How can I handle the following exception?
My code:
Public Module RecursiveEnumerableExtensions
'credits Eric Lippert https://stackoverflow.com/users/88656/eric-lippert
Iterator Function Traverse(Of T)(ByVal root As T, ByVal children As Func(Of T, IEnumerable(Of T)), ByVal Optional includeSelf As Boolean = True) As IEnumerable(Of T)
If includeSelf Then Yield root
Dim stack = New Stack(Of IEnumerator(Of T))()
Try
stack.Push(children(root).GetEnumerator())
While stack.Count <> 0
Dim enumerator = stack.Peek()
If Not enumerator.MoveNext() Then
stack.Pop()
enumerator.Dispose()
Else
Yield enumerator.Current
stack.Push(children(enumerator.Current).GetEnumerator())
End If
End While
Finally
For Each enumerator In stack
enumerator.Dispose()
Next
End Try
End Function
End Module
Friend Sub Main()
Dim dinfo As DirectoryInfo = New DirectoryInfo(curDirectory)
Dim dquery = RecursiveEnumerableExtensions.Traverse(dinfo, Function(d) d.GetDirectories())
End Sub
When I run my code, for some of the directories, which are not accessible, I receive inside the Friend Sub Main() in the part Function(d) d.GetDirectories()) the exception System.UnauthorizedAccessException. I would like to handle this by Try Catch.
I tried to edit the Friend Sub Main() and export the Lambda expression to a function funcGetDirectories, but it fails with following error: System.InvalidCastException
Friend Sub Main()
Dim dinfo As DirectoryInfo = New DirectoryInfo(curDirectory)
Dim dquery = RecursiveEnumerableExtensions.Traverse(dinfo, funcGetDirectories(dinfo))
End Sub
Function funcGetDirectories(di As DirectoryInfo)
Try
Return di.GetDirectories()
Catch ex As UnauthorizedAccessException
Throw
Catch ex_default As Exception
Throw
End Try
End Function
Whats wrong with my Return di.GetDirectories()?
Note I'm working with .NET 4.8.
One option is to pass in an error handler to your DirectoryInfo and FileSystemAccessRule enumeration methods. Those methods can catch all errors and pass then to the handler, which can optionally handle the error and allow traversal to continue:
Public Class DirectoryExtensions
Shared Function GetFileSystemAccessRules(d As DirectoryInfo, ByVal errorHandler As Action(Of Object, DirectoryTraversalErrorEventArgs)) As IEnumerable(Of FileSystemAccessRule)
Try
Dim ds As DirectorySecurity = d.GetAccessControl()
Dim arrRules As AuthorizationRuleCollection = ds.GetAccessRules(True, True, GetType(Security.Principal.NTAccount))
Return arrRules.Cast(Of FileSystemAccessRule)()
Catch ex As Exception
If (Not HandleError(errorHandler, d.FullName, ex))
Throw
End If
Return Enumerable.Empty(Of FileSystemAccessRule)()
End Try
End Function
Shared Function EnumerateDirectories(ByVal directory As String, ByVal errorHandler As Action(Of Object, DirectoryTraversalErrorEventArgs)) As IEnumerable(Of DirectoryInfo)
Dim di As DirectoryInfo
Try
di = new DirectoryInfo(directory)
Catch ex As Exception
If (Not HandleError(errorHandler, directory, ex))
Throw
End If
Return Enumerable.Empty(Of DirectoryInfo)()
End Try
' In .NET Core 2.1+ it should be able to recursively enumerate directories and ignore errors as follows:
' Dim query = { di }.Concat(di.EnumerateDirectories("*", New System.IO.EnumerationOptions With { .RecurseSubdirectories = True, .IgnoreInaccessible = True })))
' In the meantime, it's necessary to manually catch and ignore errors.
Dim query = RecursiveEnumerableExtensions.Traverse(di,
Function(d)
Try
Return d.GetDirectories()
Catch ex As Exception
If (Not HandleError(errorHandler, d.FullName, ex))
Throw
End If
Return Enumerable.Empty(Of DirectoryInfo)()
End Try
End Function
)
Return query
End Function
Shared Function EnumerateDirectoryFileSystemAccessRules(ByVal directory As String, ByVal errorHandler As Action(Of Object, DirectoryTraversalErrorEventArgs)) As IEnumerable(Of Tuple(Of DirectoryInfo, IEnumerable(Of FileSystemAccessRule)))
Return EnumerateDirectories(directory, errorHandler).Select(Function(d) Tuple.Create(d, GetFileSystemAccessRules(d, errorHandler)))
End Function
Shared Public Function SerializeFileAccessRules(ByVal directory As String, ByVal errorHandler As Action(Of Object, DirectoryTraversalErrorEventArgs), Optional ByVal formatting As Formatting = Formatting.Indented)
Dim query = EnumerateDirectoryFileSystemAccessRules(directory, errorHandler).Select(
Function(tuple) New With {
.directory = tuple.Item1.FullName,
.permissions = tuple.Item2.Select(
Function(a) New With {
.IdentityReference = a.IdentityReference.ToString(),
.AccessControlType = a.AccessControlType.ToString(),
.FileSystemRights = a.FileSystemRights.ToString(),
.IsInherited = a.IsInherited.ToString()
}
)
}
)
Return JsonConvert.SerializeObject(query, formatting)
End Function
Private Shared Function HandleError(ByVal errorHandler As Action(Of Object, DirectoryTraversalErrorEventArgs), ByVal fullName as String, ByVal ex as Exception) As Boolean
If (errorHandler Is Nothing)
Return False
End If
Dim args As New DirectoryTraversalErrorEventArgs(fullName, ex)
errorHandler(GetType(DirectoryExtensions), args)
return args.Handled
End Function
End Class
Public Class DirectoryTraversalErrorEventArgs
Inherits EventArgs
Private _directory As String
Private _exception As Exception
Public Sub New(ByVal directory as String, ByVal exception as Exception)
Me._directory = directory
Me._exception = exception
End Sub
Public Property Handled As Boolean = false
Public Readonly Property Directory As String
Get
Return _directory
End Get
End Property
Public Readonly Property Exception As Exception
Get
Return _exception
End Get
End Property
End Class
Public Module RecursiveEnumerableExtensions
' Translated to vb.net from this answer https://stackoverflow.com/a/60997251/3744182
' To https://stackoverflow.com/questions/60994574/how-to-extract-all-values-for-all-jsonproperty-objects-with-a-specified-name-fro
' which was rewritten from the answer by Eric Lippert https://stackoverflow.com/users/88656/eric-lippert
' to "Efficient graph traversal with LINQ - eliminating recursion" https://stackoverflow.com/questions/10253161/efficient-graph-traversal-with-linq-eliminating-recursion
Iterator Function Traverse(Of T)(ByVal root As T, ByVal children As Func(Of T, IEnumerable(Of T)), ByVal Optional includeSelf As Boolean = True) As IEnumerable(Of T)
If includeSelf Then Yield root
Dim stack = New Stack(Of IEnumerator(Of T))()
Try
stack.Push(children(root).GetEnumerator())
While stack.Count <> 0
Dim enumerator = stack.Peek()
If Not enumerator.MoveNext() Then
stack.Pop()
enumerator.Dispose()
Else
Yield enumerator.Current
stack.Push(children(enumerator.Current).GetEnumerator())
End If
End While
Finally
For Each enumerator In stack
enumerator.Dispose()
Next
End Try
End Function
End Module
Then call the method and accumulate the errors in a list of errors like so:
Dim errors = New List(Of Tuple(Of String, String))
Dim handler As Action(Of Object, DirectoryTraversalErrorEventArgs) =
Sub(sender, e)
errors.Add(Tuple.Create(e.Directory, e.Exception.Message))
e.Handled = true
End Sub
Dim json As String = DirectoryExtensions.SerializeFileAccessRules(curDirectory, handler)
' Output the JSON and the errors somehow
Console.WriteLine(json)
For Each e In errors
Console.WriteLine("Error in directory {0}: {1}", e.Item1, e.Item2)
Next
Notes:
I am using tuples in a couple of places. Newer versions of VB.NET have a cleaner syntax for tuples, see Tuples (Visual Basic) for details.
The code manually traverses the directory hierarchy by stacking calls to DirectoryInfo.GetDirectories() and trapping errors from each call.
In .NET Core 2.1+ it should be possible to recursively enumerate directories and ignore errors by using DirectoryInfo.EnumerateDirectories(String, EnumerationOptions) as follows:
Dim query = { di }.Concat(di.EnumerateDirectories("*", New System.IO.EnumerationOptions With { .RecurseSubdirectories = True, .IgnoreInaccessible = True })))
This overload does not exist in .Net Framework 4.8 though.
Demo fiddle here