ZIM file format

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


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 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