NAME

       SSL_do_handshake - perform a TLS/SSL handshake

SYNOPSIS

        #include <openssl/ssl.h>

        int SSL_do_handshake(SSL *ssl);

DESCRIPTION

       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).

NOTES

       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.

RETURN VALUES

       The following return values can occur:

       0   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.

       1   The TLS/SSL handshake was successfully completed, a TLS/SSL connection has been
           established.

       <0  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.

SEE ALSO

       SSL_get_error(3), SSL_connect(3), SSL_accept(3), ssl(3), bio(3), SSL_set_connect_state(3)