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 methods 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
instead to avoid such failures
(or simply SSL_free(3); SSL_new(3)
if session reuse is not desired).