SSL_CTX_SET_READ_AHEAD(3ossl)

💖 SSL_CTX_SET_READ_AHEAD 💖

okay bestie, this is the SSL_CTX_SET_READ_AHEAD page from the OpenSSL manuals (that's the 3ossl one, iykyk) ✨

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🌸 NAME 🌸

SSL_CTX_set_read_ahead, SSL_CTX_get_read_ahead, SSL_set_read_ahead, SSL_get_read_ahead, SSL_CTX_get_default_read_ahead — these are the girls who decide whether we read as many input bytes as possible 💅

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✨ SYNOPSIS ✨

#include <openssl/ssl.h>

void SSL_set_read_ahead(SSL *s, int yes);
int SSL_get_read_ahead(const SSL *s);

SSL_CTX_set_read_ahead(SSL_CTX *ctx, int yes);
long SSL_CTX_get_read_ahead(SSL_CTX *ctx);
long SSL_CTX_get_default_read_ahead(SSL_CTX *ctx);

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🦋 DESCRIPTION 🦋

SSL_CTX_set_read_ahead() and SSL_set_read_ahead() are the ones that set whether we should read as many input bytes as possible (for nonblocking reads) or not, periodt. here's the vibe: say x bytes are currently required by OpenSSL, but y bytes are available from the underlying BIO (where y > x) — then OpenSSL will read all y bytes into its buffer (providing that the buffer is large enough) if reading ahead is on, or x bytes otherwise. setting the parameter yes to 0 turns reading ahead off, and any other values turn it on 💫

SSL_CTX_set_default_read_ahead() is identical to SSL_CTX_set_read_ahead(). no cap, same girl, different name.

SSL_CTX_get_read_ahead() and SSL_get_read_ahead() indicate whether reading ahead has been set or not. SSL_CTX_get_default_read_ahead() is identical to SSL_CTX_get_read_ahead(). twins fr fr 👯

🚫 these functions cannot be used with QUIC SSL objects. and SSL_set_read_ahead() has no effect if called on a QUIC SSL object. like, it just doesn't show up to the party. 🙈

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🎀 NOTES 🎀

okay so listen up, these functions have no impact when used with DTLS. and the return values for SSL_CTX_get_read_head() and SSL_get_read_ahead() are undefined for DTLS — undefined is giving chaos, not cute 😭

setting read_ahead can impact the behaviour of the SSL_pending() function (go peek at SSL_pending(3)).

since SSL_read() can return SSL_ERROR_WANT_READ for non-application data records, and SSL_has_pending() can't tell the difference between processed and unprocessed data, it's recommended that if read ahead is turned on, that SSL_MODE_AUTO_RETRY is not turned off using SSL_CTX_clear_mode(). that will prevent getting SSL_ERROR_WANT_READ when there is still a complete record available that hasn't been processed. protect your peace bestie 🫶

⚠️ if the application wants to continue to use the underlying transport (e.g. TCP connection) after the SSL connection is finished using SSL_shutdown(), reading ahead should be turned off. otherwise the SSL structure might read data that it shouldn't. and that's the drama we're avoiding 💀

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🌈 RETURN VALUES 🌈

SSL_get_read_ahead() and SSL_CTX_get_read_ahead() return 0 if reading ahead is off, and non zero otherwise. simple as that, slay ⭐

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👑 SEE ALSO 👑

ssl(7), SSL_pending(3)

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💜 COPYRIGHT 💜

Copyright 2015-2023 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 page, bestie!! this was the 3ossl manual, version 3.5.9, dated 2026-09-29 — go forth and read ahead (or don't, your call) 🧚✨💖