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File System

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Peter Flynn edited this page Oct 24, 2013 · 28 revisions

File System Evolution

Status: Proposal

Introduction

The file system APIs in Brackets are a bit chaotic, and usage is inconsistent. Here are just a few issues:

  • No centralized file system model. This makes it difficult to add file watchers, and update all file references in the app after operations like rename.
  • Inefficient. We constantly hit the disk to read timestamps, content, etc.
  • Two APIs for file i/o: brackets.fs and NativeFileSystem
  • Incorrect creation of FileEntry objects (these should never be directly instantiated)
  • No way to use alternate storage--Dropbox, Google Drive, etc.

I'm pretty sure there are many more...

Overview

The high-level goals of the new file system are:

  • Clean, consistent API.
  • Unified file system model, including file watchers.
  • High Performance. Only hit the disk when we need to.
  • Ability to swap out low-level I/O routines (for cloud storage, etc.).

Here is a block diagram of the major parts:

File System Block Diagram

Clients only interact with the blue boxes. The green boxes represent low-level file i/o implementations, which can be added as extensions. The red box replaces the old FileIndexManager functionality, and does not have a public API (indexed files are accessed through FileSystem).

Basic Usage

There are a few basic rules for using the new file system.

  • Persist full pathnames, but convert into File and Directory objects for in-memory use. Creating File and Directory objects is cheap so there is no need to worry about performance.
  • There is a forced 1:1 relationship between File and Directory objects and their representation on disk. If two pieces of code ask the FileSystem for the same file path, they will both be returned the same File object.
  • When caching file (or directory) related data, you should use the file.id property as the key, and not the file.fullPath. The path of a file is subject to change if any of its parent directories are renamed.
  • Listen for "change" events on FileSystem to be notified of file or directory changes.

Prototype

A prototype implementation can be found in the glenn/file-system branch.

Most functionality works. Existing unit tests pass, but there are no unit tests for the new code (yes, shame on me...). Many extensions are broken.

##API##

For a guide to converting from current Brackets file APIs to these new APIs, see File System API Migration.

FileSystem

The main module is FileSystem. This is the public API for getting files and directories, showing open/save dialogs, and getting notified about file system changes.

/src/filesystem/FileSystem.js

###FileSystemEntry### This is an abstract representation of a FileSystem entry, and the base class for the File and Directory classes. FileSystemEntry objects are never created directly by client code. Use FileSystem.getFileForPath(), FileSystem.getDirectoryForPath(), or Directory.getContents() to create the entry.

/src/filesystem/FileSystemEntry.js

###File### This class represents a file on disk (this could be a local disk or cloud storage). This is a subclass of FileSystemEntry.

/src/filesystem/File.js

###Directory### This class represents a directory on disk (this could be a local disk or cloud storage). This is a subclass of FileSystemEntry.

/src/filesystem/Directory.js

##Performance & Caching## The main performance gains come from caching. The file system provides two caching levels:

  • File contents & metadata - reads are guaranteed to be up to date. Caches may be used to reduce bandwidth, but we always ping the impl and wait to ensure the cached copy is the latest.
  • Directory structure / file listing - reads are fast, but may not reflect external changes quickly. Cached info is returned immediately without waiting for the underlying storage impl.

In both cases, changes made via the file system's own APIs are always reflected immediately (as soon as the operation's callback signals success).

##File Watchers## FileSystem dispatches a "change" event whenever a file or directory changes on disk. This event is passed an entry parameter, which can be a File, Directory, or null. If entry is null, a "wholesale" change has occurred and the code should assume everything has changed.

For now, the prototype refreshes the entire file tree whenever a directory changes. This is overkill, but was easy to implement. Ideally, only the directory that changed will be updated.

##Next Steps## Several core developers are working on getting this implemented. We will share a more detailed API proposal with the community soon, but in the meantime feel free to take a look at the unstable file-system dev branch.

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