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7z Format description (2.30 Beta 25)
-----------------------------------
This file contains description of 7z archive format.
7z archive can contain files compressed with any method.
See "Methods.txt" for description for defined compressing methods.
Format structure Overview
-------------------------
Some fields can be optional.
Archive structure
~~~~~~~~~~~~~~~~~
SignatureHeader
[PackedStreams]
[PackedStreamsForHeaders]
[
Header
or
{
Packed Header
HeaderInfo
}
]
Header structure
~~~~~~~~~~~~~~~~
{
ArchiveProperties
AdditionalStreams
{
PackInfo
{
PackPos
NumPackStreams
Sizes[NumPackStreams]
CRCs[NumPackStreams]
}
CodersInfo
{
NumFolders
Folders[NumFolders]
{
NumCoders
CodersInfo[NumCoders]
{
ID
NumInStreams;
NumOutStreams;
PropertiesSize
Properties[PropertiesSize]
}
NumBindPairs
BindPairsInfo[NumBindPairs]
{
InIndex;
OutIndex;
}
PackedIndices
}
UnPackSize[Folders][Folders.NumOutstreams]
CRCs[NumFolders]
}
SubStreamsInfo
{
NumUnPackStreamsInFolders[NumFolders];
UnPackSizes[]
CRCs[]
}
}
MainStreamsInfo
{
(Same as in AdditionalStreams)
}
FilesInfo
{
NumFiles
Properties[]
{
ID
Size
Data
}
}
}
HeaderInfo structure
~~~~~~~~~~~~~~~~~~~~
{
(Same as in AdditionalStreams)
}
Notes about Notation and encoding
---------------------------------
7z uses little endian encoding.
7z archive format has optional headers that are marked as
[]
Header
[]
REAL_UINT64 means real UINT64.
UINT64 means real UINT64 encoded with the following scheme:
Size of encoding sequence depends from first byte:
First_Byte Extra_Bytes Value
(binary)
0xxxxxxx : ( xxxxxxx )
10xxxxxx BYTE y[1] : ( xxxxxx << (8 * 1)) + y
110xxxxx BYTE y[2] : ( xxxxx << (8 * 2)) + y
...
1111110x BYTE y[6] : ( x << (8 * 6)) + y
11111110 BYTE y[7] : y
11111111 BYTE y[8] : y
Property IDs
------------
0x00 = kEnd,
0x01 = kHeader,
0x02 = kArchiveProperties,
0x03 = kAdditionalStreamsInfo,
0x04 = kMainStreamsInfo,
0x05 = kFilesInfo,
0x06 = kPackInfo,
0x07 = kUnPackInfo,
0x08 = kSubStreamsInfo,
0x09 = kSize,
0x0A = kCRC,
0x0B = kFolder,
0x0C = kCodersUnPackSize,
0x0D = kNumUnPackStream,
0x0E = kEmptyStream,
0x0F = kEmptyFile,
0x10 = kAnti,
0x11 = kName,
0x12 = kCreationTime,
0x13 = kLastAccessTime,
0x14 = kLastWriteTime,
0x15 = kWinAttributes,
0x16 = kComment,
0x17 = kEncodedHeader,
7z format headers
-----------------
SignatureHeader
~~~~~~~~~~~~~~~
BYTE kSignature[6] = {'7', 'z', 0xBC, 0xAF, 0x27, 0x1C};
ArchiveVersion
{
BYTE Major; // now = 0
BYTE Minor; // now = 2
};
UINT32 StartHeaderCRC;
StartHeader
{
REAL_UINT64 NextHeaderOffset
REAL_UINT64 NextHeaderSize
UINT32 NextHeaderCRC
}
...........................
ArchiveProperties
~~~~~~~~~~~~~~~~~
BYTE NID::kArchiveProperties (0x02)
for (;;)
{
BYTE PropertyType;
if (aType == 0)
break;
UINT64 PropertySize;
BYTE PropertyData[PropertySize];
}
Digests (NumStreams)
~~~~~~~~~~~~~~~~~~~~~
BYTE AllAreDefined
if (AllAreDefined == 0)
{
for(NumStreams)
BIT Defined
}
UINT32 CRCs[NumDefined]
PackInfo
~~~~~~~~~~~~
BYTE NID::kPackInfo (0x06)
UINT64 PackPos
UINT64 NumPackStreams
[]
BYTE NID::kSize (0x09)
UINT64 PackSizes[NumPackStreams]
[]
[]
BYTE NID::kCRC (0x0A)
PackStreamDigests[NumPackStreams]
[]
BYTE NID::kEnd
Folder
~~~~~~
UINT64 NumCoders;
for (NumCoders)
{
BYTE
{
0:3 DecompressionMethod.IDSize
4:
0 - IsSimple
1 - Is not simple
5:
0 - No Attributes
1 - There Are Attributes
7:
0 - Last Method in Alternative_Method_List
1 - There are more alternative methods
}
BYTE DecompressionMethod.ID[DecompressionMethod.IDSize]
if (!IsSimple)
{
UINT64 NumInStreams;
UINT64 NumOutStreams;
}
if (DecompressionMethod[0] != 0)
{
UINT64 PropertiesSize
BYTE Properties[PropertiesSize]
}
}
NumBindPairs = NumOutStreamsTotal - 1;
for (NumBindPairs)
{
UINT64 InIndex;
UINT64 OutIndex;
}
NumPackedStreams = NumInStreamsTotal - NumBindPairs;
if (NumPackedStreams > 1)
for(NumPackedStreams)
{
UINT64 Index;
};
Coders Info
~~~~~~~~~~~
BYTE NID::kUnPackInfo (0x07)
BYTE NID::kFolder (0x0B)
UINT64 NumFolders
BYTE External
switch(External)
{
case 0:
Folders[NumFolders]
case 1:
UINT64 DataStreamIndex
}
BYTE ID::kCodersUnPackSize (0x0C)
for(Folders)
for(Folder.NumOutStreams)
UINT64 UnPackSize;
[]
BYTE NID::kCRC (0x0A)
UnPackDigests[NumFolders]
[]
BYTE NID::kEnd
SubStreams Info
~~~~~~~~~~~~~~
BYTE NID::kSubStreamsInfo; (0x08)
[]
BYTE NID::kNumUnPackStream; (0x0D)
UINT64 NumUnPackStreamsInFolders[NumFolders];
[]
[]
BYTE NID::kSize (0x09)
UINT64 UnPackSizes[]
[]
[]
BYTE NID::kCRC (0x0A)
Digests[Number of streams with unknown CRC]
[]
BYTE NID::kEnd
Streams Info
~~~~~~~~~~~~
[]
PackInfo
[]
[]
CodersInfo
[]
[]
SubStreamsInfo
[]
BYTE NID::kEnd
FilesInfo
~~~~~~~~~
BYTE NID::kFilesInfo; (0x05)
UINT64 NumFiles
for (;;)
{
BYTE PropertyType;
if (aType == 0)
break;
UINT64 Size;
switch(PropertyType)
{
kEmptyStream: (0x0E)
for(NumFiles)
BIT IsEmptyStream
kEmptyFile: (0x0F)
for(EmptyStreams)
BIT IsEmptyFile
kAnti: (0x10)
for(EmptyStreams)
BIT IsAntiFile
case kCreationTime: (0x12)
case kLastAccessTime: (0x13)
case kLastWriteTime: (0x14)
BYTE AllAreDefined
if (AllAreDefined == 0)
{
for(NumFiles)
BIT TimeDefined
}
BYTE External;
if(External != 0)
UINT64 DataIndex
[]
for(Definded Items)
UINT32 Time
[]
kNames: (0x11)
BYTE External;
if(External != 0)
UINT64 DataIndex
[]
for(Files)
{
wchar_t Names[NameSize];
wchar_t 0;
}
[]
kAttributes: (0x15)
BYTE AllAreDefined
if (AllAreDefined == 0)
{
for(NumFiles)
BIT AttributesAreDefined
}
BYTE External;
if(External != 0)
UINT64 DataIndex
[]
for(Definded Attributes)
UINT32 Attributes
[]
}
}
Header
~~~~~~
BYTE NID::kHeader (0x01)
[]
ArchiveProperties
[]
[]
BYTE NID::kAdditionalStreamsInfo; (0x03)
StreamsInfo
[]
[]
BYTE NID::kMainStreamsInfo; (0x04)
StreamsInfo
[]
[]
FilesInfo
[]
BYTE NID::kEnd
HeaderInfo
~~~~~~~~~~
[]
BYTE NID::kEncodedHeader; (0x17)
StreamsInfo for Encoded Header
[]
---
End of document