BIO_FIND_TYPE(3)

💅 BIO_FIND_TYPE(3) — like, the whole BIO chain traversal moment

okay bestie, so this is the libcrypto page — the Library Functions Manual one — and it's literally all about walking through a chain of BIOs and finding the one you want. it's giving scavenger hunt but make it ✨cryptographic✨. let's get into it 🫶

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✨ SYNOPSIS ✨

library “libcrypto” #include <openssl/bio.h>

BIO *
BIO_find_type(BIO *bio, int type);

BIO *
BIO_next(BIO *bio);

int
BIO_method_type(const BIO *bio);

const char *
BIO_method_name(const BIO *bio);

#define BIO_TYPE_NONE         0
#define BIO_TYPE_START        128

like, yes, that's a lot of BIO * up there, don't panic 💖

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🌸 DESCRIPTION 🌸

So BIO_find_type() goes searching through the chain starting at bio, looking for a BIO that matches the type you passed in. Here's the tea on how matching works, because it's lowkey the whole plot twist:

• if the least significant byte of the type argument is non-zero, only exact matches of the type get accepted. no vibes-based matching, periodt.
• otherwise, a match just requires that any of the bits set in the type argument is also set in the candidate BIO. bitwise bestie behavior 💅

Types whose least significant byte is in the range from 0 to BIO_TYPE_START, inclusive, are reserved for BIO types built into the library. Types whose least significant byte is greater than BIO_TYPE_START are available for user-defined BIO types — see BIO_get_new_index(3) for the details, iykyk 🔥

BIO_next() returns the next BIO in the chain after bio. use this to traverse all the BIOs in a chain, or team it up with BIO_find_type() to find all the BIOs of a certain type. dynamic duo energy fr fr 🦋

BIO_method_type() returns the type of the given bio.

BIO_method_name() returns an ASCII string representing the type of the bio.

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🎀 the built-in source/sink BIO types that operate on file descriptors

bestie these all have both the bits BIO_TYPE_SOURCE_SINK and BIO_TYPE_DESCRIPTOR set in their type constant — but not the bit BIO_TYPE_FILTER. noted! 📝

• BIO_TYPE_ACCEPT — name string socket accept — BIO_s_accept(3)
• BIO_TYPE_CONNECT — name string socket connect — BIO_s_connect(3)
• BIO_TYPE_DGRAM — name string datagram socket — BIO_s_datagram(3)
• BIO_TYPE_FD — name string file descriptor — BIO_s_fd(3)
• BIO_TYPE_SOCKET — name string socket — BIO_s_socket(3)

🌈 the built-in source/sink BIO types that don't directly operate on file descriptors

these all have the bit BIO_TYPE_SOURCE_SINK set — but not BIO_TYPE_DESCRIPTOR and not BIO_TYPE_FILTER. different flavor, same source/sink slay ⭐

• BIO_TYPE_BIO — name string BIO pair — BIO_s_bio(3)
• BIO_TYPE_FILE — name string FILE pointer — BIO_s_file(3)
• BIO_TYPE_MEM — name string memory buffer — BIO_s_mem(3)
• BIO_TYPE_NULL — name string NULL — BIO_s_null(3)

🧚 the built-in filter BIO types

these all have the bit BIO_TYPE_FILTER set — and not BIO_TYPE_SOURCE_SINK or BIO_TYPE_DESCRIPTOR. filter era 💜

• BIO_TYPE_BASE64 — name string base64 encoding — BIO_f_base64(3)
• BIO_TYPE_BUFFER — name string buffer — BIO_f_buffer(3)
• BIO_TYPE_CIPHER — name string cipher — BIO_f_cipher(3)
• BIO_TYPE_MD — name string message digest — BIO_f_md(3)
• BIO_TYPE_NULL_FILTER — name string NULL filter — BIO_f_null(3)
• BIO_TYPE_SSL — name string ssl — BIO_f_ssl(3)

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⚠️ okay important caveat time, don't skip this: the constants BIO_TYPE_BER, BIO_TYPE_PROXY_CLIENT, and BIO_TYPE_PROXY_SERVER do not correspond to any BIO types implemented by the library, and they are not intended to be used for application-defined types either. so like... don't. 🙈

also: the constants BIO_TYPE_COMP, BIO_TYPE_LINEBUFFER, and BIO_TYPE_NBIO_TEST correspond to deprecated BIO types that are intentionally undocumented. they're the mysterious exes of the BIO world 💀

And a cute little life tip: if a variable in your application program is intended to store a BIO type but temporarily doesn't refer to any BIO, or refers to a BIO of an unknown type, setting that variable to BIO_TYPE_NONE is recommended. do it for the plot 🍓

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👑 RETURN VALUES 👑

• BIO_find_type() returns the next matching BIO — or NULL if bio is a NULL pointer, or if no matching BIO is found. 😭
• BIO_next() returns the next BIO — or NULL if bio is a NULL pointer, or if it points to the last BIO in a chain.
• BIO_method_type() returns one of the BIO_TYPE_* constants.
• BIO_method_name() returns an internal pointer to a string.

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🔥 EXAMPLES 🔥

Traverse a chain looking for digest BIOs — this is the moment, bestie, study it:

BIO *btmp;

btmp = in_bio;  /* in_bio is the chain to search through */
while (btmp != NULL) {
        btmp = BIO_find_type(btmp, BIO_TYPE_MD);
        if (btmp == NULL)
                break;  /* Not found */

        /* btmp is a digest BIO, do something with it ... */
        ...

        btmp = BIO_next(btmp);
}

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🌸 SEE ALSO 🌸

BIO_meth_new(3), BIO_new(3)

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💖 HISTORY 💖

BIO_method_type() and BIO_method_name() first appeared in SSLeay 0.6.0. BIO_find_type() first appeared in SSLeay 0.6.6. these functions have been available since OpenBSD 2.4. vintage icons only 👑

BIO_next() first appeared in OpenSSL 0.9.6 and has been available since OpenBSD 2.9. late bloomer, still iconic 🌸

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k bye bestie, go traverse that chain 🦋✨ — this page came from Debian, dated June 8, 2025, and yeah that's the whole BIO_FIND_TYPE(3) situation, no cap 💅