Add logdog support to gardening tools.

tools/gardening/lib/src/logdog.dart

Index: tools/gardening/lib/src/logdog.dart
diff --git a/tools/gardening/lib/src/logdog.dart b/tools/gardening/lib/src/logdog.dart
new file mode 100644
index 0000000000000000000000000000000000000000..776d4fbb815125e5729be7628f6d52ed7b81c0fd
--- /dev/null
+++ b/tools/gardening/lib/src/logdog.dart
@@ -0,0 +1,127 @@
+// 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:io';
+import 'dart:async';
+import 'dart:collection';
+
+class LogdogException implements Exception {
+  final int errorCode;
+  final String stdout;
+  final String stderr;
+
+  LogdogException(this.errorCode, this.stdout, this.stderr);
+  LogdogException.fromProcessResult(ProcessResult result)
+      : this(result.exitCode, result.stdout, result.stderr);
+
+  toString() => "Error during logdog execution:\n$stderr";
+}
+
+bool logdogCheckDone = false;
+
+void checkLogdog({bool tryToInstall: true}) {
+  if (logdogCheckDone) return;
+  var result = Process.runSync("cit", []);
+  if (result.exitCode != 0) {
+    print("cit (from depot_tools) must be in the path.");
+    throw new StateError("cit not accessible");
+  }
+  String stdout = result.stdout;
+  if (stdout.contains("logdog")) {
+    logdogCheckDone = true;
+    return;
+  }
+  if (tryToInstall) {
+    print("logdog isn't yet installed. Installation might take some time");
+    result = Process.runSync("cit", ["logdog"]);
+    checkLogdog(tryToInstall: false);
+  } else {
+    print("Couldn't install logdog");
+    throw new StateError("logdog not accessible");
+  }
+}
+
+String logdog(List<String> args) {
+  checkLogdog();
+  args = args.toList()..insert(0, "logdog");
+  var result = Process.runSync("cit", args);
+  if (result.exitCode == 0) return result.stdout;
+  throw new LogdogException.fromProcessResult(result);
+}
+
+String cat(String log) {
+  return logdog(["cat", "-raw", log]);
+}
+
+class LogResult<T> {
+  final String log;
+  final T result;
+
+  LogResult(this.log, this.result);
+}
+
+const int maxConcurrentLogdogs = 20;
+
+/// Fetches the given [logs] concurrently using [logdog].
+///
+/// At most [maxConcurrentLogdogs] connections are opened at the same time.
+///
+/// The resulting [LogResult] has a [LogResult.result] equal to `null` if
+/// the log didn't exist.
+Stream<LogResult<String>> catN(Iterable<String> logs) async* {
+  var queue = new Queue<Future<LogResult<ProcessResult>>>();
+  var it = logs.iterator;
+
+  // Launches a new logdog to fetch the next log.
+  // Returns false when nothing was left to enqueue.
+  bool enqueueNext() {
+    if (!it.moveNext()) return false;
+    var log = it.current;
+    queue.add(new Future.sync(() async {
+      var logPath = log.substring(0, log.lastIndexOf("/"));
+      var lsResult = await Process.run("cit", ["logdog", "ls", logPath]);
+      if (lsResult.exitCode != 0) return new LogResult(log, lsResult);
+      if (lsResult.stdout == "") return new LogResult(log, null);
+      return new LogResult(
+          log, await Process.run("cit", ["logdog", "cat", "-raw", log]));
+    }));
+    return true;
+  }
+
+  for (int i = 0; i < maxConcurrentLogdogs; i++) {
+    enqueueNext();
+  }
+
+  while (queue.isNotEmpty) {
+    var logResult =
+        await queue.removeFirst().timeout(const Duration(seconds: 15));
+    enqueueNext();
+    if (logResult.result == null) {
+      yield new LogResult(logResult.log, null);
+    } else if (logResult.result.exitCode != 0) {
+      throw new LogdogException.fromProcessResult(logResult.result);
+    } else {
+      yield new LogResult(logResult.log, logResult.result.stdout);
+    }
+  }
+}
+
+/*

[floitsch, 2017/03/16 18:23:08]

I can remove these lines, but currently they serve as a nice example. Once we
actually use the code they definitely will disappear.

+main() async {
+//  print(cat(
+//      "chromium/bb/client.dart/dart2js-win7-ie11ff-4-4-be/4215/+/recipes/steps/dart2js_ie11_tests/0/stdout"));
+  catN(new Iterable.generate(10, (i) {
+    return "chromium/bb/client.dart/dart2js-win7-ie11ff-4-4-be/"
+        "${4200 + i}"
+        "/+/recipes/steps/dart2js_ie11_tests/0/stdout";
+  })).listen((logResult) {
+    print("--------------------------");
+    if (logResult.result == null) {
+      print("${logResult.log} - empty");
+    } else {
+      print(logResult.result.substring(0, 200));
+    }
+  });
+}
+*/