use local fnv hash everywhere

prometheus/desc.go

@@ -1,10 +1,8 @@
 package prometheus
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
-	"hash/fnv"
 	"regexp"
 	"sort"
 	"strings"
@@ -131,31 +129,24 @@ func NewDesc(fqName, help string, variableLabels []string, constLabels Labels) *
 		d.err = errors.New("duplicate label names")
 		return d
 	}
-	h := fnv.New64a()
-	var b bytes.Buffer // To copy string contents into, avoiding []byte allocations.
+	vh := hashNew()
 	for _, val := range labelValues {
-		b.Reset()
-		b.WriteString(val)
-		b.WriteByte(separatorByte)
-		h.Write(b.Bytes())
+		vh = hashAdd(vh, val)
+		vh = hashAddByte(vh, separatorByte)
 	}
-	d.id = h.Sum64()
+	d.id = vh
 	// 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.
-	h.Reset()
-	b.Reset()
-	b.WriteString(help)
-	b.WriteByte(separatorByte)
-	h.Write(b.Bytes())
+	lh := hashNew()
+	lh = hashAdd(lh, help)
+	lh = hashAddByte(lh, separatorByte)
 	for _, labelName := range labelNames {
-		b.Reset()
-		b.WriteString(labelName)
-		b.WriteByte(separatorByte)
-		h.Write(b.Bytes())
+		lh = hashAdd(lh, labelName)
+		lh = hashAddByte(lh, separatorByte)
 	}
-	d.dimHash = h.Sum64()
+	d.dimHash = lh
 
 	d.constLabelPairs = make([]*dto.LabelPair, 0, len(constLabels))
 	for n, v := range constLabels {

prometheus/fnv.go

@@ -20,3 +20,10 @@ func hashAdd(h uint64, s string) uint64 {
 	}
 	return h
 }
+
+// hashAddByte adds a byte to a fnv64a hash value, returning the updated hash.
+func hashAddByte(h uint64, b byte) uint64 {
+	h ^= uint64(b)
+	h *= prime64
+	return h
+}

prometheus/registry.go

@@ -24,7 +24,6 @@ import (
 	"compress/gzip"
 	"errors"
 	"fmt"
-	"hash/fnv"
 	"io"
 	"net/http"
 	"net/url"
@@ -528,30 +527,25 @@ func (r *registry) checkConsistency(metricFamily *dto.MetricFamily, dtoMetric *d
 	}
 
 	// Is the metric unique (i.e. no other metric with the same name and the same label values)?
-	h := fnv.New64a()
-	var buf bytes.Buffer
-	buf.WriteString(metricFamily.GetName())
-	buf.WriteByte(separatorByte)
-	h.Write(buf.Bytes())
+	h := hashNew()
+	h = hashAdd(h, metricFamily.GetName())
+	h = hashAddByte(h, separatorByte)
 	// Make sure label pairs are sorted. We depend on it for the consistency
 	// check. Label pairs must be sorted by contract. But the point of this
 	// method is to check for contract violations. So we better do the sort
 	// now.
 	sort.Sort(LabelPairSorter(dtoMetric.Label))
 	for _, lp := range dtoMetric.Label {
-		buf.Reset()
-		buf.WriteString(lp.GetValue())
-		buf.WriteByte(separatorByte)
-		h.Write(buf.Bytes())
+		h = hashAdd(h, lp.GetValue())
+		h = hashAddByte(h, separatorByte)
 	}
-	metricHash := h.Sum64()
-	if _, exists := metricHashes[metricHash]; exists {
+	if _, exists := metricHashes[h]; exists {
 		return fmt.Errorf(
 			"collected metric %s %s was collected before with the same name and label values",
 			metricFamily.GetName(), dtoMetric,
 		)
 	}
-	metricHashes[metricHash] = struct{}{}
+	metricHashes[h] = struct{}{}
 
 	if desc == nil {
 		return nil // Nothing left to check if we have no desc.