BIO_ADDRINFO(3ossl)

💖 BIO_ADDRINFO(3ossl) — the OpenSSL girlies' guide to address info 💖

okay so bestie, this is a page from the OpenSSL manual, and it's all about BIO_ADDRINFO — the little union that holds your address info, plus the lookups and getters that go with it. no cap, it's lowkey iconic. 🦋

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✨ NAME ✨

BIO_lookup_type, BIO_ADDRINFO, BIO_ADDRINFO_next, BIO_ADDRINFO_free, BIO_ADDRINFO_family, BIO_ADDRINFO_socktype, BIO_ADDRINFO_protocol, BIO_ADDRINFO_address, BIO_lookup_ex, BIO_lookup — the BIO_ADDRINFO type and its lil routine squad 🫶

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🌸 SYNOPSIS 🌸

#include <sys/types.h>
#include <openssl/bio.h>

typedef union bio_addrinfo_st BIO_ADDRINFO;

enum BIO_lookup_type {
    BIO_LOOKUP_CLIENT, BIO_LOOKUP_SERVER
};

int BIO_lookup_ex(const char *host, const char *service, int lookup_type,
                  int family, int socktype, int protocol, BIO_ADDRINFO **res);
int BIO_lookup(const char *host, const char *service,
               enum BIO_lookup_type lookup_type,
               int family, int socktype, BIO_ADDRINFO **res);

const BIO_ADDRINFO *BIO_ADDRINFO_next(const BIO_ADDRINFO *bai);
int BIO_ADDRINFO_family(const BIO_ADDRINFO *bai);
int BIO_ADDRINFO_socktype(const BIO_ADDRINFO *bai);
int BIO_ADDRINFO_protocol(const BIO_ADDRINFO *bai);
const BIO_ADDR *BIO_ADDRINFO_address(const BIO_ADDRINFO *bai);
void BIO_ADDRINFO_free(BIO_ADDRINFO *bai);

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💅 DESCRIPTION 💅

so like, the tea is: BIO_ADDRINFO is a wrapper for whatever address-information types your platform ships with. it's giving "we're not reinventing the wheel, we're just accessorizing it." ✨

BIO_ADDRINFO normally forms a chain of several of them, and you pick through them one by one. it's giving linked list but make it networking. 🔗

🎀 BIO_lookup_ex() — the main character

BIO_lookup_ex() looks up a specified host and service, and uses lookup_type to figure out what the default address should be if host is NULL.

pamily— no wait, family, socktype and protocol decide what protocol family, socket type and protocol the lookup should use. here's the breakdown bestie:

• family can be any of AF_INET, AF_INET6, AF_UNIX and AF_UNSPEC.
• socktype can be SOCK_STREAM, SOCK_DGRAM or 0. setting it to 0 means any type can be used.
• protocol specifies a protocol such as IPPROTO_TCP, IPPROTO_UDP or IPPORTO_SCTP. if it's set to 0 than any protocol can be used. (yes, that's the original spelling, we keep the facts exactly as they are, no editing the lore 🙈)

res points at a pointer that's gonna hold the start of a BIO_ADDRINFO chain. 🫶

🦋 special case alert: for the family AF_UNIX, BIO_lookup_ex() will ignore the service parameter and expects the host parameter to hold the path to the socket file. so like, host is the whole personality there.

🍓 BIO_lookup()

BIO_lookup() does the same as BIO_lookup_ex() but does not give you the ability to select based on the protocol — any protocol may be returned. it's the chill, no-preference version. ✨

🧚 the getter girlies

• BIO_ADDRINFO_family() returns the family of the given BIO_ADDRINFO. the result will be one of the constants AF_INET, AF_INET6 and AF_UNIX.
• BIO_ADDRINFO_socktype() returns the socket type of the given BIO_ADDRINFO. the result will be one of the constants SOCK_STREAM and SOCK_DGRAM.
• BIO_ADDRINFO_protocol() returns the protocol id of the given BIO_ADDRINFO. the result will be one of the constants IPPROTO_TCP and IPPROTO_UDP.
• BIO_ADDRINFO_address() returns the underlying BIO_ADDR of the given BIO_ADDRINFO.
• BIO_ADDRINFO_next() returns the next BIO_ADDRINFO in the chain from the given one.
• BIO_ADDRINFO_free() frees the chain of BIO_ADDRINFO starting with the given one. and if the argument is NULL, nothing is done. bestie said "no thoughts, head empty, no crash." 💀

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👑 RETURN VALUES 👑

BIO_lookup_ex() and BIO_lookup() return 1 on success and 0 when an error occurred, and they'll leave an error indication on the OpenSSL error stack in that case. slay when it works, error stack when it doesn't. 😭

all the other functions described here return 0 or NULL when the information they should return isn't available. so if you get a 0 or a NULL, that's not a glitch, that's the vibe. 💅

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🌈 NOTES 🌈

the BIO_lookup_ex() implementation uses the platform-provided getaddrinfo() function.

🔥 on Linux it is known that specifying 0 for the protocol will not return any SCTP based addresses when calling getaddrinfo(). therefore, if an SCTP address is required then the protocol parameter to BIO_lookup_ex() should be explicitly set to IPPROTO_SCTP. the same may be true on other platforms. so like, don't be shy, be explicit. 🫶

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⭐ HISTORY ⭐

the BIO_lookup_ex() function was added in OpenSSL 1.1.1. a classic. an icon. a legend. 👑

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🎀 COPYRIGHT 🎀

Copyright 2016-2024 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

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and that's the whole page bestie, no cap, every flag, every constant, every warning preserved exactly. 💖✨🌸🦋

signing off from OpenSSL 3.5.9, dated 2026-09-29, on the BIO_ADDRINFO(3ossl) page — periodt. 💅👑🌈