mtx-decompressor

mtx-decompressor

A zero-dependency TypeScript library that decompresses MicroType Express (MTX) compressed font data found inside EOT (Embedded OpenType) containers, producing standard TrueType (.ttf) font binaries.

MTX is a font compression format developed by Monotype, used inside EOT containers commonly found in older web pages and embedded in Microsoft Office documents. This library parses the EOT container, extracts the compressed data, and reconstructs a standard .ttf file usable with standard font APIs (e.g. the FontFace API). It has no dependencies and works in both the browser and Node.js.

Live demo · npm

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Demo

Try it right in your browser — drop in an .eot file, download the extracted .ttf, and preview text rendered in the decompressed font:

https://christophervr.github.io/mtx-decompressor/

Install

npm install mtx-decompressor

Quick start

The simplest path takes a whole .eot file and hands back a .ttf:

import { eotToTtf } from 'mtx-decompressor';

const eotBytes: Uint8Array = /* the raw bytes of a .eot file */;
const ttfBytes = eotToTtf(eotBytes);
// => Uint8Array containing a valid TrueType font

eotToTtf parses the EOT header, locates the embedded font data, and applies the container's own compression/encryption flags for you.

If you already have the MTX blob (or want the metadata), the lower-level API is still available:

import { parseEotMetadata, decompressMtx, decompressEotFont } from 'mtx-decompressor';

// Inspect the container and slice out the font data yourself
const meta = parseEotMetadata(eotBytes);
const fontData = eotBytes.subarray(meta.fontDataOffset, meta.fontDataOffset + meta.fontDataSize);
const ttf = decompressMtx(fontData, { compressed: meta.compressed, encrypted: meta.encrypted });

// Or, with an already-extracted blob and explicit flags:
const ttf2 = decompressEotFont(fontData, /* compressed */ true, /* encrypted */ false);

// XOR-obfuscated data
const decrypted = decompressMtx(encryptedData, { encrypted: true, compressed: true });

Errors are thrown as EotError with a machine-readable code (see EotErrorCode) so corrupt vs. truncated vs. unsupported inputs can be told apart.

API

eotToTtf(eotBytes)

Parse a raw EOT container and return the reconstructed TrueType binary. Handles header parsing, font-data extraction, and the container's compression/encryption flags. Throws EotError on a corrupt or truncated container.

parseEotMetadata(eotBytes)

Parse just the EOT header. Returns an EotMetadata object: version, flags, compressed, encrypted, familyName / styleName / versionName / fullName, fontDataOffset, fontDataSize, permissions, and more. Includes libeot's version-retry logic for files whose declared version disagrees with their layout (metadata.badVersion is set rather than throwing). Throws EotError on corrupt input.

canLegallyEdit(metadata)

Given an EotMetadata, returns whether the font's fsType embedding permissions allow editing.

decompressMtx(fontData, options?)

Decompress an MTX-compressed font into a TrueType binary.

Parameter	Type	Description
fontData	Uint8Array	Raw font bytes (MTX-compressed, optionally encrypted)
options.encrypted	boolean (default: false)	If true, XOR-decrypt with key 0x50 before decompression
options.compressed	boolean (default: true)	If false, skip decompression and return the (possibly decrypted) data as-is
options.onWarn	(message: string) => void	Optional hook called for each non-fatal diagnostic (e.g. a dropped hdmx/VDMX table); the font is still produced
Returns	Uint8Array	A valid TrueType (.ttf) font binary

decompressEotFont(fontData, compressed, encrypted)

Convenience wrapper around decompressMtx taking explicit boolean parameters; returns a TrueType binary.

unpackMtx(data, size)

Low-level: unpack an MTX blob into three LZCOMP-decompressed streams. Returns { streams: Uint8Array[], sizes: number[] }.

The exported SFNTContainer and SFNTTable types describe the reconstructed font tables. EotError / EotErrorCode provide machine-discriminable error handling.

How it works

The pipeline: EOT container parsing (little-endian header → font-data offset + flags) → optional XOR decryption → MTX header parsing (splits into three LZCOMP blocks) → LZCOMP decompression (sliding-window LZ with adaptive Huffman coding) → CTF parsing (reconstructs TrueType tables from the three Compact TrueType Font streams) → SFNT assembly (table directory, alignment, checksums).

Provenance

A TypeScript port of the MTX decompression code from libeot by Brennan Vincent (MPL-2.0). The original C implementation is based on the MicroType Express specification submitted to the W3C by Monotype Imaging.

License

MPL-2.0. As a TypeScript port of the MPL-2.0-licensed libeot, this library inherits the Mozilla Public License 2.0 — modifications to the licensed files must remain open under the same terms.