UnauthorizedAccessException when programatically accessing mp3 file in WinRT XAML app - vb.net

Question

Problem accessing mp3 files in WinRT app.
'System.UnauthorizedAccessException' occurs when app tries to open a mp3 file by name in the same folder as a file returned by FileOpenPicker. Put another way, the user picks an info file in Documents with the same name as a mp3 file. App opens the info file just fine but cannot open the mp3 file.
For example: I have a pair of files (file1.info) and (file1.mp3). A filepicker allows selecting a (*.info) file.
The user selects (file1.info). The app then opens both (file1.info) and (file1.mp3). Both files reside in a DocumentsLibrary folder, but are NOT in the MusicLibrary. The problem is when I try to open (file1.mp3) I get the 'UnauthorizedAccessException'.
To prepro the issue:
Files:
Copy an mp3 file to Documents.
Create a text file with the same base name as the mp3 file and change its extension to .info.
In Package.appxmanifest > Declarations add a 'File Type Associations' declaration. Check 'Open is safe'. Add
supported file types '.mp3' and '.info'. Leave 'Content type' empty.
Code:
Dim file as StorageFile
Dim fileopenpicker As FileOpenPicker
Dim infofile As StorageFile
Dim mp3file As StorageFile
Dim filename As String
fileopenpicker = New FileOpenPicker()
fileopenpicker.FileTypeFilter.Add(".info")
fileopenpicker.FileTypeFilter.Add(".mp3")
fileopenpicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary
file = Await fileopenpicker.PickSingleFileAsync()
If file.Path.EndsWith(".info") Then
infofile = file
filename = file.Path.Substring(0, file.Path.Length - 4) & "mp3"
' This command fails with 'System.UnauthorizedAccessException'
mp3file = Await StorageFile.GetFileFromPathAsync(filename)
Else 'file is an mp3 file
mp3file = file
filename = file.Path.Substring(0, file.Path.Length - 3) & "info"
' This command succeeds!
infofile = Await StorageFile.GetFileFromPathAsync(filename)
End If
So it appears that there is some specific problem with opening an mp3 file when the file is not actually chosen by the fileopenpicker.

Answer 1

I checked this issue with an app that has the capability Documents Library and the filetypes .mp3 and .info declared. I figured out that it seems to be a very strange bug. If you pass the path to the documents library folder using an uppercase drive letter after having opened a FileOpenPicker you get an UnauthorizedAccessException. Using the path with a lowercase drive letter works. Strangely you can use an uppercase drive letter before having opened a FileOpenPicker.
So the workaround is to lowercase the path.
Here's the code I used (C#):
// Trying to get some files from the documents library
// Note: F:\Program Data is my primary documents library folder
string mp3FilePath = #"F:\Program Data\2Mann1Maus.mp3";
// This works even if the drive letter is uppercase
StorageFile file1 = await StorageFile.GetFileFromPathAsync(mp3FilePath);
// It also works with a lowercase drive letter
string infoFilePath = #"f:\Program Data\2Mann1Maus.info";
StorageFile file2 = await StorageFile.GetFileFromPathAsync(infoFilePath);
FileOpenPicker fileopenpicker = new FileOpenPicker();
fileopenpicker.FileTypeFilter.Add(".info");
fileopenpicker.FileTypeFilter.Add(".mp3");
fileopenpicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
StorageFile file = await fileopenpicker.PickSingleFileAsync();
if (file.Path.EndsWith(".info"))
{
string filename = file.Path.Substring(0, file.Path.Length - 4) + "mp3";
// This works
string testFileName1 = filename.Substring(0, 1).ToLower() +
filename.Substring(1, filename.Length - 1);
StorageFile mp3file1 = await StorageFile.GetFileFromPathAsync(testFileName1);
// This works as well
string testFileName2 = filename.ToLower();
StorageFile mp3file2 = await StorageFile.GetFileFromPathAsync(testFileName2);
// This does cause an UnauthorizedAccessException
StorageFile mp3file3 = await StorageFile.GetFileFromPathAsync(filename);
}
else
{
StorageFile mp3file = file;
String filename = file.Path.Substring(0, file.Path.Length - 3) + "info";
// This works
string testFileName1 = filename.Substring(0, 1).ToLower() +
filename.Substring(1, filename.Length - 1);
StorageFile infoFile1 = await StorageFile.GetFileFromPathAsync(testFileName1);
// This works as well
string testFileName2 = filename.ToLower();
StorageFile infoFile2 = await StorageFile.GetFileFromPathAsync(testFileName2);
// This does cause an UnauthorizedAccessException
StorageFile infoFile3 = await StorageFile.GetFileFromPathAsync(filename);
}