Section: OpenSSL (3SSL)
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SSL_do_handshake - perform a TLS/SSL handshake
int SSL_do_handshake(SSL *ssl);
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
The behaviour of SSL_do_handshake()
depends on the underlying BIO.
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 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 successfully completed, a TLS/SSL connection has been
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.
- RETURN VALUES
- SEE ALSO