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unix: add functions to encode Inet4Pktinfo and Inet6Pktinfo

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It's possible to control the source address of a UDP packet by
passing a socket control message of type IP_PKTINFO or IPV6_PKTINFO.
This is a somewhat esoteric feature of the network stack, but it's
extremely useful feature when you really need it.

Change-Id: I8300575f975679f6689d6f1282af253ba62e8f9d
Reviewed-on: https://go-review.googlesource.com/c/sys/+/355610
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Tobias Klauser <tobias.klauser@gmail.com>
This commit is contained in:
Lorenz Bauer
2021-10-22 21:59:31 +00:00
committed by Tobias Klauser
parent 9d61738499
commit 8e5104632a
2 changed files with 99 additions and 0 deletions
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unix/sockcmsg_linux.go
+22
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@@ -34,3 +34,25 @@ func ParseUnixCredentials(m *SocketControlMessage) (*Ucred, error) {
ucred := *(*Ucred)(unsafe.Pointer(&m.Data[0]))
return &ucred, nil
}
// PktInfo4 encodes Inet4Pktinfo into a socket control message of type IP_PKTINFO.
func PktInfo4(info *Inet4Pktinfo) []byte {
b := make([]byte, CmsgSpace(SizeofInet4Pktinfo))
h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
h.Level = SOL_IP
h.Type = IP_PKTINFO
h.SetLen(CmsgLen(SizeofInet4Pktinfo))
*(*Inet4Pktinfo)(h.data(0)) = *info
return b
}
// PktInfo6 encodes Inet6Pktinfo into a socket control message of type IPV6_PKTINFO.
func PktInfo6(info *Inet6Pktinfo) []byte {
b := make([]byte, CmsgSpace(SizeofInet6Pktinfo))
h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
h.Level = SOL_IPV6
h.Type = IPV6_PKTINFO
h.SetLen(CmsgLen(SizeofInet6Pktinfo))
*(*Inet6Pktinfo)(h.data(0)) = *info
return b
}