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

components/requestreply/requestreply.go

@@ -0,0 +1,91 @@
+package requestreply
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/ThreeDotsLabs/watermill/message"
+)
+
+// NoResult is a result type for commands that don't have result.
+type NoResult = struct{}
+
+type Reply[Result any] struct {
+	// HandlerResult contains the handler result.
+	// It's preset only when NewCommandHandlerWithResult is used. If NewCommandHandler is used, HandlerResult is empty.
+	//
+	// Result is sent even if the handler returns an error.
+	HandlerResult Result
+
+	// Error contains the error returned by the command handler or the Backend when handling notification fails.
+	// Handling the notification can fail, for example, when unmarshaling the message or if there's a timeout.
+	// If listening for a reply times out or the context is canceled, the Error is ReplyTimeoutError.
+	//
+	// If an error from the handler is returned, CommandHandlerError is returned.
+	// If processing was successful, Error is nil.
+	Error error
+
+	// NotificationMessage contains the notification message sent after the command is handled.
+	// It's present only if the request/reply backend uses a Pub/Sub for notifications (for example, PubSubBackend).
+	//
+	// Warning: NotificationMessage is nil if a timeout occurs.
+	NotificationMessage *message.Message
+}
+
+type Backend[Result any] interface {
+	ListenForNotifications(ctx context.Context, params BackendListenForNotificationsParams) (<-chan Reply[Result], error)
+	OnCommandProcessed(ctx context.Context, params BackendOnCommandProcessedParams[Result]) error
+}
+
+type BackendListenForNotificationsParams struct {
+	Command     any
+	OperationID OperationID
+}
+
+type BackendOnCommandProcessedParams[Result any] struct {
+	Command        any
+	CommandMessage *message.Message
+
+	HandlerResult Result
+	HandleErr     error
+}
+
+// OperationID is a unique identifier of a command.
+// It correlates commands with replies between the bus and the handler.
+type OperationID string
+
+// ReplyTimeoutError is returned when the reply timeout is exceeded.
+type ReplyTimeoutError struct {
+	Duration time.Duration
+	Err      error
+}
+
+func (e ReplyTimeoutError) Error() string {
+	return fmt.Sprintf("reply timeout after %s: %s", e.Duration, e.Err)
+}
+
+type ReplyUnmarshalError struct {
+	Err error
+}
+
+func (r ReplyUnmarshalError) Error() string {
+	return fmt.Sprintf("cannot unmarshal reply: %s", r.Err)
+}
+
+func (r ReplyUnmarshalError) Unwrap() error {
+	return r.Err
+}
+
+// CommandHandlerError is returned when the command handler returns an error.
+type CommandHandlerError struct {
+	Err error
+}
+
+func (e CommandHandlerError) Error() string {
+	return e.Err.Error()
+}
+
+func (e CommandHandlerError) Unwrap() error {
+	return e.Err
+}