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+// 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
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package prometheus
+
+import (
+ "strings"
+
+ dto "github.com/prometheus/client_model/go"
+)
+
+const separatorByte byte = 255
+
+// A Metric models a single sample value with its meta data being exported to
+// Prometheus. Implementers of Metric in this package inclued Gauge, Counter,
+// Untyped, and Summary. Users can implement their own Metric types, but that
+// should be rarely needed. See the example for SelfCollector, which is also an
+// example for a user-implemented Metric.
+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.
+ //
+ // Implementers of custom Metric types 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.
+ //
+ // The Prometheus client library attempts to minimize memory allocations
+ // and will provide a pre-existing reset dto.Metric pointer. Prometheus
+ // may recycle the dto.Metric proto message, so Metric implementations
+ // should just populate the provided dto.Metric and then should not keep
+ // any reference to it.
+ //
+ // While populating dto.Metric, labels must be sorted lexicographically.
+ // (Implementers may find LabelPairSorter useful for that.)
+ 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 be
+// an alias of this type (which might change when the requirement arises.)
+//
+// It is mandatory to set Name and Help to a non-empty string. All other fields
+// are optional and can safely be left at their zero value.
+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. Mandatory!
+ //
+ // 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.
+ //
+ // Note that in most cases, labels have a value that varies during the
+ // lifetime of a process. Those labels are usually managed with a metric
+ // vector collector (like CounterVec, GaugeVec, UntypedVec). ConstLabels
+ // serve only special purposes. One is for the special case where the
+ // value of a label does not change during the lifetime of a process,
+ // e.g. if the revision of the running binary is put into a
+ // label. Another, more advanced purpose is if more than one Collector
+ // needs to collect Metrics with the same fully-qualified name. In that
+ // case, those Metrics must differ in the values of their
+ // ConstLabels. See the Collector examples.
+ //
+ // If the value of a label never changes (not even between binaries),
+ // that label most likely should not be a label at all (but part of the
+ // metric name).
+ 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. This is useful for implementing the Write method of
+// custom metrics.
+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 hashSorter []uint64
+
+func (s hashSorter) Len() int {
+ return len(s)
+}
+
+func (s hashSorter) Swap(i, j int) {
+ s[i], s[j] = s[j], s[i]
+}
+
+func (s hashSorter) Less(i, j int) bool {
+ return s[i] < s[j]
+}
+
+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 }