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
37=head1 NOTES
38
39These functions have no impact when used with DTLS. The return values for
40SSL_CTX_get_read_head() and SSL_get_read_ahead() are undefined for DTLS. Setting
41B<read_ahead> can impact the behaviour of the SSL_pending() function
42(see L<SSL_pending(3)>).
43
44Since SSL_read() can return B<SSL_ERROR_WANT_READ> for non-application data
45records, and SSL_has_pending() can't tell the difference between processed and
46unprocessed data, it's recommended that if read ahead is turned on that
47B<SSL_MODE_AUTO_RETRY> is not turned off using SSL_CTX_clear_mode().
48That will prevent getting B<SSL_ERROR_WANT_READ> when there is still a complete
49record available that hasn't been processed.
50
51If the application wants to continue to use the underlying transport (e.g. TCP
52connection) after the SSL connection is finished using SSL_shutdown() reading
53ahead should be turned off.
54Otherwise the SSL structure might read data that it shouldn't.
55
56=head1 RETURN VALUES
57
58SSL_get_read_ahead() and SSL_CTX_get_read_ahead() return 0 if reading ahead is off,
59and non zero otherwise.
60
61=head1 SEE ALSO
62
63L<ssl(7)>, L<SSL_pending(3)>
64
65=head1 COPYRIGHT
66
67Copyright 2015-2020 The OpenSSL Project Authors. All Rights Reserved.
68
69Licensed under the Apache License 2.0 (the "License").  You may not use
70this file except in compliance with the License.  You can obtain a copy
71in the file LICENSE in the source distribution or at
72L<https://www.openssl.org/source/license.html>.
73
74=cut
75