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SSL_CTX_set_read_ahead(3) OpenSSL SSL_CTX_set_read_ahead(3)
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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
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_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
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.
Copyright 2015-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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
1.1.1i 2020-12-10 SSL_CTX_set_read_ahead(3)