Add VirtualPathProvider infrastructure

src/Microsoft.AspNetCore.SystemWebAdapters/Generated/Ref.Standard.cs

@@ -835,6 +835,42 @@ public static partial class HostingEnvironment
         public static string ApplicationID { get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
         public static bool IsHosted { get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
         public static string SiteName { get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
+        public static System.Web.Hosting.VirtualPathProvider VirtualPathProvider { get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
+        public static void RegisterVirtualPathProvider(System.Web.Hosting.VirtualPathProvider provider) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+    }
+    public abstract partial class VirtualDirectory : System.Web.Hosting.VirtualFileBase
+    {
+        protected VirtualDirectory(string virtualPath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public abstract System.Collections.IEnumerable Children { get; }
+        public abstract System.Collections.IEnumerable Directories { get; }
+        public abstract System.Collections.IEnumerable Files { get; }
+        public override bool IsDirectory { get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
+    }
+    public abstract partial class VirtualFile : System.Web.Hosting.VirtualFileBase
+    {
+        protected VirtualFile(string virtualPath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public override bool IsDirectory { get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
+        public abstract System.IO.Stream Open();
+    }
+    public abstract partial class VirtualFileBase
+    {
+        internal VirtualFileBase() { }
+        public abstract bool IsDirectory { get; }
+        public virtual string Name { get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
+        public string VirtualPath { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
+    }
+    public abstract partial class VirtualPathProvider
+    {
+        protected VirtualPathProvider() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        protected internal System.Web.Hosting.VirtualPathProvider Previous { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");} }
+        public virtual string CombineVirtualPaths(string basePath, string relativePath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public virtual bool DirectoryExists(string virtualDir) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public virtual bool FileExists(string virtualPath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public virtual System.Web.Caching.CacheDependency GetCacheDependency(string virtualPath, System.Collections.IEnumerable virtualPathDependencies, System.DateTime utcStart) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public virtual System.Web.Hosting.VirtualDirectory GetDirectory(string virtualDir) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public virtual System.Web.Hosting.VirtualFile GetFile(string virtualPath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public virtual string GetFileHash(string virtualPath, System.Collections.IEnumerable virtualPathDependencies) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        protected virtual void Initialize() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
     }
 }
 namespace System.Web.Security

src/Microsoft.AspNetCore.SystemWebAdapters/Generated/TypeForwards.Framework.cs

@@ -68,6 +68,10 @@
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Caching.CacheItemUpdateReason))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Configuration.HttpCapabilitiesBase))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Hosting.HostingEnvironment))]
+[assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Hosting.VirtualDirectory))]
+[assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Hosting.VirtualFile))]
+[assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Hosting.VirtualFileBase))]
+[assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Hosting.VirtualPathProvider))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Security.MachineKey))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.SessionState.HttpSessionState))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.SessionState.SessionStateBehavior))]

src/Microsoft.AspNetCore.SystemWebAdapters/Hosting/HostingEnvironment.cs

@@ -10,4 +10,13 @@ public static class HostingEnvironment
     public static bool IsHosted => HostingEnvironmentAccessor.TryGet(out var current) && current.Options.IsHosted;
 
     public static string SiteName => HostingEnvironmentAccessor.Current.Options.SiteName;
+
+    public static VirtualPathProvider? VirtualPathProvider => HostingEnvironmentAccessor.Current.Options.VirtualPathProvider;
+
+    public static void RegisterVirtualPathProvider(VirtualPathProvider provider)
+    {
+        ArgumentNullException.ThrowIfNull(provider);
+
+        HostingEnvironmentAccessor.Current.Options.VirtualPathProvider = provider;
+    }
 }

src/Microsoft.AspNetCore.SystemWebAdapters/Hosting/VirtualDirectory.cs

@@ -0,0 +1,31 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+
+namespace System.Web.Hosting;
+
+public abstract class VirtualDirectory : VirtualFileBase
+{
+    protected VirtualDirectory(string virtualPath)
+        : base(VirtualPathUtility.AppendTrailingSlash(virtualPath))
+    {
+    }
+
+    public override bool IsDirectory => true;
+
+    /// <summary>
+    /// Returns an object that enumerates all the children VirtualDirectory's of this directory.
+    /// </summary>
+    public abstract IEnumerable Directories { get; }
+
+    /// <summary>
+    ///Returns an object that enumerates all the children VirtualFile's of this directory.
+    /// </summary>
+    public abstract IEnumerable Files { get; }
+
+    /// <summary>
+    /// Returns an object that enumerates all the children VirtualDirectory's and VirtualFiles of this directory.
+    /// </summary>
+    public abstract IEnumerable Children { get; }
+}

src/Microsoft.AspNetCore.SystemWebAdapters/Hosting/VirtualFile.cs

@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO;
+
+namespace System.Web.Hosting;
+
+public abstract class VirtualFile : VirtualFileBase
+{
+    protected VirtualFile(string virtualPath)
+        : base(virtualPath)
+    {
+    }
+
+    public override bool IsDirectory => false;
+
+    public abstract Stream Open();
+}

src/Microsoft.AspNetCore.SystemWebAdapters/Hosting/VirtualFileBase.cs

@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Web.Hosting;
+
+public abstract class VirtualFileBase
+{
+    private protected VirtualFileBase(string virtualPath)
+    {
+        VirtualPath = virtualPath;
+    }
+
+    public virtual string Name => VirtualPathUtility.GetFileName(VirtualPath);
+
+    public string VirtualPath { get; }
+
+    public abstract bool IsDirectory { get; }
+}

src/Microsoft.AspNetCore.SystemWebAdapters/Hosting/VirtualPathProvider.cs

@@ -0,0 +1,68 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+using System.Web.Caching;
+using System.Web.Util;
+
+namespace System.Web.Hosting;
+
+public abstract class VirtualPathProvider
+{
+    internal virtual void Initialize(VirtualPathProvider? previous)
+    {
+        Previous = previous;
+        Initialize();
+    }
+
+    protected virtual void Initialize()
+    {
+    }
+
+    protected internal VirtualPathProvider? Previous { get; private set; }
+
+    public virtual string? GetFileHash(string virtualPath, IEnumerable virtualPathDependencies)
+        => Previous?.GetFileHash(virtualPath, virtualPathDependencies);
+
+    public virtual CacheDependency? GetCacheDependency(string virtualPath, IEnumerable virtualPathDependencies, DateTime utcStart)
+        => Previous?.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart);
+
+    public virtual bool FileExists(string virtualPath) => Previous != null && Previous.FileExists(virtualPath);
+
+    public virtual bool DirectoryExists(string virtualDir) => Previous != null && Previous.DirectoryExists(virtualDir);
+
+    public virtual VirtualFile? GetFile(string virtualPath) => Previous?.GetFile(virtualPath);
+
+    internal VirtualFile? GetFileWithCheck(string virtualPath)
+    {
+        var virtualFile = GetFile(virtualPath);
+
+        if (virtualFile == null)
+        {
+            return null;
+        }
+
+        // Make sure the VirtualFile's path is the same as what was passed to GetFile
+        if (!string.Equals(virtualPath, virtualFile.VirtualPath, StringComparison.OrdinalIgnoreCase))
+        {
+            throw new HttpException($"Bad virtual path {virtualFile} in VirtuaPathBase");
+        }
+
+        return virtualFile;
+    }
+
+    public virtual VirtualDirectory? GetDirectory(string virtualDir) => Previous?.GetDirectory(virtualDir);
+
+    public virtual string CombineVirtualPaths(string basePath, string relativePath)
+    {
+        if (string.IsNullOrEmpty(basePath))
+        {
+            throw new ArgumentException($"'{nameof(basePath)}' cannot be null or empty.", nameof(basePath));
+        }
+
+        var baseDir = UrlPath.GetDirectory(basePath);
+
+        // By default, just combine them normally
+        return VirtualPathUtility.Combine(baseDir, relativePath);
+    }
+}

src/Microsoft.AspNetCore.SystemWebAdapters/SystemWebAdaptersOptions.cs

@@ -4,11 +4,14 @@
 #if NETCOREAPP
 
 using System;
+using System.Web.Hosting;
 
 namespace Microsoft.AspNetCore.SystemWebAdapters;
 
 public class SystemWebAdaptersOptions
 {
+    private VirtualPathProvider? _virtualPathProvider;
+
     public string ApplicationID { get; set; } = string.Empty;
 
     public bool IsHosted { get; set; }
@@ -18,6 +21,20 @@ public class SystemWebAdaptersOptions
     public string AppDomainAppVirtualPath { get; set; } = "/";
 
     public string AppDomainAppPath { get; set; } = AppContext.BaseDirectory;
+
+    /// <summary>
+    /// Gets or sets the value used by <see cref="HostingEnvironment.VirtualPathProvider"/>.
+    /// </summary>
+    public VirtualPathProvider? VirtualPathProvider
+    {
+        get => _virtualPathProvider;
+        set
+        {
+            value?.Initialize(_virtualPathProvider);
+
+            _virtualPathProvider = value;
+        }
+    }
 }
 
 #endif

src/Microsoft.AspNetCore.SystemWebAdapters/Utilities/UrlPath.cs

@@ -75,6 +75,35 @@ private static bool HasScheme(string virtualPath)
         return indexOfSlash == -1 || indexOfColon < indexOfSlash;
     }
 
+    internal static string GetDirectory(string path)
+    {
+        if (string.IsNullOrEmpty(path))
+        {
+            throw new ArgumentException("Path must not be empty", nameof(path));
+        }
+
+        if (path[0] != '/' && path[0] != AppRelativeCharacter)
+        {
+            throw new ArgumentException($"Path {path} must be rooted");
+        }
+
+        // If it's just "~" or "/", return it unchanged
+        if (path.Length == 1)
+        {
+            return path;
+        }
+
+        int slashIndex = path.LastIndexOf('/');
+
+        // This could happen if the input looks like "~abc"
+        if (slashIndex < 0)
+        {
+            throw new ArgumentException($"Path {path} must be rooted");
+        }
+
+        return path[..(slashIndex + 1)];
+    }
+
     private static bool IsDirectorySeparatorChar(char ch) => ch == '\\' || ch == '/';
 
     // e.g \\server\share\foo or //server/share/foo
@@ -532,6 +561,7 @@ internal string MakeRelative(string fromPath, string toPath)
         return relativePath + queryString + toUri.Fragment;
     }
 
+    [return: NotNullIfNotNull(nameof(virtualPath))]
     internal static string? GetFileName(string virtualPath)
     {
         if (virtualPath is not null)

src/Microsoft.AspNetCore.SystemWebAdapters/VirtualPathUtility.cs

@@ -49,6 +49,8 @@ public static class VirtualPathUtility
     /// <param name="virtualPath">The virtual path. </param>
     /// <exception cref="ArgumentException">
     ///   <paramref name="virtualPath" /> contains one or more characters that are not valid, as defined in <see cref="IO.Path.InvalidPathChars" />. </exception>
+
+    [return: NotNullIfNotNull(nameof(virtualPath))]
     public static string? GetFileName(string virtualPath) => VirtualPathUtilityImpl.GetFileName(virtualPath);
 
     /// <summary>Returns a Boolean value indicating whether the specified virtual path is absolute; that is, it starts with a literal slash mark (/).</summary>

src/Microsoft.AspNetCore.SystemWebAdapters/VirtualPathUtilityImpl.cs

@@ -90,6 +90,7 @@ public string Combine(string basePath, string relativePath)
         return UrlPath.GetExtension(virtualPath);
     }
 
+    [return: NotNullIfNotNull(nameof(virtualPath))]
     public static string? GetFileName(string virtualPath)
     {
         if (string.IsNullOrEmpty(virtualPath))