From 1c7f53ae39f28384438122e44c72c9edc8ef857d Mon Sep 17 00:00:00 2001
From: Kiran Challa <kichalla@microsoft.com>
Date: Thu, 12 Jul 2018 16:00:51 -0700
Subject: [PATCH] Fix TemplateBinder to consider null and empty string values
 the same

---
 .../Template/TemplateBinder.cs                |  8 ++-
 .../Template/TemplateBinderTests.cs           | 62 ++++++++++++++++++-
 2 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Routing/Template/TemplateBinder.cs b/src/Microsoft.AspNetCore.Routing/Template/TemplateBinder.cs
index 802352e935..241705523b 100644
--- a/src/Microsoft.AspNetCore.Routing/Template/TemplateBinder.cs
+++ b/src/Microsoft.AspNetCore.Routing/Template/TemplateBinder.cs
@@ -375,7 +375,13 @@ namespace Microsoft.AspNetCore.Routing.Template
             var sa = a as string;
             var sb = b as string;
 
-            if (sa != null && sb != null)
+            // In case of strings, consider empty and null the same.
+            // Since null cannot tell us the type, consider it to be a string if the other value is a string.
+            if ((sa == string.Empty && sb == null) || (sb == string.Empty && sa == null))
+            {
+                return true;
+            }
+            else if (sa != null && sb != null)
             {
                 // For strings do a case-insensitive comparison
                 return string.Equals(sa, sb, StringComparison.OrdinalIgnoreCase);
diff --git a/test/Microsoft.AspNetCore.Routing.Tests/Template/TemplateBinderTests.cs b/test/Microsoft.AspNetCore.Routing.Tests/Template/TemplateBinderTests.cs
index d4dacaaa6b..c5fd2e7b9e 100644
--- a/test/Microsoft.AspNetCore.Routing.Tests/Template/TemplateBinderTests.cs
+++ b/test/Microsoft.AspNetCore.Routing.Tests/Template/TemplateBinderTests.cs
@@ -708,7 +708,7 @@ namespace Microsoft.AspNetCore.Routing.Template.Tests
         }
 
         [Fact]
-        public void TemplateBinder_KeepsExplicitlySuppliedRouteValues_OnFailedRouetMatch()
+        public void TemplateBinder_KeepsExplicitlySuppliedRouteValues_OnFailedRouteMatch()
         {
             // Arrange
             var template = "{area?}/{controller=Home}/{action=Index}/{id?}";
@@ -1211,6 +1211,8 @@ namespace Microsoft.AspNetCore.Routing.Template.Tests
 
         [Theory]
         [InlineData(null, null, true)]
+        [InlineData("", null, true)]
+        [InlineData(null, "", true)]
         [InlineData("blog", null, false)]
         [InlineData(null, "store", false)]
         [InlineData("Cool", "cool", true)]
@@ -1228,6 +1230,64 @@ namespace Microsoft.AspNetCore.Routing.Template.Tests
             }
         }
 
+        [Fact]
+        public void GetValues_SuccessfullyMatchesRouteValues_ForExplicitEmptyStringValue_AndNullDefault()
+        {
+            // Arrange
+            var expected = "/Home/Index";
+            var template = "Home/Index";
+            var defaults = new RouteValueDictionary(new { controller = "Home", action = "Index", area = (string)null });
+            var ambientValues = new RouteValueDictionary(new { controller = "Rail", action = "Schedule", area = "Travel" });
+            var explicitValues = new RouteValueDictionary(new { controller = "Home", action = "Index", area = "" });
+            var binder = new TemplateBinder(
+                UrlEncoder.Default,
+                new DefaultObjectPoolProvider().Create(new UriBuilderContextPooledObjectPolicy()),
+                TemplateParser.Parse(template),
+                defaults);
+
+            // Act1
+            var result = binder.GetValues(ambientValues, explicitValues);
+
+            // Assert1
+            Assert.NotNull(result);
+
+            // Act2
+            var boundTemplate = binder.BindValues(result.AcceptedValues);
+
+            // Assert2
+            Assert.NotNull(boundTemplate);
+            Assert.Equal(expected, boundTemplate);
+        }
+
+        [Fact]
+        public void GetValues_SuccessfullyMatchesRouteValues_ForExplicitNullValue_AndEmptyStringDefault()
+        {
+            // Arrange
+            var expected = "/Home/Index";
+            var template = "Home/Index";
+            var defaults = new RouteValueDictionary(new { controller = "Home", action = "Index", area = "" });
+            var ambientValues = new RouteValueDictionary(new { controller = "Rail", action = "Schedule", area = "Travel" });
+            var explicitValues = new RouteValueDictionary(new { controller = "Home", action = "Index", area = (string)null });
+            var binder = new TemplateBinder(
+                UrlEncoder.Default,
+                new DefaultObjectPoolProvider().Create(new UriBuilderContextPooledObjectPolicy()),
+                TemplateParser.Parse(template),
+                defaults);
+
+            // Act1
+            var result = binder.GetValues(ambientValues, explicitValues);
+
+            // Assert1
+            Assert.NotNull(result);
+
+            // Act2
+            var boundTemplate = binder.BindValues(result.AcceptedValues);
+
+            // Assert2
+            Assert.NotNull(boundTemplate);
+            Assert.Equal(expected, boundTemplate);
+        }
+
         private static IInlineConstraintResolver GetInlineConstraintResolver()
         {
             var services = new ServiceCollection().AddOptions();