Bug 194758

Summary:	Need an API to obtain original destination port of locally forwarded UDP packet
Product:	Base System	Reporter:	hoomanfazaeli
Component:	kern	Assignee:	Adrian Chadd <adrian>
Status:	New ---
Severity:	Affects Some People	CC:	adrian, thj
Priority:	---	Keywords:	feature
Version:	10.0-RELEASE
Hardware:	Any
OS:	Any

Description hoomanfazaeli 2014-11-02 14:59:30 UTC

For UDP packets forwarded to a local daemon with a rule like below:

ipfw add 10 fwd localhost,7000 udp from any to any in recv em1

The daemon may obtain the original destination address of forwarded packets
using recvmsg(2) and IP_RECVDSTADDR socket option. However, there is no
API to obtain the original destination _port_.

One possible solution is to add a new socket option, say IP_RECVDSTSOADDR.
If set on a datagram socket, ip_savecontorl/ip6_savecontrol_v4 would record 
the datagram's destination address and port as a 'sockaddr_in[6]' structure.