feat: Add client-prereq-events capability

docs/service_spec.md

@@ -60,6 +60,14 @@ This means that the SDK supports Big Segments and can be configured with a custo
 
 For tests that involve Big Segments, the test harness will provide parameters in the `bigSegments` property of the configuration object, including a `callbackUri` that points to one of the test harness's callback services (see [Callback endpoints](#callback-endpoints)). The test service should configure the SDK with its own implementation of a Big Segment store, where every method of the store delegates to a corresponding endpoint in the callback service.
 
+#### Capability `"client-prereq-events"`
+
+This means that the SDK supports client-side prerequisite events.
+
+In short, this means that a client SDK emits prerequisite evaluation events along side the main evaluation event. This requires an updated understanding of the flag evaluation model.
+
+For server side SDKs, this means `allFlagData` will reflect that updated flag evaluation model.
+
 #### Capability `"context-type"`
 
 This means that the SDK has its own type for evaluation contexts (as opposed to just representing them as a JSON-equivalent generic data structure) and convert that type to and from JSON.

mockld/sdk_data.go

@@ -78,6 +78,7 @@ type ClientSDKFlag struct {
 	TrackEvents          bool                                `json:"trackEvents"`
 	TrackReason          bool                                `json:"trackReason"`
 	DebugEventsUntilDate o.Maybe[ldtime.UnixMillisecondTime] `json:"debugEventsUntilDate"`
+	Prerequisites        []string                            `json:"prerequisites"`
 }
 
 // ClientSDKFlagWithKey is used only in stream updates, where the key is within the same object.

sdktests/client_side_events_all.go

@@ -22,6 +22,9 @@ func doClientSideEventTests(t *ldtest.T) {
 	t.Run("context properties", doClientSideEventContextTests)
 	t.Run("event capacity", doClientSideEventBufferTests)
 	t.Run("disabling", doClientSideEventDisableTests)
+
+	t.RequireCapability(servicedef.CapabilityClientPrereqEvents)
+	t.Run("prerequisite events emit in order", doClientSideInOrderPrereqEventTests)
 }
 
 func doClientSideEventRequestTests(t *ldtest.T) {

sdktests/client_side_events_eval.go

@@ -6,6 +6,7 @@ import (
 	"github.com/launchdarkly/sdk-test-harness/v2/data"
 	h "github.com/launchdarkly/sdk-test-harness/v2/framework/helpers"
 	"github.com/launchdarkly/sdk-test-harness/v2/framework/ldtest"
+	o "github.com/launchdarkly/sdk-test-harness/v2/framework/opt"
 	"github.com/launchdarkly/sdk-test-harness/v2/mockld"
 	"github.com/launchdarkly/sdk-test-harness/v2/servicedef"
 
@@ -253,6 +254,79 @@ func doClientSideFeatureEventTests(t *ldtest.T) {
 	})
 }
 
+func doClientSideInOrderPrereqEventTests(t *ldtest.T) {
+	dataBuilder := mockld.NewClientSDKDataBuilder()
+	dataBuilder.
+		Flag("topLevel", mockld.ClientSDKFlag{
+			Value:         ldvalue.String("value1"),
+			Variation:     o.Some(0),
+			TrackEvents:   true,
+			Prerequisites: []string{"prereq1", "preqreq2"},
+		}).
+		Flag("prereq1", mockld.ClientSDKFlag{
+			Value:         ldvalue.String("value2"),
+			TrackEvents:   true,
+			Variation:     o.Some(0),
+			Prerequisites: []string{"prereq2"},
+		}).
+		Flag("prereq2", mockld.ClientSDKFlag{
+			Value:       ldvalue.String("value3"),
+			TrackEvents: true,
+			Variation:   o.Some(0),
+		})
+	dataSource := NewSDKDataSource(t, dataBuilder.Build())
+	context := ldcontext.New("user")
+
+	events := NewSDKEventSink(t)
+	client := NewSDKClient(t,
+		WithClientSideInitialContext(context),
+		dataSource, events)
+
+	_ = client.EvaluateFlag(t, servicedef.EvaluateFlagParams{
+		FlagKey:      "topLevel",
+		DefaultValue: ldvalue.Null(),
+		ValueType:    servicedef.ValueTypeAny,
+	})
+
+	client.FlushEvents(t)
+	payload := events.ExpectAnalyticsEvents(t, defaultEventTimeout)
+
+	prereq2FeatureEvent := IsValidFeatureEventWithConditions(
+		t, false, context,
+		m.JSONProperty("key").Should(m.Equal("prereq2")),
+		m.JSONProperty("version").Should(m.Equal(0)),
+		m.JSONProperty("value").Should(m.JSONEqual(ldvalue.String("value3"))),
+		m.JSONOptProperty("variation").Should(m.JSONEqual(0)),
+		JSONPropertyNullOrAbsent("prereqOf"),
+	)
+
+	prereq1FeatureEvent := IsValidFeatureEventWithConditions(
+		t, false, context,
+		m.JSONProperty("key").Should(m.Equal("prereq1")),
+		m.JSONProperty("version").Should(m.Equal(0)),
+		m.JSONProperty("value").Should(m.JSONEqual(ldvalue.String("value2"))),
+		m.JSONOptProperty("variation").Should(m.JSONEqual(0)),
+		JSONPropertyNullOrAbsent("prereqOf"),
+	)
+
+	topLevelFeatureEvent := IsValidFeatureEventWithConditions(
+		t, false, context,
+		m.JSONProperty("key").Should(m.Equal("topLevel")),
+		m.JSONProperty("version").Should(m.Equal(0)),
+		m.JSONProperty("value").Should(m.JSONEqual(ldvalue.String("value1"))),
+		m.JSONOptProperty("variation").Should(m.JSONEqual(0)),
+		JSONPropertyNullOrAbsent("prereqOf"),
+	)
+
+	m.In(t).Assert(payload, m.ItemsInAnyOrder(
+		IsIdentifyEventForContext(context),
+		prereq2FeatureEvent,
+		prereq1FeatureEvent,
+		topLevelFeatureEvent,
+		IsSummaryEvent(),
+	))
+}
+
 func doClientSideDebugEventTests(t *ldtest.T) {
 	// These tests could misbehave if the system clocks of the host that's running the test harness
 	// and the host that's running the test service are out of sync by at least an hour. However,

sdktests/client_side_events_summary.go

@@ -21,6 +21,12 @@ func doClientSideSummaryEventTests(t *ldtest.T) {
 	t.Run("context kinds", doClientSideSummaryEventContextKindsTest)
 	t.Run("unknown flag", doClientSideSummaryEventUnknownFlagTest)
 	t.Run("reset after each flush", doClientSideSummaryEventResetTest)
+
+	t.Run("prerequisites", func(t *ldtest.T) {
+		t.RequireCapability(servicedef.CapabilityClientPrereqEvents)
+		t.Run("basic behavior", doClientSideSummaryBasicPrereqTest)
+		t.Run("emits unknown event", doClientSideSummaryPrereqUnknownFlagTest)
+	})
 }
 
 func doClientSideSummaryEventBasicTest(t *ldtest.T) {
@@ -276,3 +282,148 @@ func doClientSideSummaryEventResetTest(t *ldtest.T) {
 		)),
 	)
 }
+
+func doClientSideSummaryBasicPrereqTest(t *ldtest.T) {
+	topLevelKey := "flag1"
+	topLevelResult := mockld.ClientSDKFlag{
+		Value:         ldvalue.String("value1-a"),
+		Variation:     o.Some(0),
+		FlagVersion:   o.Some(1),
+		Version:       11,
+		Prerequisites: []string{"prereq1", "prereq2"},
+	}
+
+	prereq1Key := "prereq1"
+	prereq1Result := mockld.ClientSDKFlag{
+		Value:         ldvalue.String("prereq1"),
+		Variation:     o.Some(0),
+		FlagVersion:   o.Some(1),
+		Version:       11,
+		Prerequisites: []string{"prereq3"},
+	}
+
+	prereq2Key := "prereq2"
+	prereq2Result := mockld.ClientSDKFlag{
+		Value:       ldvalue.String("prereq2"),
+		Variation:   o.Some(0),
+		FlagVersion: o.Some(1),
+		Version:     11,
+	}
+
+	prereq3Key := "prereq3"
+	prereq3Result := mockld.ClientSDKFlag{
+		Value:       ldvalue.String("prereq3"),
+		Variation:   o.Some(0),
+		FlagVersion: o.Some(1),
+		Version:     11,
+	}
+
+	contextA := ldcontext.New("user-a")
+	default1 := ldvalue.String("default1")
+	default2 := ldvalue.String("default2")
+	default3 := ldvalue.String("default3")
+
+	dataBuilder := mockld.NewClientSDKDataBuilder()
+	dataBuilder.Flag(topLevelKey, topLevelResult).
+		Flag(prereq1Key, prereq1Result).
+		Flag(prereq2Key, prereq2Result).
+		Flag(prereq3Key, prereq3Result)
+
+	dataSource := NewSDKDataSource(t, dataBuilder.Build())
+	events := NewSDKEventSinkWithGzip(t, t.Capabilities().Has(servicedef.CapabilityEventGzip))
+	client := NewSDKClient(t,
+		WithClientSideInitialContext(contextA),
+		dataSource, events)
+
+	_ = client.EvaluateFlag(t, servicedef.EvaluateFlagParams{FlagKey: prereq1Key, DefaultValue: default1})
+	_ = client.EvaluateFlag(t, servicedef.EvaluateFlagParams{FlagKey: topLevelKey, DefaultValue: default2})
+	_ = client.EvaluateFlag(t, servicedef.EvaluateFlagParams{FlagKey: prereq2Key, DefaultValue: default3})
+
+	client.FlushEvents(t)
+	payload := events.ExpectAnalyticsEvents(t, defaultEventTimeout)
+
+	m.In(t).Assert(payload, m.ItemsInAnyOrder(
+		IsIdentifyEventForContext(contextA),
+		IsValidSummaryEventWithFlags(
+			m.KV(topLevelKey, m.MapOf(
+				// Was first evaluated through the EvaluateFlag call, so it has a default value.
+				m.KV("default", m.JSONEqual(default2)),
+				m.KV("counters", m.ItemsInAnyOrder(
+					flagCounter(topLevelResult.Value, topLevelResult.Variation.Value(), topLevelResult.FlagVersion.Value(), 1),
+				)),
+				m.KV("contextKinds", anyContextKindsList()),
+			)),
+			m.KV(prereq1Key, m.MapOf(
+				// Was first evaluated through the EvaluateFlag call, so it has a default value.
+				m.KV("default", m.JSONEqual(default1)),
+				m.KV("counters", m.ItemsInAnyOrder(
+					flagCounter(prereq1Result.Value, prereq1Result.Variation.Value(), prereq1Result.FlagVersion.Value(), 2),
+				)),
+				m.KV("contextKinds", anyContextKindsList()),
+			)),
+			m.KV(prereq2Key, m.MapOf(
+				m.KV("counters", m.ItemsInAnyOrder(
+					flagCounter(prereq2Result.Value, prereq2Result.Variation.Value(), prereq2Result.FlagVersion.Value(), 2),
+				)),
+				m.KV("contextKinds", anyContextKindsList()),
+			)),
+			m.KV(prereq3Key, m.MapOf(
+				m.KV("counters", m.ItemsInAnyOrder(
+					flagCounter(prereq3Result.Value, prereq3Result.Variation.Value(), prereq3Result.FlagVersion.Value(), 2),
+				)),
+				m.KV("contextKinds", anyContextKindsList()),
+			)),
+		)),
+	)
+}
+
+func doClientSideSummaryPrereqUnknownFlagTest(t *ldtest.T) {
+	topLevelKey := "flag1"
+	topLevelResult := mockld.ClientSDKFlag{
+		Value:         ldvalue.String("value1-a"),
+		Variation:     o.Some(0),
+		FlagVersion:   o.Some(1),
+		Version:       11,
+		Prerequisites: []string{"unknown"},
+	}
+
+	contextA := ldcontext.New("user-a")
+	default1 := ldvalue.String("default1")
+
+	dataBuilder := mockld.NewClientSDKDataBuilder()
+	dataBuilder.Flag(topLevelKey, topLevelResult)
+
+	dataSource := NewSDKDataSource(t, dataBuilder.Build())
+	events := NewSDKEventSinkWithGzip(t, t.Capabilities().Has(servicedef.CapabilityEventGzip))
+	client := NewSDKClient(t,
+		WithClientSideInitialContext(contextA),
+		dataSource, events)
+
+	_ = client.EvaluateFlag(t, servicedef.EvaluateFlagParams{FlagKey: topLevelKey, DefaultValue: default1})
+
+	client.FlushEvents(t)
+	payload := events.ExpectAnalyticsEvents(t, defaultEventTimeout)
+
+	m.In(t).Assert(payload, m.ItemsInAnyOrder(
+		IsIdentifyEventForContext(contextA),
+		IsValidSummaryEventWithFlags(
+			m.KV(topLevelKey, m.MapOf(
+				// Was first evaluated through the EvaluateFlag call, so it has a default value.
+				m.KV("default", m.JSONEqual(default1)),
+				m.KV("counters", m.ItemsInAnyOrder(
+					flagCounter(topLevelResult.Value, topLevelResult.Variation.Value(), topLevelResult.FlagVersion.Value(), 1),
+				)),
+				m.KV("contextKinds", anyContextKindsList()),
+			)),
+			m.KV("unknown", m.AllOf(
+				m.JSONOptProperty("default").Should(m.BeNil()),
+				m.MapIncluding(
+					m.KV("counters", m.ItemsInAnyOrder(
+						unknownFlagCounter(ldvalue.Null(), 1),
+					)),
+					m.KV("contextKinds", anyContextKindsList()),
+				),
+			)),
+		)),
+	)
+}