Zip

.ZIP is an archive file format that supports lossless data compression.

TODO describe ZIP64

File format

	ZIP	ZIP64
Maximum archive size (bytes)	4,294,967,295	18,446,755,073,709,551,615 ( 2⁶⁴-1 )
Maximum object size in archive (bytes)	4,294,967,295	18,446,755,073,709,551,615 ( 2⁶⁴-1 )
Maximum objects in archive	65,535	18,446,755,073,709,551,615 ( 2⁶⁴-1 )
Maximum central directory size (bytes)	4,294,967,295	18,446,755,073,709,551,615 ( 2⁶⁴-1 )
Maximum spanned archive segments	999	4,294,967,294
Maximum split archive segments	65,535	4,294,967,294

Overall ZIP File Structure
Files
local file header 1
encryption header 1
file data 1
data descriptor 1
...
local file header n
encryption header n
file data n
data descriptor n
Central directory
archive decryption header
archive extra data record
central directory header 1
...
central directory header n
zip64 end of central directory record
zip64 end of central directory locator
end of central directory record

The central directory (archived) file header is variable of size and consists of:

Offset	Size	Value	Description
0	4	"PK\x01\x02"	Signature
4	2		Creator version
6	2		Extractor version
8	2		Flags
10	2		Compression method
12	2		Last modification time
14	2		Last modification date
16	4		Checksum (CRC-32)
20	4		Compressed data size
24	4		Uncompressed data size
28	2		File name size
30	2		Extra field size
32	2		File comment size
34	2		Segment file (disk) number
36	2		Internal file attributes
38	4		External file attributes
42	4		Local header offset, which is relative to the start of the segment file it is stored in
46	...		File name
...	...		Extra field
...	...		File comment

The creator (or version made by) is 2 bytes of size and consists of:

Offset	Size	Value	Description
0	1		ZIP format version The value is stored as: ( major number x 10 ) + minor number
1	1		Creator system indicator

Value	Identifier	Description
0		MS-DOS and OS/2 (FAT / VFAT / FAT32 file systems) or compatible systems
1		Amiga
2		OpenVMS
3		UNIX
4		VM/CMS
5		Atari ST
6		OS/2 H.P.F.S.
7		Macintosh
8		Z-System
9		CP/M
10		Windows NTFS
11		MVS (OS/390 - Z/OS)
12		VSE
13		Acorn Risc
14		VFAT
15		alternate MVS
16		BeOS
17		Tandem
18		OS/400
19		OS X (Darwin)
20 - 255		unused

Value	Identifier	Description
0x01		If set the uncompressed data needs to be treated as text instead of binary data. This flag hints end-of-line conversion for cross-platform text files but does not enforce it.
0x02		If set the file contains control fields for mainframe data transfer support.

The external attributes are creator system dependent.

The external attributes MS-DOS (0) is 4 bytes of size and consists of:

Offset	Size	Value	Description
0	1		FAT (MS-DOS) file attributes.
1	3		Unknown

The external attributes UNIX (3) is 4 bytes of size and consists of:

Offset	Size	Description
0	1	FAT (MS-DOS) file attributes.
1	1	Unknown
2	16 bits	The UNIX mode (or permission). The value seems to be similar to stat.st_mode value.