Bluetooth: BAP: Disallow bt_bap_stream_stop when CIS is not connected

include/zephyr/bluetooth/audio/bap.h

@@ -815,6 +815,16 @@ int bt_bap_stream_start(struct bt_bap_stream *stream);
  *
  * @param stream Stream object
  *
+ * @retval 0 Success
+ * @retval -EINVAL The @p stream does not have an endpoint or a connection, of the stream's
+ *                 connection's role is not @p BT_HCI_ROLE_CENTRAL
+ * @retval -EBADMSG The state of the @p stream endpoint is not @ref BT_BAP_EP_STATE_DISABLING
+ * @retval -EALREADY The CIS state of the @p is not in a connected state, and thus is already
+ *                   stopping
+ * @retval -EBUSY The @p stream is busy with another operation
+ * @retval -ENOTCONN The @p stream ACL connection is not connected
+ * @retval -ENOMEM No memory to send request
+ * @retval -ENOEXEC The request was rejected by GATT
  * @return 0 in case of success or negative value in case of error.
  */
 int bt_bap_stream_stop(struct bt_bap_stream *stream);

subsys/bluetooth/audio/bap_stream.c

@@ -699,6 +699,7 @@ int bt_bap_stream_enable(struct bt_bap_stream *stream, const uint8_t meta[], siz
 
 int bt_bap_stream_stop(struct bt_bap_stream *stream)
 {
+	enum bt_iso_state iso_state;
 	struct bt_bap_ep *ep;
 	uint8_t role;
 	int err;
@@ -725,6 +726,27 @@ int bt_bap_stream_stop(struct bt_bap_stream *stream)
 		return -EBADMSG;
 	}
 
+	/* ASCS_v1.0 3.2 ASE state machine transitions
+	 *
+	 * If the server detects link loss of a CIS for an ASE in the Streaming state or the
+	 * Disabling state, the server shall immediately transition that ASE to the QoS Configured
+	 * state.
+	 *
+	 * This effectively means that if an ASE no longer has a connected CIS, the server shall
+	 * bring it to the QoS Configured state. That means that we, as a unicast client, should not
+	 * attempt to stop it
+	 */
+	if (ep->iso == NULL) {
+		LOG_DBG("Stream endpoint does not have a CIS, server will stop the ASE");
+		return -EALREADY;
+	}
+
+	iso_state = ep->iso->chan.state;
+	if (iso_state != BT_ISO_STATE_CONNECTED && iso_state != BT_ISO_STATE_CONNECTING) {
+		LOG_DBG("Stream endpoint CIS is not connected, server will stop the ASE");
+		return -EALREADY;
+	}
+
 	err = bt_bap_unicast_client_stop(stream);
 	if (err != 0) {
 		LOG_DBG("Stopping stream failed: %d", err);

subsys/bluetooth/audio/bap_unicast_client.c

@@ -3395,7 +3395,18 @@ int bt_bap_unicast_client_stop(struct bt_bap_stream *stream)
 		}
 		req->num_ases++;
 
-		return bt_bap_unicast_client_ep_send(stream->conn, ep, buf);
+		err = bt_bap_unicast_client_ep_send(stream->conn, ep, buf);
+		if (err != 0) {
+			/* Return expected error directly */
+			if (err == -ENOTCONN || err == -ENOMEM) {
+				return err;
+			}
+
+			LOG_DBG("bt_bap_unicast_client_ep_send failed with unexpected error %d",
+				err);
+
+			return -ENOEXEC;
+		}
 	}
 
 	return 0;