From 8eba70e0045d85f2604bcd43e7bd5b51eb41883e Mon Sep 17 00:00:00 2001
From: Conor Breen <breenbob@users.noreply.github.com>
Date: Tue, 21 Jun 2022 19:12:31 +0100
Subject: [PATCH] Fix for #5523 MauiWebView not loading local files on Windows
 (#7672)

* Fix for #5523 MauiWebView not loading local files on Windows

* Unpackaged app support for local HTML files.

* Use property for path

* Auto map/unmap virtual host for app dir when navigating to safe/unsafe URIs

Co-authored-by: Conor Breen <conor.breen@civica.co.uk>
---
 src/Core/src/Platform/Windows/MauiWebView.cs | 53 ++++++++++++++++++--
 1 file changed, 50 insertions(+), 3 deletions(-)

diff --git a/src/Core/src/Platform/Windows/MauiWebView.cs b/src/Core/src/Platform/Windows/MauiWebView.cs
index 2880166c15d9..a4028f258c39 100644
--- a/src/Core/src/Platform/Windows/MauiWebView.cs
+++ b/src/Core/src/Platform/Windows/MauiWebView.cs
@@ -1,15 +1,39 @@
 using System;
 using System.Diagnostics;
 using System.Text.RegularExpressions;
+using Microsoft.Maui.ApplicationModel;
 using Microsoft.UI.Xaml.Controls;
+using Windows.ApplicationModel;
 
 namespace Microsoft.Maui.Platform
 {
 	public class MauiWebView : WebView2, IWebViewDelegate
 	{
+		public MauiWebView()
+		{
+			NavigationStarting += (sender, args) =>
+			{
+				// Auto map local virtual app dir host, e.g. if navigating back to local site from a link to an external site
+				if (args?.Uri?.ToLowerInvariant().StartsWith(LocalScheme.TrimEnd('/').ToLowerInvariant()) == true)
+				{
+					CoreWebView2.SetVirtualHostNameToFolderMapping(
+						LocalHostName,
+						ApplicationPath,
+						Web.WebView2.Core.CoreWebView2HostResourceAccessKind.Allow);
+				}
+				// Auto unmap local virtual app dir host if navigating to any other potentially unsafe domain
+				else
+				{
+					CoreWebView2.ClearVirtualHostNameToFolderMapping(LocalHostName);
+				}
+			};
+		}
+
 		WebView2? _internalWebView;
 
-		const string LocalScheme = "ms-appx-web:///";
+		// Arbitrary local host name for virtual folder mapping
+		const string LocalHostName = "appdir";
+		const string LocalScheme = $"https://{LocalHostName}/";
 
 		// Script to insert a <base> tag into an HTML document
 		const string BaseInsertionScript = @"
@@ -19,11 +43,19 @@ public class MauiWebView : WebView2, IWebViewDelegate
 				head.innerHTML = 'baseTag' + head.innerHTML;
 			}";
 
+		// Allow for packaged/unpackaged app support
+		string ApplicationPath => AppInfoUtils.IsPackagedApp
+			? Package.Current.InstalledLocation.Path
+			: AppContext.BaseDirectory;
+
 		public async void LoadHtml(string? html, string? baseUrl)
 		{
+			var mapBaseDirectory = false;
+
 			if (string.IsNullOrEmpty(baseUrl))
 			{
 				baseUrl = LocalScheme;
+				mapBaseDirectory = true;
 			}
 
 			// Generate a base tag for the document
@@ -36,7 +68,7 @@ public async void LoadHtml(string? html, string? baseUrl)
 			_internalWebView = new WebView2();
 
 			// TODO: For now, the CoreWebView2 won't be created without either setting Source or
-			// calling EnsureCoreWebView2Async(). 
+			// calling EnsureCoreWebView2Async().
 			await _internalWebView.EnsureCoreWebView2Async();
 
 			// When the 'navigation' to the original HTML string is done, we can modify it to include our <base> tag
@@ -55,6 +87,14 @@ public async void LoadHtml(string? html, string? baseUrl)
 
 				await EnsureCoreWebView2Async();
 
+				if (mapBaseDirectory)
+				{
+					CoreWebView2.SetVirtualHostNameToFolderMapping(
+						LocalHostName,
+						ApplicationPath,
+						Web.WebView2.Core.CoreWebView2HostResourceAccessKind.Allow);
+				}
+
 				// Set the HTML for the 'real' WebView to the updated HTML
 				NavigateToString(!string.IsNullOrEmpty(htmlWithBaseTag) ? htmlWithBaseTag : html);
 
@@ -66,12 +106,19 @@ public async void LoadHtml(string? html, string? baseUrl)
 			_internalWebView.NavigateToString(html);
 		}
 
-		public void LoadUrl(string? url)
+		public async void LoadUrl(string? url)
 		{
 			Uri uri = new Uri(url ?? string.Empty, UriKind.RelativeOrAbsolute);
 
 			if (!uri.IsAbsoluteUri)
 			{
+				await EnsureCoreWebView2Async();
+
+				CoreWebView2.SetVirtualHostNameToFolderMapping(
+					LocalHostName,
+					ApplicationPath,
+					Web.WebView2.Core.CoreWebView2HostResourceAccessKind.Allow);
+
 				uri = new Uri(LocalScheme + url, UriKind.RelativeOrAbsolute);
 			}