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

components/cqrs/command_bus.go

@@ -0,0 +1,168 @@
+package cqrs
+
+import (
+	"context"
+	stdErrors "errors"
+
+	"github.com/ThreeDotsLabs/watermill"
+	"github.com/pkg/errors"
+
+	"github.com/ThreeDotsLabs/watermill/message"
+)
+
+type CommandBusConfig struct {
+	// GeneratePublishTopic is used to generate topic for publishing command.
+	GeneratePublishTopic CommandBusGeneratePublishTopicFn
+
+	// OnSend is called before publishing the command.
+	// The *message.Message can be modified.
+	//
+	// This option is not required.
+	OnSend CommandBusOnSendFn
+
+	// Marshaler is used to marshal and unmarshal commands.
+	// It is required.
+	Marshaler CommandEventMarshaler
+
+	// Logger instance used to log.
+	// If not provided, watermill.NopLogger is used.
+	Logger watermill.LoggerAdapter
+}
+
+func (c *CommandBusConfig) setDefaults() {
+	if c.Logger == nil {
+		c.Logger = watermill.NopLogger{}
+	}
+}
+
+func (c CommandBusConfig) 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 GeneratePublishTopic"))
+	}
+
+	return err
+}
+
+type CommandBusGeneratePublishTopicFn func(CommandBusGeneratePublishTopicParams) (string, error)
+
+type CommandBusGeneratePublishTopicParams struct {
+	CommandName string
+	Command     any
+}
+
+type CommandBusOnSendFn func(params CommandBusOnSendParams) error
+
+type CommandBusOnSendParams struct {
+	CommandName string
+	Command     any
+
+	// Message is never nil and can be modified.
+	Message *message.Message
+}
+
+// CommandBus transports commands to command handlers.
+type CommandBus struct {
+	publisher message.Publisher
+
+	config CommandBusConfig
+}
+
+// NewCommandBusWithConfig creates a new CommandBus.
+func NewCommandBusWithConfig(publisher message.Publisher, config CommandBusConfig) (*CommandBus, 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 &CommandBus{publisher, config}, nil
+}
+
+// NewCommandBus creates a new CommandBus.
+// Deprecated: use NewCommandBusWithConfig instead.
+func NewCommandBus(
+	publisher message.Publisher,
+	generateTopic func(commandName string) string,
+	marshaler CommandEventMarshaler,
+) (*CommandBus, 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 &CommandBus{publisher, CommandBusConfig{
+		GeneratePublishTopic: func(params CommandBusGeneratePublishTopicParams) (string, error) {
+			return generateTopic(params.CommandName), nil
+		},
+		Marshaler: marshaler,
+	}}, nil
+}
+
+// Send sends command to the command bus.
+func (c CommandBus) Send(ctx context.Context, cmd any) error {
+	return c.SendWithModifiedMessage(ctx, cmd, nil)
+}
+
+func (c CommandBus) SendWithModifiedMessage(ctx context.Context, cmd any, modify func(*message.Message) error) error {
+	msg, topicName, err := c.newMessage(ctx, cmd)
+	if err != nil {
+		return err
+	}
+
+	if modify != nil {
+		if err := modify(msg); err != nil {
+			return errors.Wrap(err, "cannot modify message")
+		}
+	}
+
+	if err := c.publisher.Publish(topicName, msg); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (c CommandBus) newMessage(ctx context.Context, command any) (*message.Message, string, error) {
+	msg, err := c.config.Marshaler.Marshal(command)
+	if err != nil {
+		return nil, "", err
+	}
+
+	commandName := c.config.Marshaler.Name(command)
+	topicName, err := c.config.GeneratePublishTopic(CommandBusGeneratePublishTopicParams{
+		CommandName: commandName,
+		Command:     command,
+	})
+	if err != nil {
+		return nil, "", errors.Wrap(err, "cannot generate topic name")
+	}
+
+	msg.SetContext(ctx)
+
+	if c.config.OnSend != nil {
+		err := c.config.OnSend(CommandBusOnSendParams{
+			CommandName: commandName,
+			Command:     command,
+			Message:     msg,
+		})
+		if err != nil {
+			return nil, "", errors.Wrap(err, "cannot execute OnSend")
+		}
+	}
+
+	return msg, topicName, nil
+}