Android 仅限 BLE 客户端 returns onCharacteristicRead 中的 600 字节数据

Android BLE client only returns 600 byte of data in onCharacteristicRead

我有一个使用 bleno 的蓝牙服务器和 return 客户端可用的 Wifi 网络列表。 readCharacteristic 的代码基本上是这样的:

class ReadCharacteristic extends bleno.Characteristic {

constructor(uuid, name, action) {
    super({
        uuid: uuid,
        properties: ["read"],
        value: null,
        descriptors: [
            new bleno.Descriptor({
                uuid: "2901",
                value: name
              })
        ]
    });
    this.actionFunction = action;
}

onReadRequest(offset, callback) {
    console.log("Offset: " + offset);

if(offset === 0) {
        const result = this.actionFunction();
    result.then(value => {
        this.actionFunctionResult = value;
            const data = new Buffer.from(value).slice(0,bleno.mtu);
            console.log("onReadRequest: " + data.toString('utf-8'));

            callback(this.RESULT_SUCCESS, data);
        }, err => {
            console.log("onReadRequest error: " + err);
            callback(this.RESULT_UNLIKELY_ERROR);
        }).catch( err => {
            console.log("onReadRequest error: " + err);
            callback(this.RESULT_UNLIKELY_ERROR);
        });
}
else {
    let data = new Buffer.from(this.actionFunctionResult);
    if(offset > data.length) {
        callback(this.RESULT_INVALID_OFFSET, null);
    }
    data = data.slice(offset+1, offset+bleno.mtu);
    console.log(data.toString('utf-8'));
    callback(this.RESULT_SUCCESS, data);
}
}
}

(我试过 data = data.slice(offset+1, offset+bleno.mtu); 并且喜欢这样 data = data.slice(offset+1);

客户端是读取此特征的 Android 应用程序。

用于阅读的 Android 部分如下所示:

            @Override
            public void onConnectionStateChange(BluetoothGatt gatt, int status,
                                                int newState) {
                if (newState == BluetoothProfile.STATE_CONNECTED) {
                    gatt.requestMtu(256);

                } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                    Log.i(TAG, "Disconnected from GATT server.");

                    mFancyShowCaseView.show();
                    gatt.close();
                    scanForBluetoothDevices();
                }
            }


            @Override
            public void onMtuChanged(BluetoothGatt gatt, int mtu, int status) {
                if (status != BluetoothGatt.GATT_SUCCESS) {
                    Log.e(TAG, "Can't set mtu to: " + mtu);
                } else {
                    Log.i(TAG, "Connected to GATT server. MTU: " + mtu);
                    Log.i(TAG, "Attempting to start service discovery:" +
                            mWifiProvisioningService.discoverServices());
                }
            }


            @Override
            // New services discovered
            public void onServicesDiscovered(BluetoothGatt gatt, int status) {
                if (status == BluetoothGatt.GATT_SUCCESS) {
                    Log.d(TAG, "ACTION_GATT_SERVICES_DISCOVERED");

                    BluetoothGattService wifiProvisioningService = gatt.getService(WIFI_PROVISIONING_SERVICE_UUID);
                    BluetoothGattCharacteristic currentConnectedWifiCharacteristic = wifiProvisioningService.getCharacteristic(WIFI_ID_UUID);
                    BluetoothGattCharacteristic availableWifiCharacteristic = wifiProvisioningService.getCharacteristic(WIFI_SCAN_UUID);

                    // Only read the first characteristic and add the 2nd one to a list as we have to wait
                    // for the read return before we read the 2nd one.
                    if (!gatt.readCharacteristic(currentConnectedWifiCharacteristic)) {
                        Log.e(TAG, "Error while reading current connected wifi name.");
                    }
                    readCharacteristics.add(availableWifiCharacteristic);

                } else {
                    Log.w(TAG, "onServicesDiscovered received: " + status);
                }
            }


            @Override
            // Result of a characteristic read operation
            public void onCharacteristicRead(BluetoothGatt gatt,
                                             BluetoothGattCharacteristic characteristic,
                                             int status) {
                if (status == BluetoothGatt.GATT_SUCCESS) {
                    UUID characteristicUUID = characteristic.getUuid();
                    if (WIFI_ID_UUID.equals(characteristicUUID)) {
                        Log.d(TAG, "HEUREKA we found the current wifi name: " + new String(characteristic.getValue()));
                        final String currentWifiName = new String(characteristic.getValue());
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                ((TextView) findViewById(R.id.currentWifiTxt)).setText(currentWifiName);
                                findViewById(R.id.currentWifiTxtProgress).setVisibility(View.GONE);
                            }
                        });

                    } else if (WIFI_SCAN_UUID.equals(characteristicUUID)) {
                        Log.d(TAG, "HEUREKA we found the wifi list: " + new String(characteristic.getValue()));
                        List<String> wifiListArrayList = new ArrayList<>();

                        try {
                            JSONObject wifiListRoot = new JSONObject(characteristic.getStringValue(0));
                            JSONArray wifiListJson = wifiListRoot.getJSONArray("list");

                            for (int i = 0; i < wifiListJson.length(); i++) {
                                wifiListArrayList.add(wifiListJson.get(i).toString());
                            }

                        } catch (JSONException e) {
                            Log.e(TAG, e.toString());
                            return;
                        }
                        final String[] wifiList = new String[wifiListArrayList.size()];
                        wifiListArrayList.toArray(wifiList);

                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                ((ListView) findViewById(R.id.availableWifiList)).setAdapter(new ArrayAdapter<String>(mContext, R.layout.wifi_name_list_item, wifiList));
                                findViewById(R.id.currentWifiTxtProgress).setVisibility(View.GONE);
                            }
                        });
                    } else {
                        Log.i(TAG, "Unexpected Gatt vale: " + new String(characteristic.getValue()));
                    }

                    if (readCharacteristics.size() > 0) {
                        BluetoothGattCharacteristic readCharacteristic = readCharacteristics.get(0);
                        if (!gatt.readCharacteristic(readCharacteristic)) {
                            Log.e(TAG, "Error while writing descriptor for connected wifi");
                        }
                        readCharacteristics.remove(readCharacteristic);
                    }
                }
            }

MTU调整为256字节。我在阅读列表时反映在服务器上。调用本身工作正常并且 returns 列表但是如果列表包含更多然后 600 字节只有 600 字节在 Android 上可用。我以某种方式确定 JS 服务器发送了所有数据,但由于某种原因,Android 客户端仅接收或缓存 600 个字节,这似乎不正确。

我找到了这个 post:Android BLE - Peripheral | onCharacteristicRead return wrong value or part of it (but repeated)

还有这个:

但是两者都没有解决我的问题。我知道在开始下一次读取之前我需要等待一次读取到 return,并且我需要等到写入 MTU 之后才能继续读取数据。据我所知,这反映在您在上面看到的来源中。我有点迷路了。

任何想法都受到高度赞赏。

非常感谢

对于遇到此问题的任何人 post 也想知道为什么 Android 似乎 return 只有 600 字节用于像这个问题所询问的长 GATT 特性,这一切都归结为Bluedroid(Android 的蓝牙堆栈)如何实现他们的 GATT 客户端以及它如何超出规范。就我而言,我使用基于 ESP32 的物联网设备作为我的 GATT 服务器,并使用 Android (SDK 24) 作为 GATT 客户端。

根据规范(蓝牙核心 4.2;第 3 卷,F 部分:3.2.9),特征值(继承自 ATT 的属性值)的最大大小为 512 字节。然而,出于某种原因,Bluedroid 并没有尝试强制执行此要求,而是决定将最大大小设置为 600;如果您深入研究 Bluedroid 源代码并找到设置为 600 (stack/include/gatt_api.h:125) 的宏 GATT_MAX_ATTR_LEN,就可以看到这一点。因为在我的情况下(和你的情况似乎)我正在实现读取请求响应代码,所以我也没有看到对特征读取强制执行 512 字节限制。

现在,重要的是要了解 Bluedroid 的读取特性,以及它与 MTU 大小、读取的最大大小(应为 512,但 Bluedroid 为 600)以及如何处理数据的关系长于最大尺寸。 MTU 大小是您可以使用的 ATT 级别的最大数据包大小。因此,对于 BluetoothGatt.readCharacteristic 的每次调用,您可能会向服务器发送一个或多个读取请求,具体取决于 Bluedroid 是否认为特征大小超过 MTU 大小。在低级别上,Bluedroid 将首先发送一个 ATT 读取请求(0x0a),如果数据包的长度为 MTU 字节,它将跟进一个带有偏移量的 ATT 读取 Blob 请求(0x0c)设置为 MTU 大小。它将继续发送 ATT 读取 Blob 请求,直到 ATT 读取 Blob 响应的长度小于 MTU 字节或直到达到最大特征大小(即 Bluedroid 为 600)。重要的是要注意,如果对于超过 600 字节的数据,MTU 大小不是 600 的完美倍数,则剩余字节将被丢弃(因为 Bluedroid 实际上从未期望读取 600 字节,因为它认为 GATT 服务器将强制执行 512 字节特征尺寸的限制)。因此,如果您的数据超过 600 字节限制(或 512 安全限制),您应该多次调用 BluetoothGatt.readCharacteristic。这是一个在 Android 端读取大量数据的简单示例(抱歉,我没有使用 bleno,所以无法为您提供修复该端的代码),它依赖于首先将数据长度作为无符号 32-位整数,然后如果数据超过 600 字节,则通过重复调用 BluetoothGatt.readCharacteristic 来读取数据:

private int readLength;
private StringBuilder packet; // In my case, Im building a string out of the data

@Override
public void onConnectionStateChange(BluetoothGatt gatt, int status,
                                    int newState) {
    if (newState == BluetoothProfile.STATE_CONNECTED) {
        gatt.requestMtu(201); // NOTE: If you are going to read a long piece of data, its best to make this value a factor of 600 + 1, like 51, 61, 101, 151, etc due to the risk of data loss if the last packet contains more than 600 bytes of cumulative data
    }
}

@Override
public void onMtuChanged(BluetoothGatt gatt, int mtu, int status) {
    gatt.discoverServices();
}

@Override
public void onServicesDiscovered(BluetoothGatt gatt, int status) {
    // Kick off a read
    BluetoothGattCharacteristic characteristic = gatt.getService(UUID.fromString(SERVICE_UUID)).getCharacteristic(UUID.fromString(CHAR_UUID));
    readLength = 0;
    gatt.readCharacteristic(characteristic);
}

@Override
public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
    if (readLength == 0) {
        readLength = characteristic.getIntValue(BluetoothGattCharacteristic.FORMAT_UINT32, 0);
        packet = new StringBuilder();
        gatt.readCharacteristic(characteristic);
    } else {
        byte[] data = charactertic.getValue();
        packet.append(new String(data));
        readLength -= data.length;

        if (readLength == 0) {
            // Got all data this time; you can now process the data however you want
        } else {
            gatt.readCharacteristic(characteristic);
        }
    }
}