SSL_clear is used to prepare an SSL object for a new connection. While all settings are kept, a side effect is the handling of the current SSL session. If a session is still open, it is considered bad and will be removed from the session cache, as required by RFC2246. A session is considered open, if SSL_shutdown(3) was not called for the connection or at least SSL_set_shutdown(3) was used to set the SSL_SENT_SHUTDOWN state.
If a session was closed cleanly, the session object will be kept and all settings corresponding. This explicitly means, that e.g. the special method used during the session will be kept for the next handshake. So if the session was a TLSv1 session, a SSL client object will use a TLSv1 client method for the next handshake and a SSL server object will use a TLSv1 server method, even if SSLv23_*_methods were chosen on startup. This will might lead to connection failures (see SSL_new(3)) for a description of the method's properties.
SSL_clear() resets the SSL object to allow for another connection. The reset operation however keeps several settings of the last sessions (some of these settings were made automatically during the last handshake). It only makes sense for a new connection with the exact same peer that shares these settings, and may fail if that peer changes its settings between connections. Use the sequence SSL_get_session(3); SSL_new(3); SSL_set_session(3); SSL_free(3) instead to avoid such failures (or simply SSL_free(3); SSL_new(3) if session reuse is not desired).
The following return values can occur:
The SSL_clear() operation could not be performed. Check the error stack to find out the reason.
The SSL_clear() operation was successful.