Error reporting on File in dart:io

runtime/bin/common.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.
+
+/**
+  * An [OSError] object holds information about an error from the
+  * operating system.
+  */
+class OSError {
+  static final int noErrorCode = -1;
+
+  const OSError([String this.message = "", int this.errorCode = noErrorCode]);
+
+  String toString() {
+    StringBuffer sb = new StringBuffer();
+    sb.add("OS Error");
+    if (!message.isEmpty()) {
+      sb.add(": ");
+      sb.add(message);
+      if (errorCode != noErrorCode) {
+        sb.add(", errno = ");
+        sb.add(errorCode.toString());
+      }
+    } else if (errorCode != noErrorCode) {
+      sb.add(": errno = ");
+      sb.add(errorCode.toString());
+    }
+    return sb.toString();
+  }
+
+  /**
+    * Error message supplied by the operating system. null if no message is
+    * associated with the error.
+    */
+  final String message;
+
+  /**
+    * Error code supplied by the operating system. Will have the value
+    * [noErrorCode] if there is no error code associated with the error.
+    */
+  final int errorCode;
+}
+
+
+/**
+  * Utility for creating an OSError instance. NOTE: This will go away
+  * soon, so please don't use this utility function. The reason for
+  * having it temporarily is that the Dart C API does not currently
+  * support constructing objects.
+  */
+// TODO(sgjesse): Remove this once Dart constructors can be invoked
+// through the API.
+class IOUtils {
+  static OSError makeOSError(message, code) => new OSError(message, code);
+}