mtu-{darwin,linux,windows,sd}: add get mtu function

Author: jagobagascon

gattc_darwin.go

@@ -173,6 +173,11 @@ func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) err
 	return nil
 }
 
+// GetMTU returns the MTU for the characteristic.
+func (c DeviceCharacteristic) GetMTU() (uint16, error) {
+	return uint16(c.service.device.prph.MaximumWriteValueLength(false)), nil
+}
+
 // Read reads the current characteristic value.
 func (c *deviceCharacteristic) Read(data []byte) (n int, err error) {
 	c.readChan = make(chan error)

gattc_linux.go

@@ -238,6 +238,15 @@ func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) err
 	return c.characteristic.StartNotify()
 }
 
+// GetMTU returns the MTU for the characteristic.
+func (c DeviceCharacteristic) GetMTU() (uint16, error) {
+	mtu, err := c.characteristic.GetProperty("MTU")
+	if err != nil {
+		return uint16(0), err
+	}
+	return mtu.Value().(uint16), nil
+}
+
 // Read reads the current characteristic value.
 func (c *DeviceCharacteristic) Read(data []byte) (int, error) {
 	options := make(map[string]interface{})

gattc_sd.go

@@ -451,3 +451,8 @@ func (c *DeviceCharacteristic) Read(data []byte) (n int, err error) {
 
 	return
 }
+
+// GetMTU returns the MTU for the characteristic.
+func (c DeviceCharacteristic) GetMTU() (uint16, error) {
+	return uint16(C.BLE_GATT_ATT_MTU_DEFAULT), nil
+}

gattc_windows.go

@@ -100,6 +100,7 @@ func (d *Device) DiscoverServices(filterUUIDs []UUID) ([]DeviceService, error) {
 		services = append(services, DeviceService{
 			uuidWrapper: serviceUuid,
 			service:     srv,
+			device:      d,
 		})
 	}
 
@@ -132,6 +133,7 @@ type DeviceService struct {
 	uuidWrapper
 
 	service *genericattributeprofile.GattDeviceService
+	device  *Device
 }
 
 // UUID returns the UUID for this DeviceService.
@@ -180,12 +182,12 @@ func (s *DeviceService) DiscoverCharacteristics(filterUUIDs []UUID) ([]DeviceCha
 
 	var characteristics []DeviceCharacteristic
 	for i := uint32(0); i < characteristicsSize; i++ {
-		s, err := charVector.GetAt(i)
+		c, err := charVector.GetAt(i)
 		if err != nil {
 			return nil, err
 		}
 
-		characteristic := (*genericattributeprofile.GattCharacteristic)(s)
+		characteristic := (*genericattributeprofile.GattCharacteristic)(c)
 		guid, err := characteristic.GetUuid()
 		if err != nil {
 			return nil, err
@@ -215,6 +217,7 @@ func (s *DeviceService) DiscoverCharacteristics(filterUUIDs []UUID) ([]DeviceCha
 
 		characteristics = append(characteristics, DeviceCharacteristic{
 			uuidWrapper:    characteristicUUID,
+			service:        s,
 			characteristic: characteristic,
 			properties:     properties,
 		})
@@ -230,6 +233,8 @@ type DeviceCharacteristic struct {
 
 	characteristic *genericattributeprofile.GattCharacteristic
 	properties     genericattributeprofile.GattCharacteristicProperties
+
+	service *DeviceService
 }
 
 // UUID returns the UUID for this DeviceCharacteristic.
@@ -241,6 +246,11 @@ func (c *DeviceCharacteristic) Properties() uint32 {
 	return uint32(c.properties)
 }
 
+// GetMTU returns the MTU for the characteristic.
+func (c *DeviceCharacteristic) GetMTU() (uint16, error) {
+	return c.service.device.session.GetMaxPduSize()
+}
+
 // Write replaces the characteristic value with a new value. The
 // call will return after all data has been written.
 func (c DeviceCharacteristic) Write(p []byte) (n int, err error) {

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/go-ole/go-ole v1.2.6
 	github.com/godbus/dbus/v5 v5.0.3
 	github.com/muka/go-bluetooth v0.0.0-20220830075246-0746e3a1ea53
-	github.com/saltosystems/winrt-go v0.0.0-20220826130236-ddc8202da421
+	github.com/saltosystems/winrt-go v0.0.0-20220913104103-712830fcd2ad
 	github.com/sirupsen/logrus v1.9.0 // indirect
 	github.com/tinygo-org/cbgo v0.0.4
 	golang.org/x/crypto v0.0.0-20210921155107-089bfa567519

go.sum

@@ -34,8 +34,8 @@ github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINE
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sago35/go-bdf v0.0.0-20200313142241-6c17821c91c4/go.mod h1:rOebXGuMLsXhZAC6mF/TjxONsm45498ZyzVhel++6KM=
-github.com/saltosystems/winrt-go v0.0.0-20220826130236-ddc8202da421 h1:eOgynOew0HzvLwtAsughGzqkrcuTJ6XFpT7+WNCuRNU=
-github.com/saltosystems/winrt-go v0.0.0-20220826130236-ddc8202da421/go.mod h1:UvKm1lyhg+8ehk99i8g5Q7AX1LXUJgks0lRyAkG/ahQ=
+github.com/saltosystems/winrt-go v0.0.0-20220913104103-712830fcd2ad h1:sE3kYG0WAV8eML/eK3uoKgsD85qH8yvlKuPGWOgAecg=
+github.com/saltosystems/winrt-go v0.0.0-20220913104103-712830fcd2ad/go.mod h1:UvKm1lyhg+8ehk99i8g5Q7AX1LXUJgks0lRyAkG/ahQ=
 github.com/sirupsen/logrus v1.5.0/go.mod h1:+F7Ogzej0PZc/94MaYx/nvG9jOFMD2osvC3s+Squfpo=
 github.com/sirupsen/logrus v1.6.0/go.mod h1:7uNnSEd1DgxDLC74fIahvMZmmYsHGZGEOFrfsX/uA88=
 github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=