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signature.go
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signature.go
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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 model
import (
"bytes"
"hash"
"hash/fnv"
"sync"
)
// SeparatorByte is a byte that cannot occur in valid UTF-8 sequences and is
// used to separate label names, label values, and other strings from each other
// when calculating their combined hash value (aka signature aka fingerprint).
const SeparatorByte byte = 255
var (
// cache the signature of an empty label set.
emptyLabelSignature = fnv.New64a().Sum64()
hashAndBufPool sync.Pool
)
type hashAndBuf struct {
h hash.Hash64
b bytes.Buffer
}
func getHashAndBuf() *hashAndBuf {
hb := hashAndBufPool.Get()
if hb == nil {
return &hashAndBuf{h: fnv.New64a()}
}
return hb.(*hashAndBuf)
}
func putHashAndBuf(hb *hashAndBuf) {
hashAndBufPool.Put(hb)
}
// LabelsToSignature returns a unique signature (i.e., fingerprint) for a given
// label set.
func LabelsToSignature(labels map[string]string) uint64 {
if len(labels) == 0 {
return emptyLabelSignature
}
var result uint64
hb := getHashAndBuf()
defer putHashAndBuf(hb)
for labelName, labelValue := range labels {
hb.b.WriteString(labelName)
hb.b.WriteByte(SeparatorByte)
hb.b.WriteString(labelValue)
hb.h.Write(hb.b.Bytes())
result ^= hb.h.Sum64()
hb.h.Reset()
hb.b.Reset()
}
return result
}
// metricToFingerprint works exactly as LabelsToSignature but takes a Metric as
// parameter (rather than a label map) and returns a Fingerprint.
func metricToFingerprint(m Metric) Fingerprint {
if len(m) == 0 {
return Fingerprint(emptyLabelSignature)
}
var result uint64
hb := getHashAndBuf()
defer putHashAndBuf(hb)
for labelName, labelValue := range m {
hb.b.WriteString(string(labelName))
hb.b.WriteByte(SeparatorByte)
hb.b.WriteString(string(labelValue))
hb.h.Write(hb.b.Bytes())
result ^= hb.h.Sum64()
hb.h.Reset()
hb.b.Reset()
}
return Fingerprint(result)
}
// SignatureForLabels works like LabelsToSignature but takes a Metric as
// parameter (rather than a label map) and only includes the labels with the
// specified LabelNames into the signature calculation.
func SignatureForLabels(m Metric, labels LabelNames) uint64 {
if len(m) == 0 || len(labels) == 0 {
return emptyLabelSignature
}
var result uint64
hb := getHashAndBuf()
defer putHashAndBuf(hb)
for _, label := range labels {
hb.b.WriteString(string(label))
hb.b.WriteByte(SeparatorByte)
hb.b.WriteString(string(m[label]))
hb.h.Write(hb.b.Bytes())
result ^= hb.h.Sum64()
hb.h.Reset()
hb.b.Reset()
}
return result
}
// SignatureWithoutLabels works like LabelsToSignature but takes a Metric as
// parameter (rather than a label map) and excludes the labels with any of the
// specified LabelNames from the signature calculation.
func SignatureWithoutLabels(m Metric, labels map[LabelName]struct{}) uint64 {
if len(m) == 0 {
return emptyLabelSignature
}
var result uint64
hb := getHashAndBuf()
defer putHashAndBuf(hb)
for labelName, labelValue := range m {
if _, exclude := labels[labelName]; exclude {
continue
}
hb.b.WriteString(string(labelName))
hb.b.WriteByte(SeparatorByte)
hb.b.WriteString(string(labelValue))
hb.h.Write(hb.b.Bytes())
result ^= hb.h.Sum64()
hb.h.Reset()
hb.b.Reset()
}
if result == 0 {
return emptyLabelSignature
}
return result
}