SignHere

An implementation of file signature validation as documented in ASP.NET Core file upload document. This library can validate signatures of 518 different file types, all taken from https://filesignatures.net/, as the document suggests.

Usage

There are two main ways to use this library:

1. SignHere.FindSignature() method

   var stream = new MemoryStream(new byte[] { 0xFF, 0xD8, 0xFF, 0xE2, 0xB7, }); // "CANNON EOS JPEG FILE"
   var signature = SignHere.FindSignature(stream);
   
   // Comes out as:
   // signature.Extension = Extension.JPEG,
   // signature.MagicBytes = new byte[] { 0xFF, 0xD8, 0xFF, 0xE2 },
   // signature.Description = "CANNON EOS JPEG FILE"

2. .Is() extension method

   • stream.Is() extension: Works with any Stream object. Expects the stream content to be a byte[]. There are three different overloads to go with, all of them also have IEnumerable variants too:
     • stream.Is(Extension): Checks by Extension enum.

       var stream = new MemoryStream(new byte[] { 0xFF, 0xD8, 0xFF, 0xE2, 0xB7, })
       var isJPEG = stream.Is(Extension.JPEG); // true

     • stream.Is(Category): Checks by Category. A Category is a predefined constant string which is checked against Signature.Description.

       var stream = new MemoryStream(new byte[] { 0x9C, 0xCB, 0xCB, 0x8D, 0x13, 0x75, 0xD2, 0x11 })
       var whitelistedCategoryies = new List<Category>() { Category.Video, Category.Audio };
       var isVideoOrAudio = stream.Is(whitelistedCategoryies); // false

     • stream.Is(string): Checks by string. Matches if Signature.Description contains it.

       var stream = new MemoryStream(new byte[] { 0xE3, 0x10, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00 })
       var isAmigaFile = stream.Is("Amiga"); // true

   There are also Is() overloads that works with IFormFile and take Extension(s), Category(s) or string(s) as parameters.

Notes

• Files with no extension are represented as Extension.None.
• Extensions starting with a number are escaped with an underscore _ in Extension enum, since an enum member cannot start with a number. (eg. Extension 3GP is represented as Extension._3GP)
• Category relies on definition field in filesignatures.net (example, JPEG extension). Until all extensions are processed and categorised manually, validating with this type might be deceiving. Category.Video will only filter the extensions with the word "video" in their descriptions.

TODO

• Performance improvements
• Include other file signature databases
• Support for File type if requested
• Manual assigning of Categorys
• More tests
• Better icon