RAR version 2.02 - Technical information Archive file consists of variable length blocks. The order of these blocks may vary, but the first block must be a er block followed by an archive header block. Each block begins with the 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 er block HEAD_TYPE=0x73 archive header HEAD_TYPE=0x74 file header HEAD_TYPE=0x75 comment header HEAD_TYPE=0x76 extra information HEAD_TYPE=0x77 subblock HEAD_TYPE=0x78 recovery record Comment block is actually used only within other blocks and doesn't exist separately. Archive processing is made in the following manner:1. Read and check er 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.
Block Formats Marker block ( MARK_HEAD )HEAD_CRC Always 0x6152 2 bytesHEAD_TYPE Header type: 0x72 1 byteHEAD_FLAGS Always 0x1a21 2 bytesHEAD_SIZE Block size = 0x0007 2 bytes The er 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 bytesHEAD_TYPE Header type: 0x73 1 byteHEAD_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 useHEAD_SIZE Archive header total size including archive comments 2 bytesRESERVED1 Reserved 2 bytesRESERVED2 Reserved 4 bytesComment block present if (HEAD_FLAGS & 0x02) != 0 File header (File in archive) HEAD_CRC CRC of fields from HEAD_TYPE to FILEATTR 2 bytes and file nameHEAD_TYPE Header type: 0x74 1 byteHEAD_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 0x10 - information from previous files is used (solid flag) (for RAR 2.0 and later) bits 7 6 5 (for RAR 2.0 and later) 0 0 0 - dictionary size 64 Kb 0 0 1 - dictionary size 128 Kb 0 1 0 - dictionary size 256 Kb 0 1 1 - dictionary size 512 Kb 1 0 0 - dictionary size 1024 Kb 1 0 1 - reserved 1 1 0 - reserved 1 1 1 - file is directory (HEAD_FLAGS & 0x8000) == 1, because full block size is HEAD_SIZE + PACK_SIZEHEAD_SIZE File header full size including file name and comments 2 bytesPACK_SIZE Compressed file size 4 bytesUNP_SIZE Uncompressed file size 4 bytesHOST_OS Operating system used for archiving 1 byte 0 - MS DOS 1 - OS/2 2 - Win32 3 - UnixFILE_CRC File CRC 4 bytesFTIME Date and time in standard MS DOS format 4 bytesUNP_VER RAR version needed to extract file 1 byteMETHOD Packing method 1 byteNAME_SIZE File name size 2 bytesATTR File attributes 4 bytesFILE_NAME File name - string of NAME_SIZE bytes sizeCmment block present if (HEAD_FLAGS & 0x08) != 0 Comment blockHEAD_CRC CRC of fields from HEAD_TYPE to COMM_CRC 2 bytesHEAD_TYPE Header type: 0x75 1 byteHEAD_FLAGS Bit flags 2 bytesHEAD_SIZE Comment header size + comment size 2 bytesUNP_SIZE Uncompressed comment size 2 bytesUNP_VER RAR version needed to extract comment 1 byteMETHOD Packing method 1 byteCOMM_CRC Comment CRC 2 bytesCOMMENT Comment text Extra info block HEAD_CRC Block CRC 2 bytesHEAD_TYPE Header type: 0x76 1 byteHEAD_FLAGS Bit flags 2 bytesHEAD_SIZE Total block size 2 bytesINFO Other data SubblockAn object in the archive (the block or header) can be followed by a subblock. The subblock is dependant upon the main object. Subblock can be erased or moved to a new version of the archive when it is updated. The subblock contains the following fields:HEAD_CRC Block CRC 2 bytesHEAD_TYPE Header type: 0x77 1 byteHEAD_FLAGS Bit flags 2 bytes (HEAD_FLAGS & 0x8000) == 1, because full block size is HEAD_SIZE + DATA_SIZEHEAD_SIZE Total block size 2 bytesDATA_SIZE Total data size 4 bytesSUB_TYPE Subblock type 2 bytesRESERVED Must be 0 1 byteOther Other fields depending on the subblock type fields OS/2 extended attributes subblock HEAD_CRC Block CRC 2 bytesHEAD_TYPE Header type: 0x77 1 byteHEAD_FLAGS Bit flags 2 bytes (HEAD_FLAGS & 0x8000) == 1, because full block size is HEAD_SIZE + DATA_SIZEHEAD_SIZE Total block size 2 bytesDATA_SIZE Total data size (packed extended attributes size) 4 bytesSUB_TYPE 0x100 2 bytesRESERVED Must be 0 1 byteUNP_SIZE Uncompressed extended attributes size 4 bytesUNP_VER RAR version needed to extract extended attributes 1 byteMETHOD Packing method 1 byteEA_CRC Extended attributes CRC 4 bytes
Archive file consists of variable length blocks. The order of these
blocks may vary, but the first block must be a er block followed by
an archive header block. Each block begins with the 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 er block
HEAD_TYPE=0x73 archive header
HEAD_TYPE=0x74 file header
HEAD_TYPE=0x75 comment header
HEAD_TYPE=0x76 extra information
HEAD_TYPE=0x77 subblock
HEAD_TYPE=0x78 recovery record Comment block is actually used only within other blocks and doesn't
exist separately. Archive processing is made in the following manner:1. Read and check er 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.
Marker block ( MARK_HEAD )HEAD_CRC Always 0x6152
2 bytesHEAD_TYPE Header type: 0x72
1 byteHEAD_FLAGS Always 0x1a21
2 bytesHEAD_SIZE Block size = 0x0007
2 bytes The er 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 bytesHEAD_TYPE Header type: 0x73
1 byteHEAD_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 useHEAD_SIZE Archive header total size including archive comments
2 bytesRESERVED1 Reserved
2 bytesRESERVED2 Reserved
4 bytesComment block present if (HEAD_FLAGS & 0x02) != 0 File header (File in archive)
HEAD_CRC CRC of fields from HEAD_TYPE to FILEATTR
2 bytes and file nameHEAD_TYPE Header type: 0x74
1 byteHEAD_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
0x10 - information from previous files is used (solid flag)
(for RAR 2.0 and later) bits 7 6 5 (for RAR 2.0 and later) 0 0 0 - dictionary size 64 Kb
0 0 1 - dictionary size 128 Kb
0 1 0 - dictionary size 256 Kb
0 1 1 - dictionary size 512 Kb
1 0 0 - dictionary size 1024 Kb
1 0 1 - reserved
1 1 0 - reserved
1 1 1 - file is directory (HEAD_FLAGS & 0x8000) == 1, because full
block size is HEAD_SIZE + PACK_SIZEHEAD_SIZE File header full size including file name and comments
2 bytesPACK_SIZE Compressed file size
4 bytesUNP_SIZE Uncompressed file size
4 bytesHOST_OS Operating system used for archiving
1 byte 0 - MS DOS
1 - OS/2
2 - Win32
3 - UnixFILE_CRC File CRC
4 bytesFTIME Date and time in standard MS DOS format
4 bytesUNP_VER RAR version needed to extract file
1 byteMETHOD Packing method
1 byteNAME_SIZE File name size
2 bytesATTR File attributes
4 bytesFILE_NAME File name - string of NAME_SIZE bytes sizeCmment block present if (HEAD_FLAGS & 0x08) != 0 Comment blockHEAD_CRC CRC of fields from HEAD_TYPE to COMM_CRC
2 bytesHEAD_TYPE Header type: 0x75
1 byteHEAD_FLAGS Bit flags
2 bytesHEAD_SIZE Comment header size + comment size
2 bytesUNP_SIZE Uncompressed comment size
2 bytesUNP_VER RAR version needed to extract comment
1 byteMETHOD Packing method
1 byteCOMM_CRC Comment CRC
2 bytesCOMMENT Comment text
Extra info block
HEAD_CRC Block CRC
2 bytesHEAD_TYPE Header type: 0x76
1 byteHEAD_FLAGS Bit flags
2 bytesHEAD_SIZE Total block size
2 bytesINFO Other data
SubblockAn object in the archive (the block or header) can be followed
by a subblock. The subblock is dependant upon the main object.
Subblock can be erased or moved to a new version of the archive
when it is updated. The subblock contains the following fields:HEAD_CRC Block CRC
2 bytesHEAD_TYPE Header type: 0x77
1 byteHEAD_FLAGS Bit flags
2 bytes
(HEAD_FLAGS & 0x8000) == 1, because full
block size is HEAD_SIZE + DATA_SIZEHEAD_SIZE Total block size
2 bytesDATA_SIZE Total data size
4 bytesSUB_TYPE Subblock type
2 bytesRESERVED Must be 0
1 byteOther Other fields depending on the subblock type
fields
OS/2 extended attributes subblock
HEAD_CRC Block CRC
2 bytesHEAD_TYPE Header type: 0x77
1 byteHEAD_FLAGS Bit flags
2 bytes
(HEAD_FLAGS & 0x8000) == 1, because full
block size is HEAD_SIZE + DATA_SIZEHEAD_SIZE Total block size
2 bytesDATA_SIZE Total data size (packed extended attributes size)
4 bytesSUB_TYPE 0x100
2 bytesRESERVED Must be 0
1 byteUNP_SIZE Uncompressed extended attributes size
4 bytesUNP_VER RAR version needed to extract extended attributes
1 byteMETHOD Packing method
1 byteEA_CRC Extended attributes CRC
4 bytes