feat: Add support for Dynamic Sampling

.craft.yml

@@ -1,6 +1,5 @@
 minVersion: 0.23.1
-preReleaseCommand: bash scripts/craft-pre-release.sh
-changelogPolicy: auto
+changelogPolicy: simple
 artifactProvider:
   name: none
 targets:

client.go

@@ -624,12 +624,12 @@ func (client *Client) prepareEvent(event *Event, hint *EventHint, scope EventMod
 
 	event.Platform = "go"
 	event.Sdk = SdkInfo{
-		Name:         "sentry.go",
-		Version:      Version,
+		Name:         SDKIdentifier,
+		Version:      SDKVersion,
 		Integrations: client.listIntegrations(),
 		Packages: []SdkPackage{{
 			Name:    "sentry-go",
-			Version: Version,
+			Version: SDKVersion,
 		}},
 	}
 

client_test.go

@@ -78,11 +78,15 @@ func TestCaptureMessageEmptyString(t *testing.T) {
 		},
 	}
 	got := transport.lastEvent
-	opts := cmp.Transformer("SimplifiedEvent", func(e *Event) *Event {
-		return &Event{
-			Exception: e.Exception,
-		}
-	})
+	opts := cmp.Options{
+		cmpopts.IgnoreFields(Event{}, "sdkMetaData"),
+		cmp.Transformer("SimplifiedEvent", func(e *Event) *Event {
+			return &Event{
+				Exception: e.Exception,
+			}
+		}),
+	}
+
 	if diff := cmp.Diff(want, got, opts); diff != "" {
 		t.Errorf("(-want +got):\n%s", diff)
 	}
@@ -266,14 +270,14 @@ func TestCaptureEvent(t *testing.T) {
 		Platform:   "go",
 		Sdk: SdkInfo{
 			Name:         "sentry.go",
-			Version:      Version,
+			Version:      SDKVersion,
 			Integrations: []string{},
 			Packages: []SdkPackage{
 				{
 					// FIXME: name format doesn't follow spec in
 					// https://docs.sentry.io/development/sdk-dev/event-payloads/sdk/
 					Name:    "sentry-go",
-					Version: Version,
+					Version: SDKVersion,
 				},
 				// TODO: perhaps the list of packages is incomplete or there
 				// should not be any package at all. We may include references
@@ -282,7 +286,7 @@ func TestCaptureEvent(t *testing.T) {
 		},
 	}
 	got := transport.lastEvent
-	opts := cmp.Options{cmpopts.IgnoreFields(Event{}, "Release")}
+	opts := cmp.Options{cmpopts.IgnoreFields(Event{}, "Release", "sdkMetaData")}
 	if diff := cmp.Diff(want, got, opts); diff != "" {
 		t.Errorf("Event mismatch (-want +got):\n%s", diff)
 	}
@@ -309,11 +313,14 @@ func TestCaptureEventNil(t *testing.T) {
 		},
 	}
 	got := transport.lastEvent
-	opts := cmp.Transformer("SimplifiedEvent", func(e *Event) *Event {
-		return &Event{
-			Exception: e.Exception,
-		}
-	})
+	opts := cmp.Options{
+		cmpopts.IgnoreFields(Event{}, "sdkMetaData"),
+		cmp.Transformer("SimplifiedEvent", func(e *Event) *Event {
+			return &Event{
+				Exception: e.Exception,
+			}
+		}),
+	}
 	if diff := cmp.Diff(want, got, opts); diff != "" {
 		t.Errorf("(-want +got):\n%s", diff)
 	}
@@ -476,13 +483,17 @@ func TestRecover(t *testing.T) {
 			t.Fatalf("events = %s\ngot %d events, want 1", b, len(events))
 		}
 		got := events[0]
-		opts := cmp.Transformer("SimplifiedEvent", func(e *Event) *Event {
-			return &Event{
-				Message:   e.Message,
-				Exception: e.Exception,
-				Level:     e.Level,
-			}
-		})
+		opts := cmp.Options{
+			cmpopts.IgnoreFields(Event{}, "sdkMetaData"),
+			cmp.Transformer("SimplifiedEvent", func(e *Event) *Event {
+				return &Event{
+					Message:   e.Message,
+					Exception: e.Exception,
+					Level:     e.Level,
+				}
+			}),
+		}
+
 		if diff := cmp.Diff(want, got, opts); diff != "" {
 			t.Errorf("(-want +got):\n%s", diff)
 		}

dynamic_sampling_context.go

@@ -0,0 +1,45 @@
+package sentry
+
+import (
+	"strings"
+
+	"github.com/getsentry/sentry-go/internal/otel/baggage"
+)
+
+const (
+	sentryPrefix = "sentry-"
+)
+
+// DynamicSamplingContext holds information about the current event that can be used to make dynamic sampling decisions.
+type DynamicSamplingContext struct {
+	Entries map[string]string
+	Frozen  bool
+}
+
+func NewDynamicSamplingContext(header []byte) (DynamicSamplingContext, error) {
+	bag, err := baggage.Parse(string(header))
+	if err != nil {
+		return DynamicSamplingContext{}, err
+	}
+
+	entries := map[string]string{}
+	for _, member := range bag.Members() {
+		// We only store baggage members if their key starts with "sentry-".
+		if k, v := member.Key(), member.Value(); strings.HasPrefix(k, sentryPrefix) {
+			entries[strings.TrimPrefix(k, sentryPrefix)] = v
+		}
+	}
+
+	return DynamicSamplingContext{
+		Entries: entries,
+		Frozen:  true,
+	}, nil
+}
+
+func (d DynamicSamplingContext) HasEntries() bool {
+	return len(d.Entries) > 0
+}
+
+func (d DynamicSamplingContext) String() string {
+	return ""
+}

dynamic_sampling_context_test.go

@@ -0,0 +1,50 @@
+package sentry
+
+import (
+	"testing"
+)
+
+func TestNewDynamicSamplingContext(t *testing.T) {
+	tests := []struct {
+		input []byte
+		want  DynamicSamplingContext
+	}{
+		{
+			input: []byte(""),
+			want: DynamicSamplingContext{
+				Frozen:  true,
+				Entries: map[string]string{},
+			},
+		},
+		{
+			input: []byte("sentry-trace_id=d49d9bf66f13450b81f65bc51cf49c03,sentry-public_key=public,sentry-sample_rate=1"),
+			want: DynamicSamplingContext{
+				Frozen: true,
+				Entries: map[string]string{
+					"trace_id":    "d49d9bf66f13450b81f65bc51cf49c03",
+					"public_key":  "public",
+					"sample_rate": "1",
+				},
+			},
+		},
+		{
+			input: []byte("sentry-trace_id=d49d9bf66f13450b81f65bc51cf49c03,sentry-public_key=public,sentry-sample_rate=1,foo=bar;foo;bar;bar=baz"),
+			want: DynamicSamplingContext{
+				Frozen: true,
+				Entries: map[string]string{
+					"trace_id":    "d49d9bf66f13450b81f65bc51cf49c03",
+					"public_key":  "public",
+					"sample_rate": "1",
+				},
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		got, err := NewDynamicSamplingContext(tc.input)
+		if err != nil {
+			t.Fatal(err)
+		}
+		assertEqual(t, got, tc.want)
+	}
+}

fasthttp/sentryfasthttp_test.go

@@ -208,6 +208,7 @@ func TestIntegration(t *testing.T) {
 			sentry.Event{},
 			"Contexts", "EventID", "Extra", "Platform", "Modules",
 			"Release", "Sdk", "ServerName", "Tags", "Timestamp",
+			"sdkMetaData",
 		),
 		cmpopts.IgnoreMapEntries(func(k string, v string) bool {
 			// fasthttp changed Content-Length behavior in

http/sentryhttp_test.go

@@ -216,6 +216,7 @@ func TestIntegration(t *testing.T) {
 			sentry.Event{},
 			"Contexts", "EventID", "Extra", "Platform", "Modules",
 			"Release", "Sdk", "ServerName", "Tags", "Timestamp",
+			"sdkMetaData",
 		),
 		cmpopts.IgnoreFields(
 			sentry.Request{},

interfaces.go

@@ -215,6 +215,12 @@ type Exception struct {
 	Stacktrace *Stacktrace `json:"stacktrace,omitempty"`
 }
 
+// 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
+}
+
 // EventID is a hexadecimal string representing a unique uuid4 for an Event.
 // An EventID must be 32 characters long, lowercase and not have any dashes.
 type EventID string
@@ -251,6 +257,10 @@ type Event struct {
 	Type      string    `json:"type,omitempty"`
 	StartTime time.Time `json:"start_timestamp"`
 	Spans     []*Span   `json:"spans,omitempty"`
+
+	// The fields below are not part of the final JSON payload.
+
+	sdkMetaData SDKMetaData
 }
 
 // TODO: Event.Contexts map[string]interface{} => map[string]EventContext,