Make ASP.NET Core server (Kestrel) case sensitive on Windows

Based on @Tratcher proposal and this blog post, here is a solution to have case aware physical file provider where you can choose to force case sensitivity or allow any casing regardless of OS.

public class CaseAwarePhysicalFileProvider : IFileProvider
{
    private readonly PhysicalFileProvider _provider;
    //holds all of the actual paths to the required files
    private static Dictionary<string, string> _paths;

    public bool CaseSensitive { get; set; } = false;

    public CaseAwarePhysicalFileProvider(string root)
    {
        _provider = new PhysicalFileProvider(root);
        _paths = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
    }

    public CaseAwarePhysicalFileProvider(string root, ExclusionFilters filters)
    {
        _provider = new PhysicalFileProvider(root, filters);
        _paths = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
    }

    public IFileInfo GetFileInfo(string subpath)
    {
        var actualPath = GetActualFilePath(subpath);
        if(CaseSensitive && actualPath != subpath) return new NotFoundFileInfo(subpath);
        return _provider.GetFileInfo(actualPath);
    }

    public IDirectoryContents GetDirectoryContents(string subpath)
    {
        var actualPath = GetActualFilePath(subpath);
        if(CaseSensitive && actualPath != subpath) return NotFoundDirectoryContents.Singleton;
        return _provider.GetDirectoryContents(actualPath);
    }

    public IChangeToken Watch(string filter) => _provider.Watch(filter);

    // Determines (and caches) the actual path for a file
    private string GetActualFilePath(string path)
    {
        // Check if this has already been matched before
        if (_paths.ContainsKey(path)) return _paths[path];

        // Break apart the path and get the root folder to work from
        var currPath = _provider.Root;
        var segments = path.Split(new [] { '/' }, StringSplitOptions.RemoveEmptyEntries);

        // Start stepping up the folders to replace with the correct cased folder name
        for (var i = 0; i < segments.Length; i++)
        {
            var part = segments[i];
            var last = i == segments.Length - 1;

            // Ignore the root
            if (part.Equals("~")) continue;

            // Process the file name if this is the last segment
            part = last ? GetFileName(part, currPath) : GetDirectoryName(part, currPath);

            // If no matches were found, just return the original string
            if (part == null) return path;

            // Update the actualPath with the correct name casing
            currPath = Path.Combine(currPath, part);
            segments[i] = part;
        }

        // Save this path for later use
        var actualPath = string.Join(Path.DirectorySeparatorChar, segments);
        _paths.Add(path, actualPath);
        return actualPath;
    }

    // Searches for a matching file name in the current directory regardless of case
    private static string GetFileName(string part, string folder) =>
        new DirectoryInfo(folder).GetFiles().FirstOrDefault(file => file.Name.Equals(part, StringComparison.OrdinalIgnoreCase))?.Name;

    // Searches for a matching folder in the current directory regardless of case
    private static string GetDirectoryName(string part, string folder) =>
        new DirectoryInfo(folder).GetDirectories().FirstOrDefault(dir => dir.Name.Equals(part, StringComparison.OrdinalIgnoreCase))?.Name;
}

Then in Startup class, make sure you register a provider for content and web root as follow:

        _environment.ContentRootFileProvider = new CaseAwarePhysicalFileProvider(_environment.ContentRootPath);
        _environment.WebRootFileProvider = new CaseAwarePhysicalFileProvider(_environment.WebRootPath);

I fixed that using a middleware in ASP.NET Core. Instead of the standard app.UseStaticFiles() I used:

 if (env.IsDevelopment()) app.UseStaticFilesCaseSensitive();
 else app.UseStaticFiles();

And defined that method as:

/// <summary>
/// Enforces case-correct requests on Windows to make it compatible with Linux.
/// </summary>
public static IApplicationBuilder UseStaticFilesCaseSensitive(this IApplicationBuilder app)
{
    var fileOptions = new StaticFileOptions
    {
        OnPrepareResponse = x =>
        {
            if (!x.File.PhysicalPath.AsFile().Exists()) return;
            var requested = x.Context.Request.Path.Value;
            if (requested.IsEmpty()) return;

            var onDisk = x.File.PhysicalPath.AsFile().GetExactFullName().Replace("\\", "/");
            if (!onDisk.EndsWith(requested))
            {
                throw new Exception("The requested file has incorrect casing and will fail on Linux servers." +
                    Environment.NewLine + "Requested:" + requested + Environment.NewLine +
                    "On disk: " + onDisk.Right(requested.Length));
            }
        }
    };

    return app.UseStaticFiles(fileOptions);
}

Which also uses:

public static string GetExactFullName(this FileSystemInfo @this)
{
    var path = @this.FullName;
    if (!File.Exists(path) && !Directory.Exists(path)) return path;

    var asDirectory = new DirectoryInfo(path);
    var parent = asDirectory.Parent;

    if (parent == null) // Drive:
        return asDirectory.Name.ToUpper();

    return Path.Combine(parent.GetExactFullName(), parent.GetFileSystemInfos(asDirectory.Name)[0].Name);
}