'Cancel' for PromiseKit -- provides the ability to cancel promises and promise chains

Author: dougzilla32

Cartfile

@@ -1 +1,2 @@
-github "mxcl/PromiseKit" ~> 6.0
+#github "mxcl/PromiseKit" ~> 6.0
+github "dougzilla32/PromiseKit" "CoreCancel"

Cartfile.resolved

@@ -1 +1 @@
-github "mxcl/PromiseKit" "6.3.3"
+github "dougzilla32/PromiseKit" "ff694600d4d03458121515bdc027ba76df14f7ef"

Sources/SKProductsRequest+Promise.swift

@@ -20,7 +20,7 @@ extension SKProductsRequest {
      - Returns: A promise that fulfills if the request succeeds.
     */
     public func start(_: PMKNamespacer) -> Promise<SKProductsResponse> {
-        let proxy = SKDelegate()
+        let proxy = SKDelegate(request: self)
         delegate = proxy
         proxy.retainCycle = proxy
         start()
@@ -29,10 +29,17 @@ extension SKProductsRequest {
 }
 
 
-fileprivate class SKDelegate: NSObject, SKProductsRequestDelegate {
+fileprivate class SKDelegate: NSObject, SKProductsRequestDelegate, CancellableTask {
     let (promise, seal) = Promise<SKProductsResponse>.pending()
+    let request: SKRequest
     var retainCycle: SKDelegate?
 
+    init(request: SKRequest) {
+        self.request = request
+        super.init()
+        promise.setCancellableTask(self, reject: seal.reject)
+    }
+
     @objc fileprivate func request(_ request: SKRequest, didFailWithError error: Error) {
         seal.reject(error)
         retainCycle = nil
@@ -42,6 +49,14 @@ fileprivate class SKDelegate: NSObject, SKProductsRequestDelegate {
         seal.fulfill(response)
         retainCycle = nil
     }
+
+    var isCancelled = false
+    
+    func cancel() {
+        request.cancel()
+        retainCycle = nil
+        isCancelled = true
+    }
 }
 
 // perhaps one day Apple will actually make their errors into Errors…
@@ -50,3 +65,16 @@ fileprivate class SKDelegate: NSObject, SKProductsRequestDelegate {
 //        return true
 //    }
 //}
+
+//////////////////////////////////////////////////////////// Cancellable wrapper
+
+extension SKProductsRequest {
+    /**
+     Sends the request to the Apple App Store.
+     
+     - Returns: A cancellable promise that fulfills if the request succeeds.
+     */
+    public func cancellableStart(_: PMKNamespacer) -> CancellablePromise<SKProductsResponse> {
+        return cancellable(start(.promise))
+    }
+}

Sources/SKReceiptRefreshRequest+Promise.swift

@@ -9,7 +9,7 @@ extension SKReceiptRefreshRequest {
     }
 }
 
-private class ReceiptRefreshObserver: NSObject, SKRequestDelegate {
+private class ReceiptRefreshObserver: NSObject, SKRequestDelegate, CancellableTask {
     let (promise, seal) = Promise<SKReceiptRefreshRequest>.pending()
     let request: SKReceiptRefreshRequest
     var retainCycle: ReceiptRefreshObserver?
@@ -32,4 +32,21 @@ private class ReceiptRefreshObserver: NSObject, SKRequestDelegate {
         seal.reject(error)
         retainCycle = nil
     }
+
+    var isCancelled = false
+    
+    func cancel() {
+        request.cancel()
+        retainCycle = nil
+        isCancelled = true
+    }
+}
+
+//////////////////////////////////////////////////////////// Cancellation
+
+extension SKReceiptRefreshRequest {
+    public func cancellablePromise() -> CancellablePromise<SKReceiptRefreshRequest> {
+        let rro = ReceiptRefreshObserver(request: self)
+        return CancellablePromise(task: rro, promise: rro.promise, resolver: rro.seal)
+    }
 }

Tests/TestStoreKit.swift

@@ -20,3 +20,33 @@ class SKProductsRequestTests: XCTestCase {
         waitForExpectations(timeout: 1, handler: nil)
     }
 }
+
+//////////////////////////////////////////////////////////// Cancellation
+
+extension SKProductsRequestTests {
+    func testCancel() {
+        class MockProductsRequest: SKProductsRequest {            
+            var isCancelled = false
+
+            override func start() {
+                after(seconds: 0.1).done {
+                    if !self.isCancelled {
+                        self.delegate?.productsRequest(self, didReceive: SKProductsResponse())
+                    }
+                }
+            }
+        }
+        
+        let ex = expectation(description: "")
+        
+        let request = MockProductsRequest()
+        request.cancellableStart(.promise).done { _ in
+            XCTFail()
+        }.catch(policy: .allErrors) {
+            $0.isCancelled ? ex.fulfill() : XCTFail()
+        }.cancel()
+        request.isCancelled = true
+        
+        waitForExpectations(timeout: 1, handler: nil)
+    }
+}