Add BuildBotClient to abstract http/logdog access

tools/gardening/lib/src/client.dart

Index: tools/gardening/lib/src/client.dart
diff --git a/tools/gardening/lib/src/client.dart b/tools/gardening/lib/src/client.dart
new file mode 100644
index 0000000000000000000000000000000000000000..05eb1ad29f7a80be0fe57d1bbcb75dbba667793a
--- /dev/null
+++ b/tools/gardening/lib/src/client.dart
@@ -0,0 +1,92 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import 'buildbot_data.dart';
+import 'buildbot_loading.dart';
+import 'buildbot_structures.dart';
+import 'logdog.dart';
+import 'util.dart';
+
+/// Interface for pulling build bot results.
+abstract class BuildbotClient {
+  /// Reads the [BuildResult] for the [buildUri].
+  Future<BuildResult> readResult(BuildUri buildUri);
+
+  int get mostRecentBuildNumber;
+
+  /// Closes the client and cleans up its state.
+  void close();
+}
+
+/// Buildbot client that pulls build bot results through http.
+class HttpBuildbotClient implements BuildbotClient {
+  final HttpClient _client = new HttpClient();
+
+  @override
+  Future<BuildResult> readResult(BuildUri buildUri) {
+    return readBuildResult(_client, buildUri);
+  }
+
+  int get mostRecentBuildNumber => -2;
+
+  @override
+  void close() {
+    _client.close();
+  }
+}
+
+/// Buildbot client that pulls build bot results through logdog.
+class LogdogBuildbotClient implements BuildbotClient {
+  Map<String, List<int>> _botBuildNumberCache = <String, List<int>>{};
+
+  int get mostRecentBuildNumber => -1;
+
+  Future<List<int>> _getAbsoluteBuildNumbers(BuildUri buildUri) async {
+    List<int> absoluteBuildNumbers = _botBuildNumberCache[buildUri.botName];
+    if (absoluteBuildNumbers == null) {
+      absoluteBuildNumbers = await lookupBotBuildNumbers(buildUri.botName);
+      _botBuildNumberCache[buildUri.botName] = absoluteBuildNumbers;
+    }
+    return absoluteBuildNumbers;
+  }
+
+  @override
+  Future<BuildResult> readResult(BuildUri buildUri) async {
+    List<int> absoluteBuildNumbers;
+    int buildNumberIndex;
+    if (buildUri.buildNumber < 0) {
+      absoluteBuildNumbers = await _getAbsoluteBuildNumbers(buildUri);
+      int buildNumberIndex =
+          getBuildNumberIndex(absoluteBuildNumbers, buildUri.buildNumber);
+      if (buildNumberIndex == null) return null;
+      buildUri =
+          buildUri.withBuildNumber(absoluteBuildNumbers[buildNumberIndex]);
+    }
+    while (true) {
+      try {
+        return await readLogDogResult(buildUri);
+      } on LogdogException catch (e) {
+        if (e.exitKind != LogdogExitKind.error) {
+          return null;
+        }
+        absoluteBuildNumbers ??= await _getAbsoluteBuildNumbers(buildUri);
+        buildNumberIndex =
+            getBuildNumberIndex(absoluteBuildNumbers, buildUri.buildNumber);
+        if (buildNumberIndex == null) return null;
+        if (buildNumberIndex >= absoluteBuildNumbers.length) return null;
+        int buildNumber = absoluteBuildNumbers[buildNumberIndex + 1];
+        log('Skip build number ${buildUri.buildNumber} -> ${buildNumber}');
+        buildUri = buildUri.withBuildNumber(buildNumber);
+      }
+    }
+  }
+
+  @override
+  void close() {
+    // Nothing to do.
+  }
+}