Re: ALPN: implementation / behaviour

On Sat, Jul 10, 2021, Jeremy Harris wrote:

> Under GnuTLS you can hook into the handshake operations:

Same can be done in OpenSSL: quoting my notes:

For the client we would have to go through all the extensions:
SSL_set_tlsext_debug_callback(con, tlsext_cb);
void tlsext_cb(SSL *s, int client_server, int type,
               const unsigned char *data, int len, void *arg)
and set a flag there:
    if (TLSEXT_TYPE_application_layer_protocol_negotiation == type) {
        set flag ...

But that does not work: the extension is only returned if the
server selected a protocol.

> [I've not tried this, client-side.  Server side works fine.]

I added the code to the client side and observed the problem mentioned
above.

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