BLE外围设备在Advertising中添加ServiceData

startAdvertising失败，errorCode=1(AdvertiseCallback.ADVERTISE_FAILED_DATA_TOO_LARGE)
errorCode解释：Failed to start advertising as the advertise data to be broadcasted is larger than 31 bytes.

原因：创建AdvertiseData对象时，addServiceData(ParcelUuid serviceDataUuid, byte[] serviceData)中的serviceData过长。
下面是自定义函数：
private void startAdvertising() {
    BluetoothLeAdvertiser mBluetoothLeAdvertiser= mBluetoothAdapter.getBluetoothLeAdvertiser();
    if (mBluetoothLeAdvertiser == null) {
        Log.i(TAG, "startAdvertising failed");
        //创建失败
        return;
    }

    AdvertiseSettings settings = new AdvertiseSettings.Builder()
            .setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_BALANCED)
            .setConnectable(false)//注释1
            .setTimeout(0)
            .setTxPowerLevel(AdvertiseSettings.ADVERTISE_TX_POWER_MEDIUM)
            .build();

    AdvertiseData data = new AdvertiseData.Builder()
            .setIncludeDeviceName(false)//注释2
            .setIncludeTxPowerLevel(false)//注释3
            //.addManufacturerData(0, null)//注释4
            //.addServiceUuid(new ParcelUuid(switcherUuid))//绑定服务uuid //注释5
            .addServiceData(new ParcelUuid(switcherUuid), switcherData)//注释6
            .build();
    mBluetoothLeAdvertiser.startAdvertising(settings, data, mAdvertiseCallback);
}
byte[] switcherData = {0x02, 0x01, 0x02, 0x0B, 0x09, 0x48, 0x55, 0x41, 0x57, 0x45, 0x49, 0x20, 0x50, 0x32, 0x30,
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00/*, 0x00, 0x00, 0x00, 0x00*/};
UUID switcherUuid = UUID.fromString("0000ffff-0000-1000-8000-00805f9b34fb");

下面是mBluetoothLeAdvertiser.startAdvertising原生函数：

public void startAdvertising(AdvertiseSettings settings,
        AdvertiseData advertiseData, final AdvertiseCallback callback) {
    startAdvertising(settings, advertiseData, null, callback);
}

public void startAdvertising(AdvertiseSettings settings,
        AdvertiseData advertiseData, AdvertiseData scanResponse,
        final AdvertiseCallback callback) {
    synchronized (mLegacyAdvertisers) {
        BluetoothLeUtils.checkAdapterStateOn(mBluetoothAdapter);
        if (callback == null) {
            throw new IllegalArgumentException("callback cannot be null");
        }
        boolean isConnectable = settings.isConnectable();
        if (totalBytes(advertiseData, isConnectable) > MAX_LEGACY_ADVERTISING_DATA_BYTES
                || totalBytes(scanResponse, false) > MAX_LEGACY_ADVERTISING_DATA_BYTES) {
            postStartFailure(callback, AdvertiseCallback.ADVERTISE_FAILED_DATA_TOO_LARGE);//这里会提示数据过长，Advertising启动失败
            return;
        }
        if (mLegacyAdvertisers.containsKey(callback)) {
            postStartFailure(callback, AdvertiseCallback.ADVERTISE_FAILED_ALREADY_STARTED);
            return;
        }

        AdvertisingSetParameters.Builder parameters = new AdvertisingSetParameters.Builder();
        parameters.setLegacyMode(true);
        parameters.setConnectable(isConnectable);
        parameters.setScannable(true); // legacy advertisements we support are always scannable
        if (settings.getMode() == AdvertiseSettings.ADVERTISE_MODE_LOW_POWER) {
            parameters.setInterval(1600); // 1s
        } else if (settings.getMode() == AdvertiseSettings.ADVERTISE_MODE_BALANCED) {
            parameters.setInterval(400); // 250ms
        } else if (settings.getMode() == AdvertiseSettings.ADVERTISE_MODE_LOW_LATENCY) {
            parameters.setInterval(160); // 100ms
        }

        if (settings.getTxPowerLevel() == AdvertiseSettings.ADVERTISE_TX_POWER_ULTRA_LOW) {
            parameters.setTxPowerLevel(-21);
        } else if (settings.getTxPowerLevel() == AdvertiseSettings.ADVERTISE_TX_POWER_LOW) {
            parameters.setTxPowerLevel(-15);
        } else if (settings.getTxPowerLevel() == AdvertiseSettings.ADVERTISE_TX_POWER_MEDIUM) {
            parameters.setTxPowerLevel(-7);
        } else if (settings.getTxPowerLevel() == AdvertiseSettings.ADVERTISE_TX_POWER_HIGH) {
            parameters.setTxPowerLevel(1);
        }

        int duration = 0;
        int timeoutMillis = settings.getTimeout();
        if (timeoutMillis > 0) {
            duration = (timeoutMillis < 10) ? 1 : timeoutMillis / 10;
        }

        AdvertisingSetCallback wrapped = wrapOldCallback(callback, settings);
        mLegacyAdvertisers.put(callback, wrapped);
        startAdvertisingSet(parameters.build(), advertiseData, scanResponse, null, null,
                duration, 0, wrapped);
    }
}

源码中可以看到Advertising启动失败是因为totalBytes(advertiseData, isConnectable) > MAX_LEGACY_ADVERTISING_DATA_BYTES (=31)

下面是totalBytes源码：

private int totalBytes(AdvertiseData data, boolean isFlagsIncluded) {
    if (data == null) return 0;
    // Flags field is omitted if the advertising is not connectable.
    int size = (isFlagsIncluded) ? FLAGS_FIELD_BYTES : 0; //从上面的源码可以知道这里的isFlagsIncluded就是settings.isConnectable()
    if (data.getServiceUuids() != null) {
        int num16BitUuids = 0;
        int num32BitUuids = 0;
        int num128BitUuids = 0;
        for (ParcelUuid uuid : data.getServiceUuids()) {
            if (BluetoothUuid.is16BitUuid(uuid)) {
                ++num16BitUuids;
            } else if (BluetoothUuid.is32BitUuid(uuid)) {
                ++num32BitUuids;
            } else {
                ++num128BitUuids;
            }
        }
        // 16 bit service uuids are grouped into one field when doing advertising.
        if (num16BitUuids != 0) {
            size += OVERHEAD_BYTES_PER_FIELD + num16BitUuids * BluetoothUuid.UUID_BYTES_16_BIT;
        }
        // 32 bit service uuids are grouped into one field when doing advertising.
        if (num32BitUuids != 0) {
            size += OVERHEAD_BYTES_PER_FIELD + num32BitUuids * BluetoothUuid.UUID_BYTES_32_BIT;
        }
        // 128 bit service uuids are grouped into one field when doing advertising.
        if (num128BitUuids != 0) {
            size += OVERHEAD_BYTES_PER_FIELD
                    + num128BitUuids * BluetoothUuid.UUID_BYTES_128_BIT;
        }
    }
    for (ParcelUuid uuid : data.getServiceData().keySet()) {
        int uuidLen = BluetoothUuid.uuidToBytes(uuid).length;
        size += OVERHEAD_BYTES_PER_FIELD + uuidLen
                + byteLength(data.getServiceData().get(uuid));
    }
    for (int i = 0; i < data.getManufacturerSpecificData().size(); ++i) {
        size += OVERHEAD_BYTES_PER_FIELD + MANUFACTURER_SPECIFIC_DATA_LENGTH
                + byteLength(data.getManufacturerSpecificData().valueAt(i));
    }
    if (data.getIncludeTxPowerLevel()) {
        size += OVERHEAD_BYTES_PER_FIELD + 1; // tx power level value is one byte.
    }
    if (data.getIncludeDeviceName() && mBluetoothAdapter.getName() != null) {
        size += OVERHEAD_BYTES_PER_FIELD + mBluetoothAdapter.getName().length();
    }
    return size;
}

可以看到size有6处赋值，有6个影响点：

1、isFlagsIncluded，从上面的源码可以知道isFlagsIncluded就是settings.isConnectable()，对应的是自定义函数中注释1处的改动。如果注释1处设置为false，那size就等于0；

2、data.getServiceUuids()，对应的是自定义函数中注释5处的改动。如果不设置ServiceUuid，那size仍然等于0；

3、data.getServiceData()，对应的是自定义函数中注释6处的改动。我的主要目的就是设置ServiceData，可以看到此处size += OVERHEAD_BYTES_PER_FIELD + uuidLen + byteLength(data.getServiceData().get(uuid));

    从源码中可以获知到OVERHEAD_BYTES_PER_FIELD=2，从BluetoothUuid.uuidToBytes可以获知到uuidLen=2，按照size不能大于MAX_LEGACY_ADVERTISING_DATA_BYTES (31)的限制可以知道ServiceData的长度不能大于27。

4、data.getManufacturerSpecificData()，对应的是自定义函数中注释4处的改动。如果不设置ManufacturerSpecificData，那size不会增加。

5、data.getIncludeTxPowerLevel()，对应的是自定义函数中注释3处的改动。如果不设置IncludeTxPowerLevel，那size不会增加。

6、data.getIncludeDeviceName()，对应的是自定义函数中注释2处的改动。如果不设置IncludeDeviceName，那size不会增加。

由上可知，可供设置的ServiceData的最大长度是27字节。