arc: Add utility functions to implement ARC content file system

chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h"
 
 #include "base/files/file_path.h"
 #include "chrome/browser/chromeos/fileapi/external_file_url_util.h"
 #include "net/base/escape.h"
+#include "storage/browser/fileapi/file_system_url.h"
 
 namespace arc {
 
 const char kMountPointName[] = "arc-content";
 
 const base::FilePath::CharType kMountPointPath[] =
     FILE_PATH_LITERAL("/special/arc-content");
 
 GURL ArcUrlToExternalFileUrl(const GURL& arc_url) {
   // Return "externalfile:arc-content/<|arc_url| escaped>".
@@ skipping 11 matching lines @@
   if (!base::FilePath::FromUTF8Unsafe(kMountPointName)
            .AppendRelativePath(virtual_path, &path_after_root)) {
     return GURL();
   }
   return GURL(net::UnescapeURLComponent(
       path_after_root.AsUTF8Unsafe(),
       net::UnescapeRule::SPACES | net::UnescapeRule::PATH_SEPARATORS |
           net::UnescapeRule::URL_SPECIAL_CHARS_EXCEPT_PATH_SEPARATORS));
 }
 
+GURL FileSystemUrlToArcUrl(const storage::FileSystemURL& url) {

[hidehiko, 2016/11/04 17:19:49]

Could you share the "path_after_root" and later code, so that you do not need to
play with path conversion a lot?

[hashimoto, 2016/11/07 05:34:15]

You mean sharing the code with ExternalFileUrlToArcUrl()?

What ExternalFileUrlToArcUrl() does is reverse of ArcUrlToExternalFileUrl().
Virtual path is "arc-content/<escaped ARC URL>".

OTOH FileSystemUrlToArcUrl() deals with FileSystemURL's path which is
"/special/arc-content/<escaped ARC URL>".
(File system API is hard!)

Added a comment to clarify what's going on here.

[hidehiko, 2016/11/07 18:07:54]

My question was;

Why FileSystemUrlToArcUrl passes through virtual path?

With, e.g., ArcEscapedPathToArcUrl(),

In FileSystemUrlToArcUrl():
/special/arc-content/<ARC escaped path> -> <ARC escaped path> -> ARC URL.
IN ExternalFileUrlToArcUrl():
/arc-content/<ARC escaped path> -> <ARC escaped path> -> ARC URL.

where <ARC escaped path> = |path_after_root| in the current implementation.
So, latter code can be shared in those cases, I think?

[hashimoto, 2016/11/08 01:34:16]

That makes sense.
Done.

+  base::FilePath virtual_path = base::FilePath::FromUTF8Unsafe(kMountPointName);
+  if (!base::FilePath(kMountPointPath)
+           .AppendRelativePath(url.path(), &virtual_path)) {
+    return GURL();
+  }
+  return ExternalFileUrlToArcUrl(
+      chromeos::VirtualPathToExternalFileURL(virtual_path));
+}
+
 }  // namespace arc