gatts_windows.go

package bluetooth

import (
	"fmt"
	"sync"
	"syscall"
	"unsafe"

	"github.com/go-ole/go-ole"
	"github.com/saltosystems/winrt-go"
	"github.com/saltosystems/winrt-go/windows/devices/bluetooth/genericattributeprofile"
	"github.com/saltosystems/winrt-go/windows/foundation"
	"github.com/saltosystems/winrt-go/windows/foundation/collections"
	"github.com/saltosystems/winrt-go/windows/storage/streams"
)

// Characteristic is a single characteristic in a service. It has an UUID and a
// value.
type Characteristic struct {
	wintCharacteristic *genericattributeprofile.GattLocalCharacteristic
	writeEvent         WriteEvent
	flags              CharacteristicPermissions

	valueMtx *sync.Mutex
	value    []byte
}

// AddService creates a new service with the characteristics listed in the
// Service struct.
func (a *Adapter) AddService(s *Service) error {
	gattServiceOp, err := genericattributeprofile.GattServiceProviderCreateAsync(syscallUUIDFromUUID(s.UUID))

	if err != nil {
		return err
	}

	if err = awaitAsyncOperation(gattServiceOp, genericattributeprofile.SignatureGattServiceProviderResult); err != nil {
		return err
	}

	res, err := gattServiceOp.GetResults()
	if err != nil {
		return err
	}

	serviceProviderResult := (*genericattributeprofile.GattServiceProviderResult)(res)
	serviceProvider, err := serviceProviderResult.GetServiceProvider()
	if err != nil {
		return err
	}

	localService, err := serviceProvider.GetService()
	if err != nil {
		return err
	}

	// TODO: "ParameterizedInstanceGUID" + "foundation.NewTypedEventHandler"
	// seems to always return the same instance, need to figure out how to get different instances each time...
	// was following c# source for this flow: https://github.com/microsoft/Windows-universal-samples/blob/main/Samples/BluetoothLE/cs/Scenario3_ServerForeground.xaml.cs
	// which relies on instanced event handlers. for now we'll manually setup our handlers with a map of golang characteristics
	//
	// TypedEventHandler<GattLocalCharacteristic,GattWriteRequestedEventArgs>
	guid := winrt.ParameterizedInstanceGUID(
		foundation.GUIDTypedEventHandler,
		genericattributeprofile.SignatureGattLocalCharacteristic,
		genericattributeprofile.SignatureGattWriteRequestedEventArgs)

	goChars := map[syscall.GUID]*Characteristic{}

	writeRequestedHandler := foundation.NewTypedEventHandler(ole.NewGUID(guid), func(instance *foundation.TypedEventHandler, sender, args unsafe.Pointer) {
		writeReqArgs := (*genericattributeprofile.GattWriteRequestedEventArgs)(args)
		reqAsyncOp, err := writeReqArgs.GetRequestAsync()
		if err != nil {
			return
		}

		if err = awaitAsyncOperation(reqAsyncOp, genericattributeprofile.SignatureGattWriteRequest); err != nil {
			return
		}

		res, err := reqAsyncOp.GetResults()
		if err != nil {
			return
		}

		gattWriteRequest := (*genericattributeprofile.GattWriteRequest)(res)

		buf, err := gattWriteRequest.GetValue()
		if err != nil {
			return
		}

		offset, err := gattWriteRequest.GetOffset()
		if err != nil {
			return
		}

		characteristic := (*genericattributeprofile.GattLocalCharacteristic)(sender)
		uuid, err := characteristic.GetUuid()
		if err != nil {
			return
		}

		goChar, ok := goChars[uuid]
		if !ok {
			return
		}

		if goChar.writeEvent != nil {
			// TODO: connection?
			goChar.writeEvent(0, int(offset), bufferToSlice(buf))
		}
	})

	guid = winrt.ParameterizedInstanceGUID(
		foundation.GUIDTypedEventHandler,
		genericattributeprofile.SignatureGattLocalCharacteristic,
		genericattributeprofile.SignatureGattReadRequestedEventArgs)

	readRequestedHandler := foundation.NewTypedEventHandler(ole.NewGUID(guid), func(instance *foundation.TypedEventHandler, sender, args unsafe.Pointer) {
		readReqArgs := (*genericattributeprofile.GattReadRequestedEventArgs)(args)
		reqAsyncOp, err := readReqArgs.GetRequestAsync()
		if err != nil {
			return
		}

		if err = awaitAsyncOperation(reqAsyncOp, genericattributeprofile.SignatureGattReadRequest); err != nil {
			return
		}

		res, err := reqAsyncOp.GetResults()
		if err != nil {
			return
		}

		gattReadRequest := (*genericattributeprofile.GattReadRequest)(res)

		characteristic := (*genericattributeprofile.GattLocalCharacteristic)(sender)
		uuid, err := characteristic.GetUuid()
		if err != nil {
			return
		}

		goChar, ok := goChars[uuid]
		if !ok {
			return
		}

		writer, err := streams.NewDataWriter()
		if err != nil {
			return
		}
		defer writer.Release()

		goChar.valueMtx.Lock()
		defer goChar.valueMtx.Unlock()
		if len(goChar.value) > 0 {
			if err = writer.WriteBytes(uint32(len(goChar.value)), goChar.value); err != nil {
				return
			}
		}

		buf, err := writer.DetachBuffer()
		if err != nil {
			return
		}

		gattReadRequest.RespondWithValue(buf)
		buf.Release()
	})

	for _, char := range s.Characteristics {
		params, err := genericattributeprofile.NewGattLocalCharacteristicParameters()
		if err != nil {
			return err
		}

		if err = params.SetCharacteristicProperties(genericattributeprofile.GattCharacteristicProperties(char.Flags)); err != nil {
			return err
		}

		uuid := syscallUUIDFromUUID(char.UUID)
		createCharOp, err := localService.CreateCharacteristicAsync(uuid, params)
		if err != nil {
			return err
		}

		if err = awaitAsyncOperation(createCharOp, genericattributeprofile.SignatureGattLocalCharacteristicResult); err != nil {
			return err
		}

		res, err := createCharOp.GetResults()
		if err != nil {
			return err
		}

		characteristicResults := (*genericattributeprofile.GattLocalCharacteristicResult)(res)
		characteristic, err := characteristicResults.GetCharacteristic()
		if err != nil {
			return err
		}

		_, err = characteristic.AddWriteRequested(writeRequestedHandler)
		if err != nil {
			return err
		}

		_, err = characteristic.AddReadRequested(readRequestedHandler)
		if err != nil {
			return err
		}

		// Keep the object around for Characteristic.Write.
		if char.Handle != nil {
			char.Handle.wintCharacteristic = characteristic
			char.Handle.value = char.Value
			char.Handle.valueMtx = &sync.Mutex{}
			char.Handle.flags = char.Flags
			char.Handle.writeEvent = char.WriteEvent
			goChars[uuid] = char.Handle
		}
	}

	params, err := genericattributeprofile.NewGattServiceProviderAdvertisingParameters()
	if err != nil {
		return err
	}

	if err = params.SetIsConnectable(true); err != nil {
		return err
	}

	if err = params.SetIsDiscoverable(true); err != nil {
		return err
	}

	return serviceProvider.StartAdvertisingWithParameters(params)
}

// Write replaces the characteristic value with a new value.
func (c *Characteristic) Write(p []byte) (n int, err error) {
	length := len(p)

	if length == 0 {
		return 0, nil // nothing to do
	}

	if c.writeEvent != nil {
		c.writeEvent(0, 0, p)
	}

	// writes are only actually processed on read events from clients, we just set a variable here.
	c.valueMtx.Lock()
	defer c.valueMtx.Unlock()
	c.value = p

	// only notify if it's enabled, otherwise the below leads to an error
	if c.flags&CharacteristicNotifyPermission != 0 {
		writer, err := streams.NewDataWriter()
		if err != nil {
			return length, err
		}

		defer writer.Release()
		err = writer.WriteBytes(uint32(len(p)), p)
		if err != nil {
			return length, err
		}

		buf, err := writer.DetachBuffer()
		if err != nil {
			return length, err
		}
		defer buf.Release()

		op, err := c.wintCharacteristic.NotifyValueAsync(buf)
		if err != nil {
			return length, err
		}

		// IVectorView<GattClientNotificationResult>
		signature := fmt.Sprintf("pinterface({%s};%s)", collections.GUIDIVectorView, genericattributeprofile.SignatureGattClientNotificationResult)
		if err = awaitAsyncOperation(op, signature); err != nil {
			return length, err
		}
		defer op.Release()

		res, err := op.GetResults()
		if err != nil {
			return length, err
		}

		// TODO: process notification results, just getting this to release
		vec := (*collections.IVectorView)(res)
		vec.Release()
	}

	return length, nil
}

func syscallUUIDFromUUID(uuid UUID) syscall.GUID {
	guid := ole.NewGUID(uuid.String())
	return syscall.GUID{
		Data1: guid.Data1,
		Data2: guid.Data2,
		Data3: guid.Data3,
		Data4: guid.Data4,
	}
}