Add custom MIME type in System.Web.MimeMapping programmatically

Question

I am using MimeMapping class from System.Web assembly to get mime types from file extensions.

But in case of .HEIC extensions it is returning mime type as application/octet-stream. But the original mime type associated with this extension is image/heic.

MimeMapping.GetMimeMapping("something.HEIC")//returning application/octet-stream

Do MimeMapping class provides any api to add new mappings so that I can get the correct mime-type?

Answer 1

Thanks to the tip by Rup and reflection. I'd created a method which can be used to add custom mime-types to the private static variable which MimeMapping class uses for resolving mime types.

        public static void RegisterMimeTypes(IDictionary<string, string> mimeTypes)
        {
            if (mimeTypes == null || mimeTypes.Count == 0)
                return;
            var field = typeof(System.Web.MimeMapping).GetField("_mappingDictionary",
                        System.Reflection.BindingFlags.NonPublic |
                        System.Reflection.BindingFlags.Static);

            var currentValues = field.GetValue(null);
            var add = field.FieldType.GetMethod("AddMapping",
                      System.Reflection.BindingFlags.NonPublic |
                      System.Reflection.BindingFlags.Instance);

            foreach (var mime in mimeTypes)
            {
                add.Invoke(currentValues, new object[] { mime.Key, mime.Value });
            }

        }

Now you can register your list of custom mime-types on the application startup like below

    var mimeTypes = new Dictionary<string, string>()
    {
        { ".heic", "image/heic"},
        {".extn", "custom/mime" }
    };

    RegisterMimeTypes(mimeTypes);

Example

MimeMapping.GetMimeMapping("filename.heic")// will return image/heic