1=pod 2 3=head1 NAME 4 5SSL_CTX_set_mode, SSL_CTX_clear_mode, SSL_set_mode, SSL_clear_mode, SSL_CTX_get_mode, SSL_get_mode - manipulate SSL engine mode 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 long SSL_CTX_set_mode(SSL_CTX *ctx, long mode); 12 long SSL_CTX_clear_mode(SSL_CTX *ctx, long mode); 13 long SSL_set_mode(SSL *ssl, long mode); 14 long SSL_clear_mode(SSL *ssl, long mode); 15 16 long SSL_CTX_get_mode(SSL_CTX *ctx); 17 long SSL_get_mode(SSL *ssl); 18 19=head1 DESCRIPTION 20 21SSL_CTX_set_mode() adds the mode set via bit-mask in B<mode> to B<ctx>. 22Options already set before are not cleared. 23SSL_CTX_clear_mode() removes the mode set via bit-mask in B<mode> from B<ctx>. 24 25SSL_set_mode() adds the mode set via bit-mask in B<mode> to B<ssl>. 26Options already set before are not cleared. 27SSL_clear_mode() removes the mode set via bit-mask in B<mode> from B<ssl>. 28 29SSL_CTX_get_mode() returns the mode set for B<ctx>. 30 31SSL_get_mode() returns the mode set for B<ssl>. 32 33=head1 NOTES 34 35The following mode changes are available: 36 37=over 4 38 39=item SSL_MODE_ENABLE_PARTIAL_WRITE 40 41Allow SSL_write_ex(..., n, &r) to return with 0 < r < n (i.e. report success 42when just a single record has been written). This works in a similar way for 43SSL_write(). When not set (the default), SSL_write_ex() or SSL_write() will only 44report success once the complete chunk was written. Once SSL_write_ex() or 45SSL_write() returns successful, B<r> bytes have been written and the next call 46to SSL_write_ex() or SSL_write() must only send the n-r bytes left, imitating 47the behaviour of write(). 48 49This mode cannot be enabled while in the middle of an incomplete write 50operation. 51 52=item SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER 53 54Make it possible to retry SSL_write_ex() or SSL_write() with changed buffer 55location (the buffer contents must stay the same). This is not the default to 56avoid the misconception that nonblocking SSL_write() behaves like 57nonblocking write(). 58 59=item SSL_MODE_AUTO_RETRY 60 61During normal operations, non-application data records might need to be sent or 62received that the application is not aware of. 63If a non-application data record was processed, 64L<SSL_read_ex(3)> and L<SSL_read(3)> can return with a failure and indicate the 65need to retry with B<SSL_ERROR_WANT_READ>. 66If such a non-application data record was processed, the flag 67B<SSL_MODE_AUTO_RETRY> causes it to try to process the next record instead of 68returning. 69 70In a nonblocking environment applications must be prepared to handle 71incomplete read/write operations. 72Setting B<SSL_MODE_AUTO_RETRY> for a nonblocking B<BIO> will process 73non-application data records until either no more data is available or 74an application data record has been processed. 75 76In a blocking environment, applications are not always prepared to 77deal with the functions returning intermediate reports such as retry 78requests, and setting the B<SSL_MODE_AUTO_RETRY> flag will cause the functions 79to only return after successfully processing an application data record or a 80failure. 81 82Turning off B<SSL_MODE_AUTO_RETRY> can be useful with blocking B<BIO>s in case 83they are used in combination with something like select() or poll(). 84Otherwise the call to SSL_read() or SSL_read_ex() might hang when a 85non-application record was sent and no application data was sent. 86 87=item SSL_MODE_RELEASE_BUFFERS 88 89When we no longer need a read buffer or a write buffer for a given SSL, 90then release the memory we were using to hold it. 91Using this flag can 92save around 34k per idle SSL connection. 93This flag has no effect on SSL v2 connections, or on DTLS connections. 94 95=item SSL_MODE_SEND_FALLBACK_SCSV 96 97Send TLS_FALLBACK_SCSV in the ClientHello. 98To be set only by applications that reconnect with a downgraded protocol 99version; see draft-ietf-tls-downgrade-scsv-00 for details. 100 101DO NOT ENABLE THIS if your application attempts a normal handshake. 102Only use this in explicit fallback retries, following the guidance 103in draft-ietf-tls-downgrade-scsv-00. 104 105=item SSL_MODE_ASYNC 106 107Enable asynchronous processing. TLS I/O operations may indicate a retry with 108SSL_ERROR_WANT_ASYNC with this mode set if an asynchronous capable engine is 109used to perform cryptographic operations. See L<SSL_get_error(3)>. 110 111=item SSL_MODE_DTLS_SCTP_LABEL_LENGTH_BUG 112 113Older versions of OpenSSL had a bug in the computation of the label length 114used for computing the endpoint-pair shared secret. The bug was that the 115terminating zero was included in the length of the label. Setting this option 116enables this behaviour to allow interoperability with such broken 117implementations. Please note that setting this option breaks interoperability 118with correct implementations. This option only applies to DTLS over SCTP. 119 120=back 121 122All modes are off by default except for SSL_MODE_AUTO_RETRY which is on by 123default since 1.1.1. 124 125=head1 RETURN VALUES 126 127SSL_CTX_set_mode() and SSL_set_mode() return the new mode bit-mask 128after adding B<mode>. 129 130SSL_CTX_get_mode() and SSL_get_mode() return the current bit-mask. 131 132=head1 SEE ALSO 133 134L<ssl(7)>, L<SSL_read_ex(3)>, L<SSL_read(3)>, L<SSL_write_ex(3)> or 135L<SSL_write(3)>, L<SSL_get_error(3)> 136 137=head1 HISTORY 138 139SSL_MODE_ASYNC was added in OpenSSL 1.1.0. 140 141=head1 COPYRIGHT 142 143Copyright 2001-2023 The OpenSSL Project Authors. All Rights Reserved. 144 145Licensed under the Apache License 2.0 (the "License"). You may not use 146this file except in compliance with the License. You can obtain a copy 147in the file LICENSE in the source distribution or at 148L<https://www.openssl.org/source/license.html>. 149 150=cut 151
