Section: OpenSSL (3)
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SSL_connect - initiate the TLS/SSL handshake with an TLS/SSL server
int SSL_connect(SSL *ssl);
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
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:
The TLS/SSL handshake was successfully completed, a TLS/SSL connection has been
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_shutdown(3), ssl(3), bio(3),
- RETURN VALUES
- SEE ALSO
linux.jgfs.net manual pages