Skip to content
Cannot retrieve contributors at this time
// Copyright 2014 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package prometheus
import (
//nolint:staticcheck // Ignore SA1019. Need to keep deprecated package for compatibility.
dto ""
var separatorByteSlice = []byte{model.SeparatorByte} // For convenient use with xxhash.
// A Metric models a single sample value with its meta data being exported to
// Prometheus. Implementations of Metric in this package are Gauge, Counter,
// Histogram, Summary, and Untyped.
type Metric interface {
// Desc returns the descriptor for the Metric. This method idempotently
// returns the same descriptor throughout the lifetime of the
// Metric. The returned descriptor is immutable by contract. A Metric
// unable to describe itself must return an invalid descriptor (created
// with NewInvalidDesc).
Desc() *Desc
// Write encodes the Metric into a "Metric" Protocol Buffer data
// transmission object.
// Metric implementations must observe concurrency safety as reads of
// this metric may occur at any time, and any blocking occurs at the
// expense of total performance of rendering all registered
// metrics. Ideally, Metric implementations should support concurrent
// readers.
// While populating dto.Metric, it is the responsibility of the
// implementation to ensure validity of the Metric protobuf (like valid
// UTF-8 strings or syntactically valid metric and label names). It is
// recommended to sort labels lexicographically. Callers of Write should
// still make sure of sorting if they depend on it.
Write(*dto.Metric) error
// TODO(beorn7): The original rationale of passing in a pre-allocated
// dto.Metric protobuf to save allocations has disappeared. The
// signature of this method should be changed to "Write() (*dto.Metric,
// error)".
// Opts bundles the options for creating most Metric types. Each metric
// implementation XXX has its own XXXOpts type, but in most cases, it is just
// an alias of this type (which might change when the requirement arises.)
// It is mandatory to set Name to a non-empty string. All other fields are
// optional and can safely be left at their zero value, although it is strongly
// encouraged to set a Help string.
type Opts struct {
// Namespace, Subsystem, and Name are components of the fully-qualified
// name of the Metric (created by joining these components with
// "_"). Only Name is mandatory, the others merely help structuring the
// name. Note that the fully-qualified name of the metric must be a
// valid Prometheus metric name.
Namespace string
Subsystem string
Name string
// Help provides information about this metric.
// Metrics with the same fully-qualified name must have the same Help
// string.
Help string
// ConstLabels are used to attach fixed labels to this metric. Metrics
// with the same fully-qualified name must have the same label names in
// their ConstLabels.
// ConstLabels are only used rarely. In particular, do not use them to
// attach the same labels to all your metrics. Those use cases are
// better covered by target labels set by the scraping Prometheus
// server, or by one specific metric (e.g. a build_info or a
// machine_role metric). See also
ConstLabels Labels
// BuildFQName joins the given three name components by "_". Empty name
// components are ignored. If the name parameter itself is empty, an empty
// string is returned, no matter what. Metric implementations included in this
// library use this function internally to generate the fully-qualified metric
// name from the name component in their Opts. Users of the library will only
// need this function if they implement their own Metric or instantiate a Desc
// (with NewDesc) directly.
func BuildFQName(namespace, subsystem, name string) string {
if name == "" {
return ""
switch {
case namespace != "" && subsystem != "":
return strings.Join([]string{namespace, subsystem, name}, "_")
case namespace != "":
return strings.Join([]string{namespace, name}, "_")
case subsystem != "":
return strings.Join([]string{subsystem, name}, "_")
return name
// labelPairSorter implements sort.Interface. It is used to sort a slice of
// dto.LabelPair pointers.
type labelPairSorter []*dto.LabelPair
func (s labelPairSorter) Len() int {
return len(s)
func (s labelPairSorter) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
func (s labelPairSorter) Less(i, j int) bool {
return s[i].GetName() < s[j].GetName()
type invalidMetric struct {
desc *Desc
err error
// NewInvalidMetric returns a metric whose Write method always returns the
// provided error. It is useful if a Collector finds itself unable to collect
// a metric and wishes to report an error to the registry.
func NewInvalidMetric(desc *Desc, err error) Metric {
return &invalidMetric{desc, err}
func (m *invalidMetric) Desc() *Desc { return m.desc }
func (m *invalidMetric) Write(*dto.Metric) error { return m.err }
type timestampedMetric struct {
t time.Time
func (m timestampedMetric) Write(pb *dto.Metric) error {
e := m.Metric.Write(pb)
pb.TimestampMs = proto.Int64(m.t.Unix()*1000 + int64(m.t.Nanosecond()/1000000))
return e
// NewMetricWithTimestamp returns a new Metric wrapping the provided Metric in a
// way that it has an explicit timestamp set to the provided Time. This is only
// useful in rare cases as the timestamp of a Prometheus metric should usually
// be set by the Prometheus server during scraping. Exceptions include mirroring
// metrics with given timestamps from other metric
// sources.
// NewMetricWithTimestamp works best with MustNewConstMetric,
// MustNewConstHistogram, and MustNewConstSummary, see example.
// Currently, the exposition formats used by Prometheus are limited to
// millisecond resolution. Thus, the provided time will be rounded down to the
// next full millisecond value.
func NewMetricWithTimestamp(t time.Time, m Metric) Metric {
return timestampedMetric{Metric: m, t: t}