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 |
| uuid | integer | 8 | 16 | unique id of this zim file |
| count | integer | 24 | 4 | total number of articles |
| indexPtrPos | integer | 28 | 8 | position of the directory pointerlist |
| clusterCount | integer | 36 | 4 | number of data clusters |
| clusterPtrPos | integer | 40 | 8 | position of the cluster pointer list |
| mainPage | integer | 48 | 4 | article index of main page or 0xffffffff if no main page |
| layoutPage | integer | 52 | 4 | article index of layout page or 0xffffffffff 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.
Index pointer list
The index pointer list is a list of 4 byte offsets to the directory entries. Since directory entries has variable size, this is needed for random access.
Due to the fact, that these pointers are only 4 byte, the directory entries have to be in the first 4GB of the zim file. The pointers to data in the directory entries are 8 bytes, so that the zim file may be much larger than the 4GB.
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 | 8 | 4 | length of data chunk |
| compression | integer | 12 | 1 | 1=none; 2=zlib; 3=bzip2; 4=lzma |
| mime | integer | 13 | 1 | code of mimetype |
| redirectFlag | integer | 14 | 1 | 1 if this is a redirect |
| namespace | char | 15 | 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) |
Data
Mime types
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 |