initiate the TLS/SSL handshake with a TLS/SSL server
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 with the return value −1. In this case a call to SSL_get_error(3) 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(2) 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 TLS/SSL handshake was not successful but was shut down controlled and by the specifications of the TLS/SSL protocol. Call SSL_get_error(3) with the return value ret to find out the reason.
- The TLS/SSL handshake was successfully completed, and a TLS/SSL connection has been established.
- The TLS/SSL handshake was not successful, because either a fatal error occurred at the protocol level or a connection failure occurred. The shutdown was not clean. It can also occur if action is needed to continue the operation for non-blocking BIOs. Call SSL_get_error(3) with the return value ret to find out the reason.