reduce retry attempts for flutter creatte --list-samples (#32833)

packages/flutter_tools/lib/src/base/net.dart

@@ -14,18 +14,23 @@ const int kNetworkProblemExitCode = 50;
 typedef HttpClientFactory = HttpClient Function();
 
 /// Download a file from the given URL and return the bytes.
-Future<List<int>> fetchUrl(Uri url) async {
+Future<List<int>> fetchUrl(Uri url, {int maxAttempts}) async {
   int attempts = 0;
-  int duration = 1;
+  int durationSeconds = 1;
   while (true) {
     attempts += 1;
     final List<int> result = await _attempt(url);
     if (result != null)
       return result;
-    printStatus('Download failed -- attempting retry $attempts in $duration second${ duration == 1 ? "" : "s"}...');
-    await Future<void>.delayed(Duration(seconds: duration));
-    if (duration < 64)
-      duration *= 2;
+    if (maxAttempts != null && attempts >= maxAttempts) {
+      printStatus('Download failed -- retry $attempts');
+      return null;
+    }
+    printStatus('Download failed -- attempting retry $attempts in '
+        '$durationSeconds second${ durationSeconds == 1 ? "" : "s"}...');
+    await Future<void>.delayed(Duration(seconds: durationSeconds));
+    if (durationSeconds < 64)
+      durationSeconds *= 2;
   }
 }
 

packages/flutter_tools/lib/src/commands/create.dart

@@ -203,7 +203,8 @@ class CreateCommand extends FlutterCommand {
 
   /// Fetches the samples index file from the Flutter docs website.
   Future<String> _fetchSamplesIndexFromServer() async {
-    return utf8.decode(await fetchUrl(Uri.https(_snippetsHost, 'snippets/index.json')));
+    return utf8.decode(
+      await fetchUrl(Uri.https(_snippetsHost, 'snippets/index.json'), maxAttempts: 2));
   }
 
   /// Fetches the samples index file from the server and writes it to
@@ -214,8 +215,14 @@ class CreateCommand extends FlutterCommand {
       if (outputFile.existsSync()) {
         throwToolExit('File "$outputFilePath" already exists', exitCode: 1);
       }
-      outputFile.writeAsStringSync(await _fetchSamplesIndexFromServer());
-      printStatus('Wrote samples JSON to "$outputFilePath"');
+      final String samplesJson = await _fetchSamplesIndexFromServer();
+      if (samplesJson == null) {
+        throwToolExit('Unable to download samples', exitCode: 2);
+      }
+      else {
+        outputFile.writeAsStringSync(samplesJson);
+        printStatus('Wrote samples JSON to "$outputFilePath"');
+      }
     } catch (e) {
       throwToolExit('Failed to write samples JSON to "$outputFilePath": $e', exitCode: 2);
     }
@@ -224,6 +231,9 @@ class CreateCommand extends FlutterCommand {
   @override
   Future<FlutterCommandResult> runCommand() async {
     if (argResults['list-samples'] != null) {
+      // _writeSamplesJson can potentially be long-lived.
+      Cache.releaseLockEarly();
+
       await _writeSamplesJson(argResults['list-samples']);
       return null;
     }

packages/flutter_tools/test/base/net_test.dart

@@ -104,6 +104,30 @@ void main() {
     ),
   });
 
+  testUsingContext('max attempts', () async {
+    String error;
+    List<int> actualResult;
+    FakeAsync().run((FakeAsync time) {
+      fetchUrl(Uri.parse('http://example.invalid/'), maxAttempts: 3).then((List<int> value) {
+        actualResult = value;
+      }, onError: (dynamic exception) {
+        error = 'test failed unexpectedly: $exception';
+      });
+      expect(testLogger.statusText, '');
+      time.elapse(const Duration(milliseconds: 10000));
+      expect(testLogger.statusText,
+        'Download failed -- attempting retry 1 in 1 second...\n'
+        'Download failed -- attempting retry 2 in 2 seconds...\n'
+        'Download failed -- retry 3\n',
+      );
+    });
+    expect(testLogger.errorText, isEmpty);
+    expect(error, isNull);
+    expect(actualResult, isNull);
+  }, overrides: <Type, Generator>{
+    HttpClientFactory: () => () => MockHttpClient(500),
+  });
+
   testUsingContext('remote file non-existant', () async {
     final Uri invalid = Uri.parse('http://example.invalid/');
     final bool result = await doesRemoteFileExist(invalid);