Change Process.start to return a future that completes with a

utils/pub/io.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Helper functionality to make working with IO easier.
  */
 library io;
 
 import 'dart:io';
@@ skipping 477 matching lines @@
     args = flatten(["/c", executable, args]);
     executable = "cmd";
   }
 
   final options = new ProcessOptions();
   if (workingDir != null) {
     options.workingDirectory = _getDirectory(workingDir).path;
   }
   options.environment = environment;
 
-  final process = Process.start(executable, args, options);
-
-  final outStream = new StringInputStream(process.stdout);
-  final processStdout = <String>[];
-
-  final errStream = new StringInputStream(process.stderr);
-  final processStderr = <String>[];
-
   final completer = new Completer<PubProcessResult>();
 
-  checkComplete() {
-    // Wait until the process is done and its output streams are closed.
-    if (!pipeStdout && !outStream.closed) return;
-    if (!pipeStderr && !errStream.closed) return;
-    if (exitCode == null) return;
+  var processFuture = Process.start(executable, args, options);
+  processFuture.then((process) {
+    final outStream = new StringInputStream(process.stdout);
+    final processStdout = <String>[];
 
-    completer.complete(new PubProcessResult(
-        processStdout, processStderr, exitCode));
-  }
+    final errStream = new StringInputStream(process.stderr);
+    final processStderr = <String>[];
 
-  if (pipeStdout) {
-    process.stdout.pipe(stdout, close: false);
-  } else {
-    outStream.onLine   = () => processStdout.add(outStream.readLine());
-    outStream.onClosed = checkComplete;
-    outStream.onError  = (error) => completer.completeException(error);
-  }
+    checkComplete() {
+      // Wait until the process is done and its output streams are closed.
+      if (!pipeStdout && !outStream.closed) return;
+      if (!pipeStderr && !errStream.closed) return;
+      if (exitCode == null) return;
 
-  if (pipeStderr) {
-    process.stderr.pipe(stderr, close: false);
-  } else {
-    errStream.onLine   = () => processStderr.add(errStream.readLine());
-    errStream.onClosed = checkComplete;
-    errStream.onError  = (error) => completer.completeException(error);
-  }
+      completer.complete(new PubProcessResult(
+          processStdout, processStderr, exitCode));
+    }
 
-  process.onExit = (actualExitCode) {
-    exitCode = actualExitCode;
-    checkComplete();
-  };
+    if (pipeStdout) {
+      process.stdout.pipe(stdout, close: false);
+    } else {
+      outStream.onLine   = () => processStdout.add(outStream.readLine());
+      outStream.onClosed = checkComplete;
+      outStream.onError  = (error) => completer.completeException(error);
+    }
 
-  process.onError = (error) => completer.completeException(error);
+    if (pipeStderr) {
+      process.stderr.pipe(stderr, close: false);
+    } else {
+      errStream.onLine   = () => processStderr.add(errStream.readLine());
+      errStream.onClosed = checkComplete;
+      errStream.onError  = (error) => completer.completeException(error);
+    }
+
+    process.onExit = (actualExitCode) {
+      exitCode = actualExitCode;
+      checkComplete();
+    };
+  });
+  processFuture.handleException((error) {
+    completer.completeException(error);
+    return true;
+  });
 
   return completer.future;
 }
 
 /**
  * Wraps [input] to provide a timeout. If [input] completes before
  * [milliseconds] have passed, then the return value completes in the same way.
  * However, if [milliseconds] pass before [input] has completed, it completes
  * with a [TimeoutException] with [message].
  *
@@ skipping 83 matching lines @@
  * Extracts a `.tar.gz` file from [stream] to [destination], which can be a
  * directory or a path. Returns whether or not the extraction was successful.
  */
 Future<bool> extractTarGz(InputStream stream, destination) {
   destination = _getPath(destination);
 
   if (Platform.operatingSystem == "windows") {
     return _extractTarGzWindows(stream, destination);
   }
 
-  var process = Process.start("tar",
+  var completer = new Completer<int>();
+  var processFuture = Process.start("tar",
       ["--extract", "--gunzip", "--directory", destination]);
-  var completer = new Completer<int>();
-
-  process.onExit = completer.complete;
-  process.onError = completer.completeException;
-
-  // Wait for the process to be fully started before writing to its
-  // stdin stream.
-  process.onStart = () {
+  processFuture.then((process) {
+    process.onExit = completer.complete;
     stream.pipe(process.stdin);
     process.stdout.pipe(stdout, close: false);
     process.stderr.pipe(stderr, close: false);
-  };
+  });
+  processFuture.handleException((error) {
+    completer.completeException(error);
+    return true;
+  });
 
   return completer.future.transform((exitCode) => exitCode == 0);
 }
 
 Future<bool> _extractTarGzWindows(InputStream stream, String destination) {
   // TODO(rnystrom): In the repo's history, there is an older implementation of
   // this that does everything in memory by piping streams directly together
   // instead of writing out temp files. The code is simpler, but unfortunately,
   // 7zip seems to periodically fail when we invoke it from Dart and tell it to
   // read from stdin instead of a file. Consider resurrecting that version if
@@ skipping 107 matching lines @@
   return new Directory(entry);
 }
 
 /**
  * Gets a [Uri] for [uri], which can either already be one, or be a [String].
  */
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return new Uri.fromString(uri);
 }