1=pod
2
3=head1 NAME
4
5SSL_CTX_set_read_ahead, SSL_CTX_get_read_ahead,
6SSL_set_read_ahead, SSL_get_read_ahead,
7SSL_CTX_get_default_read_ahead
8- manage whether to read as many input bytes as possible
9
10=head1 SYNOPSIS
11
12 #include <openssl/ssl.h>
13
14 void SSL_set_read_ahead(SSL *s, int yes);
15 int SSL_get_read_ahead(const SSL *s);
16
17 SSL_CTX_set_read_ahead(SSL_CTX *ctx, int yes);
18 long SSL_CTX_get_read_ahead(SSL_CTX *ctx);
19 long SSL_CTX_get_default_read_ahead(SSL_CTX *ctx);
20
21=head1 DESCRIPTION
22
23SSL_CTX_set_read_ahead() and SSL_set_read_ahead() set whether we should read as
24many input bytes as possible (for nonblocking reads) or not. For example if
25B<x> bytes are currently required by OpenSSL, but B<y> bytes are available from
26the underlying BIO (where B<y> > B<x>), then OpenSSL will read all B<y> bytes
27into its buffer (providing that the buffer is large enough) if reading ahead is
28on, or B<x> bytes otherwise.
29Setting the parameter B<yes> to 0 turns reading ahead is off, other values turn
30it on.
31SSL_CTX_set_default_read_ahead() is identical to SSL_CTX_set_read_ahead().
32
33SSL_CTX_get_read_ahead() and SSL_get_read_ahead() indicate whether reading
34ahead has been set or not.
35SSL_CTX_get_default_read_ahead() is identical to SSL_CTX_get_read_ahead().
36
37These functions cannot be used with QUIC SSL objects. SSL_set_read_ahead()
38has no effect if called on a QUIC SSL object.
39
40=head1 NOTES
41
42These functions have no impact when used with DTLS. The return values for
43SSL_CTX_get_read_head() and SSL_get_read_ahead() are undefined for DTLS. Setting
44B<read_ahead> can impact the behaviour of the SSL_pending() function
45(see L<SSL_pending(3)>).
46
47Since SSL_read() can return B<SSL_ERROR_WANT_READ> for non-application data
48records, and SSL_has_pending() can't tell the difference between processed and
49unprocessed data, it's recommended that if read ahead is turned on that
50B<SSL_MODE_AUTO_RETRY> is not turned off using SSL_CTX_clear_mode().
51That will prevent getting B<SSL_ERROR_WANT_READ> when there is still a complete
52record available that hasn't been processed.
53
54If the application wants to continue to use the underlying transport (e.g. TCP
55connection) after the SSL connection is finished using SSL_shutdown() reading
56ahead should be turned off.
57Otherwise the SSL structure might read data that it shouldn't.
58
59=head1 RETURN VALUES
60
61SSL_get_read_ahead() and SSL_CTX_get_read_ahead() return 0 if reading ahead is off,
62and non zero otherwise.
63
64=head1 SEE ALSO
65
66L<ssl(7)>, L<SSL_pending(3)>
67
68=head1 COPYRIGHT
69
70Copyright 2015-2023 The OpenSSL Project Authors. All Rights Reserved.
71
72Licensed under the Apache License 2.0 (the "License").  You may not use
73this file except in compliance with the License.  You can obtain a copy
74in the file LICENSE in the source distribution or at
75L<https://www.openssl.org/source/license.html>.
76
77=cut
78