Add onGetValue callback to GenericCharacteristic for lazy queries

Separate functions to obtain the value of a characteristic for a HAP server and to just get a jason formatted value.

Author: gbrooker

Sources/HAP/Base/Characteristic.swift

@@ -1,5 +1,9 @@
 import Foundation
 
+#if os(Linux)
+    import Dispatch
+#endif
+
 public struct AnyCharacteristic {
     let wrapped: Characteristic
 
@@ -17,7 +21,8 @@ protocol Characteristic: class, JSONSerializable {
     var iid: InstanceID { get set }
     var type: CharacteristicType { get }
     var permissions: [CharacteristicPermission] { get }
-    func getValue() -> JSONValueType?
+    func jsonValue() -> JSONValueType?
+    func getValue(fromConnection: Server.Connection?) -> JSONValueType?
     func setValue(_: Any?, fromConnection: Server.Connection?) throws
     var description: String? { get }
     var format: CharacteristicFormat? { get }
@@ -38,7 +43,7 @@ extension Characteristic {
 
         if permissions.contains(.read) {
             // TODO: fixit
-            serialized["value"] = getValue() ?? 0 //NSNull()
+            serialized["value"] = jsonValue() ?? 0 //NSNull()
         }
 
         if let description = description { serialized["description"] = description }
@@ -89,10 +94,20 @@ public class GenericCharacteristic<T: CharacteristicValueType>: Characteristic,
         }
     }
 
-    func getValue() -> JSONValueType? {
+    func jsonValue() -> JSONValueType? {
         return value?.jsonValueType
     }
 
+    // Get Value for HAP controller
+    func getValue(fromConnection connection: Server.Connection?) -> JSONValueType? {
+        let currentValue = _value
+        DispatchQueue.global(qos: .userInitiated).async { [weak self] in
+            self?.onDidGetValue?(currentValue)
+        }
+        return jsonValue()
+    }
+
+    // Set Value by HAP controller
     func setValue(_ newValue: Any?, fromConnection connection: Server.Connection?) throws {
         switch newValue {
         case let some?:
@@ -106,6 +121,11 @@ public class GenericCharacteristic<T: CharacteristicValueType>: Characteristic,
         service?.characteristic(self, didChangeValue: _value)
     }
 
+    // Subscribe a listener to value requests from (remote) HAP controllers.
+    // Called asynchronously on a global queue with the current value.
+    // Only a single listener is permitted.
+    public var onDidGetValue: ((T?) -> Void)?
+
     public let permissions: [CharacteristicPermission]
 
     public var description: String?

Sources/HAP/Endpoints/characteristics().swift

@@ -44,7 +44,7 @@ func characteristics(device: Device) -> Application {
                 }
 
                 var value: Protocol.Value?
-                switch characteristic.getValue() {
+                switch characteristic.getValue(fromConnection: connection) {
                 case let _value as Double: value = .double(_value)
                 case let _value as Float: value = .double(Double(_value))
                 case let _value as Int: value = .int(_value)

Sources/HAP/Utils/Event.swift

@@ -62,7 +62,7 @@ struct Event {
             guard let aid = c.service?.accessory?.aid else {
                 throw Error.characteristicWithoutAccessory
             }
-            payload.append(["aid": aid, "iid": c.iid, "value": c.getValue() ?? NSNull()])
+            payload.append(["aid": aid, "iid": c.iid, "value": c.jsonValue() ?? NSNull()])
         }
         let serialized = ["characteristics": payload]
         guard let body = try? JSONSerialization.data(withJSONObject: serialized, options: []) else {