OpenSSL::SSL::SSLSocket#npn_protocol

static VALUE
ossl_ssl_npn_protocol(VALUE self)
{
    SSL *ssl;
    const unsigned char *out;
    unsigned int outlen;

    GetSSL(self, ssl);

    SSL_get0_next_proto_negotiated(ssl, &out, &outlen);
    if (!outlen)
        return Qnil;
    else
        return rb_str_new((const char *) out, outlen);
}