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// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package iptables
import (
"fmt"
"syscall"
"unsafe"
)
type originalDstError struct {
errno syscall.Errno
}
func (e originalDstError) Error() string {
return fmt.Sprintf("errno (%d) when calling getsockopt(SO_ORIGINAL_DST): %v", int(e.errno), e.errno.Error())
}
// SO_ORIGINAL_DST gets the original destination of a redirected packet via
// getsockopt.
const SO_ORIGINAL_DST = 80
func originalDestination4(connfd int) (syscall.RawSockaddrInet4, error) {
var addr syscall.RawSockaddrInet4
var addrLen uint32 = syscall.SizeofSockaddrInet4
if errno := originalDestination(connfd, syscall.SOL_IP, unsafe.Pointer(&addr), &addrLen); errno != 0 {
return syscall.RawSockaddrInet4{}, originalDstError{errno}
}
return addr, nil
}
func originalDestination6(connfd int) (syscall.RawSockaddrInet6, error) {
var addr syscall.RawSockaddrInet6
var addrLen uint32 = syscall.SizeofSockaddrInet6
if errno := originalDestination(connfd, syscall.SOL_IPV6, unsafe.Pointer(&addr), &addrLen); errno != 0 {
return syscall.RawSockaddrInet6{}, originalDstError{errno}
}
return addr, nil
}
func originalDestination(connfd int, level uintptr, optval unsafe.Pointer, optlen *uint32) syscall.Errno {
_, _, errno := syscall.Syscall6(
syscall.SYS_GETSOCKOPT,
uintptr(connfd),
level,
SO_ORIGINAL_DST,
uintptr(optval),
uintptr(unsafe.Pointer(optlen)),
0)
return errno
}
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