[Dynamic Sampling] Head of trace (#492)

Co-authored-by: Abhijeet Prasad <[email protected]>

dynamic_sampling_context.go

@@ -1,6 +1,7 @@
 package sentry
 
 import (
+	"strconv"
 	"strings"
 
 	"github.com/getsentry/sentry-go/internal/otel/baggage"
@@ -16,7 +17,7 @@ type DynamicSamplingContext struct {
 	Frozen  bool
 }
 
-func NewDynamicSamplingContext(header []byte) (DynamicSamplingContext, error) {
+func DynamicSamplingContextFromHeader(header []byte) (DynamicSamplingContext, error) {
 	bag, err := baggage.Parse(string(header))
 	if err != nil {
 		return DynamicSamplingContext{}, err
@@ -36,10 +37,58 @@ func NewDynamicSamplingContext(header []byte) (DynamicSamplingContext, error) {
 	}, nil
 }
 
+func DynamicSamplingContextFromTransaction(span *Span) DynamicSamplingContext {
+	entries := map[string]string{}
+
+	hub := hubFromContext(span.Context())
+	scope := hub.Scope()
+	client := hub.Client()
+	options := client.Options()
+
+	if traceID := span.TraceID.String(); traceID != "" {
+		entries["trace_id"] = traceID
+	}
+	if sampleRate := span.sampleRate; sampleRate != 0 {
+		entries["sample_rate"] = strconv.FormatFloat(sampleRate, 'f', -1, 64)
+	}
+
+	if dsn := client.dsn; dsn != nil {
+		if publicKey := dsn.publicKey; publicKey != "" {
+			entries["public_key"] = publicKey
+		}
+	}
+	if release := options.Release; release != "" {
+		entries["release"] = release
+	}
+	if environment := options.Environment; environment != "" {
+		entries["environment"] = environment
+	}
+
+	// Only include the transaction name if it's of good quality (not empty and not SourceURL)
+	if span.Source != "" && span.Source != SourceURL {
+		if transactionName := scope.Transaction(); transactionName != "" {
+			entries["transaction"] = transactionName
+		}
+	}
+
+	if userSegment := scope.user.Segment; userSegment != "" {
+		entries["user_segment"] = userSegment
+	}
+
+	return DynamicSamplingContext{
+		Entries: entries,
+		Frozen:  true,
+	}
+}
+
 func (d DynamicSamplingContext) HasEntries() bool {
 	return len(d.Entries) > 0
 }
 
+func (d DynamicSamplingContext) IsFrozen() bool {
+	return d.Frozen
+}
+
 func (d DynamicSamplingContext) String() string {
 	// TODO implement me
 	return ""

dynamic_sampling_context_test.go

@@ -4,7 +4,7 @@ import (
 	"testing"
 )
 
-func TestNewDynamicSamplingContext(t *testing.T) {
+func TestDynamicSamplingContextFromHeader(t *testing.T) {
 	tests := []struct {
 		input []byte
 		want  DynamicSamplingContext
@@ -41,10 +41,90 @@ func TestNewDynamicSamplingContext(t *testing.T) {
 	}
 
 	for _, tc := range tests {
-		got, err := NewDynamicSamplingContext(tc.input)
+		got, err := DynamicSamplingContextFromHeader(tc.input)
 		if err != nil {
 			t.Fatal(err)
 		}
 		assertEqual(t, got, tc.want)
 	}
 }
+
+func TestDynamicSamplingContextFromTransaction(t *testing.T) {
+	tests := []struct {
+		input *Span
+		want  DynamicSamplingContext
+	}{
+		// Normal flow
+		{
+			input: func() *Span {
+				ctx := NewTestContext(ClientOptions{
+					EnableTracing:    true,
+					TracesSampleRate: 0.5,
+					Dsn:              "http://[email protected]/sentry/1",
+					Release:          "1.0.0",
+					Environment:      "test",
+				})
+				hubFromContext(ctx).ConfigureScope(func(scope *Scope) {
+					scope.SetUser(User{Segment: "user_segment"})
+				})
+				txn := StartTransaction(ctx, "name", TransctionSource(SourceCustom))
+				txn.TraceID = TraceIDFromHex("d49d9bf66f13450b81f65bc51cf49c03")
+				return txn
+			}(),
+			want: DynamicSamplingContext{
+				Frozen: true,
+				Entries: map[string]string{
+					"sample_rate":  "0.5",
+					"trace_id":     "d49d9bf66f13450b81f65bc51cf49c03",
+					"public_key":   "public",
+					"release":      "1.0.0",
+					"environment":  "test",
+					"transaction":  "name",
+					"user_segment": "user_segment",
+				},
+			},
+		},
+		// Transaction with source url, do not include in Dynamic Sampling context
+		{
+			input: func() *Span {
+				ctx := NewTestContext(ClientOptions{
+					EnableTracing:    true,
+					TracesSampleRate: 0.5,
+					Dsn:              "http://[email protected]/sentry/1",
+					Release:          "1.0.0",
+				})
+				txn := StartTransaction(ctx, "name")
+				txn.TraceID = TraceIDFromHex("d49d9bf66f13450b81f65bc51cf49c03")
+				return txn
+			}(),
+			want: DynamicSamplingContext{
+				Frozen: true,
+				Entries: map[string]string{
+					"sample_rate": "0.5",
+					"trace_id":    "d49d9bf66f13450b81f65bc51cf49c03",
+					"public_key":  "public",
+					"release":     "1.0.0",
+				},
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		got := DynamicSamplingContextFromTransaction(tc.input)
+		assertEqual(t, got, tc.want)
+	}
+}
+
+func TestHasEntries(t *testing.T) {
+	var dsc DynamicSamplingContext
+
+	dsc = DynamicSamplingContext{}
+	assertEqual(t, dsc.HasEntries(), false)
+
+	dsc = DynamicSamplingContext{
+		Entries: map[string]string{
+			"foo": "bar",
+		},
+	}
+	assertEqual(t, dsc.HasEntries(), true)
+}

http/sentryhttp.go

@@ -71,9 +71,9 @@ func (h *Handler) Handle(handler http.Handler) http.Handler {
 // where that is convenient. In particular, use it to wrap a handler function
 // literal.
 //
-//  http.Handle(pattern, h.HandleFunc(func (w http.ResponseWriter, r *http.Request) {
-//      // handler code here
-//  }))
+//	http.Handle(pattern, h.HandleFunc(func (w http.ResponseWriter, r *http.Request) {
+//	    // handler code here
+//	}))
 func (h *Handler) HandleFunc(handler http.HandlerFunc) http.HandlerFunc {
 	return h.handle(handler)
 }
@@ -89,6 +89,7 @@ func (h *Handler) handle(handler http.Handler) http.HandlerFunc {
 		options := []sentry.SpanOption{
 			sentry.OpName("http.server"),
 			sentry.ContinueFromRequest(r),
+			sentry.TransctionSource(sentry.SourceURL),
 		}
 		// We don't mind getting an existing transaction back so we don't need to
 		// check if it is.

interfaces.go

@@ -218,7 +218,8 @@ type Exception struct {
 // SDKMetaData is a struct to stash data which is needed at some point in the SDK's event processing pipeline
 // but which shouldn't get send to Sentry.
 type SDKMetaData struct {
-	dsc DynamicSamplingContext
+	dsc               DynamicSamplingContext
+	transactionSource TransactionSource
 }
 
 // EventID is a hexadecimal string representing a unique uuid4 for an Event.

tracing.go

@@ -28,25 +28,23 @@ type Span struct { //nolint: maligned // prefer readability over optimal memory
 	StartTime    time.Time              `json:"start_timestamp"`
 	EndTime      time.Time              `json:"timestamp"`
 	Data         map[string]interface{} `json:"data,omitempty"`
+	Sampled      Sampled                `json:"-"`
+	Source       TransactionSource      `json:"-"`
 
-	Sampled Sampled `json:"-"`
-
+	// sample rate the span was sampled with.
+	sampleRate float64
 	// ctx is the context where the span was started. Always non-nil.
 	ctx context.Context
-
 	// Dynamic Sampling context
 	dynamicSamplingContext DynamicSamplingContext
-
 	// parent refers to the immediate local parent span. A remote parent span is
 	// only referenced by setting ParentSpanID.
 	parent *Span
-
 	// isTransaction is true only for the root span of a local span tree. The
 	// root span is the first span started in a context. Note that a local root
 	// span may have a remote parent belonging to the same trace, therefore
 	// isTransaction depends on ctx and not on parent.
 	isTransaction bool
-
 	// recorder stores all spans in a transaction. Guaranteed to be non-nil.
 	recorder *spanRecorder
 }
@@ -141,7 +139,6 @@ func StartSpan(ctx context.Context, operation string, options ...SpanOption) *Sp
 		option(&span)
 	}
 
-	// TODO only sample transactions?
 	span.Sampled = span.sample()
 
 	if hasParent {
@@ -273,7 +270,7 @@ func (s *Span) updateFromSentryTrace(header []byte) {
 
 func (s *Span) updateFromBaggage(header []byte) {
 	if s.isTransaction {
-		dsc, err := NewDynamicSamplingContext(header)
+		dsc, err := DynamicSamplingContextFromHeader(header)
 		if err != nil {
 			return
 		}
@@ -311,12 +308,19 @@ func (s *Span) sample() Sampled {
 	// #1 tracing is not enabled.
 	if !clientOptions.EnableTracing {
 		Logger.Printf("Dropping transaction: EnableTracing is set to %t", clientOptions.EnableTracing)
+		s.sampleRate = 0.0
 		return SampledFalse
 	}
 
 	// #2 explicit sampling decision via StartSpan/StartTransaction options.
 	if s.Sampled != SampledUndefined {
 		Logger.Printf("Using explicit sampling decision from StartSpan/StartTransaction: %v", s.Sampled)
+		switch s.Sampled {
+		case SampledTrue:
+			s.sampleRate = 1.0
+		case SampledFalse:
+			s.sampleRate = 0.0
+		}
 		return s.Sampled
 	}
 
@@ -333,6 +337,7 @@ func (s *Span) sample() Sampled {
 	samplingContext := SamplingContext{Span: s, Parent: s.parent}
 	if sampler != nil {
 		tracesSamplerSampleRate := sampler.Sample(samplingContext)
+		s.sampleRate = tracesSamplerSampleRate
 		if tracesSamplerSampleRate < 0.0 || tracesSamplerSampleRate > 1.0 {
 			Logger.Printf("Dropping transaction: Returned TracesSampler rate is out of range [0.0, 1.0]: %f", tracesSamplerSampleRate)
 			return SampledFalse
@@ -351,11 +356,18 @@ func (s *Span) sample() Sampled {
 	// #4 inherit parent decision.
 	if s.parent != nil {
 		Logger.Printf("Using sampling decision from parent: %v", s.parent.Sampled)
+		switch s.parent.Sampled {
+		case SampledTrue:
+			s.sampleRate = 1.0
+		case SampledFalse:
+			s.sampleRate = 0.0
+		}
 		return s.parent.Sampled
 	}
 
 	// #5 use TracesSampleRate from ClientOptions.
 	sampleRate := clientOptions.TracesSampleRate
+	s.sampleRate = sampleRate
 	if sampleRate < 0.0 || sampleRate > 1.0 {
 		Logger.Printf("Dropping transaction: TracesSamplerRate out of range [0.0, 1.0]: %f", sampleRate)
 		return SampledFalse
@@ -388,6 +400,12 @@ func (s *Span) toEvent() *Event {
 		finished = append(finished, child)
 	}
 
+	// Create and attach a DynamicSamplingContext to the transaction.
+	// If the DynamicSamplingContext is not frozen at this point, we can assume being head of trace.
+	if !s.dynamicSamplingContext.IsFrozen() {
+		s.dynamicSamplingContext = DynamicSamplingContextFromTransaction(s)
+	}
+
 	return &Event{
 		Type:        transactionType,
 		Transaction: hub.Scope().Transaction(),
@@ -400,7 +418,8 @@ func (s *Span) toEvent() *Event {
 		StartTime: s.StartTime,
 		Spans:     finished,
 		sdkMetaData: SDKMetaData{
-			dsc: s.dynamicSamplingContext,
+			dsc:               s.dynamicSamplingContext,
+			transactionSource: s.Source,
 		},
 	}
 }
@@ -459,6 +478,18 @@ var (
 	zeroSpanID  SpanID
 )
 
+// Contains information about how the name of the transaction was determined.
+type TransactionSource string
+
+const (
+	SourceCustom    TransactionSource = "custom"
+	SourceURL       TransactionSource = "url"
+	SourceRoute     TransactionSource = "route"
+	SourceView      TransactionSource = "view"
+	SourceComponent TransactionSource = "component"
+	SourceTask      TransactionSource = "task"
+)
+
 // SpanStatus is the status of a span.
 type SpanStatus uint8
 
@@ -639,13 +670,20 @@ func OpName(name string) SpanOption {
 	}
 }
 
+// TransctionSource sets the source of the transaction name.
+func TransctionSource(source TransactionSource) SpanOption {
+	return func(s *Span) {
+		s.Source = source
+	}
+}
+
 // ContinueFromRequest returns a span option that updates the span to continue
 // an existing trace. If it cannot detect an existing trace in the request, the
 // span will be left unchanged.
 //
 // ContinueFromRequest is an alias for:
 //
-//	ContinueFromHeaders(r.Header.Get("sentry-trace"), r.Header.Get("baggage"))
+// ContinueFromHeaders(r.Header.Get("sentry-trace"), r.Header.Get("baggage")).
 func ContinueFromRequest(r *http.Request) SpanOption {
 	return ContinueFromHeaders(r.Header.Get("sentry-trace"), r.Header.Get("baggage"))
 }