[Blazor] Get rid of the custom QueryStringHelper implementation (#42532)

* Reuse existing query string infrastructure

src/Components/WebAssembly/WebAssembly.Authentication/src/Microsoft.AspNetCore.Components.WebAssembly.Authentication.csproj

-<Project Sdk="Microsoft.NET.Sdk.Razor">
+<Project Sdk="Microsoft.NET.Sdk.Razor">
 
   <Import Project="Sdk.props" Sdk="Yarn.MSBuild" Condition=" '$(DotNetBuildFromSource)' != 'true'" />
 
@@ -9,6 +9,8 @@
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <IsTrimmable>true</IsTrimmable>
     <Nullable>disable</Nullable>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <DefineConstants>DISABLE_NULLABLE;$(DefineConstants)</DefineConstants>
   </PropertyGroup>
 
   <ItemGroup>
@@ -22,6 +24,7 @@
 
   <ItemGroup>
     <Compile Include="$(SharedSourceRoot)LinkerFlags.cs" LinkBase="Shared" />
+    <Compile Include="$(SharedSourceRoot)QueryStringEnumerable.cs" LinkBase="Shared" />
   </ItemGroup>
 
   <PropertyGroup>

src/Components/WebAssembly/WebAssembly.Authentication/src/QueryStringHelper.cs

-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-namespace Microsoft.AspNetCore.Components.WebAssembly.Authentication;
-
-internal static class QueryStringHelper
-{
-    public static string GetParameter(string queryString, string key)
-    {
-        if (string.IsNullOrEmpty(queryString) || queryString == "?")
-        {
-            return null;
-        }
-
-        var scanIndex = 0;
-        if (queryString[0] == '?')
-        {
-            scanIndex = 1;
-        }
-
-        var textLength = queryString.Length;
-        var equalIndex = queryString.IndexOf('=');
-        if (equalIndex == -1)
-        {
-            equalIndex = textLength;
-        }
-
-        while (scanIndex < textLength)
-        {
-            var ampersandIndex = queryString.IndexOf('&', scanIndex);
-            if (ampersandIndex == -1)
-            {
-                ampersandIndex = textLength;
-            }
-
-            if (equalIndex < ampersandIndex)
-            {
-                while (scanIndex != equalIndex && char.IsWhiteSpace(queryString[scanIndex]))
-                {
-                    ++scanIndex;
-                }
-                var name = queryString[scanIndex..equalIndex];
-                var value = queryString.Substring(equalIndex + 1, ampersandIndex - equalIndex - 1);
-                var processedName = Uri.UnescapeDataString(name.Replace('+', ' '));
-                if (string.Equals(processedName, key, StringComparison.OrdinalIgnoreCase))
-                {
-                    return Uri.UnescapeDataString(value.Replace('+', ' '));
-                }
-
-                equalIndex = queryString.IndexOf('=', ampersandIndex);
-                if (equalIndex == -1)
-                {
-                    equalIndex = textLength;
-                }
-            }
-            else
-            {
-                if (ampersandIndex > scanIndex)
-                {
-                    var value = queryString[scanIndex..ampersandIndex];
-                    if (string.Equals(value, key, StringComparison.OrdinalIgnoreCase))
-                    {
-                        return string.Empty;
-                    }
-                }
-            }
-
-            scanIndex = ampersandIndex + 1;
-        }
-
-        return null;
-    }
-}

src/Components/WebAssembly/WebAssembly.Authentication/src/RemoteAuthenticatorViewCore.cs

@@ -4,6 +4,7 @@
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.AspNetCore.Components.Authorization;
 using Microsoft.AspNetCore.Components.Rendering;
+using Microsoft.AspNetCore.Internal;
 using static Microsoft.AspNetCore.Internal.LinkerFlags;
 
 namespace Microsoft.AspNetCore.Components.WebAssembly.Authentication;
@@ -329,7 +330,7 @@ public class RemoteAuthenticatorViewCore<[DynamicallyAccessedMembers(JsonSeriali
             return state.ReturnUrl;
         }
 
-        var fromQuery = QueryStringHelper.GetParameter(new Uri(Navigation.Uri).Query, "returnUrl");
+        var fromQuery = GetParameterFromQueryString("returnUrl");
         if (!string.IsNullOrWhiteSpace(fromQuery) && !fromQuery.StartsWith(Navigation.BaseUri, StringComparison.Ordinal))
         {
             // This is an extra check to prevent open redirects.
@@ -337,6 +338,29 @@ public class RemoteAuthenticatorViewCore<[DynamicallyAccessedMembers(JsonSeriali
         }
 
         return fromQuery ?? defaultReturnUrl ?? Navigation.BaseUri;
+
+    }
+
+    private string GetParameterFromQueryString(ReadOnlySpan<char> parameterName)
+    {
+        var url = Navigation.Uri;
+        ReadOnlyMemory<char> query = default;
+        var queryStartPos = url.IndexOf('?');
+        if (queryStartPos >= 0)
+        {
+            var queryEndPos = url.IndexOf('#', queryStartPos);
+            query = url.AsMemory(queryStartPos..(queryEndPos < 0 ? url.Length : queryEndPos));
+        }
+
+        foreach (var parameter in new QueryStringEnumerable(query))
+        {
+            var decodedName = parameter.DecodeName().Span;
+            if (MemoryExtensions.Equals(parameterName, decodedName, StringComparison.OrdinalIgnoreCase))
+            {
+                return new string(parameter.DecodeValue().Span);
+            }
+        }
+        return null;
     }
 
     private void NavigateToReturnUrl(string returnUrl) => Navigation.NavigateTo(returnUrl, new NavigationOptions { ForceLoad = false, ReplaceHistoryEntry = true });

src/Shared/QueryStringEnumerable.cs

@@ -30,7 +30,11 @@ internal
     /// Constructs an instance of <see cref="QueryStringEnumerable"/>.
     /// </summary>
     /// <param name="queryString">The query string.</param>
+#if DISABLE_NULLABLE
+    public QueryStringEnumerable(string queryString)
+#else
     public QueryStringEnumerable(string? queryString)
+#endif
         : this(queryString.AsMemory())
     {
     }