Combine physical path and virtual path outside ASP.NET

Question

I want to convert a virtual file path to a physical file path in a windows service.

I know what the physical path is for the virtual directory, so I have the following function that works, but feels like a fudge:

public static string GetPhysicalPathFromVirtual(string rootPath, string virtualPath)
{
    int trailingSlash = virtualPath.IndexOf('/', 1) + 1;
    int length = virtualPath.Length - trailingSlash;
    string stripped = virtualPath.Substring(trailingSlash, length);
    stripped = stripped.Replace(@"/", @"\");
    return Path.Combine(rootPath, stripped);
}

The following example:

string test = FileHelper.GetPhysicalPathFromVirtual(@"T:\generateddocuments\output\", @"/virtualroot/folder/myfile.pdf");

Returns: T:\generateddocuments\output\folder\myfile.pdf

Is there a more elegant way to do this?

Answer 1

Uri class may be of help for your task.

Please note that using relative paths in services can expose a huge security hole so you should be very defensive when you code them.

Here's what I came up with:

public static string GetPhysicalPathFromVirtual(string rootPath, string virtualPath)
{
    const string mandatoryVirtualPrefix = "/virtualroot/";

    if (!virtualPath.StartsWith(mandatoryVirtualPrefix))
        throw new ArgumentOutOfRangeException(virtualPath, string.Format("Virtual '{0}' path must start with mandatory prefix '{1}'", virtualPath, mandatoryVirtualPrefix));

    var relativePath = virtualPath.Substring(mandatoryVirtualPrefix.Length);

    var rootUri = new Uri(rootPath, UriKind.Absolute);
    var relativeUri = new Uri(relativePath, UriKind.Relative);

    var absoluteUri = new Uri(rootUri, relativeUri);

    if (!rootUri.IsBaseOf(absoluteUri))
        throw new ArgumentOutOfRangeException(virtualPath, string.Format("Virtual path '{0}' can't be outside of root '{1}'", virtualPath, rootPath));

    return absoluteUri.AbsolutePath;
}