ASBasicImageDownloader.

This is a simplistic, NSURLSession-based downloader object that
implements ASImageDownloaderProtocol and can be used with
ASMultiplexImageNode and ASNetworkImageNode.

(Closes #115.  NSURLSession should suffice for most usecases, and this
code should provide a good jumping-off point for a more-complex
implementation.)

AsyncDisplayKit/AsyncDisplayKit.h

@@ -13,6 +13,7 @@
 #import <AsyncDisplayKit/ASImageNode.h>
 #import <AsyncDisplayKit/ASTextNode.h>
 
+#import <AsyncDisplayKit/ASBasicImageDownloader.h>
 #import <AsyncDisplayKit/ASMultiplexImageNode.h>
 #import <AsyncDisplayKit/ASNetworkImageNode.h>
 

AsyncDisplayKit/Details/ASBasicImageDownloader.h

@@ -0,0 +1,16 @@
+/* Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import <AsyncDisplayKit/ASImageProtocols.h>
+
+/**
+ * @abstract Simple NSURLSession-based image downloader.
+ */
+@interface ASBasicImageDownloader : NSObject <ASImageDownloaderProtocol>
+
+@end

AsyncDisplayKit/Details/ASBasicImageDownloader.mm

@@ -0,0 +1,156 @@
+/* Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import "ASBasicImageDownloader.h"
+
+#import <objc/runtime.h>
+
+#import <UIKit/UIKit.h>
+
+#import "ASThread.h"
+
+
+#pragma mark -
+/**
+ * Collection of properties associated with a download request.
+ */
+@interface ASBasicImageDownloaderMetadata : NSObject
+@property (nonatomic, strong) dispatch_queue_t callbackQueue;
+@property (nonatomic, strong) void (^downloadProgressBlock)(CGFloat);
+@property (nonatomic, strong) void (^completionBlock)(CGImageRef, NSError *);
+@end
+
+@implementation ASBasicImageDownloaderMetadata
+@end
+
+
+#pragma mark -
+/**
+ * NSURLSessionTask lacks a `userInfo` property, so add this association ourselves.
+ */
+@interface NSURLSessionTask (ASBasicImageDownloader)
+@property (nonatomic, strong) ASBasicImageDownloaderMetadata *asyncdisplaykit_metadata;
+@end
+
+@implementation NSURLSessionTask (ASBasicImageDownloader)
+static const char *kMetadataKey = NSStringFromClass(ASBasicImageDownloaderMetadata.class).UTF8String;
+- (void)setAsyncdisplaykit_metadata:(ASBasicImageDownloaderMetadata *)asyncdisplaykit_metadata
+{
+  objc_setAssociatedObject(self, kMetadataKey, asyncdisplaykit_metadata, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+}
+- (ASBasicImageDownloader *)asyncdisplaykit_metadata
+{
+  return objc_getAssociatedObject(self, kMetadataKey);
+}
+@end
+
+
+#pragma mark -
+@interface ASBasicImageDownloader () <NSURLSessionDownloadDelegate>
+{
+  NSOperationQueue *_sessionDelegateQueue;
+  NSURLSession *_session;
+}
+
+@end
+
+@implementation ASBasicImageDownloader
+
+#pragma mark Lifecycle.
+
+- (instancetype)init
+{
+  if (!(self = [super init]))
+    return nil;
+
+  _sessionDelegateQueue = [[NSOperationQueue alloc] init];
+  _session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]
+                                           delegate:self
+                                      delegateQueue:_sessionDelegateQueue];
+
+  return self;
+}
+
+
+#pragma mark ASImageDownloaderProtocol.
+
+- (id)downloadImageWithURL:(NSURL *)URL
+             callbackQueue:(dispatch_queue_t)callbackQueue
+     downloadProgressBlock:(void (^)(CGFloat))downloadProgressBlock
+                completion:(void (^)(CGImageRef, NSError *))completion
+{
+  // create download task
+  NSURLSessionTask *task = [_session downloadTaskWithURL:URL];
+
+  // associate metadata with it
+  ASBasicImageDownloaderMetadata *metadata = [[ASBasicImageDownloaderMetadata alloc] init];
+  metadata.callbackQueue = callbackQueue ?: dispatch_get_main_queue();
+  metadata.downloadProgressBlock = downloadProgressBlock;
+  metadata.completionBlock = completion;
+  task.asyncdisplaykit_metadata = metadata;
+
+  // start downloading
+  [task resume];
+
+  // return the task as an opaque cancellation token
+  return task;
+}
+
+- (void)cancelImageDownloadForIdentifier:(id)downloadIdentifier
+{
+  if (!downloadIdentifier) {
+    return;
+  }
+
+  ASDisplayNodeAssert([downloadIdentifier isKindOfClass:NSURLSessionTask.class], @"unexpected downloadIdentifier");
+  NSURLSessionTask *task = (NSURLSessionTask *)downloadIdentifier;
+
+  [task cancel];
+}
+
+
+#pragma mark NSURLSessionDownloadDelegate.
+
+- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
+                                           didWriteData:(int64_t)bytesWritten
+                                      totalBytesWritten:(int64_t)totalBytesWritten
+                              totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
+{
+  ASBasicImageDownloaderMetadata *metadata = downloadTask.asyncdisplaykit_metadata;
+  if (metadata.downloadProgressBlock) {
+    metadata.downloadProgressBlock((CGFloat)totalBytesWritten / (CGFloat)totalBytesExpectedToWrite);
+  }
+}
+
+// invoked if the download succeeded with no error
+- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
+                              didFinishDownloadingToURL:(NSURL *)location
+{
+  UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:location]];
+
+  ASBasicImageDownloaderMetadata *metadata = downloadTask.asyncdisplaykit_metadata;
+  if (metadata.completionBlock) {
+    dispatch_async(metadata.callbackQueue, ^{
+      metadata.completionBlock(image.CGImage, nil);
+    });
+  }
+}
+
+// invoked unconditionally
+- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
+                           didCompleteWithError:(NSError *)error
+{
+  ASBasicImageDownloaderMetadata *metadata = task.asyncdisplaykit_metadata;
+  if (metadata && error) {
+    dispatch_async(metadata.callbackQueue, ^{
+      metadata.completionBlock(NULL, error);
+    });
+  }
+}
+
+@end