FileTypeChecker is a easy to use library that provides quality identification of a file type. This will help you to secure your applications and validate all files that are provided by external sources with few lines of code.
Secure file type validation for .NET applications using magic number detection
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✨ Overview
FileTypeChecker is a powerful .NET library that provides reliable file type identification using magic number detection. Unlike traditional filename extension-based validation, this library analyzes the actual file content to determine the true file type, protecting your applications from malicious files and ensuring robust security.
using (var fileStream = File.OpenRead("suspicious-file.exe"))
{
// Check if file type can be identified
if (FileTypeValidator.IsTypeRecognizable(fileStream))
{
// Get the actual file type
IFileType fileType = FileTypeValidator.GetFileType(fileStream);
Console.WriteLine($"File type: {fileType.Name} ({fileType.Extension})");
// Check specific type
bool isImage = fileStream.IsImage();
bool isPdf = fileStream.Is<PortableDocumentFormat>();
}
}
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<strong>Made with ❤️ by <a href="https://github.com/AJMitev">Aleksandar J. Mitev</a></strong>
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💡 Why Use FileTypeChecker?
🎯 The Problem
Traditional file validation relies on file extensions, which can be easily manipulated:
A malicious executable can be renamed to .jpg
Untrusted files can bypass basic extension checks
The FileSystemInfo.Extension property only reads the filename
✅ The Solution
FileTypeChecker analyzes the actual file content using magic numbers:
Reliable: Identifies files by their binary signature, not filename
Secure: Prevents malicious files from masquerading as safe formats
Comprehensive: Supports 30+ file types with extensible architecture
Fast: Minimal performance overhead with efficient binary analysis
⚙️ How It Works
FileTypeChecker uses magic numbers (binary signatures) to identify file types. These are specific byte sequences found at the beginning of files that uniquely identify the format.
using FileTypeChecker;
using (var fileStream = File.OpenRead("document.pdf"))
{
// Check if file type is recognizable
if (FileTypeValidator.IsTypeRecognizable(fileStream))
{
// Get file type information
IFileType fileType = FileTypeValidator.GetFileType(fileStream);
Console.WriteLine($"Type: {fileType.Name}");
Console.WriteLine($"Extension: {fileType.Extension}");
}
}
Category-Based Validation
using (var fileStream = File.OpenRead("image.jpg"))
{
// Check by category
bool isImage = fileStream.IsImage();
bool isDocument = fileStream.IsDocument();
bool isArchive = fileStream.IsArchive();
// Check specific type
bool isPng = fileStream.Is<PortableNetworkGraphic>();
bool isJpeg = fileStream.Is<JointPhotographicExpertsGroup>();
}
File Upload Validation
public bool ValidateUploadedFile(IFormFile file)
{
using (var stream = file.OpenReadStream())
{
// Verify file is actually an image (regardless of file extension)
if (!stream.IsImage())
{
throw new InvalidOperationException("Only image files are allowed");
}
// Additional validation for specific formats
var fileType = FileTypeValidator.GetFileType(stream);
var allowedTypes = new[] { "PNG", "JPEG", "BMP" };
return allowedTypes.Contains(fileType.Name);
}
}
Custom File Type Registration
// Register your own file type
public class MyCustomType : FileType
{
public override string Name => "My Custom Format";
public override string Extension => "mycustom";
public override string MimeType => "application/x-mycustom";
public override bool IsMatch(byte[] signature, Stream stream)
{
return signature.Length >= 4 &&
signature[0] == 0x4D && signature[1] == 0x59 &&
signature[2] == 0x43 && signature[3] == 0x54;
}
}
// Use it
FileTypeValidator.RegisterType<MyCustomType>();
