add conn limiter

limiter/conn/wrapper/conn.go

@@ -0,0 +1,43 @@
+package wrapper
+
+import (
+	"errors"
+	"net"
+	"syscall"
+
+	limiter "github.com/go-gost/core/limiter/conn"
+)
+
+var (
+	errUnsupport = errors.New("unsupported operation")
+)
+
+// serverConn is a server side Conn with metrics supported.
+type serverConn struct {
+	net.Conn
+	limiter limiter.Limiter
+}
+
+func WrapConn(limiter limiter.Limiter, c net.Conn) net.Conn {
+	if limiter == nil {
+		return c
+	}
+	return &serverConn{
+		Conn:    c,
+		limiter: limiter,
+	}
+}
+
+func (c *serverConn) SyscallConn() (rc syscall.RawConn, err error) {
+	if sc, ok := c.Conn.(syscall.Conn); ok {
+		rc, err = sc.SyscallConn()
+		return
+	}
+	err = errUnsupport
+	return
+}
+
+func (c *serverConn) Close() error {
+	c.limiter.Allow(-1)
+	return c.Conn.Close()
+}