Added attribute adapter for DataAnnotation's FileExtensionsAttribute

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/FileExtensionsAttributeAdapter.cs

@@ -0,0 +1,45 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.ComponentModel.DataAnnotations;
+using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using Microsoft.Extensions.Localization;
+
+namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
+{
+    public class FileExtensionsAttributeAdapter : AttributeAdapterBase<FileExtensionsAttribute>
+    {
+        public FileExtensionsAttributeAdapter(FileExtensionsAttribute attribute, IStringLocalizer stringLocalizer)
+            : base(attribute, stringLocalizer)
+        {
+        }
+
+        /// <inheritdoc />
+        public override void AddValidation(ClientModelValidationContext context)
+        {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            MergeAttribute(context.Attributes, "data-val", "true");
+            MergeAttribute(context.Attributes, "data-val-fileextensions", GetErrorMessage(context));
+            MergeAttribute(context.Attributes, "data-val-fileextensions-extensions", Attribute.Extensions.ToLowerInvariant());
+        }
+
+        /// <inheritdoc />
+        public override string GetErrorMessage(ModelValidationContextBase validationContext)
+        {
+            if (validationContext == null)
+            {
+                throw new ArgumentNullException(nameof(validationContext));
+            }
+
+            return GetErrorMessage(
+                validationContext.ModelMetadata,
+                validationContext.ModelMetadata.GetDisplayName(),
+                Attribute.Extensions);
+        }
+    }
+}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/ValidationAttributeAdapterProvider.cs

@@ -74,6 +74,10 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations
             {
                 adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "data-val-url", stringLocalizer);
             }
+            else if (type == typeof(FileExtensionsAttribute))
+            {
+                adapter = new FileExtensionsAttributeAdapter((FileExtensionsAttribute)attribute, stringLocalizer);
+            }
             else
             {
                 adapter = null;

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/FileExtensionsAttributeAdapterTest.cs

@@ -0,0 +1,121 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Linq;
+using System.ComponentModel.DataAnnotations;
+using Microsoft.AspNetCore.Mvc.DataAnnotations.Internal;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Testing;
+using Microsoft.Extensions.Localization;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
+{
+    public class FileExtensionsAttributeAdapterTest
+    {
+        [Theory]
+        [InlineData("jpg,png")]
+        [InlineData("jpg, png")]
+        [InlineData("JPEG, Png")]
+        [ReplaceCulture]
+        public void AddValidation_WithoutLocalization(string extensions)
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(Profile), "PhotoFileName");
+
+            var attribute = new FileExtensionsAttribute() { Extensions = extensions };
+            attribute.ErrorMessage = "{0} expects only the following extensions: {1}";
+
+            var expectedExtensions = string.Join(", ", extensions.Split(',').Select(s => $".{s.Trim().ToLowerInvariant()}")); 
+            var expectedMessage = $"PhotoFileName expects only the following extensions: {expectedExtensions}";
+
+            var adapter = new FileExtensionsAttributeAdapter(attribute, stringLocalizer: null);
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-fileextensions", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
+                kvp => { Assert.Equal("data-val-fileextensions-extensions", kvp.Key); Assert.Equal(extensions.ToLowerInvariant(), kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_WithLocalization()
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(Profile), "PhotoFileName");
+
+            var attribute = new FileExtensionsAttribute() { Extensions = "jpg" };
+            attribute.ErrorMessage = "{0} expects only the following extensions: {1}";
+
+            var expectedProperties = new object[] { "PhotoFileName", "jpg" };
+            var expectedMessage = "PhotoFileName expects only the following extensions: jpg";
+
+            var stringLocalizer = new Mock<IStringLocalizer>();
+            stringLocalizer
+                .Setup(s => s[attribute.ErrorMessage, expectedProperties])
+                .Returns(new LocalizedString(attribute.ErrorMessage, expectedMessage));
+
+            var adapter = new FileExtensionsAttributeAdapter(attribute, stringLocalizer: stringLocalizer.Object);
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-fileextensions", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
+                kvp => { Assert.Equal("data-val-fileextensions-extensions", kvp.Key); Assert.Equal("jpg", kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(Profile), "PhotoFileName");
+
+            var attribute = new FileExtensionsAttribute() { Extensions = "jpg" };
+            attribute.ErrorMessage = "{0} expects only the following extensions: {1}";
+            
+            var adapter = new FileExtensionsAttributeAdapter(attribute, stringLocalizer: null);
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-fileextensions", "original");
+            context.Attributes.Add("data-val-fileextensions-extensions", "original");
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-fileextensions", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-fileextensions-extensions", kvp.Key); Assert.Equal("original", kvp.Value); });
+        }
+
+        private class Profile
+        {
+            public string PhotoFileName { get; set; }
+        }
+    }
+}