SSL_do_handshake — perform a TLS/SSL handshake
SSL_do_handshake() will wait for a SSL/TLS handshake to take
place. If the connection is in client mode, the handshake will be
started. The handshake routines may have to be explicitly set in
advance using either SSL_set_connect_state(3) or SSL_set_accept_state(3).
The behaviour of SSL_do_handshake() depends on the underlying
If the underlying BIO is blocking, SSL_do_handshake() will
only return once the handshake has been finished or an error occurred,
except for SGC (Server Gated Cryptography). For SGC, SSL_do_handshake()
may return with -1, but SSL_get_error() will yield SSL_ERROR_WANT_READ/WRITE
and SSL_do_handshake() should be called again.
If the underlying BIO is non-blocking, SSL_do_handshake()
will also return when the underlying BIO could not satisfy the needs
of SSL_do_handshake() to continue the handshake. In this case a
call to SSL_get_error() with the return value of SSL_do_handshake()
will yield SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE . The calling
process then must repeat the call after taking appropriate action to
satisfy the needs of SSL_do_handshake(). The action depends on the
underlying BIO. When using a non-blocking socket, nothing is to
be done, but select() can be used to check for the required condition.
When using a buffering BIO, like a BIO pair, data must be written
into or retrieved out of the BIO before being able to continue.
The following return values can occur:
The TLS/SSL handshake was successfully completed, a TLS/SSL
connection has been established.
The TLS/SSL handshake was not successful but was shut down
controlled and by the specifications of the TLS/SSL protocol. Call
SSL_get_error() with the return value ret to find out the reason.
The TLS/SSL handshake was not successful because a fatal error
occurred either at the protocol level or a connection failure occurred.
The shutdown was not clean. It can also occur of action is need
to continue the operation for non-blocking BIOs. Call SSL_get_error()
with the return value ret to find out the reason.
SSL_get_error(3), SSL_connect(3), SSL_accept(3), ssl(3), bio(3), SSL_set_connect_state(3)