Given full path, check if path is subdirectory of some other path, or otherwise

Question

I have 2 strings - dir1 and dir2, and I need to check if one is sub-directory for other. I tried to go with Contains method:

dir1.contains(dir2);


        

Answer 1

Based on @BrokenGlass's answer but tweaked:

using System.IO;

internal static class DirectoryInfoExt
{
    internal static bool IsSubDirectoryOfOrSame(this DirectoryInfo directoryInfo, DirectoryInfo potentialParent)
    {
        if (DirectoryInfoComparer.Default.Equals(directoryInfo, potentialParent))
        {
            return true;
        }

        return IsStrictSubDirectoryOf(directoryInfo, potentialParent);
    }

    internal static bool IsStrictSubDirectoryOf(this DirectoryInfo directoryInfo, DirectoryInfo potentialParent)
    {
        while (directoryInfo.Parent != null)
        {
            if (DirectoryInfoComparer.Default.Equals(directoryInfo.Parent, potentialParent))
            {
                return true;
            }

            directoryInfo = directoryInfo.Parent;
        }

        return false;
    }
}

using System;
using System.Collections.Generic;
using System.IO;

public class DirectoryInfoComparer : IEqualityComparer<DirectoryInfo>
{
    private static readonly char[] TrimEnd = { '\\' };
    public static readonly DirectoryInfoComparer Default = new DirectoryInfoComparer();
    private static readonly StringComparer OrdinalIgnoreCaseComparer = StringComparer.OrdinalIgnoreCase;

    private DirectoryInfoComparer()
    {
    }

    public bool Equals(DirectoryInfo x, DirectoryInfo y)
    {
        if (ReferenceEquals(x, y))
        {
            return true;
        }

        if (x == null || y == null)
        {
            return false;
        }

        return OrdinalIgnoreCaseComparer.Equals(x.FullName.TrimEnd(TrimEnd), y.FullName.TrimEnd(TrimEnd));
    }

    public int GetHashCode(DirectoryInfo obj)
    {
        if (obj == null)
        {
            throw new ArgumentNullException(nameof(obj));
        }
        return OrdinalIgnoreCaseComparer.GetHashCode(obj.FullName.TrimEnd(TrimEnd));
    }
}

Not ideal if performance is essential.

Answer 2

• Case insensitive
• Tolerates mix of \ and / folder delimiters
• Tolerates ..\ in path
• Avoids matching on partial folder names (c:\foobar not a subpath of c:\foo)

Note: This only matches on the path string and does not work for symbolic links and other kinds of links in the filesystem.

Code:

public static class StringExtensions
{
    /// <summary>
    /// Returns true if <paramref name="path"/> starts with the path <paramref name="baseDirPath"/>.
    /// The comparison is case-insensitive, handles / and \ slashes as folder separators and
    /// only matches if the base dir folder name is matched exactly ("c:\foobar\file.txt" is not a sub path of "c:\foo").
    /// </summary>
    public static bool IsSubPathOf(this string path, string baseDirPath)
    {
        string normalizedPath = Path.GetFullPath(path.Replace('/', '\\')
            .WithEnding("\\"));

        string normalizedBaseDirPath = Path.GetFullPath(baseDirPath.Replace('/', '\\')
            .WithEnding("\\"));

        return normalizedPath.StartsWith(normalizedBaseDirPath, StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>
    /// Returns <paramref name="str"/> with the minimal concatenation of <paramref name="ending"/> (starting from end) that
    /// results in satisfying .EndsWith(ending).
    /// </summary>
    /// <example>"hel".WithEnding("llo") returns "hello", which is the result of "hel" + "lo".</example>
    public static string WithEnding([CanBeNull] this string str, string ending)
    {
        if (str == null)
            return ending;

        string result = str;

        // Right() is 1-indexed, so include these cases
        // * Append no characters
        // * Append up to N characters, where N is ending length
        for (int i = 0; i <= ending.Length; i++)
        {
            string tmp = result + ending.Right(i);
            if (tmp.EndsWith(ending))
                return tmp;
        }

        return result;
    }

    /// <summary>Gets the rightmost <paramref name="length" /> characters from a string.</summary>
    /// <param name="value">The string to retrieve the substring from.</param>
    /// <param name="length">The number of characters to retrieve.</param>
    /// <returns>The substring.</returns>
    public static string Right([NotNull] this string value, int length)
    {
        if (value == null)
        {
            throw new ArgumentNullException("value");
        }
        if (length < 0)
        {
            throw new ArgumentOutOfRangeException("length", length, "Length is less than zero");
        }

        return (length < value.Length) ? value.Substring(value.Length - length) : value;
    }
}

Test cases (NUnit):

[TestFixture]
public class StringExtensionsTest
{
    [TestCase(@"c:\foo", @"c:", Result = true)]
    [TestCase(@"c:\foo", @"c:\", Result = true)]
    [TestCase(@"c:\foo", @"c:\foo", Result = true)]
    [TestCase(@"c:\foo", @"c:\foo\", Result = true)]
    [TestCase(@"c:\foo\", @"c:\foo", Result = true)]
    [TestCase(@"c:\foo\bar\", @"c:\foo\", Result = true)]
    [TestCase(@"c:\foo\bar", @"c:\foo\", Result = true)]
    [TestCase(@"c:\foo\a.txt", @"c:\foo", Result = true)]
    [TestCase(@"c:\FOO\a.txt", @"c:\foo", Result = true)]
    [TestCase(@"c:/foo/a.txt", @"c:\foo", Result = true)]
    [TestCase(@"c:\foobar", @"c:\foo", Result = false)]
    [TestCase(@"c:\foobar\a.txt", @"c:\foo", Result = false)]
    [TestCase(@"c:\foobar\a.txt", @"c:\foo\", Result = false)]
    [TestCase(@"c:\foo\a.txt", @"c:\foobar", Result = false)]
    [TestCase(@"c:\foo\a.txt", @"c:\foobar\", Result = false)]
    [TestCase(@"c:\foo\..\bar\baz", @"c:\foo", Result = false)]
    [TestCase(@"c:\foo\..\bar\baz", @"c:\bar", Result = true)]
    [TestCase(@"c:\foo\..\bar\baz", @"c:\barr", Result = false)]
    public bool IsSubPathOfTest(string path, string baseDirPath)
    {
        return path.IsSubPathOf(baseDirPath);
    }
}

Updates

• 2015-08-18: Fix bug matching on partial folder names. Add test cases.
• 2015-09-02: Support ..\ in paths, add missing code
• 2017-09-06: Add note on symbolic links.

Answer 3

public static bool IsSubpathOf(string rootPath, string subpath)
{
    if (string.IsNullOrEmpty(rootPath))
        throw new ArgumentNullException("rootPath");
    if (string.IsNullOrEmpty(subpath))
        throw new ArgumentNulLException("subpath");
    Contract.EndContractBlock();

    return subath.StartsWith(rootPath, StringComparison.OrdinalIgnoreCase);
}