cleanup interfaces for v4

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

broker/broker.go

@@ -10,13 +10,15 @@ import (
 )
 
 // DefaultBroker default memory broker
-var DefaultBroker = NewBroker()
+var DefaultBroker Broker // =  NewBroker()
 
 var (
 	// ErrNotConnected returns when broker used but not connected yet
 	ErrNotConnected = errors.New("broker not connected")
 	// ErrDisconnected returns when broker disconnected
 	ErrDisconnected = errors.New("broker disconnected")
+	// ErrInvalidMessage returns when message has nvalid format
+	ErrInvalidMessage = errors.New("broker message has invalid format")
 )
 
 // Broker is an interface used for asynchronous messaging.
@@ -33,61 +35,33 @@ type Broker interface {
 	Connect(ctx context.Context) error
 	// Disconnect disconnect from broker
 	Disconnect(ctx context.Context) error
+	// NewMessage creates new broker message
+	NewMessage(endpoint string, req interface{}, opts ...MessageOption) Message
 	// Publish message to broker topic
-	Publish(ctx context.Context, topic string, msg *Message, opts ...PublishOption) error
+	Publish(ctx context.Context, msg interface{}, opts ...PublishOption) error
 	// Subscribe subscribes to topic message via handler
-	Subscribe(ctx context.Context, topic string, h Handler, opts ...SubscribeOption) (Subscriber, error)
-	// BatchPublish messages to broker with multiple topics
-	BatchPublish(ctx context.Context, msgs []*Message, opts ...PublishOption) error
-	// BatchSubscribe subscribes to topic messages via handler
-	BatchSubscribe(ctx context.Context, topic string, h BatchHandler, opts ...SubscribeOption) (Subscriber, error)
+	Subscribe(ctx context.Context, topic string, handler interface{}, opts ...SubscribeOption) (Subscriber, error)
 	// String type of broker
 	String() string
 }
 
-// Handler is used to process messages via a subscription of a topic.
-type Handler func(Event) error
-
-// Events contains multiple events
-type Events []Event
-
-// Ack try to ack all events and return
-func (evs Events) Ack() error {
-	var err error
-	for _, ev := range evs {
-		if err = ev.Ack(); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
-// SetError sets error on event
-func (evs Events) SetError(err error) {
-	for _, ev := range evs {
-		ev.SetError(err)
-	}
-}
-
-// BatchHandler is used to process messages in batches via a subscription of a topic.
-type BatchHandler func(Events) error
-
-// Event is given to a subscription handler for processing
-type Event interface {
+// Message is given to a subscription handler for processing
+type Message interface {
+	// Context for the message
+	Context() context.Context
 	// Topic returns event topic
 	Topic() string
-	// Message returns broker message
-	Message() *Message
+	// Body returns broker message
+	Body() interface{}
 	// Ack acknowledge message
 	Ack() error
 	// Error returns message error (like decoding errors or some other)
+	// In this case Body contains raw []byte from broker
 	Error() error
-	// SetError set event processing error
-	SetError(err error)
 }
 
-// Message is used to transfer data
-type Message struct {
+// RawMessage is used to transfer data
+type RawMessage struct {
 	// Header contains message metadata
 	Header metadata.Metadata
 	// Body contains message body
@@ -95,8 +69,8 @@ type Message struct {
 }
 
 // NewMessage create broker message with topic filled
-func NewMessage(topic string) *Message {
-	m := &Message{Header: metadata.New(2)}
+func NewRawMessage(topic string) *RawMessage {
+	m := &RawMessage{Header: metadata.New(2)}
 	m.Header.Set(metadata.HeaderTopic, topic)
 	return m
 }

broker/memory.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package broker
 
 import (
@@ -6,7 +8,6 @@ import (
 	"time"
 
 	"go.unistack.org/micro/v4/logger"
-	"go.unistack.org/micro/v4/metadata"
 	maddr "go.unistack.org/micro/v4/util/addr"
 	"go.unistack.org/micro/v4/util/id"
 	mnet "go.unistack.org/micro/v4/util/net"
@@ -21,23 +22,6 @@ type memoryBroker struct {
 	connected bool
 }
 
-type memoryEvent struct {
-	err     error
-	message interface{}
-	topic   string
-	opts    Options
-}
-
-type memorySubscriber struct {
-	ctx          context.Context
-	exit         chan bool
-	handler      Handler
-	batchhandler BatchHandler
-	id           string
-	topic        string
-	opts         SubscribeOptions
-}
-
 func (m *memoryBroker) Options() Options {
 	return m.opts
 }
@@ -89,16 +73,11 @@ func (m *memoryBroker) Init(opts ...Option) error {
 	return nil
 }
 
-func (m *memoryBroker) Publish(ctx context.Context, topic string, msg *Message, opts ...PublishOption) error {
-	msg.Header.Set(metadata.HeaderTopic, topic)
-	return m.publish(ctx, []*Message{msg}, opts...)
+func (m *memoryBroker) NewMessage(endpoint string, req interface{}, opts ...MessageOption) Message {
+	return &memoryMessage{}
 }
 
-func (m *memoryBroker) BatchPublish(ctx context.Context, msgs []*Message, opts ...PublishOption) error {
-	return m.publish(ctx, msgs, opts...)
-}
-
-func (m *memoryBroker) publish(ctx context.Context, msgs []*Message, opts ...PublishOption) error {
+func (m *memoryBroker) Publish(ctx context.Context, message interface{}, opts ...PublishOption) error {
 	m.RLock()
 	if !m.connected {
 		m.RUnlock()
@@ -113,25 +92,32 @@ func (m *memoryBroker) publish(ctx context.Context, msgs []*Message, opts ...Pub
 		return ctx.Err()
 	default:
 		options := NewPublishOptions(opts...)
-
-		msgTopicMap := make(map[string]Events)
-		for _, v := range msgs {
-			p := &memoryEvent{opts: m.opts}
-
-			if m.opts.Codec == nil || options.BodyOnly {
-				p.topic, _ = v.Header.Get(metadata.HeaderTopic)
-				p.message = v.Body
-			} else {
-				p.topic, _ = v.Header.Get(metadata.HeaderTopic)
-				p.message, err = m.opts.Codec.Marshal(v)
-				if err != nil {
-					return err
+		var msgs []*memoryMessage
+		switch v := message.(type) {
+		case *memoryMessage:
+			msgs = []*memoryMessage{v}
+		case []*memoryMessage:
+			msgs = v
+		default:
+			return ErrInvalidMessage
+		}
+		msgTopicMap := make(map[string][]*memoryMessage)
+		for _, msg := range msgs {
+			p := &memoryMessage{opts: options}
+			/*
+				if mb, ok := msg.Body().(*codec.Frame); ok {
+					p.message = v.Body
+				} else {
+					p.topic, _ = v.Header.Get(metadata.HeaderTopic)
+					p.message, err = m.opts.Codec.Marshal(v)
+					if err != nil {
+						return err
+					}
 				}
-			}
-			msgTopicMap[p.topic] = append(msgTopicMap[p.topic], p)
+			*/
+			msgTopicMap[msg.Topic()] = append(msgTopicMap[p.topic], p)
 		}
 
-		beh := m.opts.BatchErrorHandler
 		eh := m.opts.ErrorHandler
 
 		for t, ms := range msgTopicMap {
@@ -152,28 +138,21 @@ func (m *memoryBroker) publish(ctx context.Context, msgs []*Message, opts ...Pub
 
 			m.opts.Meter.Counter(PublishMessageTotal, "endpoint", t, "status", "success").Add(len(ms))
 			for _, sub := range subs {
-				if sub.opts.BatchErrorHandler != nil {
-					beh = sub.opts.BatchErrorHandler
-				}
 				if sub.opts.ErrorHandler != nil {
 					eh = sub.opts.ErrorHandler
 				}
 
-				switch {
-				// batch processing
-				case sub.batchhandler != nil:
-
-					if err = sub.batchhandler(ms); err != nil {
+				for _, p := range ms {
+					if err = sub.handler(p); err != nil {
 						m.opts.Meter.Counter(SubscribeMessageTotal, "endpoint", t, "status", "failure").Inc()
-						ms.SetError(err)
-						if beh != nil {
-							_ = beh(ms)
+						if eh != nil {
+							_ = eh(p)
 						} else if m.opts.Logger.V(logger.ErrorLevel) {
 							m.opts.Logger.Error(m.opts.Context, err.Error())
 						}
 					} else {
 						if sub.opts.AutoAck {
-							if err = ms.Ack(); err != nil {
+							if err = p.Ack(); err != nil {
 								m.opts.Logger.Errorf(m.opts.Context, "ack failed: %v", err)
 								m.opts.Meter.Counter(SubscribeMessageTotal, "endpoint", t, "status", "failure").Inc()
 							} else {
@@ -183,34 +162,8 @@ func (m *memoryBroker) publish(ctx context.Context, msgs []*Message, opts ...Pub
 							m.opts.Meter.Counter(SubscribeMessageTotal, "endpoint", t, "status", "success").Inc()
 						}
 					}
-					m.opts.Meter.Counter(PublishMessageInflight, "endpoint", t).Add(-len(ms))
-					m.opts.Meter.Counter(SubscribeMessageInflight, "endpoint", t).Add(-len(ms))
-					// single processing
-				case sub.handler != nil:
-					for _, p := range ms {
-						if err = sub.handler(p); err != nil {
-							m.opts.Meter.Counter(SubscribeMessageTotal, "endpoint", t, "status", "failure").Inc()
-							p.SetError(err)
-							if eh != nil {
-								_ = eh(p)
-							} else if m.opts.Logger.V(logger.ErrorLevel) {
-								m.opts.Logger.Error(m.opts.Context, err.Error())
-							}
-						} else {
-							if sub.opts.AutoAck {
-								if err = p.Ack(); err != nil {
-									m.opts.Logger.Errorf(m.opts.Context, "ack failed: %v", err)
-									m.opts.Meter.Counter(SubscribeMessageTotal, "endpoint", t, "status", "failure").Inc()
-								} else {
-									m.opts.Meter.Counter(SubscribeMessageTotal, "endpoint", t, "status", "success").Inc()
-								}
-							} else {
-								m.opts.Meter.Counter(SubscribeMessageTotal, "endpoint", t, "status", "success").Inc()
-							}
-						}
-						m.opts.Meter.Counter(PublishMessageInflight, "endpoint", t).Add(-1)
-						m.opts.Meter.Counter(SubscribeMessageInflight, "endpoint", t).Add(-1)
-					}
+					m.opts.Meter.Counter(PublishMessageInflight, "endpoint", t).Add(-1)
+					m.opts.Meter.Counter(SubscribeMessageInflight, "endpoint", t).Add(-1)
 				}
 
 			}
@@ -226,52 +179,7 @@ func (m *memoryBroker) publish(ctx context.Context, msgs []*Message, opts ...Pub
 	return nil
 }
 
-func (m *memoryBroker) BatchSubscribe(ctx context.Context, topic string, handler BatchHandler, opts ...SubscribeOption) (Subscriber, error) {
-	m.RLock()
-	if !m.connected {
-		m.RUnlock()
-		return nil, ErrNotConnected
-	}
-	m.RUnlock()
-
-	sid, err := id.New()
-	if err != nil {
-		return nil, err
-	}
-
-	options := NewSubscribeOptions(opts...)
-
-	sub := &memorySubscriber{
-		exit:         make(chan bool, 1),
-		id:           sid,
-		topic:        topic,
-		batchhandler: handler,
-		opts:         options,
-		ctx:          ctx,
-	}
-
-	m.Lock()
-	m.subscribers[topic] = append(m.subscribers[topic], sub)
-	m.Unlock()
-
-	go func() {
-		<-sub.exit
-		m.Lock()
-		newSubscribers := make([]*memorySubscriber, 0, len(m.subscribers)-1)
-		for _, sb := range m.subscribers[topic] {
-			if sb.id == sub.id {
-				continue
-			}
-			newSubscribers = append(newSubscribers, sb)
-		}
-		m.subscribers[topic] = newSubscribers
-		m.Unlock()
-	}()
-
-	return sub, nil
-}
-
-func (m *memoryBroker) Subscribe(ctx context.Context, topic string, handler Handler, opts ...SubscribeOption) (Subscriber, error) {
+func (m *memoryBroker) Subscribe(ctx context.Context, topic string, handler interface{}, opts ...SubscribeOption) (Subscriber, error) {
 	m.RLock()
 	if !m.connected {
 		m.RUnlock()
@@ -324,38 +232,41 @@ func (m *memoryBroker) Name() string {
 	return m.opts.Name
 }
 
-func (m *memoryEvent) Topic() string {
+type memoryMessage struct {
+	err   error
+	body  interface{}
+	topic string
+	opts  PublishOptions
+	ctx   context.Context
+}
+
+func (m *memoryMessage) Topic() string {
 	return m.topic
 }
 
-func (m *memoryEvent) Message() *Message {
-	switch v := m.message.(type) {
-	case *Message:
-		return v
-	case []byte:
-		msg := &Message{}
-		if err := m.opts.Codec.Unmarshal(v, msg); err != nil {
-			if m.opts.Logger.V(logger.ErrorLevel) {
-				m.opts.Logger.Error(m.opts.Context, "[memory]: failed to unmarshal: %v", err)
-			}
-			return nil
-		}
-		return msg
-	}
+func (m *memoryMessage) Body() interface{} {
+	return m.body
+}
 
+func (m *memoryMessage) Ack() error {
 	return nil
 }
 
-func (m *memoryEvent) Ack() error {
-	return nil
-}
-
-func (m *memoryEvent) Error() error {
+func (m *memoryMessage) Error() error {
 	return m.err
 }
 
-func (m *memoryEvent) SetError(err error) {
-	m.err = err
+func (m *memoryMessage) Context() context.Context {
+	return m.ctx
+}
+
+type memorySubscriber struct {
+	ctx     context.Context
+	exit    chan bool
+	handler interface{}
+	id      string
+	topic   string
+	opts    SubscribeOptions
 }
 
 func (m *memorySubscriber) Options() SubscribeOptions {
@@ -372,7 +283,7 @@ func (m *memorySubscriber) Unsubscribe(ctx context.Context) error {
 }
 
 // NewBroker return new memory broker
-func NewBroker(opts ...Option) Broker {
+func NewBroker(opts ...Option) *memoryBroker {
 	return &memoryBroker{
 		opts:        NewOptions(opts...),
 		subscribers: make(map[string][]*memorySubscriber),

broker/options.go

@@ -7,6 +7,7 @@ import (
 
 	"go.unistack.org/micro/v4/codec"
 	"go.unistack.org/micro/v4/logger"
+	"go.unistack.org/micro/v4/metadata"
 	"go.unistack.org/micro/v4/meter"
 	"go.unistack.org/micro/v4/register"
 	"go.unistack.org/micro/v4/tracer"
@@ -37,8 +38,8 @@ type Options struct {
 	Tracer tracer.Tracer
 	// Register can be used for clustering
 	Register register.Register
-	// Codec holds the codec for marshal/unmarshal
-	Codec codec.Codec
+	// Codecs holds the codec for marshal/unmarshal
+	Codecs map[string]codec.Codec
 	// Logger used for logging
 	Logger logger.Logger
 	// Meter used for metrics
@@ -48,15 +49,16 @@ type Options struct {
 	// TLSConfig holds tls.TLSConfig options
 	TLSConfig *tls.Config
 	// ErrorHandler used when broker can't unmarshal incoming message
-	ErrorHandler Handler
-	// BatchErrorHandler used when broker can't unmashal incoming messages
-	BatchErrorHandler BatchHandler
+	ErrorHandler func(Message)
 	// Name holds the broker name
 	Name string
 	// Addrs holds the broker address
 	Addrs []string
 }
 
+// Option func
+type Option func(*Options)
+
 // NewOptions create new Options
 func NewOptions(opts ...Option) Options {
 	options := Options{
@@ -64,7 +66,7 @@ func NewOptions(opts ...Option) Options {
 		Logger:   logger.DefaultLogger,
 		Context:  context.Background(),
 		Meter:    meter.DefaultMeter,
-		Codec:    codec.DefaultCodec,
+		Codecs:   make(map[string]codec.Codec),
 		Tracer:   tracer.DefaultTracer,
 	}
 	for _, o := range opts {
@@ -80,6 +82,32 @@ func Context(ctx context.Context) Option {
 	}
 }
 
+// MessageOption func
+type MessageOption func(*MessageOptions)
+
+// MessageOptions struct
+type MessageOptions struct {
+	Metadata    metadata.Metadata
+	ContentType string
+}
+
+// MessageMetadata pass additional message metadata
+func MessageMetadata(md metadata.Metadata) MessageOption {
+	return func(o *MessageOptions) {
+		o.Metadata = md
+	}
+}
+
+// MessageContentType pass ContentType for message data
+func MessageContentType(ct string) MessageOption {
+	return func(o *MessageOptions) {
+		o.ContentType = ct
+	}
+}
+
+// PublishOption func
+type PublishOption func(*PublishOptions)
+
 // PublishOptions struct
 type PublishOptions struct {
 	// Context holds external options
@@ -104,11 +132,9 @@ type SubscribeOptions struct {
 	// Context holds external options
 	Context context.Context
 	// ErrorHandler used when broker can't unmarshal incoming message
-	ErrorHandler Handler
-	// BatchErrorHandler used when broker can't unmashal incoming messages
-	BatchErrorHandler BatchHandler
-	// Group holds consumer group
-	Group string
+	ErrorHandler func(Message)
+	// QueueGroup holds consumer group
+	QueueGroup string
 	// AutoAck flag specifies auto ack of incoming message when no error happens
 	AutoAck bool
 	// BodyOnly flag specifies that message contains only body bytes without header
@@ -119,12 +145,6 @@ type SubscribeOptions struct {
 	BatchWait time.Duration
 }
 
-// Option func
-type Option func(*Options)
-
-// PublishOption func
-type PublishOption func(*PublishOptions)
-
 // PublishBodyOnly publish only body of the message
 func PublishBodyOnly(b bool) PublishOption {
 	return func(o *PublishOptions) {
@@ -148,59 +168,29 @@ func Addrs(addrs ...string) Option {
 
 // Codec sets the codec used for encoding/decoding used where
 // a broker does not support headers
-func Codec(c codec.Codec) Option {
+// Codec to be used to encode/decode requests for a given content type
+func Codec(contentType string, c codec.Codec) Option {
 	return func(o *Options) {
-		o.Codec = c
+		o.Codecs[contentType] = c
 	}
 }
 
 // ErrorHandler will catch all broker errors that cant be handled
 // in normal way, for example Codec errors
-func ErrorHandler(h Handler) Option {
+func ErrorHandler(h func(Message)) Option {
 	return func(o *Options) {
 		o.ErrorHandler = h
 	}
 }
 
-// BatchErrorHandler will catch all broker errors that cant be handled
-// in normal way, for example Codec errors
-func BatchErrorHandler(h BatchHandler) Option {
-	return func(o *Options) {
-		o.BatchErrorHandler = h
-	}
-}
-
 // SubscribeErrorHandler will catch all broker errors that cant be handled
 // in normal way, for example Codec errors
-func SubscribeErrorHandler(h Handler) SubscribeOption {
+func SubscribeErrorHandler(h func(Message)) SubscribeOption {
 	return func(o *SubscribeOptions) {
 		o.ErrorHandler = h
 	}
 }
 
-// SubscribeBatchErrorHandler will catch all broker errors that cant be handled
-// in normal way, for example Codec errors
-func SubscribeBatchErrorHandler(h BatchHandler) SubscribeOption {
-	return func(o *SubscribeOptions) {
-		o.BatchErrorHandler = h
-	}
-}
-
-// Queue sets the subscribers queue
-// Deprecated
-func Queue(name string) SubscribeOption {
-	return func(o *SubscribeOptions) {
-		o.Group = name
-	}
-}
-
-// SubscribeGroup sets the name of the queue to share messages on
-func SubscribeGroup(name string) SubscribeOption {
-	return func(o *SubscribeOptions) {
-		o.Group = name
-	}
-}
-
 // Register sets register option
 func Register(r register.Register) Option {
 	return func(o *Options) {
@@ -243,6 +233,21 @@ func Name(n string) Option {
 	}
 }
 
+// SubscribeOption func signature
+type SubscribeOption func(*SubscribeOptions)
+
+// NewSubscribeOptions creates new SubscribeOptions
+func NewSubscribeOptions(opts ...SubscribeOption) SubscribeOptions {
+	options := SubscribeOptions{
+		AutoAck: true,
+		Context: context.Background(),
+	}
+	for _, o := range opts {
+		o(&options)
+	}
+	return options
+}
+
 // SubscribeContext set context
 func SubscribeContext(ctx context.Context) SubscribeOption {
 	return func(o *SubscribeOptions) {
@@ -250,14 +255,6 @@ func SubscribeContext(ctx context.Context) SubscribeOption {
 	}
 }
 
-// DisableAutoAck disables auto ack
-// Deprecated
-func DisableAutoAck() SubscribeOption {
-	return func(o *SubscribeOptions) {
-		o.AutoAck = false
-	}
-}
-
 // SubscribeAutoAck contol auto acking of messages
 // after they have been handled.
 func SubscribeAutoAck(b bool) SubscribeOption {
@@ -287,17 +284,16 @@ func SubscribeBatchWait(td time.Duration) SubscribeOption {
 	}
 }
 
-// SubscribeOption func
-type SubscribeOption func(*SubscribeOptions)
-
-// NewSubscribeOptions creates new SubscribeOptions
-func NewSubscribeOptions(opts ...SubscribeOption) SubscribeOptions {
-	options := SubscribeOptions{
-		AutoAck: true,
-		Context: context.Background(),
+// SubscribeQueueGroup sets the shared queue name distributed messages across subscribers
+func SubscribeQueueGroup(n string) SubscribeOption {
+	return func(o *SubscribeOptions) {
+		o.QueueGroup = n
+	}
+}
+
+// SubscribeAutoAck control auto ack processing for handler
+func SubscribeAuthAck(b bool) SubscribeOption {
+	return func(o *SubscribeOptions) {
+		o.AutoAck = b
 	}
-	for _, o := range opts {
-		o(&options)
-	}
-	return options
 }

broker/subscriber.go

@@ -0,0 +1,98 @@
+package broker
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+const (
+	subSig      = "func(context.Context, interface{}) error"
+	batchSubSig = "func([]context.Context, []interface{}) error"
+)
+
+// Precompute the reflect type for error. Can't use error directly
+// because Typeof takes an empty interface value. This is annoying.
+var typeOfError = reflect.TypeOf((*error)(nil)).Elem()
+
+// Is this an exported - upper case - name?
+func isExported(name string) bool {
+	rune, _ := utf8.DecodeRuneInString(name)
+	return unicode.IsUpper(rune)
+}
+
+// Is this type exported or a builtin?
+func isExportedOrBuiltinType(t reflect.Type) bool {
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	// PkgPath will be non-empty even for an exported type,
+	// so we need to check the type name as well.
+	return isExported(t.Name()) || t.PkgPath() == ""
+}
+
+// ValidateSubscriber func signature
+func ValidateSubscriber(sub interface{}) error {
+	typ := reflect.TypeOf(sub)
+	var argType reflect.Type
+	switch typ.Kind() {
+	case reflect.Func:
+		name := "Func"
+		switch typ.NumIn() {
+		case 1: // func(Message) error
+
+		case 2: // func(context.Context, Message) error or func(context.Context, []Message) error
+			argType = typ.In(2)
+			// if sub.Options().Batch {
+			if argType.Kind() != reflect.Slice {
+				return fmt.Errorf("subscriber %v dont have required signature %s", name, batchSubSig)
+			}
+			if strings.Compare(fmt.Sprintf("%v", argType), "[]interface{}") == 0 {
+				return fmt.Errorf("subscriber %v dont have required signaure %s", name, batchSubSig)
+			}
+		//	}
+		default:
+			return fmt.Errorf("subscriber %v takes wrong number of args: %v required signature %s or %s", name, typ.NumIn(), subSig, batchSubSig)
+		}
+		if !isExportedOrBuiltinType(argType) {
+			return fmt.Errorf("subscriber %v argument type not exported: %v", name, argType)
+		}
+		if typ.NumOut() != 1 {
+			return fmt.Errorf("subscriber %v has wrong number of return values: %v require signature %s or %s",
+				name, typ.NumOut(), subSig, batchSubSig)
+		}
+		if returnType := typ.Out(0); returnType != typeOfError {
+			return fmt.Errorf("subscriber %v returns %v not error", name, returnType.String())
+		}
+	default:
+		hdlr := reflect.ValueOf(sub)
+		name := reflect.Indirect(hdlr).Type().Name()
+
+		for m := 0; m < typ.NumMethod(); m++ {
+			method := typ.Method(m)
+			switch method.Type.NumIn() {
+			case 3:
+				argType = method.Type.In(2)
+			default:
+				return fmt.Errorf("subscriber %v.%v takes wrong number of args: %v required signature %s or %s",
+					name, method.Name, method.Type.NumIn(), subSig, batchSubSig)
+			}
+
+			if !isExportedOrBuiltinType(argType) {
+				return fmt.Errorf("%v argument type not exported: %v", name, argType)
+			}
+			if method.Type.NumOut() != 1 {
+				return fmt.Errorf(
+					"subscriber %v.%v has wrong number of return values: %v require signature %s or %s",
+					name, method.Name, method.Type.NumOut(), subSig, batchSubSig)
+			}
+			if returnType := method.Type.Out(0); returnType != typeOfError {
+				return fmt.Errorf("subscriber %v.%v returns %v not error", name, method.Name, returnType.String())
+			}
+		}
+	}
+
+	return nil
+}