=pod

=head1 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

=head1 SYNOPSIS

 #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);

=head1 DESCRIPTION

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
B<x> bytes are currently required by OpenSSL, but B<y> bytes are available from
the underlying BIO (where B<y> > B<x>), then OpenSSL will read all B<y> bytes
into its buffer (providing that the buffer is large enough) if reading ahead is
on, or B<x> bytes otherwise.
Setting the parameter B<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().

=head1 NOTES

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
B<read_ahead> can impact the behaviour of the SSL_pending() function
(see L<SSL_pending(3)>).

Since SSL_read() can return B<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
B<SSL_MODE_AUTO_RETRY> is not turned off using SSL_CTX_clear_mode().
That will prevent getting B<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.

=head1 RETURN VALUES

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

=head1 SEE ALSO

L<ssl(7)>, L<SSL_pending(3)>

=head1 COPYRIGHT

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
L<https://www.openssl.org/source/license.html>.

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