feat: addGATTCService and GATTCCharacteristic common interface (#432)

* feat: addGATTCService and GATTCCharacteristic common interface

* cast nil pointers

* Update gattc.go

Co-authored-by: Ron Evans <ron@hybridgroup.com>

---------

Co-authored-by: Ron Evans <ron@hybridgroup.com>

Author: acouvreur

gattc.go

@@ -0,0 +1,41 @@
+//go:build !baremetal || !(s110v8 || s113v7)
+
+package bluetooth
+
+// GATTCService is the common interface that all platform-specific
+// DeviceService types must implement.
+type GATTCService interface {
+	// UUID returns the UUID for this DeviceService.
+	UUID() UUID
+
+	// DiscoverCharacteristics discovers characteristics in this service.
+	// Pass a list of characteristic UUIDs you are interested in to this
+	// function. Either a list of all requested services is returned, or if
+	// some services could not be discovered an error is returned.
+	DiscoverCharacteristics(uuids []UUID) ([]DeviceCharacteristic, error)
+}
+
+// GATTCCharacteristic is the common interface that all platform-specific
+// DeviceCharacteristic types must implement.
+type GATTCCharacteristic interface {
+	// UUID returns the UUID for this DeviceCharacteristic.
+	UUID() UUID
+
+	// Read reads the current characteristic value.
+	Read(data []byte) (int, error)
+
+	// Write replaces the characteristic value with a new value.
+	Write(p []byte) (n int, err error)
+
+	// WriteWithoutResponse replaces the characteristic value with a new
+	// value. The call will return before all data has been written.
+	WriteWithoutResponse(p []byte) (n int, err error)
+
+	// EnableNotifications enables notifications for this characteristic,
+	// calling the provided callback with the new value when the
+	// characteristic value is changed by the remote peripheral.
+	EnableNotifications(callback func(buf []byte)) error
+
+	// GetMTU returns the MTU for this characteristic.
+	GetMTU() (uint16, error)
+}

gattc_darwin.go

@@ -8,8 +8,11 @@ import (
 	"github.com/tinygo-org/cbgo"
 )
 
+var errCannotSendWriteWithoutResponse = errors.New("bluetooth: cannot send write without response (buffer full)")
+
 var (
-	errCannotSendWriteWithoutResponse = errors.New("bluetooth: cannot send write without response (buffer full)")
+	_ GATTCService        = (*DeviceService)(nil)
+	_ GATTCCharacteristic = (*DeviceCharacteristic)(nil)
 )
 
 // DiscoverServices starts a service discovery procedure. Pass a list of service

gattc_hci.go

@@ -17,6 +17,11 @@ var (
 	errCharacteristicNotFound    = errors.New("bluetooth: characteristic not found")
 )
 
+var (
+	_ GATTCService        = (*DeviceService)(nil)
+	_ GATTCCharacteristic = (*DeviceCharacteristic)(nil)
+)
+
 const (
 	maxDefaultServicesToDiscover        = 8
 	maxDefaultCharacteristicsToDiscover = 16
@@ -236,6 +241,13 @@ func (s DeviceService) DiscoverCharacteristics(uuids []UUID) ([]DeviceCharacteri
 	return characteristics, nil
 }
 
+// Write replaces the characteristic value with a new value.
+//
+// Not yet implemented on HCI.
+func (c DeviceCharacteristic) Write(p []byte) (n int, err error) {
+	return 0, errNotYetImplemented
+}
+
 // WriteWithoutResponse replaces the characteristic value with a new value. The
 // call will return before all data has been written. A limited number of such
 // writes can be in flight at any given time. This call is also known as a

gattc_linux.go

@@ -11,6 +11,11 @@ import (
 	"github.com/godbus/dbus/v5"
 )
 
+var (
+	_ GATTCService        = (*DeviceService)(nil)
+	_ GATTCCharacteristic = (*DeviceCharacteristic)(nil)
+)
+
 var (
 	errDupNotif = errors.New("unclosed notifications")
 )

gattc_sd.go

@@ -19,6 +19,11 @@ const (
 	maxDefaultCharacteristicsToDiscover = 8
 )
 
+var (
+_ GATTCService        = (*DeviceService)(nil)
+_ GATTCCharacteristic = (*DeviceCharacteristic)(nil)
+)
+
 var (
 	errAlreadyDiscovering = errors.New("bluetooth: already discovering a service or characteristic")
 	errNotFound           = errors.New("bluetooth: not found")
@@ -312,6 +317,13 @@ func (s DeviceService) DiscoverCharacteristics(uuids []UUID) ([]DeviceCharacteri
 	return characteristics, nil
 }
 
+// Write replaces the characteristic value with a new value.
+//
+// Not yet implemented on SoftDevice.
+func (c DeviceCharacteristic) Write(p []byte) (n int, err error) {
+	return 0, errNotFound
+}
+
 // WriteWithoutResponse replaces the characteristic value with a new value. The
 // call will return before all data has been written. A limited number of such
 // writes can be in flight at any given time. This call is also known as a

gattc_windows.go

@@ -15,6 +15,11 @@ import (
 	"github.com/saltosystems/winrt-go/windows/storage/streams"
 )
 
+var (
+	_ GATTCService        = (*DeviceService)(nil)
+	_ GATTCCharacteristic = (*DeviceCharacteristic)(nil)
+)
+
 var (
 	errNoWrite                   = errors.New("bluetooth: write not supported")
 	errNoWriteWithoutResponse    = errors.New("bluetooth: write without response not supported")