Download to a temp dir and rename on success.

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 265 matching lines @@
     if (exists) {
       // Delete it first.
       return deleteDir(dir).chain((_) => createDir(dir));
     } else {
       // Just create it.
       return createDir(dir);
     }
   });
 }
 
+/// Renames (i.e. moves) the directory [from] to [to]. Returns a [Future] with
+/// the destination directory.
+Future<Directory> renameDir(from, String to) =>_getDirectory(from).rename(to);
+
 /**
  * Creates a new symlink that creates an alias from [from] to [to], both of
  * which can be a [String], [File], or [Directory]. Returns a [Future] which
  * completes to the symlink file (i.e. [to]).
  */
 Future<File> createSymlink(from, to) {
   from = _getPath(from);
   to = _getPath(to);
 
   var command = 'ln';
@@ skipping 387 matching lines @@
     return createFileFromStream(stream, join(tempDir, 'data.tar.gz'));
   }).chain((tarGz) {
     // 7zip can't unarchive from gzip -> tar -> destination all in one step
     // first we un-gzip it to a tar file.
     // Note: Setting the working directory instead of passing in a full file
     // path because 7zip says "A full path is not allowed here."
     return runProcess(command, ['e', 'data.tar.gz'], workingDir: tempDir);
   }).chain((result) {
     if (result.exitCode != 0) {
       throw 'Could not un-gzip (exit code ${result.exitCode}). Error:\n'
+          '${Strings.join(result.stdout, "\n")}\n'
           '${Strings.join(result.stderr, "\n")}';
     }
 
     // Find the tar file we just created since we don't know its name.
     return listDir(tempDir);
   }).chain((files) {
     var tarFile;
     for (var file in files) {
       if (new Path(file).extension == 'tar') {
         tarFile = file;
@@ skipping 71 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);
 }