[PATCH 3/3] tls: Ensure callbacks are available before using them

The common callbacks for TLS ready, disconnect and transmission of
packets are required to be set for any l_tls object. The app_data
callback is made optional in case implementations want to provide
an out-of-band data path.
---
 ell/tls.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/ell/tls.c b/ell/tls.c
index 687797f1e466..207f6c3ae40f 100644
--- a/ell/tls.c
+++ b/ell/tls.c
@@ -3357,6 +3357,9 @@ LIB_EXPORT struct l_tls *l_tls_new(bool server,
 	if (!l_key_is_supported(L_KEY_FEATURE_CRYPTO))
 		return NULL;
 
+	if (!tx_handler || !ready_handler || !disconnect_handler)
+		return NULL;
+
 	tls = l_new(struct l_tls, 1);
 	tls->server = server;
 	tls->rx = app_data_handler;
@@ -3561,7 +3564,8 @@ bool tls_handle_message(struct l_tls *tls, const uint8_t *message,
 			return true;
 
 		tls->in_callback = true;
-		tls->rx(message, len, tls->user_data);
+		if (tls->rx)
+			tls->rx(message, len, tls->user_data);
 		tls->in_callback = false;
 
 		if (tls->pending_destroy) {
-- 
2.39.0