Update package model/textparse for new labels.Labels type

Parse metrics using labels.ScratchBuilder, so we reduce assumptions about
internals of Labels.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

model/textparse/openmetricsparse.go

@@ -22,7 +22,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"sort"
 	"strings"
 	"unicode/utf8"
 
@@ -82,6 +81,7 @@ func (l *openMetricsLexer) Error(es string) {
 // This is based on the working draft https://docs.google.com/document/u/1/d/1KwV0mAXwwbvvifBvDKH_LU1YjyXE_wxCkHNoCGq1GX0/edit
 type OpenMetricsParser struct {
 	l       *openMetricsLexer
+	builder labels.ScratchBuilder
 	series  []byte
 	text    []byte
 	mtype   MetricType
@@ -158,14 +158,11 @@ func (p *OpenMetricsParser) Comment() []byte {
 // Metric writes the labels of the current sample into the passed labels.
 // It returns the string from which the metric was parsed.
 func (p *OpenMetricsParser) Metric(l *labels.Labels) string {
-	// Allocate the full immutable string immediately, so we just
-	// have to create references on it below.
+	// Copy the buffer to a string: this is only necessary for the return value.
 	s := string(p.series)
 
-	*l = append(*l, labels.Label{
-		Name:  labels.MetricName,
-		Value: s[:p.offsets[0]-p.start],
-	})
+	p.builder.Reset()
+	p.builder.Add(labels.MetricName, s[:p.offsets[0]-p.start])
 
 	for i := 1; i < len(p.offsets); i += 4 {
 		a := p.offsets[i] - p.start
@@ -173,16 +170,16 @@ func (p *OpenMetricsParser) Metric(l *labels.Labels) string {
 		c := p.offsets[i+2] - p.start
 		d := p.offsets[i+3] - p.start
 
+		value := s[c:d]
 		// Replacer causes allocations. Replace only when necessary.
 		if strings.IndexByte(s[c:d], byte('\\')) >= 0 {
-			*l = append(*l, labels.Label{Name: s[a:b], Value: lvalReplacer.Replace(s[c:d])})
-			continue
+			value = lvalReplacer.Replace(value)
 		}
-		*l = append(*l, labels.Label{Name: s[a:b], Value: s[c:d]})
+		p.builder.Add(s[a:b], value)
 	}
 
-	// Sort labels.
-	sort.Sort(*l)
+	p.builder.Sort()
+	*l = p.builder.Labels()
 
 	return s
 }
@@ -204,17 +201,18 @@ func (p *OpenMetricsParser) Exemplar(e *exemplar.Exemplar) bool {
 		e.Ts = p.exemplarTs
 	}
 
+	p.builder.Reset()
 	for i := 0; i < len(p.eOffsets); i += 4 {
 		a := p.eOffsets[i] - p.start
 		b := p.eOffsets[i+1] - p.start
 		c := p.eOffsets[i+2] - p.start
 		d := p.eOffsets[i+3] - p.start
 
-		e.Labels = append(e.Labels, labels.Label{Name: s[a:b], Value: s[c:d]})
+		p.builder.Add(s[a:b], s[c:d])
 	}
 
-	// Sort the labels.
-	sort.Sort(e.Labels)
+	p.builder.Sort()
+	e.Labels = p.builder.Labels()
 
 	return true
 }

model/textparse/promparse.go

@@ -21,7 +21,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"sort"
 	"strconv"
 	"strings"
 	"unicode/utf8"
@@ -144,6 +143,7 @@ func (l *promlexer) Error(es string) {
 // Prometheus text exposition format.
 type PromParser struct {
 	l       *promlexer
+	builder labels.ScratchBuilder
 	series  []byte
 	text    []byte
 	mtype   MetricType
@@ -212,14 +212,11 @@ func (p *PromParser) Comment() []byte {
 // Metric writes the labels of the current sample into the passed labels.
 // It returns the string from which the metric was parsed.
 func (p *PromParser) Metric(l *labels.Labels) string {
-	// Allocate the full immutable string immediately, so we just
-	// have to create references on it below.
+	// Copy the buffer to a string: this is only necessary for the return value.
 	s := string(p.series)
 
-	*l = append(*l, labels.Label{
-		Name:  labels.MetricName,
-		Value: s[:p.offsets[0]-p.start],
-	})
+	p.builder.Reset()
+	p.builder.Add(labels.MetricName, s[:p.offsets[0]-p.start])
 
 	for i := 1; i < len(p.offsets); i += 4 {
 		a := p.offsets[i] - p.start
@@ -227,16 +224,16 @@ func (p *PromParser) Metric(l *labels.Labels) string {
 		c := p.offsets[i+2] - p.start
 		d := p.offsets[i+3] - p.start
 
+		value := s[c:d]
 		// Replacer causes allocations. Replace only when necessary.
 		if strings.IndexByte(s[c:d], byte('\\')) >= 0 {
-			*l = append(*l, labels.Label{Name: s[a:b], Value: lvalReplacer.Replace(s[c:d])})
-			continue
+			value = lvalReplacer.Replace(value)
 		}
-		*l = append(*l, labels.Label{Name: s[a:b], Value: s[c:d]})
+		p.builder.Add(s[a:b], value)
 	}
 
-	// Sort labels to maintain the sorted labels invariant.
-	sort.Sort(*l)
+	p.builder.Sort()
+	*l = p.builder.Labels()
 
 	return s
 }

model/textparse/protobufparse.go

@@ -19,7 +19,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"sort"
 	"strings"
 	"unicode/utf8"
 
@@ -59,6 +58,8 @@ type ProtobufParser struct {
 	// that we have to decode the next MetricFamily.
 	state Entry
 
+	builder labels.ScratchBuilder // held here to reduce allocations when building Labels
+
 	mf *dto.MetricFamily
 
 	// The following are just shenanigans to satisfy the Parser interface.
@@ -245,23 +246,19 @@ func (p *ProtobufParser) Comment() []byte {
 // Metric writes the labels of the current sample into the passed labels.
 // It returns the string from which the metric was parsed.
 func (p *ProtobufParser) Metric(l *labels.Labels) string {
-	*l = append(*l, labels.Label{
-		Name:  labels.MetricName,
-		Value: p.getMagicName(),
-	})
+	p.builder.Reset()
+	p.builder.Add(labels.MetricName, p.getMagicName())
 
 	for _, lp := range p.mf.GetMetric()[p.metricPos].GetLabel() {
-		*l = append(*l, labels.Label{
-			Name:  lp.GetName(),
-			Value: lp.GetValue(),
-		})
+		p.builder.Add(lp.GetName(), lp.GetValue())
 	}
 	if needed, name, value := p.getMagicLabel(); needed {
-		*l = append(*l, labels.Label{Name: name, Value: value})
+		p.builder.Add(name, value)
 	}
 
 	// Sort labels to maintain the sorted labels invariant.
-	sort.Sort(*l)
+	p.builder.Sort()
+	*l = p.builder.Labels()
 
 	return p.metricBytes.String()
 }
@@ -305,12 +302,12 @@ func (p *ProtobufParser) Exemplar(ex *exemplar.Exemplar) bool {
 		ex.HasTs = true
 		ex.Ts = ts.GetSeconds()*1000 + int64(ts.GetNanos()/1_000_000)
 	}
+	p.builder.Reset()
 	for _, lp := range exProto.GetLabel() {
-		ex.Labels = append(ex.Labels, labels.Label{
-			Name:  lp.GetName(),
-			Value: lp.GetValue(),
-		})
+		p.builder.Add(lp.GetName(), lp.GetValue())
 	}
+	p.builder.Sort()
+	ex.Labels = p.builder.Labels()
 	return true
 }