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