",vmrange="8.799e-01...1.000e+00"} 1
+	// request_duration_seconds_bucket{path="/foo/bar",vmrange="1.896e+00...2.154e+00"} 1
+	// request_duration_seconds_sum{path="/foo/bar"} 3
+	// request_duration_seconds_count{path="/foo/bar"} 2
+	// # HELP response_size_bytes
+	// # TYPE response_size_bytes summary
+	// response_size_bytes_sum 1
+	// response_size_bytes_count 1
+	// response_size_bytes{quantile="0.5"} 1
+	// response_size_bytes{quantile="0.9"} 1
+	// response_size_bytes{quantile="0.97"} 1
+	// response_size_bytes{quantile="0.99"} 1
+	// response_size_bytes{quantile="1"} 1
+	// # HELP set_counter
+	// # TYPE set_counter counter
+	// set_counter 1
+	// # HELP unused_bytes
+	// # TYPE unused_bytes gauge
+	// unused_bytes{foo="bar"} 58
+	// # HELP used_bytes
+	// # TYPE used_bytes gauge
+	// used_bytes{foo="bar"} 42
+	// used_bytes{foo="baz"} 43
+}

summary.go

@@ -119,6 +119,10 @@ func (sm *Summary) marshalTo(prefix string, w io.Writer) {
 	}
 }
 
+func (sm *Summary) metricType() string {
+	return "summary"
+}
+
 func splitMetricName(name string) (string, string) {
 	n := strings.IndexByte(name, '{')
 	if n < 0 {
@@ -196,6 +200,10 @@ func (qv *quantileValue) marshalTo(prefix string, w io.Writer) {
 	}
 }
 
+func (qv *quantileValue) metricType() string {
+	return "unsupported"
+}
+
 func addTag(name, tag string) string {
 	if len(name) == 0 || name[len(name)-1] != '}' {
 		return fmt.Sprintf("%s{%s}", name, tag)

vendor/github.com/valyala/fastrand/go.mod

@@ -1 +0,0 @@
-module github.com/valyala/fastrand

vendor/github.com/valyala/histogram/go.mod

@@ -1,5 +0,0 @@
-module github.com/valyala/histogram
-
-go 1.12
-
-require github.com/valyala/fastrand v1.1.0

vendor/github.com/valyala/histogram/go.sum

@@ -1,2 +0,0 @@
-github.com/valyala/fastrand v1.1.0 h1:f+5HkLW4rsgzdNoleUOB69hyT9IlD2ZQh9GyDMfb5G8=
-github.com/valyala/fastrand v1.1.0/go.mod h1:HWqCzkrkg6QXT8V2EXWvXCoow7vLwOFN002oeRzjapQ=

vendor/modules.txt

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