Introduce IUrlHelper.ActionLink (#6775)

Fixes https://github.com/aspnet/AspNetCore/issues/4890

src/Mvc/src/Microsoft.AspNetCore.Mvc.Core/UrlHelperExtensions.cs

@@ -530,5 +530,57 @@ namespace Microsoft.AspNetCore.Mvc
                 host: host,
                 fragment: fragment);
         }
+
+        /// <summary>
+        /// Generates an absolute URL for an action method, which contains the specified
+        /// <paramref name="action"/> name, <paramref name="controller"/> name, route <paramref name="values"/>,
+        /// <paramref name="protocol"/> to use, <paramref name="host"/> name, and <paramref name="fragment"/>.
+        /// Generates an absolute URL if the <paramref name="protocol"/> and <paramref name="host"/> are
+        /// non-<c>null</c>. See the remarks section for important security information.
+        /// </summary>
+        /// <param name="helper">The <see cref="IUrlHelper"/>.</param>
+        /// <param name="action">The name of the action method. When <see langword="null" />, defaults to the current executing action.</param>
+        /// <param name="controller">The name of the controller. When <see langword="null" />, defaults to the current executing controller.</param>
+        /// <param name="values">An object that contains route values.</param>
+        /// <param name="protocol">The protocol for the URL, such as "http" or "https".</param>
+        /// <param name="host">The host name for the URL.</param>
+        /// <param name="fragment">The fragment for the URL.</param>
+        /// <returns>The generated URL.</returns>
+        /// <remarks>
+        /// <para>
+        /// The value of <paramref name="host"/> should be a trusted value. Relying on the value of the current request
+        /// can allow untrusted input to influence the resulting URI unless the <c>Host</c> header has been validated.
+        /// See the deployment documentation for instructions on how to properly validate the <c>Host</c> header in
+        /// your deployment environment.
+        /// </para>
+        /// </remarks>
+        public static string ActionLink(
+            this IUrlHelper helper,
+            string action = null,
+            string controller = null,
+            object values = null,
+            string protocol = null,
+            string host = null,
+            string fragment = null)
+        {
+            if (helper == null)
+            {
+                throw new ArgumentNullException(nameof(helper));
+            }
+
+            var httpContext = helper.ActionContext.HttpContext;
+
+            if (protocol == null)
+            {
+                protocol = httpContext.Request.Protocol;
+            }
+
+            if (host == null)
+            {
+                host = httpContext.Request.Host.ToUriComponent();
+            }
+
+            return Action(helper, action, controller, values, protocol, host, fragment);
+        }
     }
 }

src/Mvc/test/Microsoft.AspNetCore.Mvc.Core.Test/Routing/UrlHelperBaseTest.cs

@@ -8,7 +8,6 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.ObjectPool;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Mvc.Routing

src/Mvc/test/Microsoft.AspNetCore.Mvc.Core.Test/Routing/UrlHelperExtensionsTest.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Routing;
 using Microsoft.AspNetCore.Routing;
@@ -601,6 +602,112 @@ namespace Microsoft.AspNetCore.Mvc.Core.Test.Routing
                 });
         }
 
+        [Fact]
+        public void ActionLink_WithActionName_Works()
+        {
+            // Arrange
+            var expectedAction = "TestAction";
+            var expectedProtocol = "testprotocol://";
+            var expectedHost = "www.example.com";
+            UrlActionContext actual = null;
+
+            var httpContext = new DefaultHttpContext
+            {
+                Request =
+                {
+                    Protocol = expectedProtocol,
+                    Host = new HostString(expectedHost),
+                }
+            };
+            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
+            var urlHelper = CreateMockUrlHelper(actionContext);
+            urlHelper.Setup(h => h.Action(It.IsAny<UrlActionContext>()))
+                .Callback((UrlActionContext context) => actual = context);
+
+            // Act
+            urlHelper.Object.ActionLink(expectedAction);
+
+            // Assert
+            urlHelper.Verify();
+            Assert.NotNull(actual);
+            Assert.Equal(expectedAction, actual.Action);
+            Assert.Null(actual.Controller);
+            Assert.Null(actual.Values);
+
+            Assert.Equal(expectedProtocol, actual.Protocol);
+            Assert.Equal(expectedHost, actual.Host);
+        }
+
+        [Fact]
+        public void ActionLink_UsesSpecifiedProtocol()
+        {
+            // Arrange
+            var expectedProtocol = "testprotocol://";
+            var expectedHost = "www.example.com";
+            UrlActionContext actual = null;
+
+            var httpContext = new DefaultHttpContext
+            {
+                Request =
+                {
+                    Protocol = "http://",
+                    Host = new HostString(expectedHost),
+                }
+            };
+            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
+            var urlHelper = CreateMockUrlHelper(actionContext);
+            urlHelper.Setup(h => h.Action(It.IsAny<UrlActionContext>()))
+                .Callback((UrlActionContext context) => actual = context);
+
+            // Act
+            urlHelper.Object.ActionLink(protocol: expectedProtocol);
+
+            // Assert
+            urlHelper.Verify();
+            Assert.NotNull(actual);
+            Assert.Null(actual.Action);
+            Assert.Null(actual.Controller);
+            Assert.Null(actual.Values);
+
+            Assert.Equal(expectedProtocol, actual.Protocol);
+            Assert.Equal(expectedHost, actual.Host);
+        }
+
+        [Fact]
+        public void ActionLink_UsesSpecifiedHost()
+        {
+            // Arrange
+            var expectedProtocol = "testprotocol://";
+            var expectedHost = "www.example.com";
+            UrlActionContext actual = null;
+
+            var httpContext = new DefaultHttpContext
+            {
+                Request =
+                {
+                    Protocol = expectedProtocol,
+                    Host = new HostString("www.asp.net"),
+                }
+            };
+            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
+            var urlHelper = CreateMockUrlHelper(actionContext);
+            urlHelper.Setup(h => h.Action(It.IsAny<UrlActionContext>()))
+                .Callback((UrlActionContext context) => actual = context);
+
+            // Act
+            urlHelper.Object.ActionLink(host: expectedHost);
+
+            // Assert
+            urlHelper.Verify();
+            Assert.NotNull(actual);
+            Assert.Null(actual.Action);
+            Assert.Null(actual.Controller);
+            Assert.Null(actual.Values);
+
+            Assert.Equal(expectedProtocol, actual.Protocol);
+            Assert.Equal(expectedHost, actual.Host);
+        }
+
         private static Mock<IUrlHelper> CreateMockUrlHelper(ActionContext context = null)
         {
             if (context == null)

src/Mvc/test/Microsoft.AspNetCore.Mvc.Core.Test/Routing/UrlHelperTestBase.cs

@@ -9,7 +9,6 @@ using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.ObjectPool;
 using Moq;
 using Xunit;
 
@@ -952,6 +951,19 @@ namespace Microsoft.AspNetCore.Mvc.Routing
             Assert.Equal("/b/Store/Checkout", url);
         }
 
+        [Fact]
+        public void ActionLink_ReturnsAbsoluteUrlToAction()
+        {
+            // Arrange
+            var urlHelper = CreateUrlHelperWithDefaultRoutes();
+
+            // Act
+            var url = urlHelper.ActionLink("contact", "home");
+
+            // Assert
+            Assert.Equal("http://localhost/app/home/contact", url);
+        }
+
         protected abstract IServiceProvider CreateServices();
 
         protected abstract IUrlHelper CreateUrlHelper(ActionContext actionContext);