蓝牙 RFCOMM

项目
09/02/2023

本主题提供通用 Windows 平台 (UWP) 应用中的蓝牙 RFCOMM 的概述，以及如何发送或接收文件的示例代码。

重要的 API

重要

必须在 Package.appxmanifest 中声明“蓝牙”功能。

<Capabilities> <DeviceCapability Name="bluetooth" /> </Capabilities>

概述

Windows.Devices.Bluetooth.Rfcomm 命名空间中的 API 基于 Windows.Devices 的现有模式而构建，其中包括枚举和实例化。数据读取和写入旨在利用 Windows.Storage.Streams 中已建立的数据流模式和对象。服务发现协议 (SDP) 属性具有一个值和一个预期类型。但是，某些常见设备的 SDP 属性实现错误，属性值不是预期类型。此外，RFCOMM 的许多用法根本不需要额外的 SDP 属性。出于上述原因，此 API 提供对未分析的 SDP 数据的访问权限，开发人员通过此类访问可以获得所需的信息。

RFCOMM API 使用服务标识符概念。尽管服务标识符只是 128 位 GUID，但它通常也被指定为 16 位或 32 位整数。 RFCOMM API 为服务标识符提供一个包装器，以便能够将这些标识符指定并用作 128 位 GUID 以及 32 位整数，但不提供 16 位整数。这不是 API 的问题，因为语言将自动扩至 32 位整数，而且仍可以正确生成标识符。

应用可以在后台任务中执行多步设备操作，以便即使应用移动到后台并挂起，其也能运行到完成。这样便能实现可靠的设备维护，例如对持久性设置或固件的更改以及内容同步，而无需用户坐看进度栏。将 DeviceServicingTrigger 用于设备维护，DeviceUseTrigger 用于内容同步。请注意，这些后台任务限制了应用可以在后台运行的时长，而且不允许无限期操作或无限期同步。

有关详细说明 RFCOMM 操作的完整代码示例，请参阅 Github 上的蓝牙 Rfcomm 聊天示例。

以客户端的形式发送文件

发送文件时，最基本的方案是基于所需的服务连接到配对设备。这包括以下步骤：

使用 RfcommDeviceService.GetDeviceSelector* 函数帮助生成高级查询语法 (AQS) 查询，该查询可用于枚举所需服务的配对设备实例。
选取枚举设备，创建 RfcommDeviceService，并根据需要读取 SDP 属性（使用已建立的数据帮助程序分析属性的数据）。
创建套接字，并使用 RfcommDeviceService.ConnectionHostName 和 RfcommDeviceService.ConnectionServiceName 属性通过 StreamSocket.ConnectAsync 方法连接到具有相应参数的远程设备服务。
按照已建立的数据流模式从文件中读取数据区块，并通过套接字的 StreamSocket.OutputStream 将其发送到设备。

using System;
using System.Threading.Tasks;
using Windows.Devices.Bluetooth.Rfcomm;
using Windows.Networking.Sockets;
using Windows.Storage.Streams;
using Windows.Devices.Bluetooth;

Windows.Devices.Bluetooth.Rfcomm.RfcommDeviceService _service;
Windows.Networking.Sockets.StreamSocket _socket;

async void Initialize()
{
    // Enumerate devices with the object push service
    var services =
        await Windows.Devices.Enumeration.DeviceInformation.FindAllAsync(
            RfcommDeviceService.GetDeviceSelector(
                RfcommServiceId.ObexObjectPush));

    if (services.Count > 0)
    {
        // Initialize the target Bluetooth BR device
        var service = await RfcommDeviceService.FromIdAsync(services[0].Id);

        bool isCompatibleVersion = await IsCompatibleVersionAsync(service);

        // Check that the service meets this App's minimum requirement
        if (SupportsProtection(service) && isCompatibleVersion)
        {
            _service = service;

            // Create a socket and connect to the target
            _socket = new StreamSocket();
            await _socket.ConnectAsync(
                _service.ConnectionHostName,
                _service.ConnectionServiceName,
                SocketProtectionLevel
                    .BluetoothEncryptionAllowNullAuthentication);

            // The socket is connected. At this point the App can wait for
            // the user to take some action, for example, click a button to send a
            // file to the device, which could invoke the Picker and then
            // send the picked file. The transfer itself would use the
            // Sockets API and not the Rfcomm API, and so is omitted here for
            // brevity.
        }
    }
}

// This App requires a connection that is encrypted but does not care about
// whether it's authenticated.
bool SupportsProtection(RfcommDeviceService service)
{
    switch (service.ProtectionLevel)
    {
        case SocketProtectionLevel.PlainSocket:
            if ((service.MaxProtectionLevel == SocketProtectionLevel
                    .BluetoothEncryptionWithAuthentication)
                || (service.MaxProtectionLevel == SocketProtectionLevel
                    .BluetoothEncryptionAllowNullAuthentication))
            {
                // The connection can be upgraded when opening the socket so the
                // App may offer UI here to notify the user that Windows may
                // prompt for a PIN exchange.
                return true;
            }
            else
            {
                // The connection cannot be upgraded so an App may offer UI here
                // to explain why a connection won't be made.
                return false;
            }
        case SocketProtectionLevel.BluetoothEncryptionWithAuthentication:
            return true;
        case SocketProtectionLevel.BluetoothEncryptionAllowNullAuthentication:
            return true;
    }
    return false;
}

// This App relies on CRC32 checking available in version 2.0 of the service.
const uint SERVICE_VERSION_ATTRIBUTE_ID = 0x0300;
const byte SERVICE_VERSION_ATTRIBUTE_TYPE = 0x0A;   // UINT32
const uint MINIMUM_SERVICE_VERSION = 200;
async Task<bool> IsCompatibleVersionAsync(RfcommDeviceService service)
{
    var attributes = await service.GetSdpRawAttributesAsync(
        BluetoothCacheMode.Uncached);
    var attribute = attributes[SERVICE_VERSION_ATTRIBUTE_ID];
    var reader = DataReader.FromBuffer(attribute);

    // The first byte contains the attribute's type
    byte attributeType = reader.ReadByte();
    if (attributeType == SERVICE_VERSION_ATTRIBUTE_TYPE)
    {
        // The remainder is the data
        uint version = reader.ReadUInt32();
        return version >= MINIMUM_SERVICE_VERSION;
    }
    else return false;
}

...
#include <winrt/Windows.Devices.Bluetooth.Rfcomm.h>
#include <winrt/Windows.Devices.Enumeration.h>
#include <winrt/Windows.Networking.Sockets.h>
#include <winrt/Windows.Storage.Streams.h>
...
Windows::Devices::Bluetooth::Rfcomm::RfcommDeviceService m_service{ nullptr };
Windows::Networking::Sockets::StreamSocket m_socket;

Windows::Foundation::IAsyncAction Initialize()
{
    // Enumerate devices with the object push service.
    Windows::Devices::Enumeration::DeviceInformationCollection services{
        co_await Windows::Devices::Enumeration::DeviceInformation::FindAllAsync(
            Windows::Devices::Bluetooth::Rfcomm::RfcommDeviceService::GetDeviceSelector(
                Windows::Devices::Bluetooth::Rfcomm::RfcommServiceId::ObexObjectPush())) };

    if (services.Size() > 0)
    {
        // Initialize the target Bluetooth BR device.
        Windows::Devices::Bluetooth::Rfcomm::RfcommDeviceService service{
            co_await Windows::Devices::Bluetooth::Rfcomm::RfcommDeviceService::FromIdAsync(services.GetAt(0).Id()) };

        // Check that the service meets this App's minimum
        // requirement
        if (SupportsProtection(service)
            && co_await IsCompatibleVersion(service))
        {
            m_service = service;

            // Create a socket and connect to the target
            co_await m_socket.ConnectAsync(
                m_service.ConnectionHostName(),
                m_service.ConnectionServiceName(),
                Windows::Networking::Sockets::SocketProtectionLevel::BluetoothEncryptionAllowNullAuthentication);

            // The socket is connected. At this point the App can
            // wait for the user to take some action, for example, click
            // a button to send a file to the device, which could
            // invoke the Picker and then send the picked file.
            // The transfer itself would use the Sockets API and
            // not the Rfcomm API, and so is omitted here for
            //brevity.
        }
    }
}

// This App requires a connection that is encrypted but does not care about
// whether it's authenticated.
bool SupportsProtection(Windows::Devices::Bluetooth::Rfcomm::RfcommDeviceService const& service)
{
    switch (service.ProtectionLevel())
    {
    case Windows::Networking::Sockets::SocketProtectionLevel::PlainSocket:
        if ((service.MaxProtectionLevel() == Windows::Networking::Sockets::SocketProtectionLevel::BluetoothEncryptionWithAuthentication)
            || (service.MaxProtectionLevel() == Windows::Networking::Sockets::SocketProtectionLevel::BluetoothEncryptionAllowNullAuthentication))
        {
            // The connection can be upgraded when opening the socket so the
            // App may offer UI here to notify the user that Windows may
            // prompt for a PIN exchange.
            return true;
        }
        else
        {
            // The connection cannot be upgraded so an App may offer UI here
            // to explain why a connection won't be made.
            return false;
        }
    case Windows::Networking::Sockets::SocketProtectionLevel::BluetoothEncryptionWithAuthentication:
        return true;
    case Windows::Networking::Sockets::SocketProtectionLevel::BluetoothEncryptionAllowNullAuthentication:
        return true;
    }
    return false;
}

// This application relies on CRC32 checking available in version 2.0 of the service.
const uint32_t SERVICE_VERSION_ATTRIBUTE_ID{ 0x0300 };
const byte SERVICE_VERSION_ATTRIBUTE_TYPE{ 0x0A }; // UINT32.
const uint32_t MINIMUM_SERVICE_VERSION{ 200 };

Windows::Foundation::IAsyncOperation<bool> IsCompatibleVersion(Windows::Devices::Bluetooth::Rfcomm::RfcommDeviceService const& service)
{
    auto attributes{
        co_await service.GetSdpRawAttributesAsync(Windows::Devices::Bluetooth::BluetoothCacheMode::Uncached) };

    auto attribute{ attributes.Lookup(SERVICE_VERSION_ATTRIBUTE_ID) };
    auto reader{ Windows::Storage::Streams::DataReader::FromBuffer(attribute) };

    // The first byte contains the attribute's type.
    byte attributeType{ reader.ReadByte() };
    if (attributeType == SERVICE_VERSION_ATTRIBUTE_TYPE)
    {
        // The remainder is the data
        uint32_t version{ reader.ReadUInt32() };
        co_return (version >= MINIMUM_SERVICE_VERSION);
    }
}
...

Windows::Devices::Bluetooth::Rfcomm::RfcommDeviceService^ _service;
Windows::Networking::Sockets::StreamSocket^ _socket;

void Initialize()
{
    // Enumerate devices with the object push service
    create_task(
        Windows::Devices::Enumeration::DeviceInformation::FindAllAsync(
            RfcommDeviceService::GetDeviceSelector(
                RfcommServiceId::ObexObjectPush)))
    .then([](DeviceInformationCollection^ services)
    {
        if (services->Size > 0)
        {
            // Initialize the target Bluetooth BR device
            create_task(RfcommDeviceService::FromIdAsync(services[0]->Id))
            .then([](RfcommDeviceService^ service)
            {
                // Check that the service meets this App's minimum
                // requirement
                if (SupportsProtection(service)
                    && IsCompatibleVersion(service))
                {
                    _service = service;

                    // Create a socket and connect to the target
                    _socket = ref new StreamSocket();
                    create_task(_socket->ConnectAsync(
                        _service->ConnectionHostName,
                        _service->ConnectionServiceName,
                        SocketProtectionLevel
                            ::BluetoothEncryptionAllowNullAuthentication)
                    .then([](void)
                    {
                        // The socket is connected. At this point the App can
                        // wait for the user to take some action, for example, click
                        // a button to send a file to the device, which could
                        // invoke the Picker and then send the picked file.
                        // The transfer itself would use the Sockets API and
                        // not the Rfcomm API, and so is omitted here for
                        //brevity.
                    });
                }
            });
        }
    });
}

// This App requires a connection that is encrypted but does not care about
// whether it's authenticated.
bool SupportsProtection(RfcommDeviceService^ service)
{
    switch (service->ProtectionLevel)
    {
    case SocketProtectionLevel->PlainSocket:
        if ((service->MaxProtectionLevel == SocketProtectionLevel
                ::BluetoothEncryptionWithAuthentication)
            || (service->MaxProtectionLevel == SocketProtectionLevel
                ::BluetoothEncryptionAllowNullAuthentication))
        {
            // The connection can be upgraded when opening the socket so the
            // App may offer UI here to notify the user that Windows may
            // prompt for a PIN exchange.
            return true;
        }
        else
        {
            // The connection cannot be upgraded so an App may offer UI here
            // to explain why a connection won't be made.
            return false;
        }
    case SocketProtectionLevel::BluetoothEncryptionWithAuthentication:
        return true;
    case SocketProtectionLevel::BluetoothEncryptionAllowNullAuthentication:
        return true;
    }
    return false;
}

// This App relies on CRC32 checking available in version 2.0 of the service.
const uint SERVICE_VERSION_ATTRIBUTE_ID = 0x0300;
const byte SERVICE_VERSION_ATTRIBUTE_TYPE = 0x0A;   // UINT32
const uint MINIMUM_SERVICE_VERSION = 200;
bool IsCompatibleVersion(RfcommDeviceService^ service)
{
    auto attributes = await service->GetSdpRawAttributesAsync(
        BluetoothCacheMode::Uncached);
    auto attribute = attributes[SERVICE_VERSION_ATTRIBUTE_ID];
    auto reader = DataReader.FromBuffer(attribute);

    // The first byte contains the attribute's type
    byte attributeType = reader->ReadByte();
    if (attributeType == SERVICE_VERSION_ATTRIBUTE_TYPE)
    {
        // The remainder is the data
        uint version = reader->ReadUInt32();
        return version >= MINIMUM_SERVICE_VERSION;
    }
}

以服务器的形式接收文件

另一种常见的 RFCOMM 应用方案是在电脑上托管服务，并为其他设备公开该服务。

创建 RfcommServiceProvider 以播发所需的服务。
根据需要设置 SDP 属性（使用已建立的数据帮助程序生成属性的数据），并开始播发 SDP 记录以供其他设备检索。
若要连接到客户端设备，请创建套接字侦听器以开始侦听传入的连接请求。
收到连接后，存储连接的套接字以供以后处理。
按照已建立的数据流模式从套接字的 InputStream 中读取数据区块，并将其保存至文件。

若要在后台保留 RFCOMM 服务，请使用 RfcommConnectionTrigger。后台任务在连接到服务时触发。开发人员在后台任务中接收套接字的句柄。后台任务将长期运行，其在套接字使用期间一直保留。

Windows.Devices.Bluetooth.Rfcomm.RfcommServiceProvider _provider;

async void Initialize()
{
    // Initialize the provider for the hosted RFCOMM service
    _provider =
        await Windows.Devices.Bluetooth.Rfcomm.RfcommServiceProvider.CreateAsync(
            RfcommServiceId.ObexObjectPush);

    // Create a listener for this service and start listening
    StreamSocketListener listener = new StreamSocketListener();
    listener.ConnectionReceived += OnConnectionReceivedAsync;
    await listener.BindServiceNameAsync(
        _provider.ServiceId.AsString(),
        SocketProtectionLevel
            .BluetoothEncryptionAllowNullAuthentication);

    // Set the SDP attributes and start advertising
    InitializeServiceSdpAttributes(_provider);
    _provider.StartAdvertising(listener);
}

const uint SERVICE_VERSION_ATTRIBUTE_ID = 0x0300;
const byte SERVICE_VERSION_ATTRIBUTE_TYPE = 0x0A;   // UINT32
const uint SERVICE_VERSION = 200;

void InitializeServiceSdpAttributes(RfcommServiceProvider provider)
{
    Windows.Storage.Streams.DataWriter writer = new Windows.Storage.Streams.DataWriter();

    // First write the attribute type
    writer.WriteByte(SERVICE_VERSION_ATTRIBUTE_TYPE);
    // Then write the data
    writer.WriteUInt32(MINIMUM_SERVICE_VERSION);

    IBuffer data = writer.DetachBuffer();
    provider.SdpRawAttributes.Add(SERVICE_VERSION_ATTRIBUTE_ID, data);
}

void OnConnectionReceivedAsync(
    StreamSocketListener listener,
    StreamSocketListenerConnectionReceivedEventArgs args)
{
    // Stop advertising/listening so that we're only serving one client
    _provider.StopAdvertising();
    listener.Dispose();
    _socket = args.Socket;

    // The client socket is connected. At this point the App can wait for
    // the user to take some action, for example, click a button to receive a file
    // from the device, which could invoke the Picker and then save the
    // received file to the picked location. The transfer itself would use
    // the Sockets API and not the Rfcomm API, and so is omitted here for
    // brevity.
}

...
#include <winrt/Windows.Devices.Bluetooth.Rfcomm.h>
#include <winrt/Windows.Networking.Sockets.h>
#include <winrt/Windows.Storage.Streams.h>
...
Windows::Devices::Bluetooth::Rfcomm::RfcommServiceProvider m_provider{ nullptr };
Windows::Networking::Sockets::StreamSocket m_socket;

Windows::Foundation::IAsyncAction Initialize()
{
    // Initialize the provider for the hosted RFCOMM service.
    auto provider{ co_await Windows::Devices::Bluetooth::Rfcomm::RfcommServiceProvider::CreateAsync(
        Windows::Devices::Bluetooth::Rfcomm::RfcommServiceId::ObexObjectPush()) };

    m_provider = provider;

    // Create a listener for this service and start listening.
    Windows::Networking::Sockets::StreamSocketListener listener;
    listener.ConnectionReceived({ this, &MainPage::OnConnectionReceived });

    co_await listener.BindServiceNameAsync(m_provider.ServiceId().AsString(),
        Windows::Networking::Sockets::SocketProtectionLevel::BluetoothEncryptionAllowNullAuthentication);

    // Set the SDP attributes and start advertising
    InitializeServiceSdpAttributes();
    m_provider.StartAdvertising(listener);
}

const uint32_t SERVICE_VERSION_ATTRIBUTE_ID{ 0x0300 };
const byte SERVICE_VERSION_ATTRIBUTE_TYPE{ 0x0A };   // UINT32.
const uint32_t SERVICE_VERSION{ 200 };

void InitializeServiceSdpAttributes()
{
    Windows::Storage::Streams::DataWriter writer;

    // First write the attribute type
    writer.WriteByte(SERVICE_VERSION_ATTRIBUTE_TYPE);
    // Then write the data
    writer.WriteUInt32(SERVICE_VERSION);

    auto data{ writer.DetachBuffer() };
    m_provider.SdpRawAttributes().Insert(SERVICE_VERSION_ATTRIBUTE_ID, data);
}

void OnConnectionReceived(
    Windows::Networking::Sockets::StreamSocketListener const& listener,
    Windows::Networking::Sockets::StreamSocketListenerConnectionReceivedEventArgs const& args)
{
    // Stop advertising/listening so that we're only serving one client
    m_provider.StopAdvertising();
    listener.Close();
    m_socket = args.Socket();

    // The client socket is connected. At this point the application can wait for
    // the user to take some action, for example, click a button to receive a
    // file from the device, which could invoke the Picker and then save
    // the received file to the picked location. The transfer itself
    // would use the Sockets API and not the Rfcomm API, and so is
    // omitted here for brevity.
}
...

Windows::Devices::Bluetooth::Rfcomm::RfcommServiceProvider^ _provider;
Windows::Networking::Sockets::StreamSocket^ _socket;

void Initialize()
{
    // Initialize the provider for the hosted RFCOMM service
    create_task(Windows::Devices::Bluetooth.
        RfcommServiceProvider::CreateAsync(
            RfcommServiceId::ObexObjectPush))
    .then([](RfcommServiceProvider^ provider) -> task<void> {
        _provider = provider;

        // Create a listener for this service and start listening
        auto listener = ref new StreamSocketListener();
        listener->ConnectionReceived += ref new TypedEventHandler<
                StreamSocketListener^,
                StreamSocketListenerConnectionReceivedEventArgs^>
           (&OnConnectionReceived);
        return create_task(listener->BindServiceNameAsync(
            _provider->ServiceId->AsString(),
            SocketProtectionLevel
                ::BluetoothEncryptionAllowNullAuthentication));
    }).then([listener](void) {
        // Set the SDP attributes and start advertising
        InitializeServiceSdpAttributes(_provider);
        _provider->StartAdvertising(listener);
    });
}

const uint SERVICE_VERSION_ATTRIBUTE_ID = 0x0300;
const byte SERVICE_VERSION_ATTRIBUTE_TYPE = 0x0A;   // UINT32
const uint SERVICE_VERSION = 200;
void InitializeServiceSdpAttributes(RfcommServiceProvider^ provider)
{
    auto writer = ref new Windows::Storage::Streams::DataWriter();

    // First write the attribute type
    writer->WriteByte(SERVICE_VERSION_ATTRIBUTE_TYPE);
    // Then write the data
    writer->WriteUInt32(SERVICE_VERSION);

    auto data = writer->DetachBuffer();
    provider->SdpRawAttributes->Add(SERVICE_VERSION_ATTRIBUTE_ID, data);
}

void OnConnectionReceived(
    StreamSocketListener^ listener,
    StreamSocketListenerConnectionReceivedEventArgs^ args)
{
    // Stop advertising/listening so that we're only serving one client
    _provider->StopAdvertising();
    create_task(listener->Close())
    .then([args](void) {
        _socket = args->Socket;

        // The client socket is connected. At this point the App can wait for
        // the user to take some action, for example, click a button to receive a
        // file from the device, which could invoke the Picker and then save
        // the received file to the picked location. The transfer itself
        // would use the Sockets API and not the Rfcomm API, and so is
        // omitted here for brevity.
    });
}

通过

蓝牙 RFCOMM

概述

以客户端的形式发送文件

以服务器的形式接收文件

反馈

其他资源