Add 'pathPrefix' optional argument to VirtualDirectory constructor.

pkg/http_server/test/virtual_directory_test.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.
 
 import 'dart:async';
 import 'dart:io';
 
 import "package:http_server/http_server.dart";
 import 'package:path/path.dart' as pathos;
 import "package:unittest/unittest.dart";
@@ skipping 287 matching lines @@
           // Redirect directory-requests to index.html files.
           var indexUri = new Uri.file(dir2.path).resolve('index.html');
           virDir.serveFile(new File(indexUri.toFilePath()), request);
         };
         return getAsString(virDir, '/dir/')
           .then((result) {
             expect(result, 'index file');
           });
       });
     });
+
+    group('path-prefix', () {
+      testVirtualDir('simple', (dir) {
+        var virDir = new VirtualDirectory(dir.path, pathPrefix: '/path');
+        virDir.allowDirectoryListing = true;
+        virDir.directoryHandler = (d, request) {
+          expect(FileSystemEntity.identicalSync(dir.path, d.path), isTrue);
+          return request.response.close();
+        };
+
+        return getStatusCodeForVirtDir(virDir, '/path')
+          .then((result) {
+            expect(result, HttpStatus.OK);
+          });
+      });
+
+      testVirtualDir('trailing-slash', (dir) {
+        var virDir = new VirtualDirectory(dir.path, pathPrefix: '/path/');
+        virDir.allowDirectoryListing = true;
+        virDir.directoryHandler = (d, request) {
+          expect(FileSystemEntity.identicalSync(dir.path, d.path), isTrue);
+          return request.response.close();
+        };
+
+        return getStatusCodeForVirtDir(virDir, '/path')
+          .then((result) {
+            expect(result, HttpStatus.OK);
+          });
+      });
+
+      testVirtualDir('not-matching', (dir) {
+        var virDir = new VirtualDirectory(dir.path, pathPrefix: '/path/');
+        return getStatusCodeForVirtDir(virDir, '/')
+          .then((result) {
+            expect(result, HttpStatus.NOT_FOUND);
+          });
+      });
+    });
   });
 
   group('links', () {
     if (!Platform.isWindows) {
       group('follow-links', () {
         testVirtualDir('dir-link', (dir) {
           var dir2 = new Directory('${dir.path}/dir2')..createSync();
           var link = new Link('${dir.path}/dir3')..createSync('dir2');
           var file = new File('${dir2.path}/file')..createSync();
           var virDir = new VirtualDirectory(dir.path);
@@ skipping 280 matching lines @@
           return virDir.serveFile(new File('${d.path}/file'), request);
         };
 
         return getAsString(virDir, '/')
           .then((result) {
             expect(result, 'file contents');
           });
     });
   });
 }