SSL_get_session - retrieve TLS/SSL session data
#include <openssl/ssl.h> SSL_SESSION *SSL_get_session(const SSL *ssl); SSL_SESSION *SSL_get0_session(const SSL *ssl); SSL_SESSION *SSL_get1_session(SSL *ssl);
SSL_get_session() returns a pointer to the SSL_SESSION actually used in ssl. The reference count of the SSL_SESSION is not incremented, so that the pointer can become invalid by other operations.
SSL_get0_session() is the same as SSL_get_session().
SSL_get1_session() is the same as SSL_get_session(), but the reference count of the SSL_SESSION is incremented by one.
The ssl session contains all information required to re-establish the connection without a new handshake.
A session will be automatically removed from the session cache and marked as non-resumable if the connection is not closed down cleanly, e.g. if a fatal error occurs on the connection or SSL_shutdown(3) is not called prior to SSL_free(3).
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 during SSL_CTX_flush_sessions(3).
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 object's 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).
The following return values can occur:
There is no session available in ssl.
The return value points to the data of an SSL session.
ssl(3), SSL_free(3), SSL_clear(3), SSL_SESSION_free(3)