NAME¶
SSL_CTX_set_mode, SSL_set_mode, SSL_CTX_get_mode, SSL_get_mode - manipulate SSL
engine mode
SYNOPSIS¶
#include <openssl/ssl.h>
long SSL_CTX_set_mode(SSL_CTX *ctx, long mode);
long SSL_set_mode(SSL *ssl, long mode);
long SSL_CTX_get_mode(SSL_CTX *ctx);
long SSL_get_mode(SSL *ssl);
DESCRIPTION¶
SSL_CTX_set_mode() adds the mode set via bitmask in
mode to
ctx. Options already set before are not cleared.
SSL_set_mode() adds the mode set via bitmask in
mode to
ssl. Options already set before are not cleared.
SSL_CTX_get_mode() returns the mode set for
ctx.
SSL_get_mode() returns the mode set for
ssl.
NOTES¶
The following mode changes are available:
- SSL_MODE_ENABLE_PARTIAL_WRITE
- Allow SSL_write(..., n) to return r with 0 < r < n (i.e. report
success when just a single record has been written). When not set (the
default), SSL_write() will only report success once the complete
chunk was written. Once SSL_write() returns with r, r bytes have
been successfully written and the next call to 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() with changed buffer location
(the buffer contents must stay the same). This is not the default to avoid
the misconception that non-blocking SSL_write() behaves like
non-blocking write().
- SSL_MODE_AUTO_RETRY
- Never bother the application with retries if the transport is blocking. If
a renegotiation take place during normal operation, a SSL_read(3)
or SSL_write(3) would return with -1 and indicate the need to retry
with SSL_ERROR_WANT_READ. In a non-blocking environment applications must
be prepared to handle incomplete read/write operations. In a blocking
environment, applications are not always prepared to deal with read/write
operations returning without success report. The flag SSL_MODE_AUTO_RETRY
will cause read/write operations to only return after the handshake and
successful completion.
- 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. Released memory is
either appended to a list of unused RAM chunks on the SSL_CTX, or simply
freed if the list of unused chunks would become longer than
SSL_CTX->freelist_max_len, which defaults to 32. 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.
RETURN VALUES¶
SSL_CTX_set_mode() and
SSL_set_mode() return the new mode bitmask
after adding
mode.
SSL_CTX_get_mode() and
SSL_get_mode() return the current bitmask.
SEE ALSO¶
ssl(3),
SSL_read(3),
SSL_write(3)
HISTORY¶
SSL_MODE_AUTO_RETRY as been added in OpenSSL 0.9.6.