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

components/requestreply/handler.go

@@ -0,0 +1,81 @@
+package requestreply
+
+import (
+	"context"
+
+	"github.com/ThreeDotsLabs/watermill/components/cqrs"
+	"github.com/ThreeDotsLabs/watermill/message"
+	"github.com/pkg/errors"
+)
+
+// NewCommandHandler creates a new CommandHandler which supports the request-reply pattern.
+// The result handler is handler compatible with cqrs.CommandHandler.
+//
+// The logic if a command should be acked or not is based on the logic of the Backend.
+// For example, for the PubSubBackend, it depends on the `PubSubBackendConfig.AckCommandErrors` option.
+func NewCommandHandler[Command any](
+	handlerName string,
+	backend Backend[struct{}],
+	handleFunc func(ctx context.Context, cmd *Command) error,
+) cqrs.CommandHandler {
+	return cqrs.NewCommandHandler(handlerName, func(ctx context.Context, cmd *Command) error {
+		handlerErr := handleFunc(ctx, cmd)
+
+		originalMessage, err := originalCommandMsgFromCtx(ctx)
+		if err != nil {
+			return err
+		}
+
+		return backend.OnCommandProcessed(ctx, BackendOnCommandProcessedParams[struct{}]{
+			Command:        cmd,
+			CommandMessage: originalMessage,
+			HandleErr:      handlerErr,
+		})
+	})
+}
+
+// NewCommandHandlerWithResult creates a new CommandHandler which supports the request-reply pattern with a result.
+// The result handler is handler compatible with cqrs.CommandHandler.
+//
+// In addition to cqrs.CommandHandler, it also allows returning a result from the handler.
+// The result is passed to the Backend implementation and sent to the caller.
+//
+// The logic if a command should be acked or not is based on the logic of the Backend.
+// For example, for the PubSubBackend, it depends on the `PubSubBackendConfig.AckCommandErrors` option.
+//
+// The reply is sent to the caller, even if the handler returns an error.
+func NewCommandHandlerWithResult[Command any, Result any](
+	handlerName string,
+	backend Backend[Result],
+	handleFunc func(ctx context.Context, cmd *Command) (Result, error),
+) cqrs.CommandHandler {
+	return cqrs.NewCommandHandler(handlerName, func(ctx context.Context, cmd *Command) error {
+		resp, handlerErr := handleFunc(ctx, cmd)
+
+		originalMessage, err := originalCommandMsgFromCtx(ctx)
+		if err != nil {
+			return err
+		}
+
+		return backend.OnCommandProcessed(ctx, BackendOnCommandProcessedParams[Result]{
+			Command:        cmd,
+			CommandMessage: originalMessage,
+			HandlerResult:  resp,
+			HandleErr:      handlerErr,
+		})
+	})
+}
+
+func originalCommandMsgFromCtx(ctx context.Context) (*message.Message, error) {
+	originalMessage := cqrs.OriginalMessageFromCtx(ctx)
+	if originalMessage == nil {
+		// This should not happen, as long as cqrs.CommandProcessor is used - but it's not mandatory.
+		// In this case, it's enough to use cqrs.CtxWithOriginalMessage
+		return nil, errors.New(
+			"original message not found in context, did you pass context correctly everywhere? " +
+				"did you use cqrs.CommandProcessor? " +
+				"if you are using custom implementation, please call cqrs.CtxWithOriginalMessage on the context passed to the handler",
+		)
+	}
+	return originalMessage, nil
+}