Support file download

pkgs/cupertino_http/darwin/cupertino_http/Sources/cupertino_http/utils.h

@@ -0,0 +1,19 @@
+#import <Foundation/NSLock.h>
+#import <Foundation/NSURL.h>
+#import <Foundation/NSURLSession.h>
+#include <stdint.h>
+
+#if !__has_feature(objc_arc)
+#error "This file must be compiled with ARC enabled"
+#endif
+
+typedef void (^_DidFinish)(void *, NSURLSession *session,
+                           NSURLSessionDownloadTask *downloadTask,
+                           NSURL *location);
+typedef void (^_DidFinishWithLock)(NSCondition *lock, NSURLSession *session,
+                                   NSURLSessionDownloadTask *downloadTask,
+                                   NSURL *location);
+/// Create a block useable as a
+/// `URLSession:downloadTask:didFinishDownloadingToURL:` that can be used to
+/// make an async Dart callback behave synchronously.
+_DidFinish adaptFinishWithLock(_DidFinishWithLock block);

pkgs/cupertino_http/darwin/cupertino_http/Sources/cupertino_http/utils.m

@@ -0,0 +1,13 @@
+#import "utils.h"
+
+_DidFinish adaptFinishWithLock(_DidFinishWithLock block) {
+  return ^void(void *, NSURLSession *session,
+               NSURLSessionDownloadTask *downloadTask, NSURL *location) {
+    NSCondition *lock = [[NSCondition alloc] init];
+
+    [lock lock];
+    block(lock, session, downloadTask, location);
+    [lock lock];
+    [lock unlock];
+  };
+}

pkgs/cupertino_http/example/integration_test/url_session_delegate_test.dart

@@ -232,7 +232,7 @@ void testOnFinishedDownloading(URLSessionConfiguration Function() config) {
       expect(actualContent, 'Hello World');
       session.finishTasksAndInvalidate();
     });
-  }, skip: 'XXX will not work with current approach');
+  });
 }
 
 void testOnRedirect(URLSessionConfiguration Function() config) {

pkgs/cupertino_http/ffigen.yaml

@@ -24,10 +24,7 @@ headers:
     - '/System/Volumes/Data/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/Foundation.framework/Versions/C/Headers/NSOperation.h'
     - '/System/Volumes/Data/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/Foundation.framework/Versions/C/Headers/NSError.h'
     - '/System/Volumes/Data/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/Foundation.framework/Versions/C/Headers/NSDictionary.h'
-#    - 'src/CUPHTTPClientDelegate.h'
-#    - 'src/CUPHTTPForwardedDelegate.h'
-#    - 'src/CUPHTTPCompletionHelper.h'
-    - 'darwin/cupertino_http/Sources/cupertino_http/CUPHTTPStreamToNSInputStreamAdapter.h'
+    - 'darwin/cupertino_http/Sources/cupertino_http/utils.h'
 preamble: |
   // ignore_for_file: always_specify_types
   // ignore_for_file: camel_case_types

pkgs/cupertino_http/lib/src/cupertino_api.dart

@@ -911,15 +911,28 @@ class URLSession extends _ObjectHolder<ncb.NSURLSession> {
     }
 
     if (onFinishedDownloading != null) {
-      ncb.NSURLSessionDownloadDelegate.addToBuilderAsListener(protoBuilder,
-          URLSession_downloadTask_didFinishDownloadingToURL_:
-              (nsSession, nsTask, nsUrl) {
-        onFinishedDownloading(
-            URLSession._(nsSession,
-                isBackground: isBackground, hasDelegate: true),
-            URLSessionDownloadTask._(nsTask),
-            nsurlToUri(nsUrl));
+      final asyncFinishDownloading =
+          ncb.ObjCBlock_ffiVoid_NSCondition_NSURLSession_NSURLSessionDownloadTask_NSURL
+              .listener((nsCondition, nsSession, nsTask, nsUrl) {
+        try {
+          onFinishedDownloading(
+              URLSession._(nsSession,
+                  isBackground: isBackground, hasDelegate: true),
+              URLSessionDownloadTask._(nsTask),
+              nsurlToUri(nsUrl));
+        } finally {
+          nsCondition.unlock();
+        }
       });
+
+      final downloadDelegate = objc.getProtocol('NSURLSessionDownloadDelegate');
+      final didFinishDownloadingToURL = objc
+          .registerName('URLSession:downloadTask:didFinishDownloadingToURL:');
+      final signature = objc.getProtocolMethodSignature(
+          downloadDelegate, didFinishDownloadingToURL,
+          isRequired: true, isInstanceMethod: true);
+      protoBuilder.implementMethod(didFinishDownloadingToURL, signature,
+          linkedLibs.adaptFinishWithLock(asyncFinishDownloading));
     }
 
     if (onWebSocketTaskOpened != null) {