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
#include <openssl/ssl.h>
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
from
ctx.
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 from
ssl.
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:
- SSL_MODE_ENABLE_PARTIAL_WRITE
- 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().
- SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
- 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().
- SSL_MODE_AUTO_RETRY
- 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.
- SSL_MODE_RELEASE_BUFFERS
- 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.
- SSL_MODE_SEND_FALLBACK_SCSV
- 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.
- SSL_MODE_ASYNC
- 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 SSL_get_error(3).
- SSL_MODE_DTLS_SCTP_LABEL_LENGTH_BUG
- 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(7),
SSL_read_ex(3),
SSL_read(3),
SSL_write_ex(3)
or
SSL_write(3),
SSL_get_error(3)
SSL_MODE_ASYNC was added in OpenSSL 1.1.0.
Copyright 2001-2021 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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
<
https://www.openssl.org/source/license.html>.