Add message queue agent (#6463)

* scaffold message queue agent

* adjust proto, add mq_agent

* add agent client implementation

* remove unused function

* agent publish server implementation

* adding agent

weed/mq/agent/agent_server.go

@@ -0,0 +1,52 @@
+package agent
+
+import (
+	"github.com/seaweedfs/seaweedfs/weed/mq/client/pub_client"
+	"github.com/seaweedfs/seaweedfs/weed/mq/client/sub_client"
+	"github.com/seaweedfs/seaweedfs/weed/pb"
+	"github.com/seaweedfs/seaweedfs/weed/pb/mq_agent_pb"
+	"google.golang.org/grpc"
+	"sync"
+)
+
+type SessionId int64
+type SessionEntry[T any] struct {
+	entry          T
+	lastActiveTsNs int64
+}
+
+type MessageQueueAgentOptions struct {
+	SeedBrokers []pb.ServerAddress
+}
+
+type MessageQueueAgent struct {
+	mq_agent_pb.UnimplementedSeaweedMessagingAgentServer
+	option          *MessageQueueAgentOptions
+	brokers         []pb.ServerAddress
+	grpcDialOption  grpc.DialOption
+	publishers      map[SessionId]*SessionEntry[*pub_client.TopicPublisher]
+	publishersLock  sync.RWMutex
+	subscribers     map[SessionId]*SessionEntry[*sub_client.TopicSubscriber]
+	subscribersLock sync.RWMutex
+}
+
+func NewMessageQueueAgent(option *MessageQueueAgentOptions, grpcDialOption grpc.DialOption) *MessageQueueAgent {
+
+	// check masters to list all brokers
+
+	return &MessageQueueAgent{
+		option:         option,
+		brokers:        []pb.ServerAddress{},
+		grpcDialOption: grpcDialOption,
+		publishers:     make(map[SessionId]*SessionEntry[*pub_client.TopicPublisher]),
+		subscribers:    make(map[SessionId]*SessionEntry[*sub_client.TopicSubscriber]),
+	}
+}
+
+func (a *MessageQueueAgent) brokersList() []string {
+	var brokers []string
+	for _, broker := range a.brokers {
+		brokers = append(brokers, broker.String())
+	}
+	return brokers
+}