1// Copyright 2016 The Prometheus Authors 2// Licensed under the Apache License, Version 2.0 (the "License"); 3// you may not use this file except in compliance with the License. 4// You may obtain a copy of the License at 5// 6// http://www.apache.org/licenses/LICENSE-2.0 7// 8// Unless required by applicable law or agreed to in writing, software 9// distributed under the License is distributed on an "AS IS" BASIS, 10// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 11// See the License for the specific language governing permissions and 12// limitations under the License. 13 14package prometheus 15 16import ( 17 "errors" 18 "fmt" 19 "sort" 20 "strings" 21 22 "github.com/cespare/xxhash/v2" 23 //nolint:staticcheck // Ignore SA1019. Need to keep deprecated package for compatibility. 24 "github.com/golang/protobuf/proto" 25 "github.com/prometheus/common/model" 26 27 dto "github.com/prometheus/client_model/go" 28) 29 30// Desc is the descriptor used by every Prometheus Metric. It is essentially 31// the immutable meta-data of a Metric. The normal Metric implementations 32// included in this package manage their Desc under the hood. Users only have to 33// deal with Desc if they use advanced features like the ExpvarCollector or 34// custom Collectors and Metrics. 35// 36// Descriptors registered with the same registry have to fulfill certain 37// consistency and uniqueness criteria if they share the same fully-qualified 38// name: They must have the same help string and the same label names (aka label 39// dimensions) in each, constLabels and variableLabels, but they must differ in 40// the values of the constLabels. 41// 42// Descriptors that share the same fully-qualified names and the same label 43// values of their constLabels are considered equal. 44// 45// Use NewDesc to create new Desc instances. 46type Desc struct { 47 // fqName has been built from Namespace, Subsystem, and Name. 48 fqName string 49 // help provides some helpful information about this metric. 50 help string 51 // constLabelPairs contains precalculated DTO label pairs based on 52 // the constant labels. 53 constLabelPairs []*dto.LabelPair 54 // variableLabels contains names of labels for which the metric 55 // maintains variable values. 56 variableLabels []string 57 // id is a hash of the values of the ConstLabels and fqName. This 58 // must be unique among all registered descriptors and can therefore be 59 // used as an identifier of the descriptor. 60 id uint64 61 // dimHash is a hash of the label names (preset and variable) and the 62 // Help string. Each Desc with the same fqName must have the same 63 // dimHash. 64 dimHash uint64 65 // err is an error that occurred during construction. It is reported on 66 // registration time. 67 err error 68} 69 70// NewDesc allocates and initializes a new Desc. Errors are recorded in the Desc 71// and will be reported on registration time. variableLabels and constLabels can 72// be nil if no such labels should be set. fqName must not be empty. 73// 74// variableLabels only contain the label names. Their label values are variable 75// and therefore not part of the Desc. (They are managed within the Metric.) 76// 77// For constLabels, the label values are constant. Therefore, they are fully 78// specified in the Desc. See the Collector example for a usage pattern. 79func NewDesc(fqName, help string, variableLabels []string, constLabels Labels) *Desc { 80 d := &Desc{ 81 fqName: fqName, 82 help: help, 83 variableLabels: variableLabels, 84 } 85 if !model.IsValidMetricName(model.LabelValue(fqName)) { 86 d.err = fmt.Errorf("%q is not a valid metric name", fqName) 87 return d 88 } 89 // labelValues contains the label values of const labels (in order of 90 // their sorted label names) plus the fqName (at position 0). 91 labelValues := make([]string, 1, len(constLabels)+1) 92 labelValues[0] = fqName 93 labelNames := make([]string, 0, len(constLabels)+len(variableLabels)) 94 labelNameSet := map[string]struct{}{} 95 // First add only the const label names and sort them... 96 for labelName := range constLabels { 97 if !checkLabelName(labelName) { 98 d.err = fmt.Errorf("%q is not a valid label name for metric %q", labelName, fqName) 99 return d 100 } 101 labelNames = append(labelNames, labelName) 102 labelNameSet[labelName] = struct{}{} 103 } 104 sort.Strings(labelNames) 105 // ... so that we can now add const label values in the order of their names. 106 for _, labelName := range labelNames { 107 labelValues = append(labelValues, constLabels[labelName]) 108 } 109 // Validate the const label values. They can't have a wrong cardinality, so 110 // use in len(labelValues) as expectedNumberOfValues. 111 if err := validateLabelValues(labelValues, len(labelValues)); err != nil { 112 d.err = err 113 return d 114 } 115 // Now add the variable label names, but prefix them with something that 116 // cannot be in a regular label name. That prevents matching the label 117 // dimension with a different mix between preset and variable labels. 118 for _, labelName := range variableLabels { 119 if !checkLabelName(labelName) { 120 d.err = fmt.Errorf("%q is not a valid label name for metric %q", labelName, fqName) 121 return d 122 } 123 labelNames = append(labelNames, "$"+labelName) 124 labelNameSet[labelName] = struct{}{} 125 } 126 if len(labelNames) != len(labelNameSet) { 127 d.err = errors.New("duplicate label names") 128 return d 129 } 130 131 xxh := xxhash.New() 132 for _, val := range labelValues { 133 xxh.WriteString(val) 134 xxh.Write(separatorByteSlice) 135 } 136 d.id = xxh.Sum64() 137 // Sort labelNames so that order doesn't matter for the hash. 138 sort.Strings(labelNames) 139 // Now hash together (in this order) the help string and the sorted 140 // label names. 141 xxh.Reset() 142 xxh.WriteString(help) 143 xxh.Write(separatorByteSlice) 144 for _, labelName := range labelNames { 145 xxh.WriteString(labelName) 146 xxh.Write(separatorByteSlice) 147 } 148 d.dimHash = xxh.Sum64() 149 150 d.constLabelPairs = make([]*dto.LabelPair, 0, len(constLabels)) 151 for n, v := range constLabels { 152 d.constLabelPairs = append(d.constLabelPairs, &dto.LabelPair{ 153 Name: proto.String(n), 154 Value: proto.String(v), 155 }) 156 } 157 sort.Sort(labelPairSorter(d.constLabelPairs)) 158 return d 159} 160 161// NewInvalidDesc returns an invalid descriptor, i.e. a descriptor with the 162// provided error set. If a collector returning such a descriptor is registered, 163// registration will fail with the provided error. NewInvalidDesc can be used by 164// a Collector to signal inability to describe itself. 165func NewInvalidDesc(err error) *Desc { 166 return &Desc{ 167 err: err, 168 } 169} 170 171func (d *Desc) String() string { 172 lpStrings := make([]string, 0, len(d.constLabelPairs)) 173 for _, lp := range d.constLabelPairs { 174 lpStrings = append( 175 lpStrings, 176 fmt.Sprintf("%s=%q", lp.GetName(), lp.GetValue()), 177 ) 178 } 179 return fmt.Sprintf( 180 "Desc{fqName: %q, help: %q, constLabels: {%s}, variableLabels: %v}", 181 d.fqName, 182 d.help, 183 strings.Join(lpStrings, ","), 184 d.variableLabels, 185 ) 186} 187