Level 1 Header

• Introduction
  Level 1 header is defined for shift to Level 2 header from Level 0 header. Level 1 header has irregular specification which uses base header of Level 0 header and extended header of level 2 header. Moreover, Level 1 header uses Skip size in place of Compressed size, so that an old version(for example, LArc) can list files which are in the archive. Development of new LHA which output Level 2 header by default was late, and LHA ver 2.13 which output Level 1 header by default was distributed as the standard version for a long time, so Level 1 header had spread widely in contrast to intention of author.
  
  
  
• Sample

  	+0	+1	+2	+3	+4	+5	+6	+7	+8	+9	+A	+B	+C	+D	+E	+F		0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
  0x0000	1D	FF	2D	6C	68	30	2D	0D	00	00	00	00	00	00	00	CA			ÿ	-	l	h	0	-		.	.	.	.	.	.	.	Ê
  0x0010	83	E7	2C	20	01	04	74	65	73	74	00	00	4A	05	00	00		ƒ	ç	,				t	e	s	t	.	.	J		.	.
  0x0020	40	7F	08	00	02	74	65	73	74	FF	00	00	--	--	--	--		@			.		t	e	s	t	ÿ	.	.	-	-	-	-

  
  
• Construction

  offset	caption	description
  00	Size of base header	This is the byte count of the base header without 2 bytes of the head. Size of base header is 0x1D(29) in the foregoing sample. (Size of the base header:31 - 2 bytes of the head:2)
  01	Base header checksum	This is low 1 byte of the total of each bytes of the base header without 2 bytes of the head. Base header checksum is 0xFF in the foregoing sample. (Total of each bytes of the base header without 2 bytes of the head is 0x05FF.)
  02	Compress method(1)	Compress method identifies the compression algorithm of compressed data which is following this header. The format of compress method is "-???-". (the 1st byte and the 5th byte must be '-', and the length must be 5bytes) Compress method is "-lh0-" which means no compression, in the foregoing sample.
  03	Compress method(2)
  04	Compress method(3)
  05	Compress method(4)
  06	Compress method(5)
  07	Skip size(LL)	This is the sum of byte count of total of all extended headers and the byte count of the compressed file which is following this header. Old implementation can display list of the files in a archive by using such an irregular value. However, old implementation can not extract an archive which has level 1 header. Skip size is 0x0000000D in the foregoing sample. (The byte count of compressed file : 0 + Total of the byte count of each extended headers : 13)
  08	Skip size(LH)
  09	Skip size(HL)
  10	Skip size(HH)
  11	Original size(LL)	This is the byte count of the file before the compression. Original size is 0x00000000 in the foregoing sample.
  12	Original size(LH)
  13	Original size(HL)
  14	Original size(HH)
  15	Last modified time(L)	This is the last modified time of file with MS-DOS format. Note that this is a local time. Last modified time is 16:30:20 in the foregoing sample.
  16	Last modified time(H)
  17	Last modified date(L)	This is the last modified date of file with MS-DOS format. Note that this is a local time. Last modified time is Jul 7, 2002 in the foregoing sample.
  18	Last modified date(H)
  19	Resurved	You must set 0x20 which means normal file in MS-DOS attribute.
  20	Header level	You must set 0x01 which means header level.
  21	Length of Filename	This is the byte count of the following Filename. Length of Filename is 4 in the foregoing sample.
  22	Filename(1)	This is the string which contains the filename (without directory name). Note that you must use the filename header when Length of Filename exceeds the following restriction. Filename is "test" in the foregoing sample.
  ??	...
  21 + len	Filename(end)
  22 + len	CRC16(L)	This is CRC16 of the file before the compression. CRC16 is 0x0000 in the foregoing sample.
  23 + len	CRC16(H)
  24 + len	OS ID	This is a identifier of Operating System which compressed the file. OS ID is 'J'(0x4A) which means Java in the foregoing sample.
  25 + len	Extended area(1)	This is the area for storing another infomation when you need. No Extended area is in the foregoing sample.
  ??	...
  size - 3	Extended area(end)
  size - 2	Size of next extended header(L)	This is the byte count of following extended header. Set this field as 0, when there is not following extended header. Size of next extended header is 0x0005 in the foregoing sample.
  size -1	Size of next extended header(H)

  
  
• About restriction of Length of Filename
  • According to old log in Nifty
    
    Size of header structure is 101 bytes in LHarc, So Length of Filename is restricted by the following values according to Extended area which is defined for each OS.
    
    MS-DOS or no Extend area::74 bytes
    (Size of header structure : 101 - Header size without Filename : 27)
    
    With extended area for UNIX::62 bytes
    (Size of header structure : 101 - Header size without Filename : 27 - Size of extended area for UNIX : 12)
    
    With extended area for MacOS::49 bytes
    (Size of header structure : 101 - Header size without Filename : 27 - Size of extended area for MacOS : 25)
    
    
  • According to document in LHA for OS/2
    230 bytes(Maximum size of header : 257 - Header size without Filename : 27)
    
    
  • According to document in UNLHA32.DLL
    
    255 bytes, However document in UNLHA32.DLL has some mistakes, So I think this number is iincorrect.
    
    
    
  You must use the file name header when Length of Filename exceeds the foregoing restriction. like this :
  
  

  	+0	+1	+2	+3	+4	+5	+6	+7	+8	+9	+A	+B	+C	+D	+E	+F		0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
  0x0000	19	85	2D	6C	68	30	2D	8A	00	00	00	00	00	00	00	BC			…	-	l	h	0	-	Š	.	.	.	.	.	.	.	¼
  0x0010	54	F1	2C	20	01	00	00	00	4A	05	00	00	63	AF	85	00		T	ñ	,			.	.	.	J		.	.	c	¯	…	.
  0x0020	01	75	73	65	20	61	20	66	69	6C	65	6E	61	6D	65	20			u	s	e		a		f	i	l	e	n	a	m	e
  0x0030	68	65	61	64	65	72	20	61	73	20	61	20	73	75	62	73		h	e	a	d	e	r		a	s		a		s	u	b	s
  0x0040	74	69	74	75	74	65	20	66	6F	72	20	74	68	65	20	66		t	i	t	u	t	e		f	o	r		t	h	e		f
  0x0050	69	6C	65	6E	61	6D	65	20	66	69	65	6C	64	20	77	68		i	l	e	n	a	m	e		f	i	e	l	d		w	h
  0x0060	65	6E	20	62	79	74	65	20	63	6F	75	6E	74	20	6F	66		e	n		b	y	t	e		c	o	u	n	t		o	f
  0x0070	20	66	69	6C	65	6E	61	6D	65	20	69	73	20	69	6E	20			f	i	l	e	n	a	m	e		i	s		i	n
  0x0080	65	78	63	65	73	73	20	6F	66	20	74	68	65	20	66	6F		e	x	c	e	s	s		o	f		t	h	e		f	o
  0x0090	72	65	67	6F	69	6E	67	20	72	65	73	74	72	69	63	74		r	e	g	o	i	n	g		r	e	s	t	r	i	c	t
  0x00A0	69	6F	6E	00	00	--	--	--	--	--	--	--	--	--	--	--		i	o	n	.	.	-	-	-	-	-	-	-	-	-	-	-

  
  
  
  
• Reference
  • Joe Jared's document
    http://www.osirusoft.com/joejared/lzhformat.html
    
    
  • Eriko Tachibana's document of LHA header(Japanese)
    http://kuwa.omosiro.com/KGARC2/ARC/LHAHED15.ZIP
    
    
  • Satoshi Hiramatsu's header.tex which is attached to LHA for OS/2(Japanese)
    http://www02.so-net.ne.jp/~hiramatu/lha/lha2-2.08.lzh
    
    
  • Micco's header.txt which is attached to UNLHA32.DLL(Japanese)
    http://www2.nsknet.or.jp/~micco/unlha32.htm
    
    
  • old log in Nifty FLABO MES(6) 1(1989/05/13)-256(1989/08/17) (Japanese)
    (when you access this file, Nifty is required ID and password.)
    https://enter.nifty.com/iw/nifty/flabo/lib/6/DLB.7/archive1.lzh