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// Copyright 2016 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 ( | |
"errors" | |
"fmt" | |
"sort" | |
"strings" | |
"github.com/cespare/xxhash/v2" | |
//lint:ignore SA1019 Need to keep deprecated package for compatibility. | |
"github.com/golang/protobuf/proto" | |
"github.com/prometheus/common/model" | |
dto "github.com/prometheus/client_model/go" | |
) | |
// Desc is the descriptor used by every Prometheus Metric. It is essentially | |
// the immutable meta-data of a Metric. The normal Metric implementations | |
// included in this package manage their Desc under the hood. Users only have to | |
// deal with Desc if they use advanced features like the ExpvarCollector or | |
// custom Collectors and Metrics. | |
// | |
// Descriptors registered with the same registry have to fulfill certain | |
// consistency and uniqueness criteria if they share the same fully-qualified | |
// name: They must have the same help string and the same label names (aka label | |
// dimensions) in each, constLabels and variableLabels, but they must differ in | |
// the values of the constLabels. | |
// | |
// Descriptors that share the same fully-qualified names and the same label | |
// values of their constLabels are considered equal. | |
// | |
// Use NewDesc to create new Desc instances. | |
type Desc struct { | |
// fqName has been built from Namespace, Subsystem, and Name. | |
fqName string | |
// help provides some helpful information about this metric. | |
help string | |
// constLabelPairs contains precalculated DTO label pairs based on | |
// the constant labels. | |
constLabelPairs []*dto.LabelPair | |
// variableLabels contains names of labels for which the metric | |
// maintains variable values. | |
variableLabels []string | |
// id is a hash of the values of the ConstLabels and fqName. This | |
// must be unique among all registered descriptors and can therefore be | |
// used as an identifier of the descriptor. | |
id uint64 | |
// dimHash is a hash of the label names (preset and variable) and the | |
// Help string. Each Desc with the same fqName must have the same | |
// dimHash. | |
dimHash uint64 | |
// err is an error that occurred during construction. It is reported on | |
// registration time. | |
err error | |
} | |
// NewDesc allocates and initializes a new Desc. Errors are recorded in the Desc | |
// and will be reported on registration time. variableLabels and constLabels can | |
// be nil if no such labels should be set. fqName must not be empty. | |
// | |
// variableLabels only contain the label names. Their label values are variable | |
// and therefore not part of the Desc. (They are managed within the Metric.) | |
// | |
// For constLabels, the label values are constant. Therefore, they are fully | |
// specified in the Desc. See the Collector example for a usage pattern. | |
func NewDesc(fqName, help string, variableLabels []string, constLabels Labels) *Desc { | |
d := &Desc{ | |
fqName: fqName, | |
help: help, | |
variableLabels: variableLabels, | |
} | |
if !model.IsValidMetricName(model.LabelValue(fqName)) { | |
d.err = fmt.Errorf("%q is not a valid metric name", fqName) | |
return d | |
} | |
// labelValues contains the label values of const labels (in order of | |
// their sorted label names) plus the fqName (at position 0). | |
labelValues := make([]string, 1, len(constLabels)+1) | |
labelValues[0] = fqName | |
labelNames := make([]string, 0, len(constLabels)+len(variableLabels)) | |
labelNameSet := map[string]struct{}{} | |
// First add only the const label names and sort them... | |
for labelName := range constLabels { | |
if !checkLabelName(labelName) { | |
d.err = fmt.Errorf("%q is not a valid label name for metric %q", labelName, fqName) | |
return d | |
} | |
labelNames = append(labelNames, labelName) | |
labelNameSet[labelName] = struct{}{} | |
} | |
sort.Strings(labelNames) | |
// ... so that we can now add const label values in the order of their names. | |
for _, labelName := range labelNames { | |
labelValues = append(labelValues, constLabels[labelName]) | |
} | |
// Validate the const label values. They can't have a wrong cardinality, so | |
// use in len(labelValues) as expectedNumberOfValues. | |
if err := validateLabelValues(labelValues, len(labelValues)); err != nil { | |
d.err = err | |
return d | |
} | |
// Now add the variable label names, but prefix them with something that | |
// cannot be in a regular label name. That prevents matching the label | |
// dimension with a different mix between preset and variable labels. | |
for _, labelName := range variableLabels { | |
if !checkLabelName(labelName) { | |
d.err = fmt.Errorf("%q is not a valid label name for metric %q", labelName, fqName) | |
return d | |
} | |
labelNames = append(labelNames, "$"+labelName) | |
labelNameSet[labelName] = struct{}{} | |
} | |
if len(labelNames) != len(labelNameSet) { | |
d.err = errors.New("duplicate label names") | |
return d | |
} | |
xxh := xxhash.New() | |
for _, val := range labelValues { | |
xxh.WriteString(val) | |
xxh.Write(separatorByteSlice) | |
} | |
d.id = xxh.Sum64() | |
// Sort labelNames so that order doesn't matter for the hash. | |
sort.Strings(labelNames) | |
// Now hash together (in this order) the help string and the sorted | |
// label names. | |
xxh.Reset() | |
xxh.WriteString(help) | |
xxh.Write(separatorByteSlice) | |
for _, labelName := range labelNames { | |
xxh.WriteString(labelName) | |
xxh.Write(separatorByteSlice) | |
} | |
d.dimHash = xxh.Sum64() | |
d.constLabelPairs = make([]*dto.LabelPair, 0, len(constLabels)) | |
for n, v := range constLabels { | |
d.constLabelPairs = append(d.constLabelPairs, &dto.LabelPair{ | |
Name: proto.String(n), | |
Value: proto.String(v), | |
}) | |
} | |
sort.Sort(labelPairSorter(d.constLabelPairs)) | |
return d | |
} | |
// NewInvalidDesc returns an invalid descriptor, i.e. a descriptor with the | |
// provided error set. If a collector returning such a descriptor is registered, | |
// registration will fail with the provided error. NewInvalidDesc can be used by | |
// a Collector to signal inability to describe itself. | |
func NewInvalidDesc(err error) *Desc { | |
return &Desc{ | |
err: err, | |
} | |
} | |
func (d *Desc) String() string { | |
lpStrings := make([]string, 0, len(d.constLabelPairs)) | |
for _, lp := range d.constLabelPairs { | |
lpStrings = append( | |
lpStrings, | |
fmt.Sprintf("%s=%q", lp.GetName(), lp.GetValue()), | |
) | |
} | |
return fmt.Sprintf( | |
"Desc{fqName: %q, help: %q, constLabels: {%s}, variableLabels: %v}", | |
d.fqName, | |
d.help, | |
strings.Join(lpStrings, ","), | |
d.variableLabels, | |
) | |
} |