SSL_CTX_set_read_ahead.3ssl - Man Page

manage whether to read as many input bytes as possible


 #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);


SSL_CTX_set_read_ahead() and SSL_set_read_ahead() set whether we should read as many input bytes as possible (for nonblocking reads) or not. 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 (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 is off, other values turn it on. SSL_CTX_set_default_read_ahead() is identical to SSL_CTX_set_read_ahead().

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().


These functions have no impact when used with DTLS. The return values for SSL_CTX_get_read_head() and SSL_get_read_ahead() are undefined for DTLS. Setting read_ahead can impact the behaviour of the SSL_pending() function (see 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.

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.

Return Values

SSL_get_read_ahead() and SSL_CTX_get_read_ahead() return 0 if reading ahead is off, and non zero otherwise.

See Also

ssl(7), SSL_pending(3)

Referenced By

ssl.7ssl(7), SSL_CTX_set_split_send_fragment.3ssl(3), SSL_pending.3ssl(3), SSL_read.3ssl(3).

The man pages SSL_CTX_get_default_read_ahead.3ssl(3), SSL_CTX_get_read_ahead.3ssl(3), SSL_get_read_ahead.3ssl(3) and SSL_set_read_ahead.3ssl(3) are aliases of SSL_CTX_set_read_ahead.3ssl(3).

2021-03-26 1.1.1k OpenSSL