From: "Koen Beets" To: Subject: RAR 2.00 format Date: Tue, 24 Sep 1996 18:59:29 +0200 RAR 2.00 Format ~~~~~~~~~~~~~~~ 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 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 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. Block Formats 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 comments 2 bytes RESERVED1 Reserved 2 bytes RESERVED2 Reserved 4 bytes Comment 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 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 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_SIZE HEAD_SIZE File header full size including file name and comments 2 bytes PACK_SIZE Compressed file size 4 bytes UNP_SIZE Uncompressed file size 4 bytes HOST_OS Operating system used for archiving 1 byte 0 - MS DOS 1 - OS/2 2 - Win32 3 - Unix 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_SIZE bytes size Comment block present if (HEAD_FLAGS & 0x08) != 0 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 Subblock An object in the archive (the block or header) can be followed by a subblock. The subblock is dependant on the main object. Subblock can be erased or moved to new version of the archive when it is updated. The subblock contains the following fields: HEAD_CRC Block CRC 2 bytes HEAD_TYPE Header type: 0x77 1 byte HEAD_FLAGS Bit flags 2 bytes (HEAD_FLAGS & 0x8000) == 1, because full block size is HEAD_SIZE + DATA_SIZE HEAD_SIZE Total block size 2 bytes DATA_SIZE Total data size 4 bytes SUB_TYPE Subblock type 2 bytes RESERVED Must be 0 1 byte Other Other fields depending on the subblock type fields OS/2 extended attributes subblock HEAD_CRC Block CRC 2 bytes HEAD_TYPE Header type: 0x77 1 byte HEAD_FLAGS Bit flags 2 bytes (HEAD_FLAGS & 0x8000) == 1, because full block size is HEAD_SIZE + DATA_SIZE HEAD_SIZE Total block size 2 bytes DATA_SIZE Total data size (packed extended attributes size) 4 bytes SUB_TYPE 0x100 2 bytes RESERVED Must be 0 1 byte UNP_SIZE Uncompressed extended attributes size 4 bytes UNP_VER RAR version needed to extract extended attributes 1 byte METHOD Packing method 1 byte EA_CRC Extended attributes CRC 4 bytes Application notes 1. 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. 2. 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. 3. Packing method encoding: 0x30 - storing 0x31 - fastest compression 0x32 - fast compression 0x33 - normal compression 0x34 - good compression 0x35 - best compression 4. The RAR extraction version number is encoded as 10 * Major version + minor version. Koen http://www.dma.be/p/bewoner/kbeets