feat: wire Watermill CQRS — EventBus in usecases, event handlers, router lifecycle

- Add EventPublisher interface in biz layer for domain event publishing
- Wire EventBusPublisher (Watermill EventBus adapter) into FileUsecase, FolderUsecase, ShareUsecase
- Publish events after UploadFile, DeleteFile, CreateFolder, DeleteFolder, CreateShare
- Implement CQRSHandler with logging event handlers for all 6 event types
- Register event handlers via CQRSBus.RegisterHandlers using Watermill EventProcessor
- Store subscriber and wmLogger in CQRSBus for EventProcessor wiring
- Expose SqlDB() on Data struct for Watermill SQL pub/sub
- Start Watermill router in goroutine alongside Kratos app with graceful close
- Use appContext wrapper struct to pass CQRSBus through Wire DI graph

cmd/server/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"flag"
 	"os"
 
@@ -42,13 +43,23 @@ func main() {
 		panic(err)
 	}
 
-	app, cleanup, err := initApp(&bc, logger)
+	ctx, cleanup, err := initApp(&bc, logger)
 	if err != nil {
 		panic(err)
 	}
 	defer cleanup()
 
-	if err := app.Run(); err != nil {
+	// Start Watermill router alongside the Kratos app.
+	if ctx.CQRSBus != nil {
+		go func() {
+			if err := ctx.CQRSBus.Router.Run(context.Background()); err != nil {
+				logger.Log(log.LevelError, "msg", "watermill router error", "error", err)
+			}
+		}()
+		defer ctx.CQRSBus.Router.Close()
+	}
+
+	if err := ctx.App.Run(); err != nil {
 		panic(err)
 	}
 }

cmd/server/wire.go

@@ -3,11 +3,14 @@
 package main
 
 import (
+	"database/sql"
+
 	"rag/file-system/internal/biz"
 	"rag/file-system/internal/conf"
 	"rag/file-system/internal/data"
 	"rag/file-system/internal/server"
 	"rag/file-system/internal/service"
+	"rag/file-system/internal/watermark"
 
 	"github.com/go-kratos/kratos/v2"
 	"github.com/go-kratos/kratos/v2/log"
@@ -16,6 +19,12 @@ import (
 	"github.com/google/wire"
 )
 
+// appContext holds the Kratos app and CQRS bus together for Wire.
+type appContext struct {
+	App     *kratos.App
+	CQRSBus *watermark.CQRSBus
+}
+
 // newApp creates a new Kratos application with HTTP and gRPC servers.
 func newApp(logger log.Logger, hs *http.Server, gs *grpc.Server) *kratos.App {
 	return kratos.New(
@@ -25,6 +34,11 @@ func newApp(logger log.Logger, hs *http.Server, gs *grpc.Server) *kratos.App {
 	)
 }
 
+// newAppContext wraps the app and CQRSBus into an appContext.
+func newAppContext(app *kratos.App, bus *watermark.CQRSBus) *appContext {
+	return &appContext{App: app, CQRSBus: bus}
+}
+
 // newConfServer extracts the Server config from Bootstrap.
 func newConfServer(bc *conf.Bootstrap) *conf.Server {
 	return bc.GetServer()
@@ -40,8 +54,13 @@ func newConfAuth(bc *conf.Bootstrap) *conf.Auth {
 	return bc.GetAuth()
 }
 
+// newSQLDB extracts the underlying *sql.DB from Data for Watermill.
+func newSQLDB(d *data.Data) (*sql.DB, error) {
+	return d.SqlDB()
+}
+
 // initApp wires up the entire dependency graph.
-func initApp(*conf.Bootstrap, log.Logger) (*kratos.App, func(), error) {
+func initApp(*conf.Bootstrap, log.Logger) (*appContext, func(), error) {
 	panic(wire.Build(
 		// Config extraction
 		newConfServer,
@@ -53,15 +72,23 @@ func initApp(*conf.Bootstrap, log.Logger) (*kratos.App, func(), error) {
 		biz.ProviderSet,
 		service.ProviderSet,
 		server.ProviderSet,
+		watermark.ProviderSet,
 
-		// Interface bindings: biz interfaces → data implementations
+		// Extract *sql.DB from Data for Watermill
+		newSQLDB,
+
+		// Interface bindings: biz interfaces -> data implementations
 		wire.Bind(new(biz.FileRepo), new(*data.FileRepo)),
 		wire.Bind(new(biz.FolderRepo), new(*data.FolderRepo)),
 		wire.Bind(new(biz.FileMetaRepo), new(*data.FileMetaRepo)),
 		wire.Bind(new(biz.FileMetaRepoForShare), new(*data.FileMetaRepo)),
 		wire.Bind(new(biz.ShareRepo), new(*data.ShareRepo)),
 
-		// App constructor
+		// Interface binding: biz EventPublisher -> watermark EventBusPublisher
+		wire.Bind(new(biz.EventPublisher), new(*watermark.EventBusPublisher)),
+
+		// Wire up app + CQRSBus into appContext
+		newAppContext,
 		newApp,
 	))
 }

cmd/server/wire_gen.go

@@ -7,6 +7,7 @@
 package main
 
 import (
+	"database/sql"
 	"github.com/go-kratos/kratos/v2"
 	"github.com/go-kratos/kratos/v2/log"
 	"github.com/go-kratos/kratos/v2/transport/grpc"
@@ -16,43 +17,68 @@ import (
 	"rag/file-system/internal/data"
 	"rag/file-system/internal/server"
 	"rag/file-system/internal/service"
+	"rag/file-system/internal/watermark"
 )
 
 // Injectors from wire.go:
 
 // initApp wires up the entire dependency graph.
-func initApp(bootstrap *conf.Bootstrap, logger log.Logger) (*kratos.App, func(), error) {
+func initApp(bootstrap *conf.Bootstrap, logger log.Logger) (*appContext, func(), error) {
 	confServer := newConfServer(bootstrap)
 	auth := newConfAuth(bootstrap)
 	confData := newConfData(bootstrap)
 	fileRepo := data.NewFileRepo(confData)
-	fileUsecase := biz.NewFileUsecase(fileRepo, logger)
-	bucketUsecase := biz.NewBucketUsecase(fileRepo, logger)
 	dataData, cleanup, err := data.NewData(confData, logger)
 	if err != nil {
 		return nil, nil, err
 	}
+	db, err := newSQLDB(dataData)
+	if err != nil {
+		cleanup()
+		return nil, nil, err
+	}
+	cqrsHandler := watermark.NewCQRSHandler(logger)
+	cqrsBus, err := watermark.NewCQRSBusWithHandlers(db, cqrsHandler, logger)
+	if err != nil {
+		cleanup()
+		return nil, nil, err
+	}
+	eventBusPublisher := watermark.NewEventBusPublisher(cqrsBus)
+	fileUsecase := biz.NewFileUsecase(fileRepo, eventBusPublisher, logger)
+	bucketUsecase := biz.NewBucketUsecase(fileRepo, logger)
 	folderRepo := data.NewFolderRepo(dataData, logger)
 	fileMetaRepo := data.NewFileMetaRepo(dataData, logger)
-	folderUsecase := biz.NewFolderUsecase(folderRepo, fileMetaRepo, fileRepo, logger)
+	folderUsecase := biz.NewFolderUsecase(folderRepo, fileMetaRepo, fileRepo, eventBusPublisher, logger)
 	shareRepo := data.NewShareRepo(dataData, logger)
-	shareUsecase := biz.NewShareUsecase(shareRepo, fileMetaRepo, fileRepo, logger)
+	shareUsecase := biz.NewShareUsecase(shareRepo, fileMetaRepo, fileRepo, eventBusPublisher, logger)
 	fileService := service.NewFileService(fileUsecase, bucketUsecase, folderUsecase, shareUsecase, logger)
 	httpServer := server.NewHTTPServer(confServer, auth, fileService, logger)
 	grpcServer := server.NewGRPCServer(confServer, auth, fileService, logger)
 	app := newApp(logger, httpServer, grpcServer)
-	return app, func() {
+	mainAppContext := newAppContext(app, cqrsBus)
+	return mainAppContext, func() {
 		cleanup()
 	}, nil
 }
 
 // wire.go:
 
+// appContext holds the Kratos app and CQRS bus together for Wire.
+type appContext struct {
+	App     *kratos.App
+	CQRSBus *watermark.CQRSBus
+}
+
 // newApp creates a new Kratos application with HTTP and gRPC servers.
 func newApp(logger log.Logger, hs *http.Server, gs *grpc.Server) *kratos.App {
 	return kratos.New(kratos.Name("file-system"), kratos.Logger(logger), kratos.Server(hs, gs))
 }
 
+// newAppContext wraps the app and CQRSBus into an appContext.
+func newAppContext(app *kratos.App, bus *watermark.CQRSBus) *appContext {
+	return &appContext{App: app, CQRSBus: bus}
+}
+
 // newConfServer extracts the Server config from Bootstrap.
 func newConfServer(bc *conf.Bootstrap) *conf.Server {
 	return bc.GetServer()
@@ -67,3 +93,8 @@ func newConfData(bc *conf.Bootstrap) *conf.Data {
 func newConfAuth(bc *conf.Bootstrap) *conf.Auth {
 	return bc.GetAuth()
 }
+
+// newSQLDB extracts the underlying *sql.DB from Data for Watermill.
+func newSQLDB(d *data.Data) (*sql.DB, error) {
+	return d.SqlDB()
+}

internal/biz/event.go

@@ -0,0 +1,8 @@
+package biz
+
+import "context"
+
+// EventPublisher defines the interface for publishing domain events.
+type EventPublisher interface {
+	Publish(ctx context.Context, event interface{}) error
+}

internal/biz/file.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"rag/file-system/internal/data"
+	"rag/file-system/internal/watermark"
 
 	"github.com/go-kratos/kratos/v2/log"
 )
@@ -30,20 +31,32 @@ type FileRepo interface {
 // FileUsecase wraps FileRepo and provides file-level business operations.
 type FileUsecase struct {
 	repo     FileRepo
+	eventPub EventPublisher
 	log      *log.Helper
 }
 
 // NewFileUsecase creates a new FileUsecase.
-func NewFileUsecase(repo FileRepo, logger log.Logger) *FileUsecase {
+func NewFileUsecase(repo FileRepo, eventPub EventPublisher, logger log.Logger) *FileUsecase {
 	return &FileUsecase{
 		repo:     repo,
+		eventPub: eventPub,
 		log:      log.NewHelper(logger),
 	}
 }
 
 // UploadFile uploads data to the specified bucket and key.
 func (uc *FileUsecase) UploadFile(ctx context.Context, bucket, key string, fileData io.Reader) error {
-	return uc.repo.UploadFile(ctx, bucket, key, fileData)
+	if err := uc.repo.UploadFile(ctx, bucket, key, fileData); err != nil {
+		return err
+	}
+	// Publish domain event on success.
+	if err := uc.eventPub.Publish(ctx, &watermark.FileUploadedEvent{
+		BucketName: bucket,
+		ObjectKey:  key,
+	}); err != nil {
+		uc.log.Errorf("failed to publish FileUploadedEvent: %v", err)
+	}
+	return nil
 }
 
 // DownloadFile downloads an object from S3.
@@ -58,7 +71,17 @@ func (uc *FileUsecase) GetFileContent(ctx context.Context, bucket, key string) (
 
 // DeleteFile removes a file from S3.
 func (uc *FileUsecase) DeleteFile(ctx context.Context, bucket, key string) error {
-	return uc.repo.DeleteFile(ctx, bucket, key)
+	if err := uc.repo.DeleteFile(ctx, bucket, key); err != nil {
+		return err
+	}
+	// Publish domain event on success.
+	if err := uc.eventPub.Publish(ctx, &watermark.FileDeletedEvent{
+		BucketName: bucket,
+		ObjectKey:  key,
+	}); err != nil {
+		uc.log.Errorf("failed to publish FileDeletedEvent: %v", err)
+	}
+	return nil
 }
 
 // ListObjectsV2 lists files with pagination support.

internal/biz/folder.go

@@ -8,6 +8,7 @@ import (
 
 	"rag/file-system/internal/data"
 	"rag/file-system/internal/pkg/sanitize"
+	"rag/file-system/internal/watermark"
 
 	"github.com/go-kratos/kratos/v2/log"
 	"github.com/google/uuid"
@@ -38,15 +39,17 @@ type FolderUsecase struct {
 	folderRepo FolderRepo
 	fileRepo   FileMetaRepo
 	s3Repo     FileRepo
+	eventPub   EventPublisher
 	log        *log.Helper
 }
 
 // NewFolderUsecase creates a new FolderUsecase.
-func NewFolderUsecase(folderRepo FolderRepo, fileRepo FileMetaRepo, s3Repo FileRepo, logger log.Logger) *FolderUsecase {
+func NewFolderUsecase(folderRepo FolderRepo, fileRepo FileMetaRepo, s3Repo FileRepo, eventPub EventPublisher, logger log.Logger) *FolderUsecase {
 	return &FolderUsecase{
 		folderRepo: folderRepo,
 		fileRepo:   fileRepo,
 		s3Repo:     s3Repo,
+		eventPub:   eventPub,
 		log:        log.NewHelper(logger),
 	}
 }
@@ -61,6 +64,14 @@ func (uc *FolderUsecase) CreateFolder(ctx context.Context, parentID *string, nam
 	if err := uc.folderRepo.Create(ctx, folder); err != nil {
 		return nil, fmt.Errorf("failed to create folder: %w", err)
 	}
+	// Publish domain event on success.
+	if err := uc.eventPub.Publish(ctx, &watermark.FolderCreatedEvent{
+		FolderID: folder.ID,
+		Name:     folder.Name,
+		OwnerID:  folder.OwnerID,
+	}); err != nil {
+		uc.log.Errorf("failed to publish FolderCreatedEvent: %v", err)
+	}
 	return folder, nil
 }
 
@@ -118,6 +129,15 @@ func (uc *FolderUsecase) DeleteFolder(ctx context.Context, id, ownerID string) e
 	if err := uc.folderRepo.Delete(ctx, id, ownerID); err != nil {
 		return fmt.Errorf("failed to delete folder: %w", err)
 	}
+
+	// Publish domain event on success.
+	if err := uc.eventPub.Publish(ctx, &watermark.FolderDeletedEvent{
+		FolderID: id,
+		OwnerID:  ownerID,
+	}); err != nil {
+		uc.log.Errorf("failed to publish FolderDeletedEvent: %v", err)
+	}
+
 	return nil
 }
 

internal/biz/share.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"rag/file-system/internal/data"
+	"rag/file-system/internal/watermark"
 
 	"github.com/go-kratos/kratos/v2/log"
 )
@@ -32,15 +33,17 @@ type ShareUsecase struct {
 	shareRepo  ShareRepo
 	fileRepo   FileMetaRepoForShare
 	s3Repo     FileRepo
+	eventPub   EventPublisher
 	log        *log.Helper
 }
 
 // NewShareUsecase creates a new ShareUsecase.
-func NewShareUsecase(shareRepo ShareRepo, fileRepo FileMetaRepoForShare, s3Repo FileRepo, logger log.Logger) *ShareUsecase {
+func NewShareUsecase(shareRepo ShareRepo, fileRepo FileMetaRepoForShare, s3Repo FileRepo, eventPub EventPublisher, logger log.Logger) *ShareUsecase {
 	return &ShareUsecase{
 		shareRepo: shareRepo,
 		fileRepo:  fileRepo,
 		s3Repo:    s3Repo,
+		eventPub:  eventPub,
 		log:       log.NewHelper(logger),
 	}
 }
@@ -68,6 +71,18 @@ func (uc *ShareUsecase) CreateShare(ctx context.Context, resourceType, resourceI
 	if err := uc.shareRepo.Create(ctx, share); err != nil {
 		return nil, fmt.Errorf("failed to create share link: %w", err)
 	}
+
+	// Publish domain event on success.
+	if err := uc.eventPub.Publish(ctx, &watermark.ShareCreatedEvent{
+		ShareID:      share.ID,
+		ResourceType: share.ResourceType,
+		ResourceID:   share.ResourceID,
+		Token:        share.Token,
+		CreatedBy:    share.CreatedBy,
+	}); err != nil {
+		uc.log.Errorf("failed to publish ShareCreatedEvent: %v", err)
+	}
+
 	return share, nil
 }
 

internal/data/data.go

@@ -2,6 +2,7 @@ package data
 
 import (
 	"context"
+	"database/sql"
 	"time"
 
 	"rag/file-system/internal/conf"
@@ -47,6 +48,11 @@ func NewData(c *conf.Data, logger log.Logger) (*Data, func(), error) {
 	return &Data{db: db, log: helper}, cleanup, nil
 }
 
+// SqlDB returns the underlying *sql.DB for use by Watermill.
+func (d *Data) SqlDB() (*sql.DB, error) {
+	return d.db.DB()
+}
+
 // DB returns the *gorm.DB for the given context. If a transaction is active
 // in the context, it returns the transaction DB; otherwise the global DB.
 func (d *Data) DB(ctx context.Context) *gorm.DB {

internal/watermark/cqrs_setup.go

@@ -8,14 +8,19 @@ import (
 	"github.com/ThreeDotsLabs/watermill/components/cqrs"
 	"github.com/ThreeDotsLabs/watermill/message"
 	"github.com/go-kratos/kratos/v2/log"
+	"github.com/google/wire"
 )
 
+// CQRSBus holds the Watermill CQRS buses, router, and internal references.
 type CQRSBus struct {
 	CommandBus *cqrs.CommandBus
 	EventBus   *cqrs.EventBus
 	Router     *message.Router
+	subscriber message.Subscriber
+	wmLogger   watermill.LoggerAdapter
 }
 
+// NewCQRSBus creates a new CQRSBus with PostgreSQL-backed pub/sub.
 func NewCQRSBus(db *sql.DB, logger log.Logger) (*CQRSBus, error) {
 	helper := log.NewHelper(logger)
 	wmLogger := watermill.NewStdLogger(false, false)
@@ -37,9 +42,6 @@ func NewCQRSBus(db *sql.DB, logger log.Logger) (*CQRSBus, error) {
 		return nil, err
 	}
 
-	// subscriber will be used later to wire event handlers on the router
-	_ = subscriber
-
 	router, err := message.NewRouter(message.RouterConfig{}, wmLogger)
 	if err != nil {
 		return nil, err
@@ -74,5 +76,56 @@ func NewCQRSBus(db *sql.DB, logger log.Logger) (*CQRSBus, error) {
 		CommandBus: commandBus,
 		EventBus:   eventBus,
 		Router:     router,
+		subscriber: subscriber,
+		wmLogger:   wmLogger,
 	}, nil
 }
+
+// RegisterHandlers sets up all event handlers on the router.
+func (b *CQRSBus) RegisterHandlers(handler *CQRSHandler) error {
+	eventProcessor, err := cqrs.NewEventProcessorWithConfig(
+		b.Router,
+		cqrs.EventProcessorConfig{
+			GenerateSubscribeTopic: func(params cqrs.EventProcessorGenerateSubscribeTopicParams) (string, error) {
+				return "events." + params.EventName, nil
+			},
+			SubscriberConstructor: func(params cqrs.EventProcessorSubscriberConstructorParams) (message.Subscriber, error) {
+				return b.subscriber, nil
+			},
+			Marshaler: cqrs.JSONMarshaler{},
+			Logger:    b.wmLogger,
+		},
+	)
+	if err != nil {
+		return err
+	}
+
+	err = eventProcessor.AddHandlers(
+		cqrs.NewEventHandler("OnFileUploaded", handler.OnFileUploaded),
+		cqrs.NewEventHandler("OnFileDeleted", handler.OnFileDeleted),
+		cqrs.NewEventHandler("OnFolderCreated", handler.OnFolderCreated),
+		cqrs.NewEventHandler("OnFolderDeleted", handler.OnFolderDeleted),
+		cqrs.NewEventHandler("OnShareCreated", handler.OnShareCreated),
+		cqrs.NewEventHandler("OnShareDownloaded", handler.OnShareDownloaded),
+	)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// ProviderSet is the Wire provider set for the watermark layer.
+var ProviderSet = wire.NewSet(NewCQRSBusWithHandlers, NewCQRSHandler, NewEventBusPublisher)
+
+// NewCQRSBusWithHandlers creates the CQRSBus and registers all event handlers.
+func NewCQRSBusWithHandlers(db *sql.DB, handler *CQRSHandler, logger log.Logger) (*CQRSBus, error) {
+	bus, err := NewCQRSBus(db, logger)
+	if err != nil {
+		return nil, err
+	}
+	if err := bus.RegisterHandlers(handler); err != nil {
+		return nil, err
+	}
+	return bus, nil
+}

internal/watermark/handlers.go

@@ -1,13 +1,54 @@
 package watermark
 
 import (
+	"context"
+
 	"github.com/go-kratos/kratos/v2/log"
 )
 
+// CQRSHandler holds all Watermill event handlers.
 type CQRSHandler struct {
 	log *log.Helper
 }
 
+// NewCQRSHandler creates a new CQRSHandler.
 func NewCQRSHandler(logger log.Logger) *CQRSHandler {
 	return &CQRSHandler{log: log.NewHelper(logger)}
 }
+
+// OnFileUploaded handles the FileUploadedEvent.
+func (h *CQRSHandler) OnFileUploaded(ctx context.Context, event *FileUploadedEvent) error {
+	h.log.Infof("event: file uploaded, bucket=%s key=%s size=%d", event.BucketName, event.ObjectKey, event.Size)
+	return nil
+}
+
+// OnFileDeleted handles the FileDeletedEvent.
+func (h *CQRSHandler) OnFileDeleted(ctx context.Context, event *FileDeletedEvent) error {
+	h.log.Infof("event: file deleted, bucket=%s key=%s", event.BucketName, event.ObjectKey)
+	return nil
+}
+
+// OnFolderCreated handles the FolderCreatedEvent.
+func (h *CQRSHandler) OnFolderCreated(ctx context.Context, event *FolderCreatedEvent) error {
+	h.log.Infof("event: folder created, id=%s name=%s owner=%s", event.FolderID, event.Name, event.OwnerID)
+	return nil
+}
+
+// OnFolderDeleted handles the FolderDeletedEvent.
+func (h *CQRSHandler) OnFolderDeleted(ctx context.Context, event *FolderDeletedEvent) error {
+	h.log.Infof("event: folder deleted, id=%s owner=%s", event.FolderID, event.OwnerID)
+	return nil
+}
+
+// OnShareCreated handles the ShareCreatedEvent.
+func (h *CQRSHandler) OnShareCreated(ctx context.Context, event *ShareCreatedEvent) error {
+	h.log.Infof("event: share created, id=%s token=%s resource=%s/%s by=%s",
+		event.ShareID, event.Token, event.ResourceType, event.ResourceID, event.CreatedBy)
+	return nil
+}
+
+// OnShareDownloaded handles the ShareDownloadedEvent.
+func (h *CQRSHandler) OnShareDownloaded(ctx context.Context, event *ShareDownloadedEvent) error {
+	h.log.Infof("event: share downloaded, token=%s", event.Token)
+	return nil
+}

internal/watermark/publisher.go

@@ -0,0 +1,20 @@
+package watermark
+
+import (
+	"context"
+)
+
+// EventBusPublisher implements biz.EventPublisher using Watermill EventBus.
+type EventBusPublisher struct {
+	bus *CQRSBus
+}
+
+// NewEventBusPublisher creates a new EventBusPublisher from a CQRSBus.
+func NewEventBusPublisher(bus *CQRSBus) *EventBusPublisher {
+	return &EventBusPublisher{bus: bus}
+}
+
+// Publish publishes a domain event via the Watermill EventBus.
+func (p *EventBusPublisher) Publish(ctx context.Context, event interface{}) error {
+	return p.bus.EventBus.Publish(ctx, event)
+}