HP Open Source Security for OpenVMS Volume 2: HP SSL for OpenVMS > SSL Application Programming Interface (API)
SSL_connect() initiates the TLS/SSL handshake with a server. The communication channel must already have been set and assigned to the ssl by setting an underlying BIO.
The behaviour of SSL_connect() depends on the underlying BIO.
If the underlying BIO is blocking, SSL_connect() will only return once the handshake has been finished or an error occurred.
If the underlying BIO is non-blocking, SSL_connect() will also return when the underlying BIO could not satisfy the needs of SSL_connect() to continue the handshake, indicating the problem by the return value -1. In this case a call to SSL_get_error() with the return value of SSL_connect() 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_connect(). 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: