10.4 TLS Extension Handling

As with authentication methods, the TLS extensions handlers can be implemented using the interface shown below.

typedef int (*gnutls_ext_recv_func) (gnutls_session_t session,
                                     const unsigned char *data, size_t len);
typedef int (*gnutls_ext_send_func) (gnutls_session_t session,
                                     gnutls_buffer_st *extdata);

Here there are two functions, one for receiving the extension data and one for sending. These functions have to check internally whether they operate in client or server side.

A simple example of an extension handler can be seen in ext/srp.c in GnuTLS’ source code. After implementing these functions, together with the extension number they handle, they have to be registered using _gnutls_ext_register in gnutls_extensions.c typically within _gnutls_ext_init.

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