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.