Bluetooth: Host: Conn: Add GAP service verification

Implement the verification if there is exactly one GAP service
in GATT database.
The verification is performed as soon as the GATT database
is available and forbids to enable the Bluetooth if the configuration
is not compatible with the Bluetooth Specification.
The verification may be disabled by the user for better performance
or deliberate implementation that is not compliant with the
specification.

Signed-off-by: Radosław Koppel <[email protected]>

Author: rkel

subsys/bluetooth/host/CMakeLists.txt

@@ -49,6 +49,11 @@ if(CONFIG_BT_HCI_HOST)
       gatt.c
       )
 
+    zephyr_library_sources_ifdef(
+      CONFIG_GATT_GAP_SVC_VALIDATE
+      gatt_gap_svc_validate.c
+      )
+
     if(CONFIG_BT_SMP)
       zephyr_library_sources(
         smp.c

subsys/bluetooth/host/Kconfig.gatt

@@ -267,4 +267,5 @@ config BT_GATT_AUTHORIZATION_CUSTOM
 	  with the bt_gatt_authorization_cb_register API. See the API
 	  documentation for more details.
 
+rsource 'Kconfig.gatt_gap_svc_validate'
 endmenu

subsys/bluetooth/host/Kconfig.gatt_gap_svc_validate

@@ -0,0 +1,21 @@
+# Bluetooth GATT GAP service validation
+
+# Copyright (c) 2025 Koppel Electronic
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig GATT_GAP_SVC_VALIDATE
+	bool "GATT GAP Service validation"
+	depends on BT_CONN
+	default y
+	help
+	  Validate if in the GATT database exactly one GAP service is present.
+	  This helps to debug any issues related to GAP service that may make
+	  the Bluetooth implementation not compatible with the standard.
+
+if GATT_GAP_SVC_VALIDATE
+
+module = GATT_GAP_SVC_VALIDATE
+module-str = gatt-gap-validate
+source "subsys/logging/Kconfig.template.log_config"
+
+endif # GATT_GAP_SVC_VALIDATE

subsys/bluetooth/host/conn.c

@@ -52,6 +52,7 @@
 #include "common/bt_str.h"
 #include "conn_internal.h"
 #include "direction_internal.h"
+#include "gatt_gap_svc_validate.h"
 #include "hci_core.h"
 #include "id.h"
 #include "iso_internal.h"
@@ -4285,6 +4286,14 @@ int bt_conn_init(void)
 
 	bt_att_init();
 
+	if (IS_ENABLED(CONFIG_GATT_GAP_SVC_VALIDATE)) {
+		err = gatt_gap_svc_validate();
+		if (err) {
+			LOG_ERR("GATT GAP service validation failed (err %d)", err);
+			return err;
+		}
+	}
+
 	err = bt_smp_init();
 	if (err) {
 		return err;

subsys/bluetooth/host/gatt_gap_svc_validate.c

@@ -0,0 +1,55 @@
+/* gatt_gap_validate.c - GAP service inside GATT validation functions */
+
+/*
+ * Copyright (c) 2025 Koppel Electronic
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/bluetooth/gatt.h>
+#include <zephyr/bluetooth/uuid.h>
+#include <zephyr/logging/log.h>
+
+
+#define MODULE gatt_gap_validate
+
+LOG_MODULE_REGISTER(MODULE, CONFIG_GATT_GAP_SVC_VALIDATE_LOG_LEVEL);
+
+
+static uint8_t gap_service_check_cb(const struct bt_gatt_attr *attr,
+				    uint16_t handle,
+				    void *user_data)
+{
+	size_t *cnt = user_data;
+	const struct bt_uuid *svc_uuid = attr->user_data;
+
+	if (svc_uuid && bt_uuid_cmp(svc_uuid, BT_UUID_GAP) == 0) {
+		(*cnt)++;
+		LOG_DBG("GAP service found at handle: %u", handle);
+		if (*cnt > 1) {
+			LOG_ERR("Multiple (%zu) GAP services found at handle: %u",
+				*cnt, handle);
+		}
+	}
+
+	return BT_GATT_ITER_CONTINUE;
+}
+
+int gatt_gap_svc_validate(void)
+{
+	size_t gap_svc_count = 0;
+
+	bt_gatt_foreach_attr_type(
+		BT_ATT_FIRST_ATTRIBUTE_HANDLE,
+		BT_ATT_LAST_ATTRIBUTE_HANDLE,
+		BT_UUID_GATT_PRIMARY,
+		NULL, 0,
+		gap_service_check_cb,
+		&gap_svc_count);
+
+	if (gap_svc_count != 1) {
+		LOG_ERR("GAP service count invalid: %zu", gap_svc_count);
+		return -EINVAL;
+	}
+	return 0;
+}

subsys/bluetooth/host/gatt_gap_svc_validate.h

@@ -0,0 +1,27 @@
+/** @file
+ *  @brief Internal API GATT GAP service validation.
+ */
+
+/*
+ * Copyright (c) 2025 Koppel Electronic
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef __BT_GATT_GAP_SVC_VALIDATE_H
+#define __BT_GATT_GAP_SVC_VALIDATE_H
+
+
+/** @brief Validate GATT database contains exactly one GAP service.
+ *
+ * This function iterates through the GATT attribute database and verifies
+ * that exactly one Generic Access Profile (GAP) service is present. The
+ * Bluetooth specification requires that a GATT server expose exactly one
+ * GAP service.
+ *
+ * @return 0 on success (exactly one GAP service found).
+ * @return -EINVAL if zero or multiple GAP services are found.
+ */
+int gatt_gap_svc_validate(void);
+
+#endif /* __BT_GATT_GAP_SVC_VALIDATE_H */