MagicBytesValidator 2.1.6

MagicBytesValidator

Recognize file types from Streams or IFormFiles using MIME types or file extensions and validate them against the magic bytes according to the file types. The existing IFileTypes can be expanded in various ways.

How to install?

• Install nuget package into your project:

Install-Package MagicBytesValidator -Version 2.1.5

dotnet add package MagicBytesValidator --version 2.1.5

• Reference in your csproj:

<PackageReference Include="MagicBytesValidator" Version="2.1.5" />

How to use it?

• Create new instances of the validator and providers:

var validator = new MagicBytesValidator.Services.Validator();
var formFileTypeProvider = new MagicBytesValidator.Services.Http.FormFileTypeProvider();
var streamFileTypeProvider = new MagicBytesValidator.Services.Streams.StreamFileTypeProvider();

• Find a file type by extension or MIME type:

var pngFileType = validator.Mapping.FindByExtension("png");
var pdfFileType = validator.Mapping.FindByMimeType("application/pdf");

• Determine and validate a file type by uploaded IFormFile:

var fileType = await formFileTypeProvider.FindValidatedTypeAsync(formFile, null, CancellationToken.None);

• Determine the file type of a file by its stream

var fileType = await streamFileTypeProvider.TryFindUnambiguousAsync(fileStream, CancellationToken.None);

• Check a file with its stream and file type:

var isValid = await validator.IsValidAsync(memoryStream, fileType, CancellationToken.None);

Expand the file type mapping

• Get mapping:

// use the validator:
var mapping = validator.Mapping;

// use the formFileTypeProvider:
var mapping = formFileTypeProvider.Mapping;

// or create a new instance of the mapping:
var mapping = new MagicBytesValidator.Services.Mapping(); 

• Register a single FileByteFilter:

mapping.Register(
    new FileByteFilter(
        "traperto/trp", // MIME type
        new[] { "trp" } // file extensions
    ) {
        // magic byte sequences
        StartsWith([
            0x78, 0x6c, 0x2f, 0x5f, 0x72, 0x65
        ])
        .EndsWith([
            0xFF, 0xFF
        ])
    }
)

• FileByteFilters with specific offset checks:

mapping.Register(
    new FileByteFilter(
        "traperto/trp", // MIME type
        new[] { "trp" } // file extensions
    ) {
        // magic byte sequences
        Specific(new ByteCheck(512, [0xFD]));
    }
)

ByteCheck allows for negative offset values to look for a specific offset counting from the end of file.

• Register a list of filetypes:

mapping.Register(listOfFileTypes);

You can also create variants of IFileType and register them by passing the Assembly of the new IFileTypes, e.g. mapping.Register(typeof(CustomFileType).Assembly);. This will register all IFileTypes of the given assembly that are also not abstract and have an empty constructor.

public class CustomFileType : FileTypeWithStartSequences
{
    public CustomFileType() : base(
        "traperto/trp",  // MIME type
        new[] { "trp" }, // file extensions
        new[] {          // magic byte sequences
            new byte[] { 0x74, 0x72, 0x61, 0x70, 0x65, 0x72, 0x74, 0x6f }
        }
    )
    {
    }
}

var assembly = typeof(CustomFileType).Assembly;
_mapping.Register(assembly);

CLI

There's a CLI tool (MagicBytesValidator.CLI) which can be used to determine MIME types for a local file by calling the following command:

dotnet run --project MagicBytesValidator.CLI -- [PATH]

This can be useful when debugging or validating newly added FileTypes.

List of file types

What is the licence?

MIT License

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