What are the equivalents of IP_RECVOPTS and IP_RECVRETOPTS in Windows - c

Question

I'm doing some socket programming that I'm trying to make cross-platform compatible. For Windows systems, I'm including the following headers:
#include <winsock2.h>
#include <ws2tcpip.h>
When I tried to compile my application on Windows, I got errors about the following constants' being undefined:
IP_RECVOPTS
IP_RECVRETOPTS
I thought that odd, because I thought those were pretty common socket options, but perhaps I'm wrong. Either way, sure enough, they're not listed anywhere in the Windows socket documentation.
The documentation in a Linux distro's in.h says the following about these constants:
IP_RECVOPTS /* bool; Receive all IP options w/datagram. */
IP_RECVRETOPTS /* bool; Receive IP options for response. */
In that distro's in.h, the defined value of the first one appears to be 6, while the defined value of the second one appears to be 7.
So, my questions:
Are there equivalent constants in Windows sockets for replacing these two constants (or, perhaps, do I just need to include some other header)?
If not, is the receiving of IP options even possible in Windows sockets?
If so, is it safe for me to hard-code these values on Windows systems to 6 and 7, respectively, or should they be some other value?
UPDATE 1
I continued my Google research today. I found these two interesting tidbits. I don't know whether they help me. The first is the Windows Runtime (WinRT) Socket Address header (WinRTSockAddr.h) from the MixedRealityToolkit repository on Microsoft's official GitHub account. It contains the following:
#define IP_RECVOPTS 6
#define IP_RETOPTS 7
This aligns with *nix values I've seen elsewhere (I've commonly seen IP_RETOPTS aliased to IP_RECVRETOPTS). But then there's this alleged Windows Sockets helper header from the "Geek Research Lab"'s GitHub account. I've no idea if it has any credibility, but it has different values for these constants:
#define IP_RECVOPTS 5 /* bool; receive all IP opts w/dgram */
#define IP_RECVRETOPTS 6 /* bool; receive IP opts for response */
#define IP_RECVDSTADDR 7 /* bool; receive IP dst addr w/dgram */
#define IP_RETOPTS 8 /* ip_opts; set/get IP options */
That's contradictory on all fronts: values and the aliasing of IP_RETOPTS to IP_RECVRETOPTS. :-/

Answer 1

The only somewhat portable standard for accessing IP (as well as TCP and UDP) options is via the ancillary data parameters of sendmsg and recvmsg.
Unfortunately while having access is standardized, the exact details of what options are available can still vary between OSes.
On Linux, see the cmsg man page and note:
CONFORMING TO
This ancillary data model conforms to the POSIX.1g draft, 4.4BSD-
Lite, the IPv6 advanced API described in RFC 2292 and SUSv2.
CMSG_ALIGN() is a Linux extension.
By comparison, the man page describing IP_RECVOPTS has no "CONFORMING TO" section.
The similar Windows documentation page is "IPPROTO_IP Socket Options" on MSDN
In the Windows documentation for WSARecvMsg and WSASendMsg, there's the following note:
based on the Posix.1g specification for the msghdr structure
The documentation for _WSAMSG lists the ancillary data available from Winsock.
The POSIX documentation is here
Unfortunately for portability:
The system documentation shall specify the cmsg_type definitions for the supported protocols.
which is to say, the ancillary data actually available is not portable, because it's not specified by POSIX and/or Single Unix Specification.

Answer 2

Are there equivalent constants in Windows sockets for replacing these
two constants (or, perhaps, do I just need to include some other header)?
No. Unfortunately, this wouldn't be the first time that Windows is slow to implement parts of a particular standard or an RFC. Taking a look at socket options, for example, IP_RECVTTL was added only recently, for Windows 10. So maybe if you wait long enough, you may live to see the options you want supported on Windows? The code you have seen seems to be copy-pasted from some other, non-Windows code. In the case of RakNet, note that WinRTSockAddr.h is only used for WINDOWS_STORE_RT support, which is currently limited.
If not, is the receiving of IP options even possible in Windows
sockets?
No, it does not seem to be. At least I'm not aware of such capability.
If so, is it safe for me to hard-code these values on Windows systems
to 6 and 7, respectively, or should they be some other value?
No, it's probably not safe to hard-code the values. At best, such option values would be ignored, but they could be misinterpreted and result in unwanted behavior.
Since you indicated that you aim to make your code cross-platform, you will likely have to settle for the intersection of features that are supported on all the platforms that you want to support.