1# FileSystem API
2
3This directory contains the renderer side implementation of various filesystem
4related APIs.
5
6## Related directories
7
8[`//storage/browser/file_system/`](../../../storage/browser/file_system) contains part
9of the browser side implementation, while
10[`//content/browser/fileapi/`](../../../content/browser/fileapi) contains the
11rest of the browser side implementation and
12[`blink/public/mojom/filesystem`](../../../third_party/blink/public/mojom/filesystem)
13contains the mojom interfaces for these APIs.
14
15## APIs In this directory
16
17### File and Directory Entries API
18
19First of all this directory contains the implementation of the
20[Entries API](https://wicg.github.io/entries-api). This API consists of
21types to expose read-only access to file and directory entries to the web,
22primarily used by drag-and-drop and `<input type=file>`. Our implementation
23doesn't match the interface names of the spec, but otherwise should be pretty
24close to the spec.
25
26TODO(mek): More details
27
28### File API: Directories and FileSystem
29
30Secondly this directory contains the implementation of something similar to the
31deprecated [w3c file-system-api](https://www.w3.org/TR/2012/WD-file-system-api-20120417/).
32This API is very similar to the previous Entries API, but it also adds support
33for writing and modifying to files and directories, as well as a way to get
34access to a origin scoped sandboxed filesystem.
35
36TODO(mek): More details
37
38### Writable Files
39
40Finally this directory contains the implementation of the new and still under
41development [Writable Files API](https://github.com/WICG/writable-files/blob/master/EXPLAINER.md).
42This API is mostly implemented on top of the same backend as the previous two
43APIs, but hopes to eventually replace both of those, while also adding new
44functionality.
45
46It consists of the following parts:
47
48 * `FileSystemBaseHandle`, `FileSystemFileHandle` and `FileSystemDirectoryHandle`:
49   these interfaces mimic the old `Entry` interfaces (and inherit from `EntryBase`
50   to share as much of the implementation as possible), but expose a more modern
51   promisified API.
52
53 * `getSystemDirectory`: An entry point (exposed via `FileSystemDirectoryHandle`)
54   that today only gives access to the same sandboxed filesystem as what was
55   available through the old API. In the future this could get extended to add
56   support for other directories as well.
57
58 * `FileSystemWriter`: a more modern API with similar functionality to the
59   old `FileWriter` API. The implementation of this actually does make use of
60   a different mojom interface than the old API. But since the functionality is
61   mostly the same, hopefully we will be able to migrate the old implementation
62   to the new mojom API as well.
63
64 * `chooseFileSystemEntries`: An entry point, currently on `window`, that lets
65   a website pop-up a file picker, prompting the user to select one or more
66   files or directories, to which the website than gets access.
67
68Since the `Handle` interfaces are based on the implementation of the `Entry`
69interfaces, internally and across IPC these are still represented by
70`filesystem://` URLs. Hopefully in the future we will be able to change this and
71turn it into a more capabilities based API (where having a mojo handle gives you
72access to specific files or directories), as with the current implementation it
73is very hard to properly support transferring handles to other processes via
74postMessage (which is something we do want to support in the future).
75