Merge pull request #2892 from Hixie/fetch-error-cleanup

Clean up prints in services/*

packages/flutter/lib/src/http/mojo_client.dart

@@ -149,8 +149,14 @@ class MojoClient {
       ByteData data = await mojo.DataPipeDrainer.drainHandle(response.body);
       Uint8List bodyBytes = new Uint8List.view(data.buffer);
       return new Response(bodyBytes: bodyBytes, statusCode: response.statusCode);
-    } catch (e) {
-      print("NetworkService unavailable $e");
+    } catch (exception) {
+      assert(() {
+        debugPrint('-- EXCEPTION CAUGHT BY NETWORKING HTTP LIBRARY -------------------------');
+        debugPrint('An exception was raised while sending bytes to the Mojo network library:');
+        debugPrint('$exception');
+        debugPrint('------------------------------------------------------------------------');
+        return true;
+      });
       return new Response(statusCode: 500);
     } finally {
       loader.close();

packages/flutter/lib/src/services/fetch.dart

@@ -4,32 +4,47 @@
 
 import 'dart:async';
 
-import 'package:mojo/mojo/url_request.mojom.dart';
-import 'package:mojo/mojo/url_response.mojom.dart';
-import 'package:mojo_services/mojo/url_loader.mojom.dart';
+import 'package:mojo/mojo/url_request.mojom.dart' as mojom;
+import 'package:mojo/mojo/url_response.mojom.dart' as mojom;
+import 'package:mojo_services/mojo/url_loader.mojom.dart' as mojom;
 
 import '../http/mojo_client.dart';
+import 'print.dart';
 
 export 'package:mojo/mojo/url_response.mojom.dart' show UrlResponse;
 
-Future<UrlResponse> fetch(UrlRequest request) async {
-  UrlLoaderProxy loader = new UrlLoaderProxy.unbound();
+Future<mojom.UrlResponse> fetch(mojom.UrlRequest request, { bool require200: false }) async {
+  mojom.UrlLoaderProxy loader = new mojom.UrlLoaderProxy.unbound();
   try {
     MojoClient.networkService.ptr.createUrlLoader(loader);
-    UrlResponse response = (await loader.ptr.start(request)).response;
+    mojom.UrlResponse response = (await loader.ptr.start(request)).response;
+    if (require200 && (response.error != null || response.statusCode != 200)) {
+      StringBuffer message = new StringBuffer();
+      message.writeln('Could not ${request.method ?? "fetch"} ${request.url ?? "resource"}');
+      if (response.error != null)
+        message.writeln('Network error: ${response.error.code} ${response.error.description ?? "<unknown network error>"}');
+      if (response.statusCode != 200)
+        message.writeln('Protocol error: ${response.statusCode} ${response.statusLine ?? "<no server message>"}');
+      if (response.url != request.url)
+        message.writeln('Final URL after redirects was: ${response.url}');
+      throw message;
+    }
     return response;
-  } catch (e) {
-    print("NetworkService unavailable $e");
-    return new UrlResponse()..statusCode = 500;
+  } catch (exception) {
+    debugPrint('-- EXCEPTION CAUGHT BY NETWORKING HTTP LIBRARY -------------------------');
+    debugPrint('An exception was raised while sending bytes to the Mojo network library:');
+    debugPrint('$exception');
+    debugPrint('------------------------------------------------------------------------');
+    return null;
   } finally {
     loader.close();
   }
 }
 
-Future<UrlResponse> fetchUrl(String relativeUrl) {
+Future<mojom.UrlResponse> fetchUrl(String relativeUrl, { bool require200: false }) {
   String url = Uri.base.resolve(relativeUrl).toString();
-  UrlRequest request = new UrlRequest()
+  mojom.UrlRequest request = new mojom.UrlRequest()
     ..url = url
     ..autoFollowRedirects = true;
-  return fetch(request);
+  return fetch(request, require200: require200);
 }

packages/flutter/lib/src/services/image_cache.dart

@@ -52,15 +52,14 @@ class _UrlFetcher implements ImageProvider {
 
   @override
   Future<ImageInfo> loadImage() async {
-    UrlResponse response = await fetchUrl(_url);
-    if (response.statusCode >= 400) {
-      print("Failed (${response.statusCode}) to load image $_url");
-      return null;
+    UrlResponse response = await fetchUrl(_url, require200: true);
+    if (response != null) {
+      return new ImageInfo(
+        image: await decodeImageFromDataPipe(response.body),
+        scale: _scale
+      );
     }
-    return new ImageInfo(
-      image: await decodeImageFromDataPipe(response.body),
-      scale: _scale
-    );
+    return null;
   }
 
   @override