arc: Add utility functions to implement ARC content file system

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

Index: chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
diff --git a/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc b/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
index 91747997b911eaab2939a56e2bd4f001bedf4f69..bd118871d7836caca026e1ff37d1b8e11819c2ba 100644
--- a/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
+++ b/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
@@ -7,6 +7,7 @@
 #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 {
 
@@ -38,4 +39,14 @@ GURL ExternalFileUrlToArcUrl(const GURL& external_file_url) {
           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