Bluetooth: TBS: Allow multiple callbacks for client

The TBS client callbacks are just informative so we
provide the information to multiple listeners.

To support this for the long strings, the function
handle_string_long_read was refactored.

This also allows for multiple users of the TBS client.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>

Author: Thalley

doc/releases/release-notes-4.0.rst

@@ -78,6 +78,8 @@ Bluetooth
 
 * Audio
 
+  * :c:func:`bt_tbs_client_register_cb` now supports multiple listeners and may now return an error.
+
 * Host
 
   * Added API :c:func:`bt_gatt_get_uatt_mtu` to get current Unenhanced ATT MTU of a given

include/zephyr/bluetooth/audio/tbs.h

@@ -30,6 +30,7 @@
 #include <stdbool.h>
 
 #include <zephyr/bluetooth/conn.h>
+#include <zephyr/sys/slist.h>
 #include <zephyr/sys/util_macro.h>
 
 #ifdef __cplusplus
@@ -680,6 +681,9 @@ struct bt_tbs_client_cb {
 	/** Bearer friendly name has been read */
 	bt_tbs_client_read_string_cb         friendly_name;
 #endif /* defined(CONFIG_BT_TBS_CLIENT_CALL_FRIENDLY_NAME) */
+
+	/** @internal Internally used field for list handling */
+	sys_snode_t _node;
 };
 
 /**
@@ -998,8 +1002,12 @@ int bt_tbs_client_read_optional_opcodes(struct bt_conn *conn,
  * @brief Register the callbacks for CCP.
  *
  * @param cbs Pointer to the callback structure.
+ *
+ * @retval 0 Success
+ * @retval -EINVAL @p cbs is NULL
+ * @retval -EEXIST @p cbs is already registered
  */
-void bt_tbs_client_register_cb(const struct bt_tbs_client_cb *cbs);
+int bt_tbs_client_register_cb(struct bt_tbs_client_cb *cbs);
 
 /**
  * @brief Look up Telephone Bearer Service instance by CCID

samples/bluetooth/hap_ha/src/ccp_call_ctrl.c

@@ -155,7 +155,5 @@ struct bt_tbs_client_cb tbs_client_cb = {
 
 int ccp_call_ctrl_init(void)
 {
-	bt_tbs_client_register_cb(&tbs_client_cb);
-
-	return 0;
+	return bt_tbs_client_register_cb(&tbs_client_cb);
 }

samples/bluetooth/tmap_peripheral/src/ccp_call_ctrl.c

@@ -124,7 +124,11 @@ int ccp_call_ctrl_init(struct bt_conn *conn)
 	int err;
 
 	default_conn = bt_conn_ref(conn);
-	bt_tbs_client_register_cb(&tbs_client_cb);
+	err = bt_tbs_client_register_cb(&tbs_client_cb);
+	if (err != 0) {
+		return err;
+	}
+
 	err = bt_tbs_client_discover(conn);
 	if (err != 0) {
 		return err;