=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().

These functions cannot be used with QUIC SSL objects. SSL_set_read_ahead()
has no effect if called on a QUIC SSL object.

=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 2015-2023 The OpenSSL Project Authors. All Rights Reserved.

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

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