Merge pull request #3 from LinkShen/master

use RawConn.Control to get fd instead of Fd()

tcpinfo.go

@@ -16,17 +16,22 @@ func GetsockoptTCPInfo(tcpConn *net.TCPConn) (*TCPInfo, error) {
 		return nil, fmt.Errorf("tcp conn is nil")
 	}
 
-	file, err := tcpConn.File()
+	rawConn, err := tcpConn.SyscallConn()
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("error getting raw connection. err=%v", err)
 	}
-	defer file.Close()
 
-	fd := file.Fd()
 	tcpInfo := TCPInfo{}
 	size := unsafe.Sizeof(tcpInfo)
-	_, _, errno := syscall.Syscall6(syscall.SYS_GETSOCKOPT, fd, syscall.SOL_TCP, syscall.TCP_INFO,
-		uintptr(unsafe.Pointer(&tcpInfo)), uintptr(unsafe.Pointer(&size)), 0)
+	var errno syscall.Errno
+	err = rawConn.Control(func(fd uintptr) {
+		_, _, errno = syscall.Syscall6(syscall.SYS_GETSOCKOPT, fd, syscall.SOL_TCP, syscall.TCP_INFO,
+			uintptr(unsafe.Pointer(&tcpInfo)), uintptr(unsafe.Pointer(&size)), 0)
+	})
+	if err != nil {
+		return nil, fmt.Errorf("rawconn control failed. err=%v", err)
+	}
+
 	if errno != 0 {
 		return nil, fmt.Errorf("syscall failed. errno=%d", errno)
 	}