Contributor: ANDREW EIGUS
MM> Does anyone have the structures for RAR archived files?
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ÛÛÉÍÍÛÛ» ÛÛÉÍÍÛÛ» ÛÛÉÍÍÛÛ» RAR version 1.53 - Technical information
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³THE ARCHIVE FORMAT DESCRIBED BELOW IS ONLY VALID FOR VERSIONS SINCE 1.50³
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º ±±±±±±±±±±±±±±±±±±±±±±±± RAR archive file format ±±±±±±±±±±±±±±±±±±±±±±º
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Archive file consists of variable length blocks. The order of these
blocks may vary, but the first block must be marker block followed by
an archive header block.
Each block begins with following fields:
HEAD_CRC 2 bytes CRC of total block or block part
HEAD_TYPE 1 byte Block type
HEAD_FLAGS 2 bytes Block flags
HEAD_SIZE 2 bytes Block size
ADD_SIZE 4 bytes Optional field - added block size
Field ADD_SIZE present only if (HEAD_FLAGS & 0x8000) != 0
Total block size is HEAD_SIZE if (HEAD_FLAGS & 0x8000) == 0
and HEAD_SIZE+ADD_SIZE if the field ADD_SIZE is present - when
(HEAD_FLAGS & 0x8000) != 0.
In each block the followings bits in HEAD_FLAGS have the same meaning:
0x4000 - if set, older RAR versions will ignore the block
and remove it when the archive is updated.
if clear, the block is copied to the new archive
file when the archive is updated;
0x8000 - if set, ADD_SIZE field is present and the full block
size is HEAD_SIZE+ADD_SIZE.
Declared block types:
HEAD_TYPE=0x72 marker block
HEAD_TYPE=0x73 archive header
HEAD_TYPE=0x74 file header
HEAD_TYPE=0x75 comment header
HEAD_TYPE=0x76 extra information
Comment block is actually used only within other blocks and does not
exist separately.
Archive processing is made in the following manner:
1. Read and check marker block
2. Read archive header
3. Read or skip HEAD_SIZE-sizeof(MAIN_HEAD) bytes
4. If end of archive encountered then terminate archive processing,
else read 7 bytes into fields HEAD_CRC, HEAD_TYPE, HEAD_FLAGS,
HEAD_SIZE.
5. Check HEAD_TYPE.
In case block read needed:
if HEAD_TYPE==0x74
read file header ( first 7 bytes already read )
read or skip HEAD_SIZE-sizeof(FILE_HEAD) bytes
read or skip FILE_SIZE bytes
else
read corresponding HEAD_TYPE block:
read HEAD_SIZE-7 bytes
if (HEAD_FLAGS & 0x8000)
read ADD_SIZE bytes
In case block skip needed:
skip HEAD_SIZE-7 bytes
if (HEAD_FLAGS & 0x8000)
skip ADD_SIZE bytes
6. go to 4.
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º±±±±±±±±±±±±±±±±±±±±±±±±±±± Block Formats ±±±±±±±±±±±±±±±±±±±±±±±±±±±±º
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Marker block ( MARK_HEAD )
HEAD_CRC Always 0x6152
2 bytes
HEAD_TYPE Header type: 0x72
1 byte
HEAD_FLAGS Always 0x1a21
2 bytes
HEAD_SIZE Block size = 0x0007
2 bytes
The marker block is actually considered as a fixed byte
sequence: 0x52 0x61 0x72 0x21 0x1a 0x07 0x00
Archive header ( MAIN_HEAD )
HEAD_CRC CRC of fields HEAD_TYPE to RESERVED2
2 bytes
HEAD_TYPE Header type: 0x73
1 byte
HEAD_FLAGS Bit flags:
2 bytes
0x01 - Volume attribute (archive volume)
0x02 - Archive comment present
0x04 - Archive lock attribute
0x08 - Solid attribute (solid archive)
0x10 - Unused
0x20 - Authenticity information present
other bits in HEAD_FLAGS are reserved for
internal use
HEAD_SIZE Archive header total size including archive
2 bytes comments and other added fields
RESERVED1 Reserved
2 bytes
RESERVED2 Reserved
4 bytes
Comment block present if (HEAD_FLAGS & 0x02) != 0
???? Other included blocks - reserved for
future use
File header (File in archive)
HEAD_CRC CRC of fields from HEAD_TYPE to FILEATTR
2 bytes and file name
HEAD_TYPE Header type: 0x74
1 byte
HEAD_FLAGS Bit flags:
2 bytes
0x01 - file continued from previous volume
0x02 - file continued in next volume
0x04 - file encrypted with password
0x08 - file comment present
(HEAD_FLAGS & 0x8000) == 1, because full
block size is HEAD_SIZE + PACK_SIZE
HEAD_SIZE File header full size including file name,
2 bytes comments and other added fields
PACK_SIZE Compressed file size
4 bytes
UNP_SIZE Uncompressed file size
4 bytes
HOST_OS Operating system used for archiving
1 byte (value 0 stands for MS DOS)
FILE_CRC File CRC
4 bytes
FTIME Date and time in standard MS DOS format
4 bytes
UNP_VER RAR version needed to extract file
1 byte
METHOD Packing method
1 byte
NAME_SIZE File name size
2 bytes
ATTR File attributes
4 bytes
FILE_NAME File name - string of NAME_LEN bytes size
Comment block present if (HEAD_FLAGS & 0x08) != 0
???? Other extra included blocks - reserved for
future use
Comment block
HEAD_CRC CRC of fields from HEAD_TYPE to COMM_CRC
2 bytes
HEAD_TYPE Header type: 0x75
1 byte
HEAD_FLAGS Bit flags
2 bytes
HEAD_SIZE Comment header size + comment size
2 bytes
UNP_SIZE Uncompressed comment size
2 bytes
UNP_VER RAR version needed to extract comment
1 byte
METHOD Packing method
1 byte
COMM_CRC Comment CRC
2 bytes
COMMENT Comment text
Extra info block
HEAD_CRC Block CRC
2 bytes
HEAD_TYPE Header type: 0x76
1 byte
HEAD_FLAGS Bit flags
2 bytes
HEAD_SIZE Total block size
2 bytes
INFO Other data
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º±±±±±±±±±±±±±±±±±±±±±±±±±± Application notes ±±±±±±±±±±±±±±±±±±±±±±±±±º
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1. Should fields and included blocks be added in the future, their
size would be included in HEAD_SIZE.
2. To process SFX archive you need to skip the SFX module searching
marker block in the archive. There is no marker block sequence (0x52 0x61
0x72 0x21 0x1a 0x07 0x00) in the SFX module itself.
3. The CRC is calculated using the standard polynomial 0xEDB88320. In
case the size of the CRC is less than 4 bytes, only the low order bytes
are used.
4. Packing method encoding:
0x30 - storing
0x31 - fastest compression
0x32 - fast compression
0x33 - normal compression
0x34 - good compression
0x35 - best compression
5. The RAR extraction version number is encoded as 10 * Major version
+ minor version.