7zFormat.txt (7573B)
1 7z Format description (4.59) 2 ---------------------------- 3 4 This file contains description of 7z archive format. 5 7z archive can contain files compressed with any method. 6 See "Methods.txt" for description for defined compressing methods. 7 8 9 Format structure Overview 10 ------------------------- 11 12 Some fields can be optional. 13 14 Archive structure 15 ~~~~~~~~~~~~~~~~~ 16 SignatureHeader 17 [PackedStreams] 18 [PackedStreamsForHeaders] 19 [ 20 Header 21 or 22 { 23 Packed Header 24 HeaderInfo 25 } 26 ] 27 28 29 30 Header structure 31 ~~~~~~~~~~~~~~~~ 32 { 33 ArchiveProperties 34 AdditionalStreams 35 { 36 PackInfo 37 { 38 PackPos 39 NumPackStreams 40 Sizes[NumPackStreams] 41 CRCs[NumPackStreams] 42 } 43 CodersInfo 44 { 45 NumFolders 46 Folders[NumFolders] 47 { 48 NumCoders 49 CodersInfo[NumCoders] 50 { 51 ID 52 NumInStreams; 53 NumOutStreams; 54 PropertiesSize 55 Properties[PropertiesSize] 56 } 57 NumBindPairs 58 BindPairsInfo[NumBindPairs] 59 { 60 InIndex; 61 OutIndex; 62 } 63 PackedIndices 64 } 65 UnPackSize[Folders][Folders.NumOutstreams] 66 CRCs[NumFolders] 67 } 68 SubStreamsInfo 69 { 70 NumUnPackStreamsInFolders[NumFolders]; 71 UnPackSizes[] 72 CRCs[] 73 } 74 } 75 MainStreamsInfo 76 { 77 (Same as in AdditionalStreams) 78 } 79 FilesInfo 80 { 81 NumFiles 82 Properties[] 83 { 84 ID 85 Size 86 Data 87 } 88 } 89 } 90 91 HeaderInfo structure 92 ~~~~~~~~~~~~~~~~~~~~ 93 { 94 (Same as in AdditionalStreams) 95 } 96 97 98 99 Notes about Notation and encoding 100 --------------------------------- 101 102 7z uses little endian encoding. 103 104 7z archive format has optional headers that are marked as 105 [] 106 Header 107 [] 108 109 REAL_UINT64 means real UINT64. 110 111 UINT64 means real UINT64 encoded with the following scheme: 112 113 Size of encoding sequence depends from first byte: 114 First_Byte Extra_Bytes Value 115 (binary) 116 0xxxxxxx : ( xxxxxxx ) 117 10xxxxxx BYTE y[1] : ( xxxxxx << (8 * 1)) + y 118 110xxxxx BYTE y[2] : ( xxxxx << (8 * 2)) + y 119 ... 120 1111110x BYTE y[6] : ( x << (8 * 6)) + y 121 11111110 BYTE y[7] : y 122 11111111 BYTE y[8] : y 123 124 125 126 Property IDs 127 ------------ 128 129 0x00 = kEnd 130 131 0x01 = kHeader 132 133 0x02 = kArchiveProperties 134 135 0x03 = kAdditionalStreamsInfo 136 0x04 = kMainStreamsInfo 137 0x05 = kFilesInfo 138 139 0x06 = kPackInfo 140 0x07 = kUnPackInfo 141 0x08 = kSubStreamsInfo 142 143 0x09 = kSize 144 0x0A = kCRC 145 146 0x0B = kFolder 147 148 0x0C = kCodersUnPackSize 149 0x0D = kNumUnPackStream 150 151 0x0E = kEmptyStream 152 0x0F = kEmptyFile 153 0x10 = kAnti 154 155 0x11 = kName 156 0x12 = kCTime 157 0x13 = kATime 158 0x14 = kMTime 159 0x15 = kWinAttributes 160 0x16 = kComment 161 162 0x17 = kEncodedHeader 163 164 0x18 = kStartPos 165 0x19 = kDummy 166 167 168 7z format headers 169 ----------------- 170 171 SignatureHeader 172 ~~~~~~~~~~~~~~~ 173 BYTE kSignature[6] = {'7', 'z', 0xBC, 0xAF, 0x27, 0x1C}; 174 175 ArchiveVersion 176 { 177 BYTE Major; // now = 0 178 BYTE Minor; // now = 2 179 }; 180 181 UINT32 StartHeaderCRC; 182 183 StartHeader 184 { 185 REAL_UINT64 NextHeaderOffset 186 REAL_UINT64 NextHeaderSize 187 UINT32 NextHeaderCRC 188 } 189 190 191 ........................... 192 193 194 ArchiveProperties 195 ~~~~~~~~~~~~~~~~~ 196 BYTE NID::kArchiveProperties (0x02) 197 for (;;) 198 { 199 BYTE PropertyType; 200 if (aType == 0) 201 break; 202 UINT64 PropertySize; 203 BYTE PropertyData[PropertySize]; 204 } 205 206 207 Digests (NumStreams) 208 ~~~~~~~~~~~~~~~~~~~~~ 209 BYTE AllAreDefined 210 if (AllAreDefined == 0) 211 { 212 for(NumStreams) 213 BIT Defined 214 } 215 UINT32 CRCs[NumDefined] 216 217 218 PackInfo 219 ~~~~~~~~~~~~ 220 BYTE NID::kPackInfo (0x06) 221 UINT64 PackPos 222 UINT64 NumPackStreams 223 224 [] 225 BYTE NID::kSize (0x09) 226 UINT64 PackSizes[NumPackStreams] 227 [] 228 229 [] 230 BYTE NID::kCRC (0x0A) 231 PackStreamDigests[NumPackStreams] 232 [] 233 234 BYTE NID::kEnd 235 236 237 Folder 238 ~~~~~~ 239 UINT64 NumCoders; 240 for (NumCoders) 241 { 242 BYTE 243 { 244 0:3 CodecIdSize 245 4: Is Complex Coder 246 5: There Are Attributes 247 6: Reserved 248 7: There are more alternative methods. (Not used anymore, must be 0). 249 } 250 BYTE CodecId[CodecIdSize] 251 if (Is Complex Coder) 252 { 253 UINT64 NumInStreams; 254 UINT64 NumOutStreams; 255 } 256 if (There Are Attributes) 257 { 258 UINT64 PropertiesSize 259 BYTE Properties[PropertiesSize] 260 } 261 } 262 263 NumBindPairs = NumOutStreamsTotal - 1; 264 265 for (NumBindPairs) 266 { 267 UINT64 InIndex; 268 UINT64 OutIndex; 269 } 270 271 NumPackedStreams = NumInStreamsTotal - NumBindPairs; 272 if (NumPackedStreams > 1) 273 for(NumPackedStreams) 274 { 275 UINT64 Index; 276 }; 277 278 279 280 281 Coders Info 282 ~~~~~~~~~~~ 283 284 BYTE NID::kUnPackInfo (0x07) 285 286 287 BYTE NID::kFolder (0x0B) 288 UINT64 NumFolders 289 BYTE External 290 switch(External) 291 { 292 case 0: 293 Folders[NumFolders] 294 case 1: 295 UINT64 DataStreamIndex 296 } 297 298 299 BYTE ID::kCodersUnPackSize (0x0C) 300 for(Folders) 301 for(Folder.NumOutStreams) 302 UINT64 UnPackSize; 303 304 305 [] 306 BYTE NID::kCRC (0x0A) 307 UnPackDigests[NumFolders] 308 [] 309 310 311 312 BYTE NID::kEnd 313 314 315 316 SubStreams Info 317 ~~~~~~~~~~~~~~ 318 BYTE NID::kSubStreamsInfo; (0x08) 319 320 [] 321 BYTE NID::kNumUnPackStream; (0x0D) 322 UINT64 NumUnPackStreamsInFolders[NumFolders]; 323 [] 324 325 326 [] 327 BYTE NID::kSize (0x09) 328 UINT64 UnPackSizes[] 329 [] 330 331 332 [] 333 BYTE NID::kCRC (0x0A) 334 Digests[Number of streams with unknown CRC] 335 [] 336 337 338 BYTE NID::kEnd 339 340 341 Streams Info 342 ~~~~~~~~~~~~ 343 344 [] 345 PackInfo 346 [] 347 348 349 [] 350 CodersInfo 351 [] 352 353 354 [] 355 SubStreamsInfo 356 [] 357 358 BYTE NID::kEnd 359 360 361 FilesInfo 362 ~~~~~~~~~ 363 BYTE NID::kFilesInfo; (0x05) 364 UINT64 NumFiles 365 366 for (;;) 367 { 368 BYTE PropertyType; 369 if (aType == 0) 370 break; 371 372 UINT64 Size; 373 374 switch(PropertyType) 375 { 376 kEmptyStream: (0x0E) 377 for(NumFiles) 378 BIT IsEmptyStream 379 380 kEmptyFile: (0x0F) 381 for(EmptyStreams) 382 BIT IsEmptyFile 383 384 kAnti: (0x10) 385 for(EmptyStreams) 386 BIT IsAntiFile 387 388 case kCTime: (0x12) 389 case kATime: (0x13) 390 case kMTime: (0x14) 391 BYTE AllAreDefined 392 if (AllAreDefined == 0) 393 { 394 for(NumFiles) 395 BIT TimeDefined 396 } 397 BYTE External; 398 if(External != 0) 399 UINT64 DataIndex 400 [] 401 for(Definded Items) 402 UINT64 Time 403 [] 404 405 kNames: (0x11) 406 BYTE External; 407 if(External != 0) 408 UINT64 DataIndex 409 [] 410 for(Files) 411 { 412 wchar_t Names[NameSize]; 413 wchar_t 0; 414 } 415 [] 416 417 kAttributes: (0x15) 418 BYTE AllAreDefined 419 if (AllAreDefined == 0) 420 { 421 for(NumFiles) 422 BIT AttributesAreDefined 423 } 424 BYTE External; 425 if(External != 0) 426 UINT64 DataIndex 427 [] 428 for(Definded Attributes) 429 UINT32 Attributes 430 [] 431 } 432 } 433 434 435 Header 436 ~~~~~~ 437 BYTE NID::kHeader (0x01) 438 439 [] 440 ArchiveProperties 441 [] 442 443 [] 444 BYTE NID::kAdditionalStreamsInfo; (0x03) 445 StreamsInfo 446 [] 447 448 [] 449 BYTE NID::kMainStreamsInfo; (0x04) 450 StreamsInfo 451 [] 452 453 [] 454 FilesInfo 455 [] 456 457 BYTE NID::kEnd 458 459 460 HeaderInfo 461 ~~~~~~~~~~ 462 [] 463 BYTE NID::kEncodedHeader; (0x17) 464 StreamsInfo for Encoded Header 465 [] 466 467 468 --- 469 End of document