This function performs the handshake of the TLS/SSL protocol, and
initializes the TLS session parameters.
The non-fatal errors expected by this function are:
GNUTLS_E_WARNING_ALERT_RECEIVED. When this function is called for
re-handshake under TLS 1.2 or earlier, the non-fatal error code
GNUTLS_E_GOT_APPLICATION_DATA may also be returned.
The former two interrupt the handshake procedure due to the
transport layer being interrupted, and the latter because of a
"warning" alert that was sent by the peer (it is always a good
idea to check any received alerts). On these non-fatal errors
call this function again, until it returns 0; cf.
gnutls_record_get_direction() and gnutls_error_is_fatal(). In
DTLS sessions the non-fatal error GNUTLS_E_LARGE_PACKET is also
possible, and indicates that the MTU should be adjusted.
When this function is called by a server after a rehandshake
request under TLS 1.2 or earlier the
GNUTLS_E_GOT_APPLICATION_DATA error code indicates that some data
were pending prior to peer initiating the handshake. Under TLS
1.3 this function when called after a successful handshake, is a
no-op and always succeeds in server side; in client side this
function is equivalent to gnutls_session_key_update() with
This function handles both full and abbreviated TLS handshakes
(resumption). For abbreviated handshakes, in client side, the
gnutls_session_set_data() should be called prior to this function
to set parameters from a previous session. In server side,
resumption is handled by either setting a DB back-end, or setting
up keys for session tickets.
This page is part of the GnuTLS (GnuTLS Transport Layer Security
Library) project. Information about the project can be found at
⟨http://www.gnutls.org/⟩. If you have a bug report for this
manual page, send it to firstname.lastname@example.org. This page was obtained
from the tarball gnutls-3.7.2.tar.xz fetched from
⟨http://www.gnutls.org/download.html⟩ on 2021-06-20. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
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gnutls 3.7.2 gnutls_handshake(3)