From 1c74eedf76cefc0e74b6fe3f380d360c896d44bf Mon Sep 17 00:00:00 2001
From: "Matt T. Proud" <matt.proud@gmail.com>
Date: Fri, 8 Feb 2013 13:05:35 +0100
Subject: [PATCH] Create initial Metric fingerprinter.

The old system relies off of super-careful notion that the serialized
form of a Protocol Buffer should be used for fingerprint formulation.
Of course this is both wrong and inefficient.  This commit breaks
ground for swapping to a pure attribute-oriented digest.
---
 model/metric.go      | 33 ++++++++++++++++++++++++
 model/metric_test.go | 61 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 94 insertions(+)
 create mode 100644 model/metric_test.go

diff --git a/model/metric.go b/model/metric.go
index de7a7620f..b18a265b0 100644
--- a/model/metric.go
+++ b/model/metric.go
@@ -14,10 +14,19 @@
 package model
 
 import (
+	"bytes"
+	"crypto/md5"
+	"encoding/hex"
 	"fmt"
+	"sort"
 	"time"
 )
 
+const (
+	// XXX: Re-evaluate down the road.
+	reservedDelimiter = '"'
+)
+
 // A Fingerprint is a simplified representation of an entity---e.g., a hash of
 // an entire Metric.
 type Fingerprint string
@@ -40,6 +49,30 @@ type LabelSet map[LabelName]LabelValue
 // a singleton and refers to one and only one stream of samples.
 type Metric map[LabelName]LabelValue
 
+// Fingerprint generates a fingerprint for this given Metric.
+func (m Metric) Fingerprint() string {
+	labelLength := len(m)
+	labelNames := make([]string, 0, labelLength)
+
+	for labelName := range m {
+		labelNames = append(labelNames, string(labelName))
+	}
+
+	sort.Strings(labelNames)
+
+	summer := md5.New()
+
+	buffer := bytes.Buffer{}
+	for _, labelName := range labelNames {
+		buffer.WriteString(labelName)
+		buffer.WriteRune(reservedDelimiter)
+		buffer.WriteString(string(m[LabelName(labelName)]))
+	}
+	summer.Write(buffer.Bytes())
+
+	return hex.EncodeToString(summer.Sum(nil))
+}
+
 // A SampleValue is a representation of a value for a given sample at a given
 // time.  It is presently float32 due to that being the representation that
 // Protocol Buffers provide of floats in Go.  This is a smell and should be
diff --git a/model/metric_test.go b/model/metric_test.go
new file mode 100644
index 000000000..9addf7858
--- /dev/null
+++ b/model/metric_test.go
@@ -0,0 +1,61 @@
+// 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 (
+	"github.com/prometheus/prometheus/utility/test"
+	"testing"
+)
+
+func testMetric(t test.Tester) {
+	var scenarios = []struct {
+		input  map[string]string
+		output string
+	}{
+		{
+			input:  map[string]string{},
+			output: "d41d8cd98f00b204e9800998ecf8427e",
+		},
+		{
+			input: map[string]string{
+				"first_name":   "electro",
+				"occupation":   "robot",
+				"manufacturer": "westinghouse",
+			},
+			output: "18596f03fce001153495d903b8b577c0",
+		},
+	}
+
+	for i, scenario := range scenarios {
+		metric := Metric{}
+		for key, value := range scenario.input {
+			metric[LabelName(key)] = LabelValue(value)
+		}
+
+		expected := scenario.output
+		actual := metric.Fingerprint()
+
+		if expected != actual {
+			t.Errorf("%d. expected %s, got %s", i, expected, actual)
+		}
+	}
+}
+
+func TestMetric(t *testing.T) {
+	testMetric(t)
+}
+
+func BenchmarkMetric(b *testing.B) {
+	testMetric(b)
+}