BLE workflow: add a guard service so user-created services don't break the web editor

supervisor/shared/bluetooth/bluetooth.c

@@ -32,11 +32,20 @@
 #include "supervisor/shared/bluetooth/serial.h"
 #endif
 
+// BLE workflow exists if either or both of these are turned on.
+#define BLE_WORKFLOW (CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE)
+
+#if BLE_WORKFLOW
+#include "shared-bindings/_bleio/Characteristic.h"
+#include "shared-bindings/_bleio/Service.h"
+#include "shared-bindings/_bleio/UUID.h"
+#endif
+
 #if CIRCUITPY_STATUS_BAR
 #include "supervisor/shared/status_bar.h"
 #endif
 
-#if (CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE || (CIRCUITPY_WEB_WORKFLOW && CIRCUITPY_WIFI)) && CIRCUITPY_SETTINGS_TOML
+#if (BLE_WORKFLOW || (CIRCUITPY_WEB_WORKFLOW && CIRCUITPY_WIFI)) && CIRCUITPY_SETTINGS_TOML
 #include "supervisor/shared/settings.h"
 #endif
 
@@ -67,7 +76,7 @@ const uint8_t private_advertising_data[] = {
 // This scan response advertises the full device name (if it fits.)
 uint8_t circuitpython_scan_response_data[31];
 
-#if CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+#if BLE_WORKFLOW
 static bool boot_in_discovery_mode = false;
 static bool advertising = false;
 static bool _private_advertising = false;
@@ -180,13 +189,13 @@ static void supervisor_bluetooth_start_advertising(void) {
     advertising = status == 0;
 }
 
-#endif  // CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+#endif  // BLE_WORKFLOW
 
 #define BLE_DISCOVERY_DATA_GUARD 0xbb0000bb
 #define BLE_DISCOVERY_DATA_GUARD_MASK 0xff0000ff
 
 void supervisor_bluetooth_init(void) {
-    #if (CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE)
+    #if BLE_WORKFLOW
 
     #if CIRCUITPY_SETTINGS_TOML
     // Check if the user disabled BLE workflow in settings.toml. The default is that it's enabled.
@@ -297,7 +306,7 @@ void supervisor_bluetooth_init(void) {
 }
 
 void supervisor_bluetooth_background(void) {
-    #if CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+    #if BLE_WORKFLOW
     if (!ble_started) {
         return;
     }
@@ -328,8 +337,21 @@ void supervisor_bluetooth_background(void) {
     #endif
 }
 
+#if BLE_WORKFLOW
+// adafXXXX-4369-7263-7569-74507974686e, stored little-endian. The XXXX bytes are
+// filled in by common_hal_bleio_uuid_construct().
+const uint8_t circuitpython_base_uuid[16] = {0x6e, 0x68, 0x74, 0x79, 0x50, 0x74, 0x69, 0x75, 0x63, 0x72, 0x69, 0x43, 0x00, 0x00, 0xaf, 0xad };
+
+static bleio_service_obj_t guard_service;
+static bleio_uuid_obj_t guard_service_uuid;
+static bleio_characteristic_obj_t guard_characteristic;
+static bleio_uuid_obj_t guard_characteristic_uuid;
+static mp_obj_list_t guard_characteristic_list;
+static mp_obj_t guard_characteristic_list_items[1];
+#endif
+
 void supervisor_start_bluetooth(void) {
-    #if CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+    #if BLE_WORKFLOW
 
     if (workflow_state != WORKFLOW_ENABLED || ble_started) {
         return;
@@ -345,6 +367,45 @@ void supervisor_start_bluetooth(void) {
     supervisor_start_bluetooth_serial();
     #endif
 
+    // Create an unused service that will be in the GATT table immediately after
+    // the BLE workflow services. This protects the workflow services from being
+    // invalidated if user code creates services.
+    //
+    // A peripheral reports its last primary service with End Group Handle 0xffff,
+    // and hosts cache that literally. So a service that user code adds later lands
+    // inside the cached range of whichever service was last, and hosts treat the
+    // addition as a change to that service: Chrome invalidates the page's object
+    // for it (and has no event to report that to JavaScript), and BlueZ drops it
+    // from its cache entirely. This guard is created last so that it,
+    // not a workflow service, is the one affected, and file transfer and serial
+    // keep working. Costs three attribute handles.
+    guard_service_uuid.base.type = &bleio_uuid_type;
+    common_hal_bleio_uuid_construct(&guard_service_uuid, 0x0004, circuitpython_base_uuid);
+    guard_characteristic_list.base.type = &mp_type_list;
+    guard_characteristic_list.alloc = 1;
+    guard_characteristic_list.len = 0;
+    guard_characteristic_list.items = guard_characteristic_list_items;
+    guard_characteristic_list_items[0] = MP_OBJ_NULL;
+    guard_service.base.type = &bleio_service_type;
+    _common_hal_bleio_service_construct(&guard_service, &guard_service_uuid, false /* is secondary */, &guard_characteristic_list);
+
+    // One read-only characteristic: we need at least one because on espressif
+    // a service is not registered with NimBLE until its first characteristic is added.
+    guard_characteristic_uuid.base.type = &bleio_uuid_type;
+    common_hal_bleio_uuid_construct(&guard_characteristic_uuid, 0x0005, circuitpython_base_uuid);
+    guard_characteristic.base.type = &bleio_characteristic_type;
+    common_hal_bleio_characteristic_construct(&guard_characteristic,
+        &guard_service,
+        0,                                       // handle (for remote only)
+        &guard_characteristic_uuid,
+        CHAR_PROP_READ,
+        SECURITY_MODE_ENC_NO_MITM,
+        SECURITY_MODE_NO_ACCESS,
+        1,                                       // max length
+        true,                                    // fixed length
+        NULL,                                    // no initial value
+        NULL);
+
     // Mark as started so that the background call does something.
     ble_started = true;
 
@@ -359,7 +420,7 @@ void supervisor_start_bluetooth(void) {
 }
 
 void supervisor_stop_bluetooth(void) {
-    #if CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+    #if BLE_WORKFLOW
 
     if (!ble_started && workflow_state != WORKFLOW_ENABLED) {
         return;
@@ -375,11 +436,15 @@ void supervisor_stop_bluetooth(void) {
     supervisor_stop_bluetooth_serial();
     #endif
 
+    // Tear down the guard service too.
+    common_hal_bleio_characteristic_deinit(&guard_characteristic);
+    common_hal_bleio_service_deinit(&guard_service);
+
     #endif
 }
 
 void supervisor_bluetooth_enable_workflow(void) {
-    #if CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+    #if BLE_WORKFLOW
     if (!ble_workflow_setting || workflow_state == WORKFLOW_DISABLED) {
         return;
     }
@@ -388,13 +453,13 @@ void supervisor_bluetooth_enable_workflow(void) {
 }
 
 void supervisor_bluetooth_disable_workflow(void) {
-    #if CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+    #if BLE_WORKFLOW
     workflow_state = WORKFLOW_DISABLED;
     #endif
 }
 
 bool supervisor_bluetooth_workflow_is_enabled(void) {
-    #if CIRCUITPY_BLE_FILE_SERVICE || CIRCUITPY_BLE_SERIAL_SERVICE
+    #if BLE_WORKFLOW
     if (workflow_state == WORKFLOW_ENABLED) {
         return true;
     }

supervisor/shared/bluetooth/bluetooth.h

@@ -7,6 +7,9 @@
 #pragma once
 
 #include <stdbool.h>
+#include <stdint.h>
+
+extern const uint8_t circuitpython_base_uuid[16];
 
 void supervisor_bluetooth_background(void);
 void supervisor_bluetooth_init(void);

supervisor/shared/bluetooth/serial.c

@@ -15,6 +15,7 @@
 #include "shared-bindings/_bleio/Service.h"
 #include "shared-bindings/_bleio/UUID.h"
 #include "shared-module/storage/__init__.h"
+#include "supervisor/shared/bluetooth/bluetooth.h"
 #include "supervisor/shared/bluetooth/serial.h"
 
 #include "common-hal/_bleio/__init__.h"
@@ -30,9 +31,6 @@ static bleio_uuid_obj_t supervisor_ble_circuitpython_tx_uuid;
 static bleio_characteristic_obj_t supervisor_ble_circuitpython_version_characteristic;
 static bleio_uuid_obj_t supervisor_ble_circuitpython_version_uuid;
 
-// This is the base UUID for the CircuitPython service.
-const uint8_t circuitpython_base_uuid[16] = {0x6e, 0x68, 0x74, 0x79, 0x50, 0x74, 0x69, 0x75, 0x63, 0x72, 0x69, 0x43, 0x00, 0x00, 0xaf, 0xad };
-
 static mp_obj_list_t characteristic_list;
 static mp_obj_t characteristic_list_items[3];