Add GATT descriptor support for Linux

gattc_descriptor_linux.go

@@ -0,0 +1,103 @@
+//go:build !baremetal
+
+package bluetooth
+
+import (
+	"errors"
+	"slices"
+	"strings"
+
+	"github.com/godbus/dbus/v5"
+)
+
+// DeviceDescriptor is a GATT descriptor on a characteristic of a connected
+// peripheral device.
+type DeviceDescriptor struct {
+	uuidWrapper
+	descriptor dbus.BusObject
+}
+
+// UUID returns the UUID for this DeviceDescriptor.
+func (d DeviceDescriptor) UUID() UUID {
+	return d.uuidWrapper
+}
+
+// DiscoverDescriptors discovers the descriptors of this characteristic. Pass a
+// list of descriptor UUIDs you are interested in to this function, or a nil slice
+// to return all descriptors. When UUIDs are given the result has the same length
+// and order as the request, and an error is returned if any could not be found.
+func (c DeviceCharacteristic) DiscoverDescriptors(uuids []UUID) ([]DeviceDescriptor, error) {
+	var descs []DeviceDescriptor
+	if len(uuids) > 0 {
+		descs = make([]DeviceDescriptor, len(uuids))
+	}
+
+	// Descriptors live as D-Bus objects directly under the characteristic path,
+	// so walk the managed objects and match on that prefix (mirrors how
+	// DiscoverCharacteristics finds characteristics under a service).
+	charPath := string(c.characteristic.Path())
+	var list map[dbus.ObjectPath]map[string]map[string]dbus.Variant
+	if err := c.adapter.bluez.Call("org.freedesktop.DBus.ObjectManager.GetManagedObjects", 0).Store(&list); err != nil {
+		return nil, err
+	}
+	objects := make([]string, 0, len(list))
+	for objectPath := range list {
+		objects = append(objects, string(objectPath))
+	}
+	slices.Sort(objects)
+	for _, objectPath := range objects {
+		if !strings.HasPrefix(objectPath, charPath+"/desc") {
+			continue
+		}
+		properties, ok := list[dbus.ObjectPath(objectPath)]["org.bluez.GattDescriptor1"]
+		if !ok {
+			continue
+		}
+		duuid, _ := ParseUUID(properties["UUID"].Value().(string))
+		desc := DeviceDescriptor{
+			uuidWrapper: duuid,
+			descriptor:  c.adapter.bus.Object("org.bluez", dbus.ObjectPath(objectPath)),
+		}
+		if len(uuids) > 0 {
+			for i, uuid := range uuids {
+				if descs[i] != (DeviceDescriptor{}) {
+					continue // already found; supports duplicate UUIDs
+				}
+				if duuid == uuid {
+					descs[i] = desc
+					break
+				}
+			}
+		} else {
+			descs = append(descs, desc)
+		}
+	}
+
+	for _, desc := range descs {
+		if desc == (DeviceDescriptor{}) {
+			return nil, errors.New("bluetooth: could not find some descriptors")
+		}
+	}
+	return descs, nil
+}
+
+// Read reads the current descriptor value, copying it into data and returning the
+// number of bytes read.
+func (d DeviceDescriptor) Read(data []byte) (int, error) {
+	options := make(map[string]interface{})
+	var result []byte
+	if err := d.descriptor.Call("org.bluez.GattDescriptor1.ReadValue", 0, options).Store(&result); err != nil {
+		return 0, err
+	}
+	copy(data, result)
+	return len(result), nil
+}
+
+// Write writes a new value to the descriptor.
+func (d DeviceDescriptor) Write(p []byte) (int, error) {
+	options := make(map[string]interface{})
+	if err := d.descriptor.Call("org.bluez.GattDescriptor1.WriteValue", 0, p, options).Err; err != nil {
+		return 0, err
+	}
+	return len(p), nil
+}