SSL_SET_BIO(3SSL)

💖 SSL_SET_BIO — the OpenSSL version, bestie edition 💖

okay so this is a page from the OpenSSL manual, section 3SSL, and it's literally all about introducing an SSL object to a BIO. yes it's a blind date situation. no I will not elaborate. 🎀

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✨ NAME ✨

SSL_set_bio, SSL_set0_rbio, SSL_set0_wbio — connect the SSL object with a BIO 🫶

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🌸 SYNOPSIS 🌸

#include <openssl/ssl.h>

void SSL_set_bio(SSL *ssl, BIO *rbio, BIO *wbio);
void SSL_set0_rbio(SSL *s, BIO *rbio);
void SSL_set0_wbio(SSL *s, BIO *wbio);

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💅 DESCRIPTION 💅

okay so let's break this down because there's lore here.

🌈 SSL_set0_rbio()

SSL_set0_rbio() connects the BIO rbio for the read operations of the ssl object. the SSL engine inherits the behaviour of rbio — so if the BIO is nonblocking, then the ssl object is gonna have nonblocking behaviour too. it's giving "you are who you hang out with." ✨

this function transfers ownership of rbio to ssl. that means it'll be automatically freed using BIO_free_all(3) when the ssl is freed. and when you call this function, any existing rbio that was previously set will also be freed via a call to BIO_free_all(3) — and yes, that includes the case where the rbio is set to the same value as previously. so like. even if it's the same one. it still gets freed. iconic but also be careful bestie 😭

if you're using a custom BIO, rbio must implement either BIO_meth_set_read_ex(3) or BIO_meth_set_read(3).

🌈 SSL_set0_wbio()

SSL_set0_wbio() works the same as SSL_set0_rbio() except it connects the BIO wbio for the write operations of the ssl object.

⚠️ note that if the rbio and wbio are the same, then SSL_set0_rbio() and SSL_set0_wbio() each take ownership of one reference. so it may be necessary to increment the number of references available using BIO_up_ref(3) before calling the set0 functions. do not skip this. I am begging. 🙈

if you're using a custom BIO, wbio must implement BIO_meth_set_write_ex(3) or BIO_meth_set_write(3). it additionally must implement BIO_flush(3) using BIO_CTRL_FLUSH and BIO_meth_set_ctrl(3). and if flushing is not necessary with wbio, then BIO_flush(3) should return 1 and do nothing. periodt.

🌈 SSL_set_bio()

SSL_set_bio() is similar to SSL_set0_rbio() and SSL_set0_wbio() except that it connects both the rbio and the wbio at the same time, and transfers the ownership of rbio and wbio to ssl according to the following set of rules:

• if neither the rbio nor wbio have changed from their previous values then nothing is done. 🦋
• if the rbio and wbio parameters are different and both are different to their previously set values then one reference is consumed for the rbio and one reference is consumed for the wbio.
• if the rbio and wbio parameters are the same and the rbio is not the same as the previously set value then one reference is consumed.
• if the rbio and wbio parameters are the same and the rbio is the same as the previously set value, then no additional references are consumed.
• if the rbio and wbio parameters are different and the rbio is the same as the previously set value then one reference is consumed for the wbio and no references are consumed for the rbio.
• if the rbio and wbio parameters are different and the wbio is the same as the previously set value and the old rbio and wbio values were the same as each other then one reference is consumed for the rbio and no references are consumed for the wbio.
• if the rbio and wbio parameters are different and the wbio is the same as the previously set value and the old rbio and wbio values were different to each other, then one reference is consumed for the rbio and one reference is consumed for the wbio.

💀 because of this complexity, this function should be avoided; use SSL_set0_rbio() and SSL_set0_wbio() instead. like. I said what I said. this is not the vibe. skip it. ngl the manpage is telling you this directly, bestie.

🌈 the QUIC plot twist

where a new BIO is set on a QUIC connection SSL object, blocking mode will be disabled on that SSL object if the BIO cannot support blocking mode. 🍓

and if another BIO is subsequently set on the SSL object which can support blocking mode, blocking mode will not be automatically re-enabled. it does not come back on its own. no cap.

for more information, see SSL_set_blocking_mode(3).

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👑 RETURN VALUES 👑

the slayest part honestly: SSL_set_bio(), SSL_set0_rbio() and SSL_set0_wbio() cannot fail. they literally cannot. main character energy. ⭐

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🔥 SEE ALSO 🔥

SSL_get_rbio(3), SSL_connect(3), SSL_accept(3), SSL_shutdown(3), ssl(7), bio(7) — go read these too, iykyk 🧚

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🌸 HISTORY 🌸

SSL_set0_rbio() and SSL_set0_wbio() were added in OpenSSL 1.1.0. throwback era. 💜

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💖 COPYRIGHT 💖

Copyright 2000-2023 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 thing 🫶 this was OpenSSL 4.0.3, dated 2026-09-29, filed under SSL_SET_BIO(3SSL). go forth and manage your references responsibly, bestie. mwah 💅✨🌈