mediaview: Introduce ArcDocumentsProviderRoot.

chrome/browser/chromeos/arc/fileapi/arc_documents_provider_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_documents_provider_util.h"
+
+#include <vector>
+
+#include "base/strings/string_util.h"
+#include "storage/browser/fileapi/file_system_url.h"
+
+namespace arc {
+
+namespace {
+
+constexpr base::FilePath::CharType kSpecialDirectory[] =
+    FILE_PATH_LITERAL("special");
+
+}  // namespace
+
+bool ParseDocumentsProviderUrl(const storage::FileSystemURL& url,
+                               std::string* authority,
+                               std::string* root_document_id,
+                               base::FilePath* path) {
+  if (url.type() != storage::kFileSystemTypeArcDocumentsProvider) {

[Luis Héctor Chávez, 2016/12/14 20:53:50]

nit: elide braces

[Shuhei Takahashi, 2016/12/15 02:37:55]

Done.

+    return false;
+  }
+
+  // Filesystem URL format for documents provider is:
+  // /special/arc-documents-provider/<authority>/<root_doc_id>/<relative_path>
+  using Components = std::vector<base::FilePath::StringType>;
+  Components components;
+  url.path().GetComponents(&components);
+  if (components.size() < 5 || components[0] != FILE_PATH_LITERAL("/") ||

[Luis Héctor Chávez, 2016/12/14 20:53:50]

re: components[0] != FILE_PATH_LITERAL("/"). Does it work if you check if
url.path().IsAbsolute() instead?

[Shuhei Takahashi, 2016/12/15 02:37:55]

Strictly, those two conditions are different. If the path is "//foo/bar",
components[0] is "//", while IsAbsolute() = true.

https://cs.chromium.org/chromium/src/base/files/file_path_unittest.cc?type=cs...
https://cs.chromium.org/chromium/src/base/files/file_path_unittest.cc?type=cs...

[Luis Héctor Chávez, 2016/12/15 21:26:10]

Got it, thanks for your explanation.

+      components[1] != kSpecialDirectory ||
+      components[2] != kDocumentsProviderMountPointName) {
+    return false;
+  }
+
+  *authority = components[3];
+  *root_document_id = components[4];
+  *path = base::FilePath::FromUTF8Unsafe(base::JoinString(
+      Components(components.begin() + 5, components.end()), "/"));
+  DCHECK(!path->IsAbsolute());

[Luis Héctor Chávez, 2016/12/14 20:53:50]

nit: compute the path in a temporary and move the DCHECK before L40, so you only
modify the parameters in the success case.

[Shuhei Takahashi, 2016/12/15 02:37:55]

Hmm, if we return false in the failure case it makes sense to defer assigning to
|path|, but this is DCHECK() for sanity check. It may crash chrome on failure,
but then no one cares if |path| is assigned or not at this point.

+  return true;
+}
+
+}  // namespace arc