SSL_CTX_SET_READ_AHEAD(3)

hii bestie 💖 this is the SSL_CTX_SET_READ_AHEAD(3) page from the Library Functions Manual, and it’s all about managing whether to read as many input bytes as possible. no cap, we’re keeping every function and every tiny detail. ✨

🌸 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 — manage whether to read as many input bytes as possible 💅

✨ SYNOPSIS ✨

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

void
SSL_CTX_set_read_ahead(SSL_CTX *ctx, int yes);

long
SSL_CTX_get_read_ahead(SSL_CTX *ctx);

void
SSL_set_read_ahead(SSL *s, int yes);

long
SSL_get_read_ahead(const SSL *s);

long
SSL_CTX_get_default_read_ahead(SSL_CTX *ctx);

🦋 DESCRIPTION 🦋

okay so SSL_CTX_set_read_ahead() and SSL_set_read_ahead() set whether as many input bytes as possible are read for non-blocking reads. the vibe is: if 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 (provided that the buffer is large enough) if reading ahead is on, or x bytes otherwise. the parameter yes should be 0 to ensure reading ahead is off, or non zero otherwise. 🫶

SSL_CTX_get_read_ahead() and SSL_get_read_ahead() indicate whether reading ahead is set or not. like, they’re the vibe check 👀.

the way that SSL_CTX_get_default_read_ahead() is identical to SSL_CTX_get_read_ahead() is sending me 😭 — it’s literally a duplicate. not me being obsessed with that 💅.

these functions are implemented as macros. yep, macros. iconic.

these functions have no effect when used with DTLS. that part is important, bestie — no effect with DTLS, periodt. 💀

💖 RETURN VALUES 💖

SSL_CTX_get_read_ahead() and SSL_get_read_ahead() return 0 if reading ahead is off or non-zero otherwise, except that the return values are undefined for DTLS 😭. so pls don’t go relying on a DTLS return value, because it’s literally undefined.

🎀 SEE ALSO 🎀

• ssl(3)
• SSL_pending(3)

🌈 HISTORY 🌈

SSL_set_read_ahead() and SSL_get_read_ahead() appeared in SSLeay 0.4 or earlier and have been available since OpenBSD 2.4. history really said “we’ve been here a minute” ⏳.

SSL_CTX_set_read_ahead(), SSL_CTX_get_read_ahead(), and SSL_CTX_get_default_read_ahead() first appeared in OpenSSL 0.9.2b and have been available since OpenBSD 2.6. slay for continuity 💫.

⚠️ CAVEATS ⚠️

Switching read ahead on can impact the behaviour of the SSL_pending(3) function. 👀

that’s the caveat, bestie — keep it in mind. 🫶

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mwah 💋 that’s the whole page — this one is from Debian, dated June 8, 2025, and the manual page is SSL_CTX_SET_READ_AHEAD(3). bye bestie 🫶