Umbraco-CMS/src/Umbraco.Web.Common/Extensions/WebHostEnvironmentExtensions.cs

using System;
using System.IO;
using Microsoft.AspNetCore.Hosting;
using Umbraco.Cms.Core;

namespace Umbraco.Extensions
{
    /// <summary>
    /// Contains extension methods for the <see cref="IWebHostEnvironment" /> interface.
    /// </summary>
    public static class WebHostEnvironmentExtensions
    {
        /// <summary>
        /// Maps a virtual path to a physical path to the application's web root
        /// </summary>
        /// <remarks>
        /// Depending on the runtime 'web root', this result can vary. For example in Net Framework the web root and the content root are the same, however
        /// in netcore the web root is /wwwroot therefore this will Map to a physical path within wwwroot.
        /// </remarks>
        public static string MapPathWebRoot(this IWebHostEnvironment webHostEnvironment, string path)
        {
            var root = webHostEnvironment.WebRootPath;

            //Create if missing
            if (string.IsNullOrWhiteSpace(root))
            {
                root = webHostEnvironment.WebRootPath = Path.Combine(Directory.GetCurrentDirectory(), "wwwroot");
            }

            var newPath = path.Replace('/', Path.DirectorySeparatorChar).Replace('\\', Path.DirectorySeparatorChar);

            // TODO: This is a temporary error because we switched from IOHelper.MapPath to HostingEnvironment.MapPathXXX
            // IOHelper would check if the path passed in started with the root, and not prepend the root again if it did,
            // however if you are requesting a path be mapped, it should always assume the path is relative to the root, not
            // absolute in the file system.  This error will help us find and fix improper uses, and should be removed once
            // all those uses have been found and fixed
            if (newPath.StartsWith(root))
            {
                throw new ArgumentException("The path appears to already be fully qualified.  Please remove the call to MapPathWebRoot");
            }

            return Path.Combine(root, newPath.TrimStart(Constants.CharArrays.TildeForwardSlashBackSlash));
        }
    }
}