add subscriber api

weed/messaging/client/subscriber.go

@@ -1,14 +1,65 @@
 package client
 
-import "github.com/chrislusf/seaweedfs/weed/pb/messaging_pb"
+import (
+	"context"
+	"io"
+	"time"
+
+	"github.com/chrislusf/seaweedfs/weed/pb/messaging_pb"
+)
 
 type Subscriber struct {
+	subscriberClient messaging_pb.SeaweedMessaging_SubscribeClient
 }
 
-func (c *MessagingClient) NewSubscriber(namespace, topic string) *Subscriber {
-	return &Subscriber{}
+func (mc *MessagingClient) NewSubscriber(subscriberId, namespace, topic string) (*Subscriber, error) {
+	stream, err := messaging_pb.NewSeaweedMessagingClient(mc.grpcConnection).Subscribe(context.Background())
+	if err != nil {
+		return nil, err
+	}
+
+	// send init message
+	err = stream.Send(&messaging_pb.SubscriberMessage{
+		Init: &messaging_pb.SubscriberMessage_InitMessage{
+			Namespace:     namespace,
+			Topic:         topic,
+			Partition:     0,
+			StartPosition: messaging_pb.SubscriberMessage_InitMessage_TIMESTAMP,
+			TimestampNs:   time.Now().UnixNano(),
+			SubscriberId:  subscriberId,
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	// process init response
+	initResponse, err := stream.Recv()
+	if err != nil {
+		return nil, err
+	}
+	if initResponse.Redirect != nil {
+		// TODO follow redirection
+	}
+
+	return &Subscriber{
+		subscriberClient: stream,
+	}, nil
 }
 
-func (p *Subscriber) Subscribe(processFn func(m *messaging_pb.Message)) error{
-	return nil
+func (s *Subscriber) Subscribe(processFn func(m *messaging_pb.Message)) error {
+	for {
+		resp, listenErr := s.subscriberClient.Recv()
+		if listenErr == io.EOF {
+			return nil
+		}
+		if listenErr != nil {
+			return listenErr
+		}
+		processFn(resp.Data)
+	}
+}
+
+func (s *Subscriber) Shutdown() {
+	s.subscriberClient.CloseSend()
 }