How to access external storage with cordova file / file-system-roots plugins?

Question

Problem description: I can access the internal storage with either the file or the file-system-roots (read and write). But such a file can not be access from an other app. For example if I want to send this file through the emailComposerPlugin, the file can not be accessed by the email client. (Same goes for the "open with" function.) If I change the options {sandboxed: true} to false (to write to the external storage), it does not work and ends up in a FileUtils.UNKNOWN_ERR. I tried the application while the phone disconnected from USB, as some docs mentioned that external storage can not be accessed while mounted on the pc - same result though.

From what I read on the mailing list this should be possible. It seems I miss a crucial point?

Context: I try to enable an hybrid application created for iPhone to run on android devices. To have a little playground, I create a small test project.

Edit: There seems to be a problem between file-system-roots and file plugin. But I have the newest versions of both of them. (File: 1.0.1 File-system-roots: 0.1.0) Debugging the file-system and file classes show that

private String fullPathForLocalURL(Uri URL) {
    if (FILESYSTEM_PROTOCOL.equals(URL.getScheme()) && "localhost".equals(URL.getHost())) {
        String path = URL.getPath();
        if (URL.getQuery() != null) {
            path = path + "?" + URL.getQuery();
        }
        return path.substring(path.indexOf('/', 1));
        // path = "/cache-external" at this point
        // results in index out of bounds exception

What have I tried?

config.xml

<preference name="AndroidExtraFilesystems" value="files,files-external,documents,sdcard,cache,cache-external" />

AndroidManifest.xml

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

javascript code

function createTextDocument(filename, text) {

    cordova.filesystem.getDirectoryForPurpose('cache', {sandboxed: false}, successCallback, failureCallback);

    function successCallback(directoryEntry){
        console.log('directory found (cordova): ' + directoryEntry.toURL());
        console.log('directory found (native) : ' + directoryEntry.toNativeURL());
        directoryEntry.getFile(filename, {create: true, exclusive: false},
            function(fileEntry){
                var filePath = fileEntry.toNativeURL();
                fileEntry.createWriter(
                    function(fileWriter){
                        console.log('start writing to: ' + filePath );
                        fileWriter.write(text);
                        console.log('file written');
                    },failureCallback
                );
            }, failureCallback
        );
    }

    function failureCallback(error){
        console.log('error creating file: ' + error.code);
        // results in code 1000
    }
}

Answer 1

After digging this whole topic quite a bit, i figured out:

• There is no need for the file system roots plugin.
• There is more configuration needed in config.xml.
• You need to use not the standard FileApi way, but the following to access the files.

JavaScript usage:

window.resolveLocalFileSystemURL(path, cbSuccess, cbFail);

@param path: {string} a cordova path with scheme: 
             'cdvfile://localhost/<file-system-name>/<path-to-file>' 
             Examples: 'cdvfile://localhost/sdcard/path/to/global/file'
                       'cdvfile://localhost/cache/onlyVisibleToTheApp.txt'
@param cbSuccess: {function} a callback method that receives a DirectoryEntry object.
@param cbFail: {function} a callback method that receives a FileError object.

config.xml

<preference name="AndroidPersistentFileLocation" value="Compatibility" />
<preference name="AndroidExtraFilesystems" value="sdcard,cache" />

AndroidManifest.xml

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Answer 2

After hours of struggling, finally I'm able to scan sdcard and gain access to the files by providing a directory like "files://pathtofile/".
I've submit an API and a sample project https://github.com/xjxxjx1017/cordova-phonegap-android-sdcard-full-external-storage-access-library

Example of using the API

new ExternalStorageSdcardAccess( fileHandler ).scanPath( "file:///storage/sdcard1/music" );
function fileHandler( fileEntry ) {
    console.log( fileEntry.name + " | " + fileEntry.toURL() );
}

The API source code

var ExternalStorageSdcardAccess = function ( _fileHandler, _errorHandler ) {

    var errorHandler = _errorHandler || _defultErrorHandler;
    var fileHandler = _fileHandler || _defultFileHandler;
    var root = "file:///";

    return {
        scanRoot:scanRoot,
        scanPath:scanPath
    };

    function scanPath( path ) {
        window.resolveLocalFileSystemURL(path, _gotFiles, errorHandler );
    }

    function scanRoot() {
        scanPath( root );
    }

function _gotFiles(entry) {
    // ? Check whether the entry is a file or a directory
    if (entry.isFile) {
        // * Handle file
        fileHandler( entry );
    }
    else {
        // * Scan directory and add media
        var dirReader = entry.createReader();
        dirReader.readEntries( function(entryList) {
            entryList.forEach( function ( entr ) {
                _gotFiles( entr );
            } );
        }, errorHandler );
    }
}

    function _defultFileHandler(fileEntry){
        console.log( "FileEntry: " + fileEntry.name + " | " + fileEntry.fullPath );
    }
    function _defultErrorHandler(error){
        console.log( 'File System Error: ' + error.code );
    }
};

Configurations

• config.xml
  delete preference: preference name="AndroidExtraFilesystems"
  

• make sure testing environment can access it's own external storage at the time of testing. ( e.p. if you connect it with usb, make sure it is connected as a camera; Call the APIs after recieving the "deviceready" event )

Path example:
file:///
file:///somefile/
file:///somefile
file:///somefile/music/aaaaa.mp3