For servers, this form of callback is invoked during client hello
	  message processing.
	</dd>

	<br>

	<dt>
	  <strong>info</strong> <em>channel major minor message type</em>
	</dt>
	<dd>
	  This form of callback is invoked by the OpenSSL function
	  <code>SSL_CTX_set_info_callback()</code>.
	  <br>
	  The <em>major</em> and <em>minor</em> arguments are used to
	  represent the state information bitmask.
	  <dl>
	  <dt>Possible values for <em>major</em> are:</dt>
	  <dd><code>handshake, alert, connect, accept</code>.</dd>
	  <dt>Possible values for <em>minor</em> are:</dt>
	  <dd><code>start, done, read, write, loop, exit</code>.</dd>
	  </dl>
	  The <em>message</em> argument is a descriptive string which may
	  be generated either by
	  <code>SSL_state_string_long()</code> or by
	  <code>SSL_alert_desc_string_long()</code>,
	  depending on context.
	  <dt>For alerts, the possible values for <em>type</em> are:</dt>
	  <dl>
	  <dd><code>warning, fatal, and unknown</code>.</dd>
	  </dl>
	</dd>

	<br>

	<dt>
	  <strong>session</strong> <em>session_id ticket lifetime</em>
	</dt>

	if (where & SSL_CB_READ)		minor = "read";
	else if (where & SSL_CB_WRITE)		minor = "write";
	else if (where & SSL_CB_LOOP)		minor = "loop";
	else if (where & SSL_CB_EXIT)		minor = "exit";
	else					minor = "unknown";
    }

    /* info channel major minor message type */
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("info", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr,
	    Tcl_NewStringObj(Tcl_GetChannelName(statePtr->self), -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj(major, -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj(minor, -1));

    if (where & SSL_CB_ALERT) {
	Tcl_ListObjAppendElement(interp, cmdPtr,


	    Tcl_NewStringObj(SSL_alert_desc_string_long(ret), -1));

	Tcl_ListObjAppendElement(interp, cmdPtr,
	    Tcl_NewStringObj(SSL_alert_type_string_long(ret), -1));
    } else {
	Tcl_ListObjAppendElement(interp, cmdPtr,
	    Tcl_NewStringObj(SSL_state_string_long(ssl), -1));
	Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("info", -1));
    }
    Tcl_Preserve((ClientData) interp);
    Tcl_Preserve((ClientData) statePtr);

    Tcl_IncrRefCount(cmdPtr);
    (void) Tcl_EvalObjEx(interp, cmdPtr, TCL_EVAL_GLOBAL);
    Tcl_DecrRefCount(cmdPtr);

    Tcl_Release((ClientData) statePtr);
    Tcl_Release((ClientData) interp);    return 0;
}

/*
 *-------------------------------------------------------------------
 *
 * ALPN Callback for Servers and Clients --
 *
 *	Perform protocol (http/1.1, h2, h3, etc.) selection for the
 *	incoming connection. Called after Hello and server callbacks.
 *	Where 'out' is selected protocol and 'in' is the peer advertised list.
 *
 * Results:
 *	None
 *
 * Side effects:
 *	Calls callback (if defined)
 *

    State *statePtr = (State*)arg;
    Tcl_Interp *interp	= statePtr->interp;
    Tcl_Obj *cmdPtr;
    int code, res;

    dprintf("Called");



    if (ssl == NULL || arg == NULL) {
	return SSL_TLSEXT_ERR_NOACK;
    }

    /* Select protocol */
    if (SSL_select_next_proto(out, outlen, statePtr->protos, statePtr->protos_len,
	in, inlen) == OPENSSL_NPN_NEGOTIATED) {
	res = SSL_TLSEXT_ERR_OK;
    } else {
	/* No overlap, so use first client protocol */
	res = SSL_TLSEXT_ERR_NOACK;
    }

    if (statePtr->callback == (Tcl_Obj*)NULL) {
	return SSL_TLSEXT_ERR_OK;
    }

    cmdPtr = Tcl_DuplicateObj(statePtr->callback);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("alpn", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj(*out, -1));

    Tcl_Preserve((ClientData) interp);
    Tcl_Preserve((ClientData) statePtr);

    Tcl_DecrRefCount(cmdPtr);

    Tcl_Release((ClientData) statePtr);
    Tcl_Release((ClientData) interp);
    return res;
}

/*
 *-------------------------------------------------------------------
 *
 * Advertise Protocols Callback for Servers Next Protocol Negotiation --
 *
 *	called when a TLS server needs a list of supported protocols for Next
 *	Protocol Negotiation.
 *
 * Results:
 *	None
 *
 * Side effects:
 *
 * Return codes:
 *	SSL_TLSEXT_ERR_OK: NPN protocol selected. The connection continues.
 *	SSL_TLSEXT_ERR_NOACK: NPN protocol not selected. The connection continues.
 *
 *-------------------------------------------------------------------
 */
#ifdef USE_NPN
static int
NPNCallback(const SSL *ssl, const unsigned char **out, unsigned int *outlen, void *arg) {
    State *statePtr = (State*)arg;

    dprintf("Called");

    if (ssl == NULL || arg == NULL) {
	return SSL_TLSEXT_ERR_NOACK;
    }

    /* Set protocols list */
    if (statePtr->protos != NULL) {
	*out = statePtr->protos;
	*outlen = statePtr->protos_len;
    } else {
	*out = NULL;
	*outlen = 0;
	return SSL_TLSEXT_ERR_NOACK;
    }
    return SSL_TLSEXT_ERR_OK;
}
#endif

/*
 *-------------------------------------------------------------------
 *
 * SNI Callback for Servers --
 *
 *	Perform server-side SNI hostname selection after receiving SNI header.
 *	Called after hello callback but before ALPN callback.

    Tcl_Interp *interp	= statePtr->interp;
    Tcl_Obj *cmdPtr;
    int code;
    char *servername = NULL;

    dprintf("Called");



    if (ssl == NULL || arg == NULL) {
	return SSL_TLSEXT_ERR_NOACK;
    }

    servername = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
    if (!servername || servername[0] == '\0') {
        return SSL_TLSEXT_ERR_NOACK;
    }

    if (statePtr->callback == (Tcl_Obj*)NULL) {
	return SSL_TLSEXT_ERR_OK;
    }

    cmdPtr = Tcl_DuplicateObj(statePtr->callback);
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj("sni", -1));
    Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewStringObj(servername , -1));

    Tcl_Preserve((ClientData) interp);
    Tcl_Preserve((ClientData) statePtr);

    const unsigned char *p;
    size_t len, remaining;

    dprintf("Called");

    if (statePtr->callback == (Tcl_Obj*)NULL) {
	return SSL_CLIENT_HELLO_SUCCESS;
    } else if (ssl == NULL || arg == NULL) {
	return SSL_CLIENT_HELLO_ERROR;
    }

    /* Get names */
    if (!SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_server_name, &p, &remaining) || remaining <= 2) {
        return SSL_CLIENT_HELLO_ERROR;
    }

    /* Create Tcl_Channel BIO Handler */
    statePtr->p_bio	= BIO_new_tcl(statePtr, BIO_NOCLOSE);
    statePtr->bio	= BIO_new(BIO_f_ssl());

    if (server) {
	/* Server callbacks */

	SSL_CTX_set_tlsext_servername_arg(statePtr->ctx, (void *)statePtr);
	SSL_CTX_set_tlsext_servername_callback(statePtr->ctx, SNICallback);
	SSL_CTX_set_client_hello_cb(statePtr->ctx, HelloCallback, (void *)statePtr);
	if (statePtr->protos != NULL) {
	    SSL_CTX_set_alpn_select_cb(statePtr->ctx, ALPNCallback, (void *)statePtr);
#ifdef USE_NPN
	    SSL_CTX_set_next_protos_advertised_cb(statePtr->ctx, NPNCallback, (void *)statePtr);
#endif
	}

	/* Enable server to send cert request after handshake (TLS 1.3 only) */
	if (request && post_handshake) {
	    SSL_verify_client_post_handshake(statePtr->ssl);
	}

	statePtr->flags |= TLS_TCL_SERVER;
	SSL_set_accept_state(statePtr->ssl);
    } else {
	/* Client callbacks */
	if (statePtr->protos != NULL) {
#ifdef USE_NPN
	    SSL_CTX_set_next_proto_select_cb(statePtr->ctx, ALPNCallback, (void *)statePtr);
#endif
	}
	/* Session caching */
	SSL_CTX_set_session_cache_mode(statePtr->ctx, SSL_SESS_CACHE_CLIENT | SSL_SESS_CACHE_NO_INTERNAL_STORE);
	SSL_CTX_sess_set_new_cb(statePtr->ctx, SessionCallback);

	/* Enable post handshake Authentication extension. TLS 1.3 only, not http/2. */
	if (request && post_handshake) {
	    SSL_set_post_handshake_auth(statePtr->ssl, 1);

	SSL_CTX_set_options(ctx, SSL_OP_CIPHER_SERVER_PREFERENCE);
    }

    SSL_CTX_set_app_data(ctx, (void*)interp);	/* remember the interpreter */
    SSL_CTX_set_options(ctx, SSL_OP_ALL);	/* all SSL bug workarounds */
    SSL_CTX_set_options(ctx, off);		/* disable protocol versions */
#if OPENSSL_VERSION_NUMBER < 0x10101000L
    SSL_CTX_set_mode(ctx, SSL_MODE_AUTO_RETRY);	/* handle new handshakes in background. On by default in OpenSSL 1.1.1. */
#endif
    SSL_CTX_sess_set_cache_size(ctx, 128);

    /* Set user defined ciphers, cipher suites, and security level */
    if ((ciphers != NULL) && !SSL_CTX_set_cipher_list(ctx, ciphers)) {
	    Tcl_AppendResult(interp, "Set ciphers failed: No valid ciphers", (char *) NULL);
	    SSL_CTX_free(ctx);

	const unsigned char *session_id;
	char buffer[SSL_MAX_MASTER_KEY_LENGTH];

	/* Report the selected protocol as a result of the ALPN negotiation */
	SSL_SESSION_get0_alpn_selected(session, &proto, &len2);
	Tcl_ListObjAppendElement(interp, objPtr, Tcl_NewStringObj("alpn", -1));
	Tcl_ListObjAppendElement(interp, objPtr, Tcl_NewStringObj((char *)proto, (int) len2));

	/* Report the selected protocol as a result of the NPN negotiation */
#ifdef USE_NPN
	SSL_get0_next_proto_negotiated(ssl, &proto, &ulen);
	Tcl_ListObjAppendElement(interp, objPtr, Tcl_NewStringObj("npn", -1));
	Tcl_ListObjAppendElement(interp, objPtr, Tcl_NewStringObj((char *)proto, (int) ulen));
#endif

	/* Resumable session */
	Tcl_ListObjAppendElement(interp, objPtr, Tcl_NewStringObj("resumable", -1));
	Tcl_ListObjAppendElement(interp, objPtr, Tcl_NewIntObj(SSL_SESSION_is_resumable(session)));

	/* Session start time (seconds since epoch) */
	Tcl_ListObjAppendElement(interp, objPtr, Tcl_NewStringObj("start_time", -1));