mq(kafka): MAJOR Fix - Dynamic broker address working, one issue remains

BREAKTHROUGH ACHIEVED:
✅ Dynamic broker port detection and advertisement working!
✅ Metadata now correctly advertises actual gateway port (e.g. localhost:60430)
✅ Fixed broker address mismatch that was part of the problem

IMPLEMENTATION:
- Added SetBrokerAddress() method to Handler
- Server.Start() now updates handler with actual listening address
- GetListenerAddr() handles [::]:port and host:port formats
- Metadata response uses dynamic broker host:port instead of hardcoded 9092

EVIDENCE OF SUCCESS:
- Debug logs: 'Advertising broker at localhost:60430' ✅
- Response hex contains correct port: 0000ec0e = 60430 ✅
- No more 9092 hardcoding ✅

REMAINING ISSUE:
❌ Same '[3] Unknown Topic Or Partition' error still occurs
❌ kafka-go's internal validation logic still rejects our response

ANALYSIS:
This confirms broker address mismatch was PART of the problem but not the
complete solution. There's still another protocol validation issue preventing
kafka-go from accepting our topic metadata.

NEXT: Investigate partition leader configuration or missing Metadata v1 fields.

weed/mq/kafka/gateway/server.go

@@ -3,6 +3,8 @@ package gateway
 import (
 	"context"
 	"net"
+	"strconv"
+	"strings"
 	"sync"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
@@ -58,6 +60,11 @@ func (s *Server) Start() error {
 		return err
 	}
 	s.ln = ln
+	
+	// Update handler with actual broker address for Metadata responses
+	host, port := s.GetListenerAddr() 
+	s.handler.SetBrokerAddress(host, port)
+	glog.V(1).Infof("Kafka gateway advertising broker at %s:%d", host, port)
 	s.wg.Add(1)
 	go func() {
 		defer s.wg.Done()
@@ -117,3 +124,31 @@ func (s *Server) Addr() string {
 func (s *Server) GetHandler() *protocol.Handler {
 	return s.handler
 }
+
+// GetListenerAddr returns the actual listening address and port
+func (s *Server) GetListenerAddr() (string, int) {
+	if s.ln == nil {
+		return "localhost", 9092 // fallback
+	}
+	
+	addr := s.ln.Addr().String()
+	// Parse [::]:port or host:port format
+	if strings.HasPrefix(addr, "[::]:") {
+		port := strings.TrimPrefix(addr, "[::]:") 
+		if p, err := strconv.Atoi(port); err == nil {
+			return "localhost", p
+		}
+	}
+	
+	// Handle host:port format
+	if host, port, err := net.SplitHostPort(addr); err == nil {
+		if p, err := strconv.Atoi(port); err == nil {
+			if host == "::" || host == "" {
+				host = "localhost"
+			}
+			return host, p
+		}
+	}
+	
+	return "localhost", 9092 // fallback
+}

weed/mq/kafka/protocol/handler.go

@@ -42,6 +42,10 @@ type Handler struct {
 
 	// Consumer group coordination
 	groupCoordinator *consumer.GroupCoordinator
+	
+	// Dynamic broker address for Metadata responses
+	brokerHost string
+	brokerPort int
 }
 
 // NewHandler creates a new handler in legacy in-memory mode
@@ -51,6 +55,8 @@ func NewHandler() *Handler {
 		ledgers:          make(map[TopicPartitionKey]*offset.Ledger),
 		useSeaweedMQ:     false,
 		groupCoordinator: consumer.NewGroupCoordinator(),
+		brokerHost:       "localhost", // default fallback
+		brokerPort:       9092,        // default fallback
 	}
 }
 
@@ -122,6 +128,12 @@ func (h *Handler) GetLedger(topic string, partition int32) *offset.Ledger {
 	return h.ledgers[key]
 }
 
+// SetBrokerAddress updates the broker address used in Metadata responses  
+func (h *Handler) SetBrokerAddress(host string, port int) {
+	h.brokerHost = host
+	h.brokerPort = port
+}
+
 // HandleConn processes a single client connection
 func (h *Handler) HandleConn(conn net.Conn) error {
 	defer func() {
@@ -358,16 +370,19 @@ func (h *Handler) handleMetadata(correlationID uint32, requestBody []byte) ([]by
 	// Broker 0: node_id(4) + host + port(4) + rack
 	response = append(response, 0, 0, 0, 0) // node_id = 0
 
-	// Use "localhost" for simplicity - kafka-go should be able to connect back
-	// The port issue is more likely the problem than the host
-	host := "localhost"
+	// Use dynamic broker address set by the server
+	host := h.brokerHost
+	port := h.brokerPort
+	
+	fmt.Printf("DEBUG: Advertising broker at %s:%d\n", host, port)
 	
 	response = append(response, 0, byte(len(host)))
 	response = append(response, []byte(host)...)
 
-	// Port (4 bytes) - Use standard Kafka port for now
-	// TODO: Should get actual port from server configuration
-	response = append(response, 0, 0, 0x23, 0x84) // 9092 in big-endian
+	// Port (4 bytes) - Use actual gateway port
+	portBytes := make([]byte, 4)
+	binary.BigEndian.PutUint32(portBytes, uint32(port))
+	response = append(response, portBytes...)
 
 	// Rack - nullable string, using null (-1 length)
 	response = append(response, 0xFF, 0xFF) // null rack