The ssl session contains all information required to re-establish the
connection without a new handshake.
SSL_get0_session() returns a pointer to the actual session. As the
reference counter is not incremented, the pointer is only valid while
the connection is in use. If SSL_clear(3) or
SSL_free(3) is called, the session may be removed completely
(if considered bad), and the pointer obtained will become invalid. Even
if the session is valid, it can be removed at any time due to timeout
If the data is to be kept, SSL_get1_session() will increment the reference
count, so that the session will not be implicitly removed by other operations
but stays in memory. In order to remove the session
SSL_SESSION_free(3) must be explicitly called once
to decrement the reference count again.
SSL_SESSION objects keep internal link information about the session cache
list, when being inserted into one SSL_CTX objects session cache.
One SSL_SESSION object, regardless of its reference count, must therefore
only be used with one SSL_CTX object (and the SSL objects created
from this SSL_CTX object).