Fix logic bug in fingerprint Less() comparison.

Seems like just using String() is the easiest way of doing this.

model/fingerprinting.go

@@ -41,6 +41,7 @@ type Fingerprint interface {
 	ToDTO() *dto.Fingerprint
 	Less(Fingerprint) bool
 	Equal(Fingerprint) bool
+	String() string
 }
 
 // Builds a Fingerprint from a row key.
@@ -151,20 +152,7 @@ func (f fingerprint) LastCharacterOfLastLabelValue() string {
 }
 
 func (f fingerprint) Less(o Fingerprint) bool {
-	if f.Hash() < o.Hash() {
-		return true
-	}
-	if f.FirstCharacterOfFirstLabelName() < o.FirstCharacterOfFirstLabelName() {
-		return true
-	}
-	if f.LabelMatterLength() < o.LabelMatterLength() {
-		return true
-	}
-	if f.LastCharacterOfLastLabelValue() < o.LastCharacterOfLastLabelValue() {
-		return true
-	}
-
-	return false
+	return f.String() < o.String()
 }
 
 func (f fingerprint) Equal(o Fingerprint) (equal bool) {

model/fingerprinting_test.go

@@ -0,0 +1,68 @@
+// Copyright 2013 Prometheus Team
+// 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 (
+	"testing"
+)
+
+func TestFingerprintComparison(t *testing.T) {
+	fingerprints := []fingerprint{
+		{
+			hash: 0,
+			firstCharacterOfFirstLabelName: "b",
+			labelMatterLength:              1,
+			lastCharacterOfLastLabelValue:  "b",
+		},
+		{
+			hash: 1,
+			firstCharacterOfFirstLabelName: "a",
+			labelMatterLength:              0,
+			lastCharacterOfLastLabelValue:  "a",
+		},
+		{
+			hash: 1,
+			firstCharacterOfFirstLabelName: "a",
+			labelMatterLength:              1000,
+			lastCharacterOfLastLabelValue:  "b",
+		},
+		{
+			hash: 1,
+			firstCharacterOfFirstLabelName: "b",
+			labelMatterLength:              0,
+			lastCharacterOfLastLabelValue:  "a",
+		},
+		{
+			hash: 1,
+			firstCharacterOfFirstLabelName: "b",
+			labelMatterLength:              1,
+			lastCharacterOfLastLabelValue:  "a",
+		},
+		{
+			hash: 1,
+			firstCharacterOfFirstLabelName: "b",
+			labelMatterLength:              1,
+			lastCharacterOfLastLabelValue:  "b",
+		},
+	}
+	for i := range fingerprints {
+		if i == 0 {
+			continue
+		}
+
+		if !fingerprints[i-1].Less(fingerprints[i]) {
+			t.Errorf("%d expected %s < %s", i, fingerprints[i-1], fingerprints[i])
+		}
+	}
+}