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File System

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Glenn Ruehle edited this page Jul 19, 2013 · 28 revisions

File System Evolution

Status: Proposal

Email comments to: [email protected]

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
  • Inconsistent use of fullPath vs. FileEntry
  • 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.
  • All asyc operations return promises. If the operation succeeds, the promise is resolved. If there was an error, the promise is rejected with the error code.
  • To get the contents of a Directory, call FileSystem.getDirectoryContents(). There is no readdir() on Directory.
  • Listen for "change" events on FileSystem to be notified if a file or directory changes.

Prototype

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

Most of the basic functionality works. Unit tests are completely broken (this is the next thing I want to work on), and many extensions are broken.

File watchers require node 0.10. You will need to update the shell in order to get proper file watching (directory watching works fine in 0.8).

##API##

FileSystem

The main module is FileSystem. This is the public API for getting files and directories, showing open/save dialogs, and getting the list of all the files in the project.

/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 FileSystem.getDirectoryContents() 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## The main performance gains come from caching. The stats and contents of files and directories are cached in memory. This has a huge impact on i/o-intensive operations like "find in files", and generally speeds up many other parts of the system.

##File Watchers## FileSystem dispatches a "change" event whenever a file or directory changes on disk. 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##

  • Get unit tests working.
  • Write unit tests for the new APIs.
  • Add a third low-level implementation (Google Drive, SkyDrive, etc.) to vet the API for completeness.
  • Write a porting guide.
  • Consider adding scaffolding APIs to ease the transition. For example, the file system entry uses getPath() to enforce read-only access. Most existing code that uses fullPath just needs to change to getPath(), so we could add a fullPath getter that emits a deprecation warning.
  • Address TODOs in code.
  • Testing and bug fixing.
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