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# zlib-header-cli
CLI to print details about the 2 Byte zlib header, as defined in
[RFC 1950](https://datatracker.ietf.org/doc/html/rfc1950).
This was initially written to reverse-engineer more details about Blizzard's proprietary MPQ archive format, which uses
zlib streams to store data.
```
Usage: zlib-header-cli [OPTIONS] [HEX4CHAR]
Arguments:
[HEX4CHAR] A four-character hex string representing the ZlibHeader (Big Endian)
Options:
-e, --explain Explain the ZlibHeader struct and abbreviations
-h, --help Print help
```
```
drfrugal@karazhan:~$ zlib-header-cli 789C
CM 8 (DEFLATE)
CINFO 7 (Window: 32768 Bytes)
FCHECK 28 (valid)
FDICT false (Preset Dictionary not used)
FLEVEL 2 (default)
```
```
drfrugal@karazhan:~$ zlib-header-cli --explain
2 Byte zlib header according to https://datatracker.ietf.org/doc/html/rfc1950
1st Byte - CMF (Compression Method and Flags)
0000_1111 CM Compression Method 8, _ (DEFLATE, UNDEFINED)
1111_0000 CINFO Compression Info window size is 2.pow(CINFO + 8)
2nd Byte - FLG (Flags)
0001_1111 FCHECK Checksum Adjustment valid if (CMF * 256 + FLG) % 31 == 0
0010_0000 FDICT Preset Dictionary a preset dictionary was used
1100_0000 FLEVEL Compression Level 0, 1, 2, 3 (fastest, fast, default, best)
```
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