snapshot of https://github.com/ThreeDotsLabs/watermill.git (master, 2026-09-15; blobs > 131072B omitted)

components/cqrs/event_bus.go

@@ -0,0 +1,146 @@
+package cqrs
+
+import (
+	"context"
+	stdErrors "errors"
+
+	"github.com/ThreeDotsLabs/watermill"
+	"github.com/ThreeDotsLabs/watermill/message"
+	"github.com/pkg/errors"
+)
+
+type EventBusConfig struct {
+	// GeneratePublishTopic is used to generate topic name for publishing event.
+	GeneratePublishTopic GenerateEventPublishTopicFn
+
+	// OnPublish is called before sending the event.
+	// The *message.Message can be modified.
+	//
+	// This option is not required.
+	OnPublish OnEventSendFn
+
+	// Marshaler is used to marshal and unmarshal events.
+	// It is required.
+	Marshaler CommandEventMarshaler
+
+	// Logger instance used to log.
+	// If not provided, watermill.NopLogger is used.
+	Logger watermill.LoggerAdapter
+}
+
+func (c *EventBusConfig) setDefaults() {
+	if c.Logger == nil {
+		c.Logger = watermill.NopLogger{}
+	}
+}
+
+func (c EventBusConfig) Validate() error {
+	var err error
+
+	if c.Marshaler == nil {
+		err = stdErrors.Join(err, errors.New("missing Marshaler"))
+	}
+
+	if c.GeneratePublishTopic == nil {
+		err = stdErrors.Join(err, errors.New("missing GenerateHandlerTopic"))
+	}
+
+	return err
+}
+
+type GenerateEventPublishTopicFn func(GenerateEventPublishTopicParams) (string, error)
+
+type GenerateEventPublishTopicParams struct {
+	EventName string
+	Event     any
+}
+
+type OnEventSendFn func(params OnEventSendParams) error
+
+type OnEventSendParams struct {
+	EventName string
+	Event     any
+
+	// Message is never nil and can be modified.
+	Message *message.Message
+}
+
+// EventBus transports events to event handlers.
+type EventBus struct {
+	publisher message.Publisher
+	config    EventBusConfig
+}
+
+// NewEventBus creates a new CommandBus.
+// Deprecated: use NewEventBusWithConfig instead.
+func NewEventBus(
+	publisher message.Publisher,
+	generateTopic func(eventName string) string,
+	marshaler CommandEventMarshaler,
+) (*EventBus, error) {
+	if publisher == nil {
+		return nil, errors.New("missing publisher")
+	}
+	if generateTopic == nil {
+		return nil, errors.New("missing generateTopic")
+	}
+	if marshaler == nil {
+		return nil, errors.New("missing marshaler")
+	}
+
+	return &EventBus{
+		publisher: publisher,
+		config: EventBusConfig{
+			GeneratePublishTopic: func(params GenerateEventPublishTopicParams) (string, error) {
+				return generateTopic(params.EventName), nil
+			},
+			Marshaler: marshaler,
+		},
+	}, nil
+}
+
+// NewEventBusWithConfig creates a new EventBus.
+func NewEventBusWithConfig(publisher message.Publisher, config EventBusConfig) (*EventBus, error) {
+	if publisher == nil {
+		return nil, errors.New("missing publisher")
+	}
+
+	config.setDefaults()
+	if err := config.Validate(); err != nil {
+		return nil, errors.Wrap(err, "invalid config")
+	}
+
+	return &EventBus{publisher, config}, nil
+}
+
+// Publish sends event to the event bus.
+func (c EventBus) Publish(ctx context.Context, event any) error {
+	msg, err := c.config.Marshaler.Marshal(event)
+	if err != nil {
+		return err
+	}
+
+	eventName := c.config.Marshaler.Name(event)
+	topicName, err := c.config.GeneratePublishTopic(GenerateEventPublishTopicParams{
+		EventName: eventName,
+		Event:     event,
+	})
+	if err != nil {
+		return errors.Wrap(err, "cannot generate topic")
+	}
+
+	msg.SetContext(ctx)
+
+	if c.config.OnPublish != nil {
+		err := c.config.OnPublish(OnEventSendParams{
+			EventName: eventName,
+			Event:     event,
+			Message:   msg,
+		})
+		if err != nil {
+			return errors.Wrap(err, "cannot execute OnPublish")
+		}
+	}
+
+	return c.publisher.Publish(topicName, msg)
+}