qlibs:(socket_if)

💖 qlibs:(socket_if) — bestie's guide to interface names & scope_ids 💖

okay so real talk, this is one of those little pages from the qlibs manual (section 3, if we're being specific 👀) and honestly it's short but it matters. it's all about mapping between an interface name and a scope_id, and the two lil functions that do it for you. let's go ✨

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🌸 NAME 🌸

socket_if — grab the scope_id for an interface name, or the other way around, no cap 🔁

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🎀 SYNTAX 🎀

#include "socket_if.h"

uint32 socket_getifidx(const char *ifname);

const char *socket_getifname(uint32 scope_id);

two functions, one header, super clean. we love a tidy include 💅

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✨ DESCRIPTION ✨

• socket_getifidx — returns the scope_id of an interface named ifname, and like, typically that's something like ''eth0''. yep, that's the whole vibe 🫶
• socket_getifname — goes the other direction: it takes the scope_id that the operating system assigned, and retrieves the interface name (ifname) from it. it's giving reverse lookup main character energy 🔍

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🦋 INTERFACE_NAME VERSUS SCOPE_ID 🦋

so here's the tea ☕ for IPv6 LLU addresses, you gotta hand over an extra ifname (that's the interface name) alongside the IPv6 address, looking like this:

fe80::1%eth0

but the operating systems? they'd rather use scope_id as the index for ifname. classic OS behaviour honestly 💀

now for global IPv6 and ULA addresses, ifname can just be set to 0. and since IPv4 addresses on any interface are always unique (periodt 💯), you can simply use 0 for all cases. easy.

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🌈 BACKGROUND 🌈

Qlib's socket routines give you an easy API to set up TCP or UDP connections over IPv4 or IPv6 networks — both, bestie, we don't pick favourites 💖. and together with Qlib's IP address parsing capabilities, there's a whole set of high-level socket routines that let you handle IPv4/IPv6 in a common way. iconic behaviour, truly 👑

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🍓 SOCKET FILES 🍓

here's the whole squad of socket files, each doing their one job and doing it well:

• socket_bind.c — bind to, or reuse, the local IPv4/IPv6 address and port for a socket connection 🔗
• socket_connect.c — attempts to set up a TCP or UDP client connection 🤝
• socket_info.c — get the local/remote IPv4/IPv6 address of a socket 📍
• socket_recv.c — set up a receiving IPv4/IPv6 connection 📥
• socket_send.c — send a UDP datagram over an IPv4 or IPv6 connection 📤
• socket_setup.c — listen to and accept an IPv4/IPv6 TCP socket connection 👂
• socket_tcp.c — create a non-blocking TCP stream socket 🌊
• socket_udp.c — create a non-blocking UDP datagram socket 📨

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🧚 USAGE 🧚

most of the files above include their IPv4 and IPv6 counterparts together, plus a combined usage that needs a scope_id on top — or just simply 0 🫡. IPv4 addresses usually get converted, upon reading, into IPv4-mapped IPv6 addresses using Qlib's IP address parsing functions. and the IPv4 and IPv6 socket calls — if required — need to be told apart by the calling routines testing this:

ip6_isv4mapped(ip)

otherwise? the unified IPv6/IPv4 versions get used. simple as that 💜

ngl this is the part where you double-check which flavour you're actually dealing with before you ship it — the page is very clear that the calling routines do the distinguishing, not the library doing it behind your back 🙈

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⭐ SEE ALSO ⭐

socket_bind(3), socket_connect(3), socket_info(3), socket_recv(3), socket_send(3), socket_setup(3), socket_tcp(3), socket_udp(3) — go read them all, they're the friend group 🫶✨

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and that's the whole page!! 💖 this was qlibs:(socket_if), section 3 of the manual, signing off — mwah, go forth and resolve your interfaces, bestie 🎀🦋👑