Firefox OS/Cloud Storage: Difference between revisions

FirefoxOS cloud storage support is a project that supports a framework to integrate user's cloud storage into their FirefoxOS device.<br/>

= Current Cloud Storage User Scenario =

In android or iOS, viewing a media file on cloud, it has following possible ways.<br/>

1. Using one viewing app and one cloud app. It needs following steps.<br/>

# Using the cloud app to download the media file to device.

# Using the viewing app to open the downloaded media file.

:In this way, user must download the whole media file first. Download brings following drawbacks.<br/>

:* File duplication.

:File occupies the local storage. If device local storage is almost full, user might need to cleanup the local storage first.<br/>

:* Need to download the whole file before viewing.

:Some files might be not suitable to be downloaded, for example 4k video files.<br/>

<br/>

2. Using a viewing app which support the specified cloud accessing. It needs following steps.<br/>

:In this way, user can view the media in stream way. However, the viewing app must to support the user preferred cloud. Otherwise, user might select another app or cloud they don't want.<br/>

* <b>Choose their preferred apps and cloud in free.</b>

* <b>No need to save the whole file in local.</b>

= Cloud Storage Support Framework =

The basic idea of this framework is mounting cloud storage as a FirefoxOS fake volume in FirefoxOS Volume System. By mounting cloud as a fake volume, FirefoxOS becomes a proxy for apps to access user's cloud, such that apps needn't know how to access cloud data in special way and maintain cloud by themselves. On the other hand, FirefoxOS can support streaming access to avoid downloading the whole file into local storage.<br/>

Instead of accessing cloud directly in Gecko, we design FileSystemProvider API to provide apps/addons can create a virtual file system in Gaia, and accessing cloud in these apps/addons. According to this design, we can gain following benefits<br/>

* No need to maintain third party cloud APIs in Gecko.

:It means FirefoxOS no need to FOTA to support the third party cloud APIs upgrade. It only needs to update the corresponding Cloud Storage Addons.<br/>

* Easy to reuse the framework on other kinds of storage.

:Not only cloud storage, but also NFS, personal NAS can reuse this framework to plug into FirefoxOS Volume System, such that apps can also interact with these storage directly.<br/>

== FirefoxOS Volume System ==

FirefoxOS Volume System is a middle layer between FirefoxOS and low-level OS kernel. It supports basic volume operations, such as mounting, unmounting, and formatting, to manage volumes in the device. In addition to the basic volume operations, the Volume System also provides fake volume creation and deletion mechanism.<br/>

In this framework, we creates fake volumes for each connected cloud, therefore these connected cloud can be recognized, identified and accessed by apps through DeviceStorage API and File API.<br/>

== DeviceStorage API and File API ==

DeviceStorage API and File API are interface used by apps to access FirefoxOS file systems. Apps can use these APIs to perform file read, write, creation, and deletion. Here are more detail about [https://developer.mozilla.org/en-US/docs/Mozilla/Firefox_OS/API/Device_Storage_API DeviceStorage API] and [https://developer.mozilla.org/en-US/docs/Web/API/File File API]<br/>

In this framework, we let apps still use these APIs to access cloud data. It means apps can access user's cloud without any modification which just like they access the device local storage.<br/>

== FileSystemProvider API ==

FileSystemProvider API provides apps/addons capability to create virtual file systems in Gaia. It provides<br/>

* Methods to request Volume System to create/delete a fake volume.

* Events and callbacks to request data from virtual file systems created by apps/addons.

=== Types ===

::Mode for open a file.<br/>

::{| class="wikitable" style="width:100%"

| colspan="3" style="background:#abc2e0" | <b>Properties</b>  

| unsigned long long || size || File size in bytes.

|-

|-

| rowspan="5" | function || colspan="2" | errorCallback || rowspan="5" valign="top" | Error callback for writefilerequested event.

| colspan="2" style="background:#abc2e0" | <b>Parameter</b>

| FileSystemProviderError || errorCode

| colspan="2" style="background:#abc2e0" | <b>Return value</b>

| colspan="2" | void

== Cloud Storage Addons ==

Cloud Storage Addons are in charge of the communication with the target cloud. It should provides at least<br/>

Moreover, Cloud Storage Addons might provide more features, such as<br/>

= Usage Flow =

== Mounting a Cloud on FirefoxOS ==

To mount a cloud on FirefoxOS, FileSystemProvider API providers methods and events for Cloud Storage Addons.<br/>

The picture shows the flow that Cloud Storage Addon mounts a cloud "MyCloud" on FirefoxOS through FileSystemProvider API.<br/>

# Cloud Storage addon registers the event listener on FileSystemProviderEvents.

# Call FileSystemProvider.mount() method with parameters to request Volume System to create a fake volume.

Following is an example code to mount a cloud "MyCloud"<br/>

  // Code in Cloud Storage Addons

  var fileSystemProvider = navigator.fileSystemProvider;

  // Event handler definition

    var path = event.options.entryPath;

    // get metadata through cloud APIs with entry path

    if (metadata) {

      event.successCallback(metadata);

    } else {

   // Register event listener on FileSystemProviderEvents

  fileSystemProvider.addEventListener("getmetadatarequested", GetMetadataHandler);

   fileSystemProvider.addEventListener("openfilerequested", OpenFileHandler);

  fileSystemProvider.addEventListener("closefilerequested", CloseFileHandler);

  fileSystemProvider.addEventListener("readdirectoryrequested", ReadDirectoryHandler);

  fileSystemProvider.addEventListener("readfilerequested", ReadFileHandler);

  fileSystemProvider.mount({fileSystemId: 'MyCloud',

                            displayName: 'MyCloud',

                            function() { dump('mount successfully\n');}

                            function(aError) { dump('mount failed ['+aError+']\n');}

== Accessing Cloud through the Framework ==

To access a mounted cloud, app can reuse DeviceStorage and File APIs, just like they access local storage.<br/>

The picture shows the flow how Gallery app read the "test.jpg" on cloud "MyCloud".<br/>

# Gallery app asks "MyCloud/test.jpg" data through the File API.

# Volume System get the request and send FileSystemProvderReadFileEvent to ask corresponding Cloud Storage Addons to get the data from cloud.

# Cloud Storage Addon receives the FileSystemProviderReadFileEvent and call ReadFileEventListener to get "test.jpg" data from cloud through the cloud access API.

# Once read success or fail, call the event.successCallback with data or event.errorCallback with error code.

# Volume System receives the callback data and send it back to app through the File API.

Following is an example to access cloud 'MyCloud' through DeviceStorage and File APIs.<br/>

  // Get file through DeviceStorage API

  var myStorage = navigator.getDeviceStorage('MyCloud');

    // Request to send GetMetadataEvent to get the information of "myFile.txt"

    var request = myStorage.get('myFile.txt');

    request.onsuccess = function() {

      var file = this.result;

      var fileReader = new FileReader();

      fileRead.onloadend = function() {dump('load finished\n');}

      // Request to send OpenFileEvent, ReadFileEvents and CloseFileEvent

      fileReader.readAsArrayBuffer(file);