ZIM file format

The ZIM file format is based on the Zeno File Format. It starts with a header, which is described here:

Header

length in byte, all types are littlendian

Field Name	Type	Offset	Length	Description
magicNumber	integer	0	4	Magic number to recognise the file format, must be 72173914
version	integer	4	4	ZIM=4, version of the file format
count	integer	8	4	total number of articles
indexPtrPos	integer	12	8	position to the directory pointerlist
mainPage	integer	16	4	article index of main page or 0xffff if no main page
layoutPage	integer	20	4	article index of layout page or 0xffff if no layout page

Each article in the zim file has a directory entry. Since the directory entry has a variable size, we have a index pointerlist, which is a list of 4-byte offsets, which points to the directory entries.

Directory Entries

length in byte, all types are littlendian

Field Name	Type	Offset	Length	Description
filePos	integer	0	8	position of data chunk
fileLen	integer	4	4	length of data chunk
compression	integer	8	1	1=none; 2=zlib; 3=bzip2; 4=lzma
mime	integer	9	1	code of mimetype
redirectFlag	integer	10	1	1 if this is a redirect
namespace	char	11	1	namespace of article
articleOffset	integer	16	4	offset insize data chunk
articleSize	integer	20	4	uncompressed size of article
redirectIndex	integer	16	4	index of redirected article (field shared with articleOffset)
extraLen	integer	24	2	length of extra bytes (title and parameter)

Namespaces

Namespaces seperate different types of data stored in the ZIM File Format.

They can be distinguished by prepending the article namespace before the article name in the URL path, eg. http://localhost/A/Articlename.

Namespace	Description
-	template data
A	articles
I	images, files - see Image Handling
J	images, text - see Image Handling
U	categories, text - see Category Handling
V	categories, article list - see Category Handling
W	deprecated - see Zeno File Format
X	fulltext index
Y	deprecated - see Zeno File Format
Z	deprecated - see Zeno File Format