Merge pull request #48 from DataDog/nicolas/random

use a seeded/thread-safe random number generator for span ids

tracer/rand.go

@@ -0,0 +1,47 @@
+package tracer
+
+import (
+	cryptorand "crypto/rand"
+	"log"
+	"math"
+	"math/big"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+type randSource struct {
+	source rand.Source
+	sync.Mutex
+}
+
+func newRandSource() (*randSource, error) {
+	var seed int64
+
+	max := big.NewInt(math.MaxInt64)
+	n, err := cryptorand.Int(cryptorand.Reader, max)
+	if err == nil {
+		seed = n.Int64()
+	} else {
+		log.Printf("cannot generate random seed: %v; using current time\n", err)
+		seed = time.Now().UnixNano()
+	}
+
+	source := rand.NewSource(seed)
+
+	return &randSource{source: source}, nil
+}
+
+func (rs *randSource) Int63() int64 {
+	rs.Lock()
+	n := rs.source.Int63()
+	rs.Unlock()
+
+	return n
+}
+
+func (rs *randSource) Seed(seed int64) {
+	rs.Lock()
+	rs.Seed(seed)
+	rs.Unlock()
+}

tracer/span.go

@@ -3,7 +3,6 @@ package tracer
 import (
 	"context"
 	"fmt"
-	"math/rand"
 	"reflect"
 	"runtime/debug"
 	"strings"
@@ -221,11 +220,6 @@ func (s *Span) Tracer() *Tracer {
 	return s.tracer
 }
 
-// nextSpanID returns a new random span id.
-func nextSpanID() uint64 {
-	return uint64(rand.Int63())
-}
-
 // now returns current UTC time in nanos.
 func now() int64 {
 	return time.Now().UTC().UnixNano()

tracer/tracer.go

@@ -1,11 +1,12 @@
 package tracer
 
 import (
+	"context"
+	"fmt"
 	"log"
+	"math/rand"
 	"sync"
 	"time"
-
-	"context"
 )
 
 const (
@@ -42,6 +43,8 @@ type Tracer struct {
 
 	exit   chan struct{}
 	exitWG *sync.WaitGroup
+
+	randGen *rand.Rand
 }
 
 // NewTracer creates a new Tracer. Most users should use the package's
@@ -52,6 +55,12 @@ func NewTracer() *Tracer {
 
 // NewTracerTransport create a new Tracer with the given transport.
 func NewTracerTransport(transport Transport) *Tracer {
+	randSource, err := newRandSource()
+	if err != nil {
+		panic(fmt.Sprintf("cannot create random source: %v", err))
+	}
+	randGen := rand.New(randSource)
+
 	t := &Tracer{
 		enabled:             true,
 		transport:           transport,
@@ -64,6 +73,8 @@ func NewTracerTransport(transport Transport) *Tracer {
 
 		exit:   make(chan struct{}),
 		exitWG: &sync.WaitGroup{},
+
+		randGen: randGen,
 	}
 
 	// start a background worker
@@ -132,7 +143,7 @@ func (t *Tracer) SetServiceInfo(name, app, appType string) {
 // NewRootSpan creates a span with no parent. Its ids will be randomly
 // assigned.
 func (t *Tracer) NewRootSpan(name, service, resource string) *Span {
-	spanID := nextSpanID()
+	spanID := t.nextSpanID()
 	span := NewSpan(name, service, resource, spanID, spanID, 0, t)
 	t.sampler.Sample(span)
 	return span
@@ -141,7 +152,7 @@ func (t *Tracer) NewRootSpan(name, service, resource string) *Span {
 // NewChildSpan returns a new span that is child of the Span passed as
 // argument.
 func (t *Tracer) NewChildSpan(name string, parent *Span) *Span {
-	spanID := nextSpanID()
+	spanID := t.nextSpanID()
 
 	// when we're using parenting in inner functions, it's possible that
 	// a nil pointer is sent to this function as argument. To prevent a crash,
@@ -212,6 +223,11 @@ func (t *Tracer) FlushTraces() error {
 	return err
 }
 
+// nextSpanID returns a new random span id.
+func (t *Tracer) nextSpanID() uint64 {
+	return uint64(t.randGen.Int63())
+}
+
 func (t *Tracer) flushServices() error {
 	if !t.Enabled() || !t.servicesModified {
 		return nil

tracer/transport_test.go

@@ -60,7 +60,7 @@ func TestTracesAgentIntegration(t *testing.T) {
 	for _, tc := range testCases {
 		transport := newHTTPTransport(defaultHostname, defaultPort)
 		response, err := transport.SendTraces(tc.payload)
-		assert.Nil(err)
+		assert.NoError(err)
 		assert.NotNil(response)
 		assert.Equal(200, response.StatusCode)
 	}
@@ -74,7 +74,7 @@ func TestAPIDowngrade(t *testing.T) {
 	// if we get a 404 we should downgrade the API
 	traces := getTestTrace(2, 2)
 	response, err := transport.SendTraces(traces)
-	assert.Nil(err)
+	assert.NoError(err)
 	assert.NotNil(response)
 	assert.Equal(200, response.StatusCode)
 }
@@ -87,7 +87,7 @@ func TestEncoderDowngrade(t *testing.T) {
 	// if we get a 415 because of a wrong encoder, we should downgrade the encoder
 	traces := getTestTrace(2, 2)
 	response, err := transport.SendTraces(traces)
-	assert.Nil(err)
+	assert.NoError(err)
 	assert.NotNil(response)
 	assert.Equal(200, response.StatusCode)
 }
@@ -98,7 +98,7 @@ func TestTransportServices(t *testing.T) {
 	transport := newHTTPTransport(defaultHostname, defaultPort)
 
 	response, err := transport.SendServices(getTestServices())
-	assert.Nil(err)
+	assert.NoError(err)
 	assert.NotNil(response)
 	assert.Equal(200, response.StatusCode)
 }
@@ -110,7 +110,7 @@ func TestTransportServicesDowngrade_0_0(t *testing.T) {
 	transport.serviceURL = "http://localhost:8126/v0.0/services"
 
 	response, err := transport.SendServices(getTestServices())
-	assert.Nil(err)
+	assert.NoError(err)
 	assert.NotNil(response)
 	assert.Equal(200, response.StatusCode)
 }
@@ -122,7 +122,7 @@ func TestTransportServicesDowngrade_0_2(t *testing.T) {
 	transport.serviceURL = "http://localhost:8126/v0.2/services"
 
 	response, err := transport.SendServices(getTestServices())
-	assert.Nil(err)
+	assert.NoError(err)
 	assert.NotNil(response)
 	assert.Equal(200, response.StatusCode)
 }