Add RedirectHttpResult.IsLocalUrl() (dotnet#57363)

Add `IsLocalUrl()` method to `RedirectHttpResult`, which is just a wrapper around `SharedUrlHelper.IsLocalUrl()`.

Resolves dotnet#56770.

src/Http/Http.Results/src/PublicAPI.Unshipped.txt

@@ -6,6 +6,7 @@ Microsoft.AspNetCore.Http.HttpResults.InternalServerError<TValue>
 Microsoft.AspNetCore.Http.HttpResults.InternalServerError<TValue>.ExecuteAsync(Microsoft.AspNetCore.Http.HttpContext! httpContext) -> System.Threading.Tasks.Task!
 Microsoft.AspNetCore.Http.HttpResults.InternalServerError<TValue>.StatusCode.get -> int
 Microsoft.AspNetCore.Http.HttpResults.InternalServerError<TValue>.Value.get -> TValue?
+static Microsoft.AspNetCore.Http.HttpResults.RedirectHttpResult.IsLocalUrl(string? url) -> bool
 static Microsoft.AspNetCore.Http.Results.InternalServerError() -> Microsoft.AspNetCore.Http.IResult!
 static Microsoft.AspNetCore.Http.Results.InternalServerError<TValue>(TValue? error) -> Microsoft.AspNetCore.Http.IResult!
 static Microsoft.AspNetCore.Http.Results.Problem(string? detail = null, string? instance = null, int? statusCode = null, string? title = null, string? type = null, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string!, object?>>? extensions = null) -> Microsoft.AspNetCore.Http.IResult!

src/Http/Http.Results/src/RedirectHttpResult.cs

@@ -121,6 +121,18 @@ public Task ExecuteAsync(HttpContext httpContext)
         return Task.CompletedTask;
     }
 
+    /// <summary>
+    /// Returns a value that indicates whether the URL is local. A URL is considered
+    /// local if it does not have a host / authority part and it has an absolute path.
+    /// URLs using virtual paths (<c>'~/'</c>) are also local.
+    /// </summary>
+    /// <param name="url">The URL.</param>
+    /// <returns>
+    /// <see langword="true"/> if the URL is local; otherwise, <see langword="false"/>.
+    /// </returns>
+    public static bool IsLocalUrl([NotNullWhen(true)][StringSyntax(StringSyntaxAttribute.Uri)] string? url)
+        => SharedUrlHelper.IsLocalUrl(url);
+
     private static partial class Log
     {
         [LoggerMessage(1, LogLevel.Information,

src/Http/Http.Results/test/RedirectResultTests.cs

@@ -33,6 +33,56 @@ public void ExecuteAsync_ThrowsArgumentNullException_WhenHttpContextIsNull()
         Assert.ThrowsAsync<ArgumentNullException>("httpContext", () => result.ExecuteAsync(httpContext));
     }
 
+    [Theory]
+    [InlineData("/")]
+    [InlineData("/test/path")]
+    [InlineData("/test/path?foo=bar#baz")]
+    [InlineData("~/")]
+    [InlineData("~/Home/About")]
+    public void IsLocalUrl_True_ForLocalUrl(string url)
+    {
+        // Act
+        var actual = RedirectHttpResult.IsLocalUrl(url);
+
+        // Assert
+        Assert.True(actual);
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("//")]
+    [InlineData("/\\")]
+    [InlineData("//foo")]
+    [InlineData("/\\foo")]
+    [InlineData("Home/About")]
+    [InlineData("test/path")]
+    [InlineData("http://www.example.com")]
+    [InlineData("https://example.com/non-local-url/example")]
+    [InlineData("https://example.com/non-local-url/example?foo=bar#baz")]
+    public void IsLocalUrl_False_ForNonLocalUrl(string url)
+    {
+        // Act
+        var actual = RedirectHttpResult.IsLocalUrl(url);
+
+        // Assert
+        Assert.False(actual);
+    }
+
+    [Theory]
+    [InlineData("~//")]
+    [InlineData("~/\\")]
+    [InlineData("~//foo")]
+    [InlineData("~/\\foo")]
+    public void IsLocalUrl_False_ForNonLocalUrlTilde(string url)
+    {
+        // Act
+        var actual = RedirectHttpResult.IsLocalUrl(url);
+
+        // Assert
+        Assert.False(actual);
+    }
+
     protected override Task ExecuteAsync(HttpContext httpContext, string contentPath)
     {
         var redirectResult = new RedirectHttpResult(contentPath, false, false);