Start to use dispatcher

client/internal/lazyconn/activity/allocator.go

@@ -0,0 +1,56 @@
+package activity
+
+import (
+	"fmt"
+	"net"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	retryLimit = 5000
+)
+
+var (
+	listenIP      = net.ParseIP("127.0.0.1")
+	ErrNoFreePort = fmt.Errorf("no free port")
+)
+
+// portAllocator lookup for free port and allocate it
+type portAllocator struct {
+	nextFreePort uint16
+}
+
+func newPortAllocator() *portAllocator {
+	return &portAllocator{
+		nextFreePort: 65535,
+	}
+}
+
+func (p *portAllocator) newConn() (*net.UDPConn, *net.UDPAddr, error) {
+	for i := 0; i < retryLimit; i++ {
+		addr := &net.UDPAddr{
+			Port: p.nextPort(),
+			IP:   listenIP,
+		}
+
+		conn, err := net.ListenUDP("udp", addr)
+		if err != nil {
+			log.Errorf("failed to listen on port %d: %v", addr.Port, err)
+			// port could be allocated by another process
+			continue
+		}
+
+		return conn, addr, nil
+	}
+	return nil, nil, ErrNoFreePort
+}
+
+func (p *portAllocator) nextPort() int {
+	port := p.nextFreePort
+	p.nextFreePort--
+	if p.nextFreePort == 1024 {
+		p.nextFreePort = 65535
+	}
+	return int(port)
+}