feat: [FD-5561] implement FDv2 polling endpoint GET /sdk/poll

internal/dev_server/db/sqlite.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"io"
 	"os"
+	"strings"
 
 	_ "github.com/mattn/go-sqlite3"
 	"github.com/pkg/errors"
@@ -47,12 +48,15 @@ func (s *Sqlite) GetDevProject(ctx context.Context, key string) (*model.Project,
 	var flagStateData string
 
 	row := s.database.QueryRowContext(ctx, `
-        SELECT key, source_environment_key, context, last_sync_time, flag_state 
-        FROM projects 
+        SELECT key, source_environment_key, context, last_sync_time, flag_state, payload_version
+        FROM projects
         WHERE key = ?
     `, key)
 
-	if err := row.Scan(&project.Key, &project.SourceEnvironmentKey, &contextData, &project.LastSyncTime, &flagStateData); err != nil {
+	if err := row.Scan(
+		&project.Key, &project.SourceEnvironmentKey, &contextData,
+		&project.LastSyncTime, &flagStateData, &project.PayloadVersion,
+	); err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
 			return nil, model.NewErrNotFound("project", key)
 		}
@@ -200,14 +204,15 @@ SELECT 1 FROM projects WHERE key = ?
 		return
 	}
 	_, err = tx.Exec(`
-INSERT INTO projects (key, source_environment_key, context, last_sync_time, flag_state)
-VALUES (?, ?, ?, ?, ?)
+INSERT INTO projects (key, source_environment_key, context, last_sync_time, flag_state, payload_version)
+VALUES (?, ?, ?, ?, ?, ?)
 `,
 		project.Key,
 		project.SourceEnvironmentKey,
 		project.Context.JSONString(),
 		project.LastSyncTime,
 		string(flagsStateJson),
+		project.PayloadVersion,
 	)
 	if err != nil {
 		return
@@ -341,6 +346,20 @@ func (s *Sqlite) UpsertOverride(ctx context.Context, override model.Override) (m
 	return override, nil
 }
 
+func (s *Sqlite) IncrementProjectPayloadVersion(ctx context.Context, projectKey string) (int, error) {
+	row := s.database.QueryRowContext(ctx, `
+		UPDATE projects
+		SET payload_version = payload_version + 1
+		WHERE key = ?
+		RETURNING payload_version
+	`, projectKey)
+	var version int
+	if err := row.Scan(&version); err != nil {
+		return 0, errors.Wrap(err, "unable to increment payload version")
+	}
+	return version, nil
+}
+
 func (s *Sqlite) DeactivateOverride(ctx context.Context, projectKey, flagKey string) (int, error) {
 	row := s.database.QueryRowContext(ctx, `
 		UPDATE overrides
@@ -373,12 +392,12 @@ func (s *Sqlite) RestoreBackup(ctx context.Context, stream io.Reader) (string, e
 	}
 	err = os.Rename(filepath, s.dbPath)
 	if err != nil {
-		//panic because this would really leave the app in an invalid state
+		// panic because this would really leave the app in an invalid state
 		panic(err)
 	}
 	s.database, err = sql.Open("sqlite3", s.dbPath)
 	if err != nil {
-		//panic because this would really leave the app in an invalid state
+		// panic because this would really leave the app in an invalid state
 		panic(err)
 	}
 
@@ -445,12 +464,20 @@ func (s *Sqlite) runMigrations(ctx context.Context) error {
 		source_environment_key text NOT NULL,
 		context text NOT NULL,
 		last_sync_time timestamp NOT NULL,
-		flag_state TEXT NOT NULL
+		flag_state TEXT NOT NULL,
+		payload_version INTEGER NOT NULL DEFAULT 1
 	)`)
 	if err != nil {
 		return err
 	}
 
+	// Migration: add payload_version to existing databases that predate this column.
+	_, err = tx.Exec(`ALTER TABLE projects ADD COLUMN payload_version INTEGER NOT NULL DEFAULT 1`)
+	if err != nil && !strings.Contains(err.Error(), "duplicate column name") {
+		return err
+	}
+	err = nil
+
 	_, err = tx.Exec(`
 	CREATE TABLE IF NOT EXISTS overrides (
 		project_key text NOT NULL,

internal/dev_server/db/sqlite_test.go

@@ -36,6 +36,7 @@ func TestDBFunctions(t *testing.T) {
 			SourceEnvironmentKey: "env-1",
 			Context:              ldContext,
 			LastSyncTime:         now,
+			PayloadVersion:       1,
 			AllFlagsState: model.FlagsState{
 				"flag-1": model.FlagState{Value: ldvalue.Bool(true), Version: 2},
 				"flag-2": model.FlagState{Value: ldvalue.String("cool"), Version: 2},
@@ -71,6 +72,7 @@ func TestDBFunctions(t *testing.T) {
 			SourceEnvironmentKey: "env-2",
 			Context:              ldContext,
 			LastSyncTime:         now,
+			PayloadVersion:       1,
 			AllFlagsState: model.FlagsState{
 				"flag-1": model.FlagState{Value: ldvalue.Int(123), Version: 2},
 				"flag-2": model.FlagState{Value: ldvalue.Float64(99.99), Version: 2},
@@ -97,6 +99,7 @@ func TestDBFunctions(t *testing.T) {
 			SourceEnvironmentKey: "env-3",
 			Context:              ldContext,
 			LastSyncTime:         now,
+			PayloadVersion:       1,
 			AllFlagsState: model.FlagsState{
 				"flag-1": model.FlagState{Value: ldvalue.Int(123), Version: 2},
 				"flag-2": model.FlagState{Value: ldvalue.Float64(99.99), Version: 2},
@@ -169,6 +172,7 @@ func TestDBFunctions(t *testing.T) {
 		assert.Equal(t, expected.SourceEnvironmentKey, p.SourceEnvironmentKey)
 		assert.Equal(t, expected.Context, p.Context)
 		assert.True(t, expected.LastSyncTime.Equal(p.LastSyncTime))
+		assert.Equal(t, expected.PayloadVersion, p.PayloadVersion)
 	})
 
 	t.Run("GetAvailableVariations returns variations", func(t *testing.T) {
@@ -364,6 +368,25 @@ func TestDBFunctions(t *testing.T) {
 		assert.True(t, found)
 	})
 
+	t.Run("IncrementProjectPayloadVersion increments and returns new version", func(t *testing.T) {
+		proj, err := store.GetDevProject(ctx, projects[0].Key)
+		require.NoError(t, err)
+		initialVersion := proj.PayloadVersion
+
+		newVersion, err := store.IncrementProjectPayloadVersion(ctx, projects[0].Key)
+		require.NoError(t, err)
+		assert.Equal(t, initialVersion+1, newVersion)
+
+		proj, err = store.GetDevProject(ctx, projects[0].Key)
+		require.NoError(t, err)
+		assert.Equal(t, initialVersion+1, proj.PayloadVersion)
+
+		// Calling again should increment once more
+		newVersion2, err := store.IncrementProjectPayloadVersion(ctx, projects[0].Key)
+		require.NoError(t, err)
+		assert.Equal(t, initialVersion+2, newVersion2)
+	})
+
 	t.Run("UpdateProject deletes overrides for flags that are no longer in the project", func(t *testing.T) {
 		project := projects[2]
 

internal/dev_server/model/import_project.go

@@ -53,6 +53,7 @@ func ImportProject(ctx context.Context, projectKey string, importData ImportData
 		Context:              importData.Context,
 		AllFlagsState:        importData.FlagsState,
 		AvailableVariations:  []FlagVariation{},
+		PayloadVersion:       1,
 	}
 
 	// Convert available variations if present

internal/dev_server/model/override.go

@@ -3,6 +3,8 @@ package model
 import (
 	"context"
 
+	"github.com/pkg/errors"
+
 	"github.com/launchdarkly/go-sdk-common/v3/ldvalue"
 )
 
@@ -58,6 +60,11 @@ func UpsertOverride(ctx context.Context, projectKey, flagKey string, value ldval
 		return Override{}, err
 	}
 
+	_, err = store.IncrementProjectPayloadVersion(ctx, projectKey)
+	if err != nil {
+		return Override{}, errors.Wrap(err, "unable to increment payload version")
+	}
+
 	GetObserversFromContext(ctx).Notify(OverrideEvent{
 		FlagKey:    flagKey,
 		ProjectKey: projectKey,
@@ -76,6 +83,12 @@ func DeleteOverride(ctx context.Context, projectKey, flagKey string) error {
 	if err != nil {
 		return err
 	}
+
+	_, err = store.IncrementProjectPayloadVersion(ctx, projectKey)
+	if err != nil {
+		return errors.Wrap(err, "unable to increment payload version")
+	}
+
 	override := Override{
 		ProjectKey: projectKey,
 		FlagKey:    flagKey,

internal/dev_server/model/override_test.go

@@ -73,6 +73,7 @@ func TestUpsertOverride(t *testing.T) {
 	t.Run("override is applied, observers are notified", func(t *testing.T) {
 		store.EXPECT().GetDevProject(gomock.Any(), projKey).Return(project, nil)
 		store.EXPECT().UpsertOverride(gomock.Any(), override).Return(override, nil)
+		store.EXPECT().IncrementProjectPayloadVersion(gomock.Any(), projKey).Return(1, nil)
 		observer.
 			EXPECT().
 			Handle(model.OverrideEvent{
@@ -128,6 +129,7 @@ func TestDeleteOverride(t *testing.T) {
 	t.Run("override is applied, observers are notified", func(t *testing.T) {
 		store.EXPECT().GetDevProject(gomock.Any(), projKey).Return(project, nil)
 		store.EXPECT().DeactivateOverride(gomock.Any(), projKey, flagKey).Return(2, nil)
+		store.EXPECT().IncrementProjectPayloadVersion(gomock.Any(), projKey).Return(1, nil)
 		observer.
 			EXPECT().
 			Handle(model.OverrideEvent{
@@ -198,11 +200,13 @@ func TestDeleteOverrides(t *testing.T) {
 		// Expectations for first override
 		store.EXPECT().GetDevProject(gomock.Any(), projKey).Return(project, nil)
 		store.EXPECT().DeactivateOverride(gomock.Any(), projKey, flagKey).Return(2, nil)
+		store.EXPECT().IncrementProjectPayloadVersion(gomock.Any(), projKey).Return(1, nil)
 		observer.EXPECT().Handle(gomock.Any())
 
 		// Expectations for second override
 		store.EXPECT().GetDevProject(gomock.Any(), projKey).Return(project, nil)
 		store.EXPECT().DeactivateOverride(gomock.Any(), projKey, "flag2").Return(2, nil)
+		store.EXPECT().IncrementProjectPayloadVersion(gomock.Any(), projKey).Return(2, nil)
 		observer.EXPECT().Handle(gomock.Any())
 
 		err := model.DeleteOverrides(ctx, projKey)

internal/dev_server/model/project.go

@@ -18,13 +18,15 @@ type Project struct {
 	LastSyncTime         time.Time
 	AllFlagsState        FlagsState
 	AvailableVariations  []FlagVariation
+	PayloadVersion       int
 }
 
 // CreateProject creates a project and adds it to the database.
 func CreateProject(ctx context.Context, projectKey, sourceEnvironmentKey string, ldCtx *ldcontext.Context) (Project, error) {
 	project := Project{
 		Key:                  projectKey,
 		SourceEnvironmentKey: sourceEnvironmentKey,
+		PayloadVersion:       1,
 	}
 
 	if ldCtx == nil {
@@ -87,6 +89,12 @@ func UpdateProject(ctx context.Context, projectKey string, context *ldcontext.Co
 		return Project{}, errors.New("Project not updated")
 	}
 
+	newPayloadVersion, err := store.IncrementProjectPayloadVersion(ctx, projectKey)
+	if err != nil {
+		return Project{}, errors.Wrap(err, "unable to increment payload version")
+	}
+	project.PayloadVersion = newPayloadVersion
+
 	allFlagsWithOverrides, err := project.GetFlagStateWithOverridesForProject(ctx)
 	if err != nil {
 		return Project{}, errors.Wrapf(err, "unable to get overrides for project, %s", projectKey)

internal/dev_server/model/project_test.go

@@ -183,6 +183,7 @@ func TestUpdateProject(t *testing.T) {
 		sdk.EXPECT().GetAllFlagsState(gomock.Any(), gomock.Any(), "sdkKey").Return(allFlagsState, nil)
 		api.EXPECT().GetAllFlags(gomock.Any(), proj.Key).Return(allFlags, nil)
 		store.EXPECT().UpdateProject(gomock.Any(), gomock.Any()).Return(true, nil)
+		store.EXPECT().IncrementProjectPayloadVersion(gomock.Any(), proj.Key).Return(2, nil)
 		store.EXPECT().GetOverridesForProject(gomock.Any(), proj.Key).Return(model.Overrides{}, nil)
 		observer.
 			EXPECT().
@@ -193,7 +194,9 @@ func TestUpdateProject(t *testing.T) {
 
 		project, err := model.UpdateProject(ctx, proj.Key, nil, nil)
 		require.Nil(t, err)
-		assert.Equal(t, proj, project)
+		expectedProj := proj
+		expectedProj.PayloadVersion = 2
+		assert.Equal(t, expectedProj, project)
 	})
 }
 

internal/dev_server/model/store.go

@@ -28,6 +28,8 @@ type Store interface {
 	UpsertOverride(ctx context.Context, override Override) (Override, error)
 	GetOverridesForProject(ctx context.Context, projectKey string) (Overrides, error)
 	GetAvailableVariationsForProject(ctx context.Context, projectKey string) (map[string][]Variation, error)
+	// IncrementProjectPayloadVersion atomically increments the payload version for the project and returns the new version.
+	IncrementProjectPayloadVersion(ctx context.Context, projectKey string) (int, error)
 
 	CreateBackup(ctx context.Context) (io.ReadCloser, int64, error)
 	RestoreBackup(ctx context.Context, stream io.Reader) (string, error)

internal/dev_server/model/sync_test.go

@@ -153,8 +153,9 @@ func TestInitialSync(t *testing.T) {
 		sdk.EXPECT().GetAllFlagsState(gomock.Any(), gomock.Any(), sdkKey).Return(allFlagsState, nil)
 		api.EXPECT().GetAllFlags(gomock.Any(), projKey).Return(allFlags, nil)
 		store.EXPECT().InsertProject(gomock.Any(), gomock.Any()).Return(nil)
-		store.EXPECT().UpsertOverride(gomock.Any(), override).Return(override, nil)
 		store.EXPECT().GetDevProject(gomock.Any(), projKey).Return(&proj, nil)
+		store.EXPECT().UpsertOverride(gomock.Any(), override).Return(override, nil)
+		store.EXPECT().IncrementProjectPayloadVersion(gomock.Any(), projKey).Return(1, nil)
 
 		input := model.InitialProjectSettings{
 			Enabled:    true,