reset_linux_test.go

// +build linux

package reset

import (
	"net"
	"strings"
	"testing"
	"unsafe"

	"golang.org/x/sys/unix"
)

// resetTCPConn injects a RST on the provided ipv4 tcp connection.
func resetTCPConn(conn *net.TCPConn) error {
	// via https://stackoverflow.com/a/46264137
	// http://man7.org/linux/man-pages/man3/connect.3p.html
	// "If the sa_family member of address is AF_UNSPEC, the socket's peer
	// address shall be reset."
	sc, err := conn.SyscallConn()
	if err != nil {
		return err
	}
	tcpaddr := conn.LocalAddr().(*net.TCPAddr)
	var errno unix.Errno
	err = sc.Control(func(fd uintptr) {
		if ip := tcpaddr.IP.To4(); ip == nil {
			sa := unix.RawSockaddrInet6{
				Family: unix.AF_UNSPEC,
				Port:   uint16(tcpaddr.Port),
			}
			copy(sa.Addr[:], ip)
			e, _, _ := unix.Syscall(
				unix.SYS_CONNECT,
				fd,
				uintptr(unsafe.Pointer(&sa)),
				unsafe.Sizeof(sa),
			)
			errno = unix.Errno(e)
		} else {
			sa := unix.RawSockaddrInet4{
				Family: unix.AF_UNSPEC,
				Port:   uint16(tcpaddr.Port),
			}
			copy(sa.Addr[:], ip)
			e, _, _ := unix.Syscall(
				unix.SYS_CONNECT,
				fd,
				uintptr(unsafe.Pointer(&sa)),
				unsafe.Sizeof(sa),
			)
			errno = unix.Errno(e)
		}
	})
	if err != nil {
		return err
	}
	if errno != 0 {
		return errno
	}
	return nil
}

func TestResetTCPConn(t *testing.T) {
	for _, addr := range []string{"127.0.0.1", "[::1]"} {
		t.Run(addr, func(t *testing.T) {
			l, err := net.Listen("tcp", addr+":0")
			if err != nil {
				t.Fatal(err)
			}
			c := make(chan struct{})
			go func() {
				if conn, err := l.Accept(); err == nil {
					<-c
					resetTCPConn(conn.(*net.TCPConn))
				}
			}()
			conn, err := net.Dial("tcp", l.Addr().String())
			if err != nil {
				t.Fatal(err)
			}
			close(c)
			_, err = conn.Read([]byte{0})
			if err == nil || !strings.Contains(err.Error(), "connection reset by peer") {
				t.Errorf("unexpected error %q", err)
			}
		})
	}
}