feat(esp_hid): Enahcne esp_hid to support multiple BLE connections

1. Add neccessary data structures to manage multiple connections in the
   HID layer of BLE protocol.
2. Add interfaces to allow users to select a connection out of multiple
   connections or boradcast to all connections.
3. This change keep the single connection behavior the same.

Author: paul356

components/esp_hid/include/esp_hidd.h

@@ -1,16 +1,8 @@
-// Copyright 2017-2019 Espressif Systems (Shanghai) PTE LTD
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+/*
+ * SPDX-FileCopyrightText: 2017-2025 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 #pragma once
 
@@ -221,6 +213,63 @@ esp_err_t esp_hidd_dev_event_handler_register(esp_hidd_dev_t *dev, esp_event_han
  */
 esp_err_t esp_hidd_dev_event_handler_unregister(esp_hidd_dev_t *dev, esp_event_handler_t callback, esp_hidd_event_t event);
 
+/**
+ * @brief Connection information structure for querying connections
+ */
+typedef struct {
+    uint16_t conn_id;                           /*!< Connection ID */
+    uint8_t remote_bda[6];                      /*!< Remote device address */
+} esp_hidd_conn_info_t;
+
+/**
+ * @brief Set the active connection for unicast mode
+ * @param dev       : pointer to the device
+ * @param conn_id   : connection ID to set as active (sends to this connection only)
+ *
+ * @return: ESP_OK on success, ESP_ERR_NOT_FOUND if connection not found
+ * @note: This disables broadcast mode automatically
+ */
+esp_err_t esp_hidd_dev_set_active_conn(esp_hidd_dev_t *dev, uint16_t conn_id);
+
+/**
+ * @brief Query all active connections
+ * @param dev           : pointer to the device
+ * @param conn_list     : pointer to array to store connection info
+ * @param max_count     : maximum number of connections that can be stored
+ * @param[out] count    : actual number of connections returned
+ *
+ * @return: ESP_OK on success
+ */
+esp_err_t esp_hidd_dev_get_connections(esp_hidd_dev_t *dev, esp_hidd_conn_info_t *conn_list, size_t max_count, size_t *count);
+
+/**
+ * @brief Enable or disable broadcast mode
+ * @param dev       : pointer to the device
+ * @param enable    : true to broadcast to all connections, false for unicast to active connection
+ *
+ * @return: ESP_OK on success
+ * @note: In broadcast mode, all connected devices receive the events
+ */
+esp_err_t esp_hidd_dev_set_broadcast_mode(esp_hidd_dev_t *dev, bool enable);
+
+/**
+ * @brief Get the currently active connection (unicast) when not in broadcast mode
+ * @param dev       : pointer to the device
+ * @param[out] conn_id : connection ID of the active connection
+ *
+ * @return: ESP_OK on success, ESP_ERR_NOT_FOUND if no active connection, ESP_ERR_NOT_SUPPORTED if transport doesn't support multi-connection
+ */
+esp_err_t esp_hidd_dev_get_active_conn(esp_hidd_dev_t *dev, uint16_t *conn_id);
+
+/**
+ * @brief Query whether the device is in broadcast mode
+ * @param dev       : pointer to the device
+ * @param[out] enabled : true if broadcast mode is enabled, false otherwise
+ *
+ * @return: ESP_OK on success, ESP_ERR_NOT_SUPPORTED if transport doesn't support multi-connection
+ */
+esp_err_t esp_hidd_dev_is_broadcast_mode(esp_hidd_dev_t *dev, bool *enabled);
+
 #ifdef __cplusplus
 }
 #endif

components/esp_hid/private/ble_hidd.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2017-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2017-2025 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -18,6 +18,13 @@ extern "C" {
 
 esp_err_t esp_ble_hidd_dev_init(esp_hidd_dev_t *dev, const esp_hid_device_config_t *config, esp_event_handler_t callback);
 
+// Multi-connection management functions
+esp_err_t esp_ble_hidd_dev_set_active_conn(void *devp, uint16_t conn_id);
+esp_err_t esp_ble_hidd_dev_get_connections(void *devp, esp_hidd_conn_info_t *conn_list, size_t max_count, size_t *count);
+esp_err_t esp_ble_hidd_dev_set_broadcast_mode(void *devp, bool enable);
+esp_err_t esp_ble_hidd_dev_get_active_conn(void *devp, uint16_t *conn_id);
+esp_err_t esp_ble_hidd_dev_is_broadcast_mode(void *devp, bool *enabled);
+
 #endif /* CONFIG_GATTS_ENABLE */
 
 #ifdef __cplusplus