Extending FileSet - advanced file filtering

Question

How to filter files using custom criteria, such as regular expressions?

Answer 1

To use custom filter criteria in FileSet derive from it and implement IsMatch method yourself. Then use the derived class instead of the FileSet. E.g.

Ftp client = new Ftp();
// connect, login, ...

// download files using MyFileSet
MyFileSet set = new MyFileSet("/data", @"^data[0-9]+\.txt$");
client.Download(set, @"C:\data");

Here is a sample code for filtering using Regex:

/// <summary>
/// Matches files in BasePath directory (no subdirectory is processed) 
/// defined by a regular expression.
/// </summary>
public class MyFileSet : FileSet
{
    string _regexPattern;

    public MyFileSet(string basePath, string regexPattern)
        : base(basePath)
    {
        _regexPattern = regexPattern;
    }

    public override bool IsMatch(string relativePath, FileSetMatchMode mode)
    {
        // implement behavior for each match mode
        switch (mode)
        {
            case FileSetMatchMode.MatchFile:
                // take IsCaseSensitive into consideration
                RegexOptions options = RegexOptions.None;
                if (!IsCaseSensitive)
                    options = RegexOptions.IgnoreCase;

                // include files matching the specified pattern
                return Regex.IsMatch(relativePath, _regexPattern, options);

            case FileSetMatchMode.MatchDirectory:
                // don't match any directories (only files)
                return false;

            case FileSetMatchMode.TraverseDirectory:
                // traverse only current directory
                return relativePath == ".";

            default:
                throw new ArgumentOutOfRangeException("mode");
        }
    }
}

Please note, that this performs only SHALLOW SEARCH (no subdirectories are traversed). It is because in "case FileSetMatchMode.TraverseDirectory:" true is returned only for "." path (current directory). To perform DEEP SEARCH (traverse also subdirectories) update the class as follows:

case FileSetMatchMode.TraverseDirectory:
    // traverse all directories and subdirectories
    return true;

But please note, that this can be very time consuming. You should traverse only "meaningful" directories, however it depends on your application what "meaningful" means.

IMPLEMENTATION NOTE: for optimization issues when IsMatch is called with parameters equal to "." and FileSetMatchMode.TraverseDirectory the method should return false if no inclusion pattern was specified; true otherwise.
It means that if you return false always, current directory will not be traverses and no file or directory will be matched at all.

Answer 2

VB.NET version of the MyFileSet class:

''' <summary>
''' Matches files in BasePath directory (no subdirectory is processed) 
''' defined by a regular expression.
''' </summary>
Public Class MyFileSet
    Inherits FileSet

    Dim _regexPattern As String

    Public Sub New(ByVal basePath As String, ByVal regexPattern As String)
        MyBase.New(basePath)

        _regexPattern = regexPattern
    End Sub

    Public Overrides Function IsMatch(relativePath As String, mode As FileSetMatchMode) As Boolean
        ''# implement behavior for each match mode
        Select Case mode
            Case FileSetMatchMode.MatchFile
                ''# take IsCaseSensitive into consideration
                Dim options = RegexOptions.None
                If Not IsCaseSensitive Then options = RegexOptions.IgnoreCase

                ''# include files matching the specified pattern
                Return Regex.IsMatch(relativePath, _regexPattern, options)

            Case FileSetMatchMode.MatchDirectory
                ' don't match any directories (only files)
                Return False

            Case FileSetMatchMode.TraverseDirectory
                ''# traverse only current directory
                Return relativePath = "."

            Case Else
                Throw New ArgumentOutOfRangeException("mode")
        End Select
    End Function
End Class