From bb26c8574e67603ff22056af3768781bad6e32e4 Mon Sep 17 00:00:00 2001
From: Matthew Pound <mpound@splunk.com>
Date: Mon, 14 Aug 2023 11:59:52 -0600
Subject: [PATCH] sfxclient: Add ability to panic if we're about to emit
 duplicate datapoints

---
 go.mod                      |  1 +
 go.sum                      |  2 ++
 sfxclient/sfxclient.go      | 44 +++++++++++++++++++++++++++++++++++++
 sfxclient/sfxclient_test.go | 15 +++++++++++++
 4 files changed, 62 insertions(+)

diff --git a/go.mod b/go.mod
index b8b0257..2527a98 100644
--- a/go.mod
+++ b/go.mod
@@ -21,6 +21,7 @@ require (
 	github.com/signalfx/sapm-proto v0.12.0
 	github.com/smartystreets/goconvey v1.6.4
 	github.com/stretchr/testify v1.8.4
+	github.com/twmb/murmur3 v1.1.7
 	github.com/vaughan0/go-ini v0.0.0-20130923145212-a98ad7ee00ec
 	google.golang.org/grpc v1.56.1
 )
diff --git a/go.sum b/go.sum
index 6cf30d4..91075c6 100644
--- a/go.sum
+++ b/go.sum
@@ -87,6 +87,8 @@ github.com/tklauser/go-sysconf v0.3.10 h1:IJ1AZGZRWbY8T5Vfk04D9WOA5WSejdflXxP03O
 github.com/tklauser/go-sysconf v0.3.10/go.mod h1:C8XykCvCb+Gn0oNCWPIlcb0RuglQTYaQ2hGm7jmxEFk=
 github.com/tklauser/numcpus v0.4.0 h1:E53Dm1HjH1/R2/aoCtXtPgzmElmn51aOkhCFSuZq//o=
 github.com/tklauser/numcpus v0.4.0/go.mod h1:1+UI3pD8NW14VMwdgJNJ1ESk2UnwhAnz5hMwiKKqXCQ=
+github.com/twmb/murmur3 v1.1.7 h1:ULWBiM04n/XoN3YMSJ6Z2pHDFLf+MeIVQU71ZPrvbWg=
+github.com/twmb/murmur3 v1.1.7/go.mod h1:Qq/R7NUyOfr65zD+6Q5IHKsJLwP7exErjN6lyyq3OSQ=
 github.com/uber/jaeger-client-go v2.30.0+incompatible h1:D6wyKGCecFaSRUpo8lCVbaOOb6ThwMmTEbhRwtKR97o=
 github.com/uber/jaeger-client-go v2.30.0+incompatible/go.mod h1:WVhlPFC8FDjOFMMWRy2pZqQJSXxYSwNYOkTr/Z6d3Kk=
 github.com/uber/jaeger-lib v2.4.1+incompatible h1:td4jdvLcExb4cBISKIpHuGoVXh+dVKhn2Um6rjCsSsg=
diff --git a/sfxclient/sfxclient.go b/sfxclient/sfxclient.go
index 8c523e9..89cb271 100644
--- a/sfxclient/sfxclient.go
+++ b/sfxclient/sfxclient.go
@@ -64,7 +64,9 @@ import (
 	"context"
 	"expvar"
 	"fmt"
+	"os"
 	"reflect"
+	"sort"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -75,6 +77,7 @@ import (
 	"github.com/signalfx/golib/v3/errors"
 	"github.com/signalfx/golib/v3/log"
 	"github.com/signalfx/golib/v3/timekeeper"
+	"github.com/twmb/murmur3"
 )
 
 const (
@@ -84,6 +87,8 @@ const (
 	DefaultReportingTimeout = time.Second * 5
 	// used when group name is ""
 	defaultCallbackGroup = "default-callback-group"
+	// used if you want to check if you're emitting the same datapoint twice and causing inaccurate metrics
+	panicOnDupes = "SFXCLIENT_PANIC_ON_DUPES"
 )
 
 // DefaultErrorHandler is the default way to handle errors by a scheduler.  It simply prints them to stdout
@@ -236,6 +241,7 @@ func (s *Scheduler) collectDatapoints() []*datapoint.Datapoint {
 			ret = append(ret, p.getDatapoints(now, s.SendZeroTime)...)
 		}
 	}
+	s.checkDatapoints(ret)
 	return ret
 }
 
@@ -372,3 +378,41 @@ func (s *Scheduler) Schedule(ctx context.Context) error {
 		}
 	}
 }
+
+func (s *Scheduler) checkDatapoints(ret []*datapoint.Datapoint) {
+	if len(os.Getenv(panicOnDupes)) > 0 {
+		var dupes []*datapoint.Datapoint
+		m := make(map[uint32]*datapoint.Datapoint, len(ret))
+		buff := bytes.Buffer{}
+		for _, d := range ret {
+			buff.Reset()
+
+			buff.WriteString(d.Metric)
+			mk := make([]string, len(d.Dimensions))
+			i := 0
+			for k := range d.Dimensions {
+				mk[i] = k
+				i++
+			}
+			sort.Strings(mk)
+			for k := range mk {
+				buff.WriteString(mk[k])
+				buff.WriteString(d.Dimensions[mk[k]])
+			}
+
+			murmHash := murmur3.Sum32(buff.Bytes())
+			if _, ok := m[murmHash]; ok {
+				dupes = append(dupes, d)
+			} else {
+				m[murmHash] = d
+			}
+		}
+		if len(dupes) > 0 {
+			msg := make([]string, len(dupes))
+			for i, d := range dupes {
+				msg[i] = fmt.Sprintf("Found duplicate datapoint: %s", d)
+			}
+			panic(strings.Join(msg, "\n"))
+		}
+	}
+}
diff --git a/sfxclient/sfxclient_test.go b/sfxclient/sfxclient_test.go
index 9ff9dcd..e1a9f89 100644
--- a/sfxclient/sfxclient_test.go
+++ b/sfxclient/sfxclient_test.go
@@ -3,6 +3,7 @@ package sfxclient
 import (
 	"context"
 	"fmt"
+	"os"
 	"runtime"
 	"strconv"
 	"strings"
@@ -12,6 +13,7 @@ import (
 	"time"
 
 	"github.com/signalfx/golib/v3/datapoint"
+	"github.com/signalfx/golib/v3/datapoint/dptest"
 	"github.com/signalfx/golib/v3/errors"
 	"github.com/signalfx/golib/v3/timekeeper/timekeepertest"
 	. "github.com/smartystreets/goconvey/convey"
@@ -123,6 +125,19 @@ func TestScheduler_ReportingTimeout(t *testing.T) {
 	})
 }
 
+func TestPanicOnDupes(t *testing.T) {
+	Convey("testing panic on dupes", t, func() {
+		s := &Scheduler{}
+
+		os.Setenv(panicOnDupes, "true")
+		defer os.Setenv(panicOnDupes, "")
+		dp := dptest.DP()
+		s.checkDatapoints([]*datapoint.Datapoint{dp})
+
+		So(func() { s.checkDatapoints([]*datapoint.Datapoint{dp, dp}) }, ShouldPanic)
+	})
+}
+
 func TestCollectDatapointDebug(t *testing.T) {
 	Convey("testing collect datapoints with debug mode enabled", t, func() {
 		var handleErrRet error