SSL_DO_HANDSHAKE(3) OpenSSL SSL_DO_HANDSHAKE(3)
SSL_do_handshake - perform a TLS/SSL handshake
#include <openssl/ssl.h>
int SSL_do_handshake(SSL *ssl);
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).
The behaviour of SSL_do_handshake() depends on the underly-
ing 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:
1 The TLS/SSL handshake was successfully completed, a
TLS/SSL connection has been established.
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.
<0 The TLS/SSL handshake was not successful because a fatal
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SSL_DO_HANDSHAKE(3) OpenSSL SSL_DO_HANDSHAKE(3)
error occurred either at the protocol level or a connec-
tion failure occurred. The shutdown was not clean. It
can also occur of action is need to continue the opera-
tion for non-blocking BIOs. Call SSL_get_error() with
the return value ret to find out the reason.
SSL_get_error(3), SSL_connect(3), SSL_accept(3), ssl(3),
bio(3), SSL_set_connect_state(3)
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