Peeking Inside Gigantic Zips with Only Kilobytes

a day ago

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ZIP files have a tiny index at the end called the End of Central Directory (EOCD).
The EOCD contains metadata like the Central Directory's location, size, and number of entries.
The Central Directory (CD) acts as a table of contents, listing filenames, sizes, and offsets to Local File Headers (LFH).
Local File Headers (LFH) store per-file metadata and compressed data.
Using HTTP Range requests, you can fetch only the EOCD and CD to inspect a ZIP's contents without downloading the entire file.
This method is efficient for large ZIPs, including ZIP64 files with 64-bit fields.
The browser demo demonstrates fetching ZIP metadata in just a few HTTP requests.
Servers must support HTTP Range and expose headers like Content-Range for this to work.

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