[Rendering] Share remote image download pipeline

AsyncImageView/Renderers/RemoteImageRenderer.swift

@@ -20,17 +20,37 @@ public protocol RemoteRenderDataType: RenderDataType {
 /// download the original image.
 /// Consider chaining this with `ImageInflaterRenderer`.
 public final class RemoteImageRenderer<T: RemoteRenderDataType>: RendererType {
-	private let session: URLSession
+	private let renderer: RemoteImageDataRenderer<T, UIImage>
 
 	public init(session: URLSession = URLSession.shared) {
-		self.session = session
+		self.renderer = RemoteImageDataRenderer(session: session) { UIImage(data: $0) }
 	}
 
 	public func renderImageWithData(_ data: T) -> SignalProducer<UIImage, RemoteImageRendererError> {
+		return self.renderer.renderImageWithData(data)
+	}
+}
+
+/// `RendererType` which downloads encoded image data and decodes it into a custom render result.
+public final class RemoteImageDataRenderer<T: RemoteRenderDataType, Result: RenderResultType>: RendererType {
+	public typealias Decoder = (Data) -> Result?
+
+	private let session: URLSession
+	private let decoder: Decoder
+
+	public init(
+		session: URLSession = URLSession.shared,
+		decoder: @escaping Decoder
+	) {
+		self.session = session
+		self.decoder = decoder
+	}
+
+	public func renderImageWithData(_ data: T) -> SignalProducer<Result, RemoteImageRendererError> {
 		return self.session.reactive.data(with: URLRequest(url: data.imageURL))
 			.mapError(RemoteImageRendererError.loadingError)
 			.attemptMap { (data, response) in
-				Result(
+				Swift.Result(
 					(response as? HTTPURLResponse).map { (data, $0) },
 					failWith: .invalidResponse
 				)
@@ -47,10 +67,10 @@ public final class RemoteImageRenderer<T: RemoteRenderDataType>: RendererType {
 				}
 			}
 			.observe(on: QueueScheduler())
-			.flatMap(.merge) { data in
+			.flatMap(.merge) { [decoder = self.decoder] data in
                 return SignalProducer {
-                    Result(
-                        UIImage(data: data),
+                    Swift.Result(
+						decoder(data),
                         failWith: RemoteImageRendererError.decodingError
                     )
                 }