ZIP format

Overall zipfile format:
[Local file header + Compressed data [+ Extended local header]?]*
[Central directory]*
[End of central directory record]

Local file header:
Offset   Length   Contents
  0      4 bytes  Local file header signature (0x04034b50)
  4      2 bytes  Version needed to extract
  6      2 bytes  General purpose bit flag
  8      2 bytes  Compression method
 10      2 bytes  Last mod file time
 12      2 bytes  Last mod file date
 14      4 bytes  CRC-32
 18      4 bytes  Compressed size (n)
 22      4 bytes  Uncompressed size
 26      2 bytes  Filename length (f)
 28      2 bytes  Extra field length (e)
        (f)bytes  Filename
        (e)bytes  Extra field
        (n)bytes  Compressed data

Extended local header:
Offset   Length   Contents
  0      4 bytes  Extended Local file header signature (0x08074b50)
  4      4 bytes  CRC-32
  8      4 bytes  Compressed size
 12      4 bytes  Uncompressed size

Central directory:
Offset   Length   Contents
  0      4 bytes  Central file header signature (0x02014b50)
  4      2 bytes  Version made by
  6      2 bytes  Version needed to extract
  8      2 bytes  General purpose bit flag
 10      2 bytes  Compression method
 12      2 bytes  Last mod file time
 14      2 bytes  Last mod file date
 16      4 bytes  CRC-32
 20      4 bytes  Compressed size
 24      4 bytes  Uncompressed size
 28      2 bytes  Filename length (f)
 30      2 bytes  Extra field length (e)
 32      2 bytes  File comment length (c)
 34      2 bytes  Disk number start
 36      2 bytes  Internal file attributes
 38      4 bytes  External file attributes
 42      4 bytes  Relative offset of local header
 46     (f)bytes  Filename
        (e)bytes  Extra field
        (c)bytes  File comment

End of central directory record:
Offset   Length   Contents
  0      4 bytes  End of central dir signature (0x06054b50)
  4      2 bytes  Number of this disk
  6      2 bytes  Number of the disk with the start of the central directory
  8      2 bytes  Total number of entries in the central dir on this disk
 10      2 bytes  Total number of entries in the central dir
 12      4 bytes  Size of the central directory
 16      4 bytes  Offset of start of central directory with respect to the starting disk number
 20      2 bytes  zipfile comment length (c)
 22     (c)bytes  zipfile comment




compression method: (2 bytes)
          0 - The file is stored (no compression)
          1 - The file is Shrunk
          2 - The file is Reduced with compression factor 1
          3 - The file is Reduced with compression factor 2
          4 - The file is Reduced with compression factor 3
          5 - The file is Reduced with compression factor 4
          6 - The file is Imploded
          7 - Reserved for Tokenizing compression algorithm
          8 - The file is Deflated