SSL_CTX_SET_READ_AHEAD(3) | Library Functions Manual | SSL_CTX_SET_READ_AHEAD(3)

# 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

`SSL_CTX_set_read_ahead`() and `SSL_set_read_ahead`() set whether as many input bytes as possible are read for non-blocking reads. For example 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.

`SSL_CTX_get_default_read_ahead`() is identical to `SSL_CTX_get_read_ahead`().

These functions are implemented as macros.

These functions have no effect when used with DTLS.

# 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.

# 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.

`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.

# CAVEATS

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

June 8, 2025 | Debian