MimeTypes

Version	Package	Description
	ManagedCode.MimeTypes	Core library

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Why MimeTypes?

MIME (Multipurpose Internet Mail Extensions) values describe the media type of a payload. They appear in HTTP headers, file upload workflows, messaging protocols and countless integrations. Unfortunately the canonical values are long strings, which makes code prone to typos and hard to validate.

ManagedCode.MimeTypes ships a generated helper with official MIME data sourced from the IANA media types registry and Apache's canonical mime.types list, runtime registration APIs and rich helpers for detecting and categorising data by content.

Feature overview

• Generated extension → MIME map based on the official IANA registry plus Apache's maintained mime.types coverage.
• Generated MIME metadata API for IANA registration status, template URLs, references, extensions, intended usage and parseable magic-number prefixes.
• Reverse lookup API that returns the extensions known for a given MIME value.
• Runtime registration/unregistration so applications can plug in custom corporate formats.
• Content sniffing for common file signatures (PDF, PNG, JPEG, GIF, WebP, MP4, ZIP/OOXML, ODF, APK, etc.) so applications can verify whether bytes match the claimed type, with graceful handling of short or empty streams.
• Extended categorisation enum covering document, audio/video, script, binary, multipart and message families with convenience predicates.
• Safe-by-default mutation model powered by immutable dictionaries, configurable fallback MIME via MimeHelper.SetDefaultMimeType, and an IMimeHelper abstraction (MimeHelper.Instance) for DI scenarios.
• CLI utility to refresh mimeTypes.json and mimeTypes.metadata.json from IANA and Apache.

Quick start

using ManagedCode.MimeTypes;

// Extension based lookup (handles multi-part extensions automatically)
var gzip = MimeHelper.GetMimeType("archive.tar.gz");             // application/gzip
var image = MimeHelper.GetMimeType("avatar.png");                // image/png

// Content-based detection
using var stream = File.OpenRead("report.pdf");
var detected = MimeHelper.GetMimeTypeByContent(stream);           // application/pdf

// Categorisation helpers
if (MimeHelper.IsDocument(detected))
{
    // do something useful
}

// Reverse lookup
var jpegExtensions = MimeHelper.GetExtensions("image/jpeg");     // .jpeg, .jpg, .jpe

// Registry metadata
if (MimeHelper.TryGetMimeTypeInfoByExtension("report.pdf", out var pdfInfo))
{
    var template = pdfInfo.TemplateUrl;                           // IANA registration template URL
    var magic = pdfInfo.MagicSignatures.FirstOrDefault()?.Hex;    // 25 50 44 46 2D
}

// Runtime registration (and clean-up)
MimeHelper.RegisterMimeType("acme", "application/x-acme");
var custom = MimeHelper.GetMimeType("invoice.acme");
MimeHelper.UnregisterMimeType("acme");

// Override the fallback MIME and use the DI-friendly adapter
MimeHelper.SetDefaultMimeType(MimeHelper.JSON);
IMimeHelper helper = MimeHelper.Instance;
var fallback = helper.GetMimeType("file.unknownext");             // application/json (custom fallback)

Keeping the database fresh

A small console utility is included to synchronise mimeTypes.json and mimeTypes.metadata.json with the IANA media types registry, Apache's canonical mime.types list and no unverified third-party MIME database. The scheduled GitHub Actions workflow runs weekly, validates the generated database with tests, bumps the package patch version when MIME data changes and opens a pull request whenever new official MIME definitions are published.

The IANA templates include useful metadata such as file extensions, references, intended usage and magic-number descriptions. When a magic number is a fixed byte prefix, the sync tool stores it as parseable metadata so content detectors can be added and tested without guessing.

# Update the data file in-place
dotnet run --project ManagedCode.MimeTypes.Sync

# Provide custom sources or output
DOTNET_CLI_TELEMETRY_OPTOUT=1 dotnet run --project ManagedCode.MimeTypes.Sync -- \
    --iana-source https://www.iana.org/assignments/media-types/media-types.xml \
    --output ./artifacts/mimeTypes.json \
    --metadata-output ./artifacts/mimeTypes.metadata.json

# Preserve an existing local map only when intentionally carrying compatibility data forward
dotnet run --project ManagedCode.MimeTypes.Sync -- --preserve-existing --prefer-remote

Running the tool re-generates the JSON file, which in turn updates the generated helper during the next build.

Installation

dotnet add package ManagedCode.MimeTypes

Contributing

Issues and PRs are welcome! Run dotnet test before sending a contribution, and feel free to use the sync utility to keep the MIME catalogue current.