#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.
SSL_get_read_ahead() and SSL_CTX_get_read_ahead() return 0 if reading ahead is off, and non zero otherwise.
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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>.
SSL_CTX_set_split_send_fragment.3ossl(3), SSL_pending.3ossl(3), SSL_read.3ossl(3).
The man pages SSL_CTX_get_default_read_ahead.3ossl(3), SSL_CTX_get_read_ahead.3ossl(3), SSL_get_read_ahead.3ossl(3) and SSL_set_read_ahead.3ossl(3) are aliases of SSL_CTX_set_read_ahead.3ossl(3).