"Extensible Archiver."

Basically a fixed-size header, with an XML file gzipped and taped on, followed by a no man's land of bytes.

The manifest stores the location and size of each file as well as how it was compressed.

Used to be used a lot on the Mac. Used for Safari extensions until it wasn't.

Header

Offset# 	Size
(in bytes) 	Purpose
0 	4 	File signature used to identify the file format as Xar.
This should always equal xar!
4 	2 	Header size
6 	2 	Version of Xar format to use.
Currently there is only version 1.
8 	8 	Length of the TOC compressed data.
16 	8 	Length of the TOC uncompressed data.
24 	4 	Checksum algorithm:

    0 = none
    1 = SHA1
    2 = MD5
    3 = SHA-256[5]
    4 = SHA-512

28 	0, 4 , 36 	sometimes padding bytes or checksum algorithm name 

Manifest example

 
  
   0
   20
  
  
   staff
   20
   joe
   501
   0755
   directory
   com.foobar
   
    
    20
    
    501
    0775
    directory
    Contents
    
     
      428
      20
      1005
      
      a5f6f1461213a904f831d4ef6f214638342842ed
      21d21a0c90378248ce0dfb6f345376d1b00d65fc
     
     
     20
     
     501
     0664
     file
     Info.plist
    
    
     
     20
     
     501
     0775
     directory
     Resources
     
      
       14868
       448
       274432
       
       efe5c97921de7ccc5aebc158d158e9d4280d6814
       45c8be42d1d9afdb57ddd5e9311453010ec46161
      
      
      20
      
      501
      0664
      file
      foobar
     
     
      
       17635
       15316
       45056
       
       3c761ffcc81ee6e232e4f4a1c4a81654c26c4e52
       0ea31f8ef0e5987a1838a64ab5c26ebf3ee4bc37
      
      
      20
      
      501
      0664
      file
      docSet.skidx
     
     
      
      20
      
      501
      0775
      directory
      Documents
      
       
        35790
        32951
        209242
        
        5242cd71585c34e722932f324706f8c00e1ae0c5
        c0e013e53d829511835e2b429abb5198731e9a3e
       
       
       20
       
       501
       0664
       file
       foobar.html