nimble/host: Add method for retrieving configuration values of CCCD

This metod allows reading configuration flags of Client Characteristic
Configuration Descriptor for specified characteristic.

Author: piotrnarajowski

nimble/host/include/host/ble_gatt.h

@@ -185,6 +185,19 @@ struct ble_hs_cfg;
 
 /** @} */
 
+/**
+ * @defgroup ble_gatts_clt_cfg Client Characteristic Configuration Descriptor (CCCD) Flags Types
+ * @{
+ */
+
+/** GATT Client Charactaristic Configuration Flag: Notify. */
+#define BLE_GATT_CCCD_NOTIFY                       0x01
+
+/** GATT Client Charactaristic Configuration Flag: Indicate. */
+#define BLE_GATT_CCCD_INDICATE                     0x02
+
+/** @} */
+
 /*** @client. */
 /** Represents a GATT error. */
 struct ble_gatt_error {
@@ -1214,6 +1227,24 @@ int ble_gatts_start(void);
  */
 int ble_gatts_peer_cl_sup_feat_get(uint16_t conn_handle, uint8_t *out_supported_feat, uint8_t len);
 
+/**
+ * Reads configuration values from Client Characteristic Configuration
+ * Descriptor for specified characteristic.
+ *
+ * @param conn_handle           Connection handle identifying the connection
+ *                                  to which CCC instance is related.
+ * @param chr_val_handle        The value handle of characteristic.
+ * @param cccd_value            Configuration value of CCC.
+ *
+ * @return                      0 on success;
+ *                              BLE_HS_ENOTCONN if no matching connection
+ *                                  was found
+ *                              BLE_HS_ENOENT if descriptor could not be found.
+ *
+ */
+int ble_gatts_read_cccd(uint16_t conn_handle, uint16_t chr_val_handle,
+                        uint8_t *cccd_value);
+
 #ifdef __cplusplus
 }
 #endif

nimble/host/src/ble_gatts.c

@@ -737,6 +737,33 @@ ble_gatts_clt_cfg_access_locked(struct ble_hs_conn *conn, uint16_t attr_handle,
     return 0;
 }
 
+int
+ble_gatts_read_cccd(uint16_t conn_handle, uint16_t chr_val_handle,
+                    uint8_t *cccd_value)
+{
+    struct ble_gatts_clt_cfg *clt_cfg;
+    struct ble_hs_conn *conn;
+
+    ble_hs_lock();
+
+    conn = ble_hs_conn_find(conn_handle);
+    if (conn == NULL) {
+        return BLE_HS_ENOTCONN;
+    }
+
+    clt_cfg = ble_gatts_clt_cfg_find(conn->bhc_gatt_svr.clt_cfgs,
+                                     chr_val_handle);
+    if (clt_cfg == NULL) {
+        return BLE_HS_ENOENT;
+    }
+
+    *cccd_value = clt_cfg->flags;
+
+    ble_hs_unlock();
+
+    return 0;
+}
+
 int
 ble_gatts_clt_cfg_access(uint16_t conn_handle, uint16_t attr_handle,
                          uint8_t op, uint16_t offset, struct os_mbuf **om,