From 4a769770fe334345507b9e490d941d1ae50b8e9c Mon Sep 17 00:00:00 2001
From: James Cohen <james.cohen@digitalwindow.com>
Date: Fri, 5 Dec 2014 17:26:33 +0000
Subject: [PATCH] Relative gauges

---
 statsdaemon.go      | 70 +++++++++++++++++++++++++++++++++++++++++++--
 statsdaemon_test.go | 59 ++++++++++++++++++++++++++++++++++++--
 2 files changed, 123 insertions(+), 6 deletions(-)

diff --git a/statsdaemon.go b/statsdaemon.go
index 37ec693..941d17e 100644
--- a/statsdaemon.go
+++ b/statsdaemon.go
@@ -32,6 +32,12 @@ type Packet struct {
 	Sampling float32
 }
 
+type GaugeData struct {
+	Relative bool
+	Negative bool
+	Value    uint64
+}
+
 type Uint64Slice []uint64
 
 func (s Uint64Slice) Len() int           { return len(s) }
@@ -80,6 +86,7 @@ var (
 	In              = make(chan *Packet, MAX_UNPROCESSED_PACKETS)
 	counters        = make(map[string]int64)
 	gauges          = make(map[string]uint64)
+	trackedGauges   = make(map[string]uint64)
 	timers          = make(map[string]Uint64Slice)
 	countInactivity = make(map[string]int64)
 )
@@ -122,7 +129,39 @@ func packetHandler(s *Packet) {
 		}
 		timers[s.Bucket] = append(timers[s.Bucket], s.Value.(uint64))
 	} else if s.Modifier == "g" {
-		gauges[s.Bucket] = s.Value.(uint64)
+		var gaugeValue uint64 = 0
+		_, ok := gauges[s.Bucket]
+
+		// initialise gaugeValue as either 0 or existing value
+		if ok {
+			gaugeValue = gauges[s.Bucket]
+		} else {
+			gaugeValue = 0
+		}
+
+		gaugeData := s.Value.(GaugeData)
+		if gaugeData.Relative {
+			if gaugeData.Negative {
+				// subtract checking for -ve numbers
+				if gaugeData.Value > gaugeValue {
+					gaugeValue = 0
+				} else {
+					gaugeValue -= gaugeData.Value
+				}
+			} else {
+				// watch out for overflows
+				if gaugeData.Value > (math.MaxUint64 - gaugeValue) {
+					gaugeValue = math.MaxUint64
+				} else {
+					gaugeValue += gaugeData.Value
+				}
+			}
+		} else {
+			gaugeValue = gaugeData.Value
+		}
+
+		gauges[s.Bucket] = gaugeValue
+
 	} else if s.Modifier == "c" {
 		_, ok := counters[s.Bucket]
 		if !ok {
@@ -212,12 +251,15 @@ func processCounters(buffer *bytes.Buffer, now int64) int64 {
 
 func processGauges(buffer *bytes.Buffer, now int64) int64 {
 	var num int64
+
 	for g, c := range gauges {
-		if c == math.MaxUint64 {
+		lastValue, ok := trackedGauges[g]
+
+		if ok && c == lastValue {
 			continue
 		}
 		fmt.Fprintf(buffer, "%s %d %d\n", g, c, now)
-		gauges[g] = math.MaxUint64
+		trackedGauges[g] = c
 		num++
 	}
 	return num
@@ -349,6 +391,28 @@ func parseMessage(data []byte) []*Packet {
 				log.Printf("ERROR: failed to ParseInt %s - %s", string(val), err)
 				continue
 			}
+		} else if mtypeStr[0] == 'g' {
+			var relative, negative bool
+			var stringToParse string
+
+			switch val[0] {
+			case '+', '-':
+				relative = true
+				negative = val[0] == '-'
+				stringToParse = string(val[1:])
+			default:
+				relative = false
+				negative = false
+				stringToParse = string(val)
+			}
+
+			gaugeValue, err := strconv.ParseUint(stringToParse, 10, 64)
+			if err != nil {
+				log.Printf("ERROR: failed to ParseUint %s - %s", string(val), err)
+				continue
+			}
+
+			value = GaugeData{relative, negative, gaugeValue}
 		} else {
 			value, err = strconv.ParseUint(string(val), 10, 64)
 			if err != nil {
diff --git a/statsdaemon_test.go b/statsdaemon_test.go
index d211a96..4095287 100644
--- a/statsdaemon_test.go
+++ b/statsdaemon_test.go
@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"github.com/bmizerany/assert"
+	"math"
 	"math/rand"
 	"strconv"
 	"testing"
@@ -22,7 +23,35 @@ func TestPacketParse(t *testing.T) {
 	assert.Equal(t, len(packets), 1)
 	packet := packets[0]
 	assert.Equal(t, "gaugor", packet.Bucket)
-	assert.Equal(t, uint64(333), packet.Value.(uint64))
+	assert.Equal(t, GaugeData{false, false, 333}, packet.Value)
+	assert.Equal(t, "g", packet.Modifier)
+	assert.Equal(t, float32(1), packet.Sampling)
+
+	d = []byte("gaugor:-10|g")
+	packets = parseMessage(d)
+	assert.Equal(t, len(packets), 1)
+	packet = packets[0]
+	assert.Equal(t, "gaugor", packet.Bucket)
+	assert.Equal(t, GaugeData{true, true, 10}, packet.Value)
+	assert.Equal(t, "g", packet.Modifier)
+	assert.Equal(t, float32(1), packet.Sampling)
+
+	d = []byte("gaugor:+4|g")
+	packets = parseMessage(d)
+	assert.Equal(t, len(packets), 1)
+	packet = packets[0]
+	assert.Equal(t, "gaugor", packet.Bucket)
+	assert.Equal(t, GaugeData{true, false, 4}, packet.Value)
+	assert.Equal(t, "g", packet.Modifier)
+	assert.Equal(t, float32(1), packet.Sampling)
+
+	// >max(int64) && <max(uint64)
+	d = []byte("gaugor:18446744073709551606|g")
+	packets = parseMessage(d)
+	assert.Equal(t, len(packets), 1)
+	packet = packets[0]
+	assert.Equal(t, "gaugor", packet.Bucket)
+	assert.Equal(t, GaugeData{false, false, 18446744073709551606}, packet.Value)
 	assert.Equal(t, "g", packet.Modifier)
 	assert.Equal(t, float32(1), packet.Sampling)
 
@@ -82,7 +111,7 @@ func TestPacketParse(t *testing.T) {
 
 	packet = packets[1]
 	assert.Equal(t, "gauge", packet.Bucket)
-	assert.Equal(t, uint64(3), packet.Value.(uint64))
+	assert.Equal(t, GaugeData{false, false, 3}, packet.Value)
 	assert.Equal(t, "g", packet.Modifier)
 	assert.Equal(t, float32(1), packet.Sampling)
 
@@ -171,12 +200,36 @@ func TestGaugePacketHandling(t *testing.T) {
 
 	p := &Packet{
 		Bucket:   "gaugor",
-		Value:    uint64(333),
+		Value:    GaugeData{false, false, 333},
 		Modifier: "g",
 		Sampling: float32(1),
 	}
 	packetHandler(p)
 	assert.Equal(t, gauges["gaugor"], uint64(333))
+
+	// -10
+	p.Value = GaugeData{true, true, 10}
+	packetHandler(p)
+	assert.Equal(t, gauges["gaugor"], uint64(323))
+
+	// +4
+	p.Value = GaugeData{true, false, 4}
+	packetHandler(p)
+	assert.Equal(t, gauges["gaugor"], uint64(327))
+
+	// <0 overflow
+	p.Value = GaugeData{false, false, 10}
+	packetHandler(p)
+	p.Value = GaugeData{true, true, 20}
+	packetHandler(p)
+	assert.Equal(t, gauges["gaugor"], uint64(0))
+
+	// >2^64 overflow
+	p.Value = GaugeData{false, false, uint64(math.MaxUint64 - 10)}
+	packetHandler(p)
+	p.Value = GaugeData{true, false, 20}
+	packetHandler(p)
+	assert.Equal(t, gauges["gaugor"], uint64(math.MaxUint64))
 }
 
 func TestTimerPacketHandling(t *testing.T) {