IPV6_ADDRFORM(2const)

💫 IPV6_ADDRFORM(2const) 💫

okay bestie, gather round, because this one is such a glow-up story ✨ it's a page from the <pink>2const</pink> section of the Linux man-pages, so like, a little constant thing that lives its life inside other calls 🎀

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🌸 NAME 🌸

IPV6_ADDRFORM — turn an AF_INET6 socket into a socket of a different address family 💅

like... a socket rebrand, no cap.

📚 LIBRARY 📚

Standard C library (libc, -lc) 🫶 the classic, the icon, the one you already linked.

✨ SYNOPSIS ✨

#include <netinet/in.h>  /* Definition of IP* constants */
#include <sys/socket.h>

int setsockopt(int sockfd, IPPROTO_IPV6, IPV6_ADDRFORM,
               &(const int){AF_INET}, sizeof(int));

okay so you're calling setsockopt(2) 👑 — it's not its own function, it's a vibe you pass into setsockopt. You slide IPPROTO_IPV6 in as the level, IPV6_ADDRFORM as the option name, and then the actual value is that sneaky little compound literal &(const int){AF_INET} with sizeof(int) as the length 🌈 very "trust the process" of it.

🦋 DESCRIPTION 🦋

So. IPV6_ADDRFORM turns an AF_INET6 socket into a socket of a different address family. it's giving... metamorphosis 🧚 like a caterpillar but the caterpillar is an IPv6 socket and the butterfly is an IPv4 socket.

Right now, only AF_INET is supported for that 💖 just the one. That's the whole menu. Chef's choice.

And — this is the important part, don't skip it 🙈 — it's only allowed for IPv6 sockets that are connected and bound to a v4-mapped-on-v6 address. Both. Simultaneously. No shortcuts, bestie, the vibe check is strict here.

Now, why would you even do this? Main character reason: it's useful to pass v4-mapped sockets as file descriptors to programs that have literally no idea how to deal with the IPv6 API 😭 like handing your friend a snack in a wrapper they actually recognize. They never even have to know the IPv6 lore existed. iconic behavior honestly.

💀 ERRORS 💀

the errors live elsewhere, babe — go check setsockopt(2) and ipv6(7) 👑

like genuinely, this page is not the one holding the error list, so don't come for me, go read those two 🍓

🔥 SEE ALSO 🔥

• IPPROTO_IPV6(2const) 💜
• setsockopt(2) 🌸
• ipv6(7) ⭐

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and that's the tea 🎀 this whole page is from Linux man-pages 6.20, dated 2025-12-02 — so if you're quoting it in the group chat, cite your source, periodt 💅✨🫶