.WOFF

Introduction

WOFF is a wrapper for TrueType and OpenType fonts, made for loading fonts on web pages. It was proposed in 2009 and became a W3C Recommendation in 2012. It compresses the font’s tables and can carry licensing metadata, and browsers load it through CSS @font-face. WOFF2, which compresses better, has largely replaced it, but WOFF is still kept as a fallback for older browsers.

Structure

A WOFF file is big-endian. It starts with a 44-byte header: the signature wOFF, the flavour of the original font (00 01 00 00 for TrueType outlines or OTTO for CFF), the file length, the number of tables, the size of the original font, a version number, and the offsets and lengths of optional metadata and private data. A table directory follows, 20 bytes per table: the tag, its offset in the file, its compressed and original lengths and its checksum. Each table is then stored compressed with zlib, or as it was if compression would not make it smaller.

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