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
long SSL_CTX_set_mode(SSL_CTX *ctx, long mode);
long SSL_CTX_clear_mode(SSL_CTX *ctx, long mode);
long SSL_set_mode(SSL *ssl, long mode);
long SSL_clear_mode(SSL *ssl, long mode);
long SSL_CTX_get_mode(SSL_CTX *ctx);
long SSL_get_mode(SSL *ssl);
SSL_CTX_set_mode() adds the mode set via bit mask in mode to
ctx. Options already set before are not cleared.
SSL_CTX_clear_mode() removes the mode set via bit mask in mode
SSL_set_mode() adds the mode set via bit mask in
mode to ssl. Options already set before are not cleared.
SSL_clear_mode() removes the mode set via bit mask in mode
SSL_CTX_get_mode() returns the mode set for ctx.
SSL_get_mode() returns the mode set for ssl.
The following mode changes are available:
- Allow SSL_write_ex(..., n, &r) to return with 0 < r < n (i.e.
report success when just a single record has been written). This works in
a similar way for SSL_write(). When not set (the default),
SSL_write_ex() or SSL_write() will only report success once
the complete chunk was written. Once SSL_write_ex() or
SSL_write() returns successful, r bytes have been written
and the next call to SSL_write_ex() or SSL_write() must only
send the n-r bytes left, imitating the behaviour of write().
- Make it possible to retry SSL_write_ex() or SSL_write() with
changed buffer location (the buffer contents must stay the same). This is
not the default to avoid the misconception that nonblocking
SSL_write() behaves like nonblocking write().
- During normal operations, non-application data records might need to be
sent or received that the application is not aware of. If a
non-application data record was processed, SSL_read_ex(3) and
SSL_read(3) can return with a failure and indicate the need to
retry with SSL_ERROR_WANT_READ. If such a non-application data
record was processed, the flag SSL_MODE_AUTO_RETRY causes it to try
to process the next record instead of returning.
In a nonblocking environment applications must be prepared to
handle incomplete read/write operations. Setting
SSL_MODE_AUTO_RETRY for a nonblocking BIO will process
non-application data records until either no more data is available or
an application data record has been processed.
In a blocking environment, applications are not always
prepared to deal with the functions returning intermediate reports such
as retry requests, and setting the SSL_MODE_AUTO_RETRY flag will
cause the functions to only return after successfully processing an
application data record or a failure.
Turning off SSL_MODE_AUTO_RETRY can be useful with
blocking BIOs in case they are used in combination with something
like select() or poll(). Otherwise the call to
SSL_read() or SSL_read_ex() might hang when a
non-application record was sent and no application data was sent.
- When we no longer need a read buffer or a write buffer for a given SSL,
then release the memory we were using to hold it. Using this flag can save
around 34k per idle SSL connection. This flag has no effect on SSL v2
connections, or on DTLS connections.
- Send TLS_FALLBACK_SCSV in the ClientHello. To be set only by applications
that reconnect with a downgraded protocol version; see
draft-ietf-tls-downgrade-scsv-00 for details.
DO NOT ENABLE THIS if your application attempts a normal
handshake. Only use this in explicit fallback retries, following the
guidance in draft-ietf-tls-downgrade-scsv-00.
- Enable asynchronous processing. TLS I/O operations may indicate a retry
with SSL_ERROR_WANT_ASYNC with this mode set if an asynchronous capable
engine is used to perform cryptographic operations. See
- Older versions of OpenSSL had a bug in the computation of the label length
used for computing the endpoint-pair shared secret. The bug was that the
terminating zero was included in the length of the label. Setting this
option enables this behaviour to allow interoperability with such broken
implementations. Please note that setting this option breaks
interoperability with correct implementations. This option only applies to
DTLS over SCTP.
All modes are off by default except for SSL_MODE_AUTO_RETRY which
is on by default since 1.1.1.
SSL_CTX_set_mode() and SSL_set_mode() return the new mode bit mask
after adding mode.
SSL_CTX_get_mode() and SSL_get_mode() return the
current bit mask.
SSL_MODE_ASYNC was added in OpenSSL 1.1.0.
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Licensed under the OpenSSL license (the "License"). You
may not use this file except in compliance with the License. You can obtain
a copy in the file LICENSE in the source distribution or at