Add back alternate views for core mail provider

This functionality was inexplicably removed in b3e066f dnnsoftware#4187

Includes fixes originally from dnnsoftware#2900 (1b44e1d)
Fixes dnnsoftware#2899

DNN Platform/Library/Services/Mail/CoreMailProvider.cs

@@ -8,6 +8,7 @@ namespace DotNetNuke.Services.Mail
     using System.Linq;
     using System.Net;
     using System.Net.Mail;
+    using System.Text;
     using System.Text.RegularExpressions;
     using System.Threading;
     using System.Threading.Tasks;
@@ -77,6 +78,23 @@ public override string SendMail(MailInfo mailInfo, SmtpInfo smtpInfo = null)
             }
         }
 
+        /// <summary>Adds alternate views to the <paramref name="mailMessage"/>.</summary>
+        /// <param name="mailMessage">The message to which the alternate views should be added.</param>
+        /// <param name="body">The message body.</param>
+        /// <param name="bodyEncoding">The encoding of the message body.</param>
+        internal static void AddAlternateView(MailMessage mailMessage, string body, Encoding bodyEncoding)
+        {
+            // added support for multipart html messages
+            // add text part as alternate view
+            var plainView = AlternateView.CreateAlternateViewFromString(Mail.ConvertToText(body), bodyEncoding, "text/plain");
+            mailMessage.AlternateViews.Add(plainView);
+            if (mailMessage.IsBodyHtml)
+            {
+                var htmlView = AlternateView.CreateAlternateViewFromString(body, bodyEncoding, "text/html");
+                mailMessage.AlternateViews.Add(htmlView);
+            }
+        }
+
         private static string ValidateSmtpInfo(SmtpInfo smtpInfo)
         {
             if (smtpInfo != null && !string.IsNullOrEmpty(smtpInfo.Server))
@@ -201,6 +219,9 @@ private static MailMessage CreateMailMessage(MailInfo mailInfo, SmtpInfo smtpInf
             mailMessage.Subject = HtmlUtils.StripWhiteSpace(mailInfo.Subject, true);
             mailMessage.BodyEncoding = mailInfo.BodyEncoding;
             mailMessage.Body = mailInfo.Body;
+
+            AddAlternateView(mailMessage, mailInfo.Body, mailInfo.BodyEncoding);
+
             return mailMessage;
         }
 

DNN Platform/Tests/DotNetNuke.Tests.Core/Services/Mail/MailTests.cs

@@ -1,45 +1,161 @@
-// 
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the MIT License. See LICENSE file in the project root for full license information.
-// 
-using System;
-using NUnit.Framework;
-
-namespace DotNetNuke.Tests.Core.Services.Mail
-{
-    [TestFixture]
-    public class MailTests
-    {
-        [Test]
-        public void ConvertToText_returns_the_input_for_simple_strings()
-        {
-            //arrange
-            Func<string, string> sut = DotNetNuke.Services.Mail.Mail.ConvertToText;
-            //act
-            var result = sut("Hello World");
-            //assert
-            Assert.AreEqual("Hello World", result);
-        }
-        [Test]
-        public void ConvertToText_removes_tags()
-        {
-            //arrange
-            Func<string, string> sut = DotNetNuke.Services.Mail.Mail.ConvertToText;
-            //act
-            var result = sut("<div class=\"x\"><p>Hello World</p></div>");
-            //assert
-            Assert.AreEqual("Hello World", result.Trim());
-        }
-
-        [Test]
-        public void ConvertToText_removes_styles_including_css_defs()
-        {
-            //arrange
-            Func<string, string> sut = DotNetNuke.Services.Mail.Mail.ConvertToText;
-            //act
-            var result = sut("<style>\r\nHello</style>World");     
-            //assert
-            Assert.AreEqual("World", result.Trim());
-        }
-    }
-}
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information
+namespace DotNetNuke.Tests.Core.Services.Mail
+{
+    using System;
+    using System.Net.Mail;
+    using System.Net.Mime;
+    using System.Text;
+
+    using DotNetNuke.Services.Mail;
+    using NUnit.Framework;
+
+    [TestFixture]
+    public class MailTests
+    {
+        [Test]
+        public void ConvertToText_returns_the_input_for_simple_strings()
+        {
+            Func<string, string> sut = DotNetNuke.Services.Mail.Mail.ConvertToText;
+            var result = sut("Hello World");
+            Assert.AreEqual("Hello World", result);
+        }
+
+        [Test]
+        public void ConvertToText_removes_tags()
+        {
+            Func<string, string> sut = DotNetNuke.Services.Mail.Mail.ConvertToText;
+            var result = sut("<div class=\"x\"><p>Hello World</p></div>");
+            Assert.AreEqual("Hello World", result.Trim());
+        }
+
+        [Test]
+        public void ConvertToText_removes_styles_including_css_defs()
+        {
+            Func<string, string> sut = DotNetNuke.Services.Mail.Mail.ConvertToText;
+            var result = sut("<style>\r\nHello</style>World");
+            Assert.AreEqual("World", result.Trim());
+        }
+
+        [Test]
+        public void GivenBodyIsNotHtmlWhenAddAlternateViewThenShouldContainsPlainViewOnly()
+        {
+            // special character
+            MailMessage mailMessage = new MailMessage()
+            {
+                IsBodyHtml = false
+            };
+            ContentType plain = new ContentType("text/plain")
+            {
+                CharSet = "us-ascii"
+            };
+            AlternateView plainView = AlternateView.CreateAlternateViewFromString("body\n", plain);
+
+            CoreMailProvider.AddAlternateView(mailMessage, "body\n", Encoding.ASCII);
+
+            AssertEqualAlternativeView(plainView, mailMessage.AlternateViews[0]);
+            Assert.AreEqual(1, mailMessage.AlternateViews.Count);
+        }
+
+        [Test]
+        public void GivenBodyHtmlWhenAddAlternateViewThenShouldContainsPlainAndHtmlViews()
+        {
+            // special character
+            MailMessage mailMessage = new MailMessage()
+            {
+                IsBodyHtml = true
+            };
+            ContentType plain = new ContentType("text/plain")
+            {
+                CharSet = "us-ascii"
+            };
+            ContentType html = new ContentType("text/html")
+            {
+                CharSet = "us-ascii"
+            };
+            AlternateView plainView = AlternateView.CreateAlternateViewFromString("body\n", plain);
+            AlternateView htmlView = AlternateView.CreateAlternateViewFromString("body\n", html);
+
+            CoreMailProvider.AddAlternateView(mailMessage, "body\n", Encoding.ASCII);
+
+            AssertEqualAlternativeView(plainView, mailMessage.AlternateViews[0]);
+            AssertEqualAlternativeView(htmlView, mailMessage.AlternateViews[1]);
+            Assert.AreEqual(2, mailMessage.AlternateViews.Count);
+        }
+
+        [Test]
+        public void GivenEncodingIsAsciiWhenAddAlternateViewThenCharsetShouldAlwaysAscii()
+        {
+            // special character
+            MailMessage mailMessage = new MailMessage()
+            {
+                IsBodyHtml = true
+            };
+            ContentType plain = new ContentType("text/plain")
+            {
+                CharSet = "us-ascii"
+            };
+            ContentType html = new ContentType("text/html")
+            {
+                CharSet = "us-ascii"
+            };
+
+            CoreMailProvider.AddAlternateView(mailMessage, "body\n", Encoding.ASCII);
+
+            Assert.AreEqual(plain, mailMessage.AlternateViews[0].ContentType);
+            Assert.AreEqual(html, mailMessage.AlternateViews[1].ContentType);
+
+            // no special character
+            mailMessage = new MailMessage()
+            {
+                IsBodyHtml = true
+            };
+
+            CoreMailProvider.AddAlternateView(mailMessage, "body", Encoding.ASCII);
+
+            Assert.AreEqual(plain, mailMessage.AlternateViews[0].ContentType);
+            Assert.AreEqual(html, mailMessage.AlternateViews[1].ContentType);
+        }
+
+        [Test]
+        public void GivenBodyEncodingIsUTF8WhenAddAlternateViewThenCharsetShouldAwaysUTF8()
+        {
+            // special character
+            MailMessage mailMessage = new MailMessage()
+            {
+                IsBodyHtml = true
+            };
+            ContentType plain = new ContentType("text/plain")
+            {
+                CharSet = "utf-8"
+            };
+            ContentType html = new ContentType("text/html")
+            {
+                CharSet = "utf-8"
+            };
+
+            CoreMailProvider.AddAlternateView(mailMessage, "body\n", Encoding.UTF8);
+
+            Assert.AreEqual(plain, mailMessage.AlternateViews[0].ContentType);
+            Assert.AreEqual(html, mailMessage.AlternateViews[1].ContentType);
+
+            // no special character
+            mailMessage = new MailMessage()
+            {
+                IsBodyHtml = true
+            };
+
+            CoreMailProvider.AddAlternateView(mailMessage, "body", Encoding.UTF8);
+
+            Assert.AreEqual(plain, mailMessage.AlternateViews[0].ContentType);
+            Assert.AreEqual(html, mailMessage.AlternateViews[1].ContentType);
+        }
+
+        private static void AssertEqualAlternativeView(AlternateView expected, AlternateView actual)
+        {
+            Assert.AreEqual(expected.ContentType, actual.ContentType);
+            Assert.AreEqual(expected.ContentStream, actual.ContentStream);
+        }
+    }
+}