Core - Cef.GetMimeType custom/fallback mimeType mapping

- return application/octet-stream when no mapping found
- Add custom dictionary with some additional mimeTypes, users can add their own to this dictionary
- Add xunit test

Resolves #3041

Author: amaitland

CefSharp.Core/Cef.h

@@ -805,7 +805,17 @@ namespace CefSharp
                 extension = extension->Substring(1, extension->Length - 1);
             }
 
-            return StringUtils::ToClr(CefGetMimeType(StringUtils::ToNative(extension)));
+            auto mimeType = StringUtils::ToClr(CefGetMimeType(StringUtils::ToNative(extension)));
+
+            //Lookup to see if we have a custom mapping
+            //MimeTypeMapping::GetCustomMapping will Fallback
+            //to application/octet-stream if no mapping found
+            if (String::IsNullOrEmpty(mimeType))
+            {
+                return MimeTypeMapping::GetCustomMapping(extension);
+            }
+
+            return mimeType;
         }
 
         /// <summary>

CefSharp.Test/CefSharp.Test.csproj

@@ -128,6 +128,7 @@
     <Compile Include="Framework\BinderFacts.cs" />
     <Compile Include="Framework\AsyncExtensionFacts.cs" />
     <Compile Include="Framework\ConcurrentMethodRunnerQueueFacts.cs" />
+    <Compile Include="Framework\MimeTypeMappingFacts.cs" />
     <Compile Include="Framework\PathCheckFacts.cs" />
     <Compile Include="OffScreen\OffScreenBrowserBasicFacts.cs" />
     <Compile Include="CefSharpXunitTestFramework.cs" />

CefSharp.Test/Framework/MimeTypeMappingFacts.cs

@@ -0,0 +1,36 @@
+// Copyright © 2020 The CefSharp Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+
+using Xunit;
+
+namespace CefSharp.Test.Framework
+{
+    /// <summary>
+    /// MimeTypeMappingFacts - Tests file extension to mimeType mapping 
+    /// </summary>
+    public class MimeTypeMappingFacts
+    {
+        [Theory]
+        [InlineData("html", "text/html")]
+        [InlineData(".wasm", "application/wasm")]
+        [InlineData(".ogg", "audio/ogg")]
+        [InlineData(".oga", "audio/ogg")]
+        [InlineData(".ogv", "video/ogg")]
+        [InlineData(".opus", "audio/ogg")]
+        [InlineData(".webm", "video/webm")]
+        [InlineData(".weba", "audio/webm")]
+        [InlineData(".webp", "image/webp")]
+        [InlineData(".epub", "application/epub+zip")]
+        [InlineData(".woff", "application/font-woff")]
+        [InlineData(".woff2", "font/woff2")]
+        [InlineData(".ttf", "font/ttf")]
+        [InlineData(".otf", "font/otf")]
+        [InlineData(".dummyextension", "application/octet-stream")]
+        public void MapFileExtensionToMimeTypeTheory(string fileExtension, string expectedMimeType)
+        {
+            var actualMimeType = Cef.GetMimeType(fileExtension);
+            Assert.Equal(expectedMimeType, actualMimeType);
+        }
+    }
+}

CefSharp/CefSharp.csproj

@@ -104,6 +104,7 @@
     <Compile Include="DefaultApp.cs" />
     <Compile Include="Enums\SchemeOptions.cs" />
     <Compile Include="Internals\IBrowserRefCounter.cs" />
+    <Compile Include="Internals\MimeTypeMapping.cs" />
     <Compile Include="Internals\NoOpBrowserRefCounter.cs" />
     <Compile Include="Internals\PathCheck.cs" />
     <Compile Include="Internals\BrowserRefCounter.cs" />

CefSharp/Internals/MimeTypeMapping.cs

@@ -0,0 +1,44 @@
+// Copyright © 2020 The CefSharp Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+
+
+using System;
+using System.Collections.Generic;
+
+namespace CefSharp.Internals
+{
+    /// <summary>
+    /// Internal Mime Type Mappings.
+    /// </summary>
+    public static class MimeTypeMapping
+    {
+        /// <summary>
+        /// Dictionary containing our custom mimeType mapping, you can add your own file extension
+        /// to mimeType mappings to this dictionary.
+        /// </summary>
+        public static readonly IDictionary<string, string> CustomMappings = new Dictionary<string, string>(StringComparer.InvariantCultureIgnoreCase)
+        {
+            // Recently added entries from 
+            // https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Complete_list_of_MIME_types
+            // https://cs.chromium.org/chromium/src/net/base/mime_util.cc?sq=package:chromium&g=0&l=147
+            // https://www.w3.org/TR/WOFF2/#IMT
+            // https://tools.ietf.org/html/rfc8081#section-4.4.6
+            {"woff2", "font/woff2"},
+            {"ttf", "font/ttf"},
+            {"otf", "font/otf"}
+        };
+
+        /// <summary>
+        /// Lookup MimeType from the <see cref="CustomMappings"/>
+        /// dictionary based on file extension.
+        /// </summary>
+        /// <param name="extension">extension</param>
+        /// <returns>custom mimeType or application/octet-stream if no mapping found </returns>
+        public static string GetCustomMapping(string extension)
+        {
+            string mime;
+            return CustomMappings.TryGetValue(extension, out mime) ? mime : "application/octet-stream";
+        }
+    }
+}