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