Add a ScheduledProcess class to pkg/scheduled_test.

pkg/scheduled_test/lib/scheduled_process.dart

+// Copyright (c) 2013, 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.
+
+library scheduled_process;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'scheduled_test.dart';
+import 'src/utils.dart';
+import 'src/value_future.dart';
+
+/// A class representing a [Process] that is scheduled to run in the course of
+/// the test. This class allows actions on the process to be scheduled
+/// synchronously. All operations on this class are scheduled.
+///
+/// Before running the test, either [shouldExit] or [kill] must be called on
+/// this to ensure that the process terminates when expected.
+///
+/// If the test fails, this will automatically print out any stdout and stderr
+/// from the process to aid debugging.
+class ScheduledProcess {
+  // A description of the process. Used for error reporting.
+  String get description => _description;
+  String _description;
+
+  /// The encoding used for the process's input and output streams.
+  final Encoding _encoding;
+
+  /// The process that's scheduled to run.
+  ValueFuture<Process> _process;
+
+  /// A fork of [_stdout] that records the standard output of the process. Used
+  /// for debugging information.
+  Stream<String> _stdoutLog;
+
+  /// A line-by-line view of the standard output stream of the process.
+  Stream<String> _stdout;
+
+  /// A subscription that controls both [_stdout] and [_stdoutLog].
+  StreamSubscription<String> _stdoutSubscription;
+
+  /// A fork of [_stderr] that records the standard error of the process. Used
+  /// for debugging information.
+  Stream<String> _stderrLog;
+
+  /// A line-by-line view of the standard error stream of the process.
+  Stream<String> _stderr;
+
+  /// A subscription that controls both [_stderr] and [_stderrLog].
+  StreamSubscription<String> _stderrSubscription;
+
+  /// The exit code of the process that's scheduled to run. This will naturally
+  /// only complete once the process has terminated.
+  ValueFuture<int> _exitCode;
+
+  /// Whether the user has scheduled the end of this process by calling either
+  /// [shouldExit] or [kill].
+  var _endScheduled = false;
+
+  /// The task that runs immediately before this process is scheduled to end. If
+  /// the process ends during this task, we treat that as expected.
+  Task _taskBeforeEnd;
+
+  /// Whether the process is expected to terminate at this point.
+  var _endExpected = false;
+
+  /// Schedules a process to start. [executable], [arguments], and [options]
+  /// have the same meaning as for [Process.start]. [description] is a string
+  /// description of this process; it defaults to the command-line invocation.
+  /// [encoding] is the [Encoding] that will be used for the process's input and
+  /// output.
+  ///
+  /// [executable], [arguments], and [options] may be either a [Future] or a
+  /// concrete value. If any are [Future]s, the process won't start until the
+  /// [Future]s have completed. In addition, [arguments] may be a [List]
+  /// containing a mix of strings and [Future]s.
+  ScheduledProcess.start(executable, arguments,
+      {options, String description, Encoding encoding: Encoding.UTF_8})

[Bob Nystrom, 2013/03/04 23:52:00]

This is quite a large method with a bunch of asynchrony, futures, and closures.
Can you split it up? Below are some suggestions.

+      : _encoding = encoding {
+    assert(currentSchedule.state == ScheduleState.SET_UP);
+
+    if (executable is Future) {
+      _description = "future process";
+    } else if (arguments is Future || arguments.any((e) => e is Future)) {
+      _description = executable;
+    } else {
+      _description = "$executable ${arguments.map((a) => '"$a"').join(' ')}";
+    }

[Bob Nystrom, 2013/03/04 23:52:00]

How about pulling this into a separate _updateDescription() method?

[nweiz, 2013/03/05 02:16:09]

Done.

+
+    var exitCodeCompleter = new Completer();
+    _exitCode = new ValueFuture(exitCodeCompleter.future);
+
+    _process = new ValueFuture(schedule(() {
+      if (!_endScheduled) {
+        throw new StateError("Scheduled process '${this.description}' must "
+            "have shouldExit() or kill() called before the test is run.");
+      }
+
+      // We purposefully avoid using wrapFuture here. If an error occurs while a
+      // process is running, we want the schedule to move to the onException
+      // queue where the process will be killed, rather than blocking the tasks
+      // queue waiting for the process to exit.
+      _process.then((p) => p.exitCode).then((exitCode) {

[Bob Nystrom, 2013/03/04 23:52:00]

Asynchronously accessing the result of a future stored in a field that is set as
the return value of the asynchronous function in question makes my head hurt.

Move this to a separate fn?

[nweiz, 2013/03/05 02:16:09]

Done.

+        if (_endExpected) {
+          exitCodeCompleter.complete(exitCode);
+          return;
+        }
+
+        wrapFuture(pumpEventQueue().then((_) {
+          if (currentSchedule.currentTask != _taskBeforeEnd) return;
+          // If we're one task before the end was scheduled, wait for that task
+          // to complete and pump the event queue so that _endExpected will be
+          // set.
+          return _taskBeforeEnd.result.then((_) => pumpEventQueue());
+        }).then((_) {
+          exitCodeCompleter.complete(exitCode);
+
+          if (!_endExpected) {
+            throw "Process '${this.description}' ended earlier than scheduled "
+                "with exit code $exitCode.";
+          }
+        }));
+      });
+
+      return Future.wait([
+        new Future.of(() => executable),
+        awaitObject(arguments),
+        new Future.of(() => options)
+      ]).then((results) {
+        executable = results[0];
+        arguments = results[1];
+        options = results[2];
+        _description = "$executable ${arguments.map((a) => '"$a"').join(' ')}";

[Bob Nystrom, 2013/03/04 23:52:00]

Call _updateDescription() here.

[nweiz, 2013/03/05 02:16:09]

Done.

+        return Process.start(executable, arguments, options);
+      });
+    }, "starting process '${this.description}'"));
+
+    var stdoutWithSubscription = _lineStreamWithSubscription(
+        _process.then((p) => p.stdout));
+    _stdoutSubscription = stdoutWithSubscription.last;
+    var stdoutTee = tee(stdoutWithSubscription.first);
+    _stdout = stdoutTee.first;
+    _stdoutLog = stdoutTee.last;
+
+    var stderrWithSubscription = _lineStreamWithSubscription(
+        _process.then((p) => p.stderr));
+    _stderrSubscription = stderrWithSubscription.last;
+    var stderrTee = tee(stderrWithSubscription.first);
+    _stderr = stderrTee.first;
+    _stderrLog = stderrTee.last;
+
+    currentSchedule.onException.schedule(() {

[Bob Nystrom, 2013/03/04 23:52:00]

Move this to a separate fn.

[nweiz, 2013/03/05 02:16:09]

Done.

+      _stdoutSubscription.cancel();
+      _stderrSubscription.cancel();
+
+      if (!_process.hasValue) return;
+
+      var killedPrematurely = false;
+      if (!_exitCode.hasValue) {
+        var killedPrematurely = true;
+        _endExpected = true;
+        _process.value.kill();
+        // Ensure that the onException queue waits for the process to actually
+        // exit after being killed.
+        wrapFuture(_process.value.exitCode);
+      }
+
+      return Future.wait([
+        _stdoutLog.toList(),
+        _stderrLog.toList()
+      ]).then((results) {
+        var stdout = results[0].join("\n");
+        var stderr = results[1].join("\n");
+
+        var exitDescription = killedPrematurely
+            ? "Process was killed prematurely."
+            : "Process exited with exit code ${_exitCode.value}.";
+        currentSchedule.addDebugInfo(
+            "Results of running '${this.description}':\n"
+            "$exitDescription\n"
+            "Standard output:\n"
+            "${prefixLines(stdout)}\n"
+            "Standard error:\n"
+            "${prefixLines(stderr)}");
+      });
+    }, "cleaning up process '${this.description}'");
+  }
+
+  /// Converts a stream of bytes to a stream of lines and returns that along
+  /// with a [StreamSubscription] controlling it.
+  Pair<Stream<String>, StreamSubscription<String>> _lineStreamWithSubscription(
+      Future<Stream<int>> streamFuture) {
+    return streamWithSubscription(futureStream(streamFuture)
+        .handleError((e) => currentSchedule.signalError(e))
+        .transform(new StringDecoder(_encoding))
+        .transform(new LineTransformer()));
+  }
+
+  /// Reads the next line of stdout from the process.
+  Future<String> nextLine() => schedule(() => streamFirst(_stdout),
+      "reading the next stdout line from process '$description'");
+
+  /// Reads the next line of stderr from the process.
+  Future<String> nextErrLine() => schedule(() => streamFirst(_stderr),
+      "reading the next stderr line from process '$description'");
+
+  /// Reads the remaining stdout from the process. This should only be called
+  /// after kill() or shouldExit().
+  Future<String> remainingStdout() {
+    if (!_endScheduled) {
+      throw new StateError("remainingStdout() should only be called after "
+          "kill() or shouldExit().");
+    }
+
+    return schedule(() => _stdout.toList().then((lines) => lines.join("\n")),
+        "reading the remaining stdout from process '$description'");
+  }
+
+  /// Reads the remaining stderr from the process. This should only be called
+  /// after kill() or shouldExit().
+  Future<String> remainingStderr() {
+    if (!_endScheduled) {
+      throw new StateError("remainingStderr() should only be called after "
+          "kill() or shouldExit().");
+    }
+
+    return schedule(() => _stderr.toList().then((lines) => lines.join("\n")),
+        "reading the remaining stderr from process '$description'");
+  }
+
+  /// Writes [line] to the process as stdin.
+  void writeLine(String line) {
+    schedule(() {
+      return _process.then((p) => p.stdin.addString('$line\n', _encoding));
+    }, "writing '$line' to stdin for process '$description'");
+  }
+
+  /// Closes the process's stdin stream.
+  void closeStdin() {
+    schedule(() => _process.then((p) => p.stdin.close()),
+        "closing stdin for process '$description'");
+  }
+
+  /// Kills the process, and waits until it's dead.
+  void kill() {
+    if (_endScheduled) {
+      throw new StateError("shouldExit() or kill() already called.");
+    }
+
+    _endScheduled = true;
+    _taskBeforeEnd = currentSchedule.tasks.contents.last;
+    schedule(() {
+      _endExpected = true;
+      return _process.then((p) => p.kill()).then((_) => _exitCode);
+    }, "waiting for process '$description' to die");
+  }
+
+  /// Waits for the process to exit, and verifies that the exit code matches
+  /// [expectedExitCode] (if given).
+  void shouldExit([int expectedExitCode]) {
+    if (_endScheduled) {
+      throw new StateError("shouldExit() or kill() already called.");
+    }
+
+    _endScheduled = true;
+    _taskBeforeEnd = currentSchedule.tasks.contents.last;
+    schedule(() {
+      _endExpected = true;
+      return _exitCode.then((exitCode) {
+        if (expectedExitCode != null) {
+          expect(exitCode, equals(expectedExitCode));
+        }
+      });
+    }, "waiting for process '$description' to exit");
+  }
+}