Add the beginnings of a Dart wrapper for libarchive.

utils/archive/utils.dart

Index: utils/archive/utils.dart
diff --git a/utils/archive/utils.dart b/utils/archive/utils.dart
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+++ b/utils/archive/utils.dart
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+// 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.
+
+#library("utils");
+
+#import("dart-ext:dart_archive");
+#import("dart:isolate");
+#import("archive.dart", prefix: "archive");
+
+/** The cache of the port used to communicate with the C extension. */
+SendPort _port;
+
+/** The port used to communicate with the C extension. */
+SendPort get servicePort() {
+  if (_port == null) _port = _newServicePort();
+  return _port;
+}
+
+/** Creates a new port to communicate with the C extension. */
+SendPort _newServicePort() native "Archive_ServicePort";
+
+/**
+ * Send a message to the C extension.
+ *
+ * [requestType] is the specific request id to send. [id] is the id of the
+ * archive; it may be null for requests that don't operate on a specific
+ * archive. [args] are arguments that will be passed on to the extension. They
+ * should all be C-safe.
+ *
+ * Returns a future that completes with the C extension's reply.
+ */
+Future call(int requestType, int id, [List args]) {
+  var fullArgs = [requestType, id];
+  if (args != null) fullArgs.addAll(args);
+  return servicePort.call(listForC(fullArgs)).transform((response) {
+    var success = response[0];
+    var errno = response[1];
+    var message = response[2];
+
+    if (!success) throw new ArchiveException(message, errno);
+    return message;
+  });
+}
+
+/** Converts [input] to a fixed-length list which C can understand. */
+List listForC(List input) {
+  var list = new List(input.length);
+  list.setRange(0, input.length, input);
+  return list;
+}
+
+/** Converts [input] to a [Uint8List] that C can process easily. */
+Uint8List bytesForC(List<int> input) {
+  var list = new Uint8List(input.length);
+  list.setRange(0, input.length, input);
+  return list;
+}
+
+/**
+ * Returns a [Future] that completes immediately upon hitting the event loop.
+ */
+Future async() {
+  var completer = new Completer();
+  new Timer(0, (_) => completer.complete(null));
+  return completer.future;
+}
+
+/** An error raised by the archive library. */
+class ArchiveException implements archive.ArchiveException {
+  /** A description of the error that occurred. */   
+  final String message;
+
+  /** The error code for the error, or null. */
+  final int errno;
+
+  ArchiveException(this.message, [this.errno]);
+
+  String toString() {
+    if (errno == null) return "Archive error: $message";
+    return "Archive error $errno: $message";
+  }
+}