ZIM is the open single-file archive format Kiwix uses for offline content:
a fixed header, a MIME list, URL/title/cluster pointer lists, directory
entries, zstd-compressed or stored clusters, and a trailing MD5. The writer
lays out a mirror in two passes (assign positions, then emit bytes) and
derives the UUID from the content so packing is deterministic. The reader
random-accesses entries by namespace and url, follows redirects, and reads
xz clusters too so archives from other tooling open.
Cross-checked against an independent reader (gozim): header, MIME list,
namespaces, urls, dirents, and a non-last cluster's blob all read back
byte-for-byte.
Duc-Tam Nguyen
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