Files Info

This document specifies the FilesInfo structure that contains metadata for all entries in a 7z archive.

Overview

FilesInfo contains:

File and directory names
Empty stream/file markers
Anti-item markers (deletion)
Timestamps (creation, access, modification)
File attributes (Windows and Unix)
Comments (rarely used)

Structure

FilesInfo ::= 0x05 NumFiles Property* 0x00

NumFiles ::= NUMBER
Property ::= PropertyID Size PropertyData

Property Order

Properties MUST appear in ascending order by property ID:

Order	ID	Name	Description
1	0x0E	EmptyStream	Marks entries without data
2	0x0F	EmptyFile	Distinguishes empty files from directories
3	0x10	Anti	Marks deletion entries
4	0x11	Name	File/directory names
5	0x12	CTime	Creation time
6	0x13	ATime	Last access time
7	0x14	MTime	Last modification time
8	0x15	Attributes	Windows/Unix attributes
9	0x16	Comment	Archive comment
10	0x19	Dummy	Padding for alignment

EmptyStream Property (0x0E)

Marks entries that have no associated data stream.

EmptyStream ::= 0x0E Size BitField

Size ::= NUMBER  # Total byte count of data following this field (i.e., BitField only)
BitField ::= BYTE[(NumFiles + 7) / 8]

Size field semantics: The Size field specifies the number of bytes in the BitField that follows. For EmptyStream, this equals (NumFiles + 7) / 8. Readers MUST verify that Size matches the expected BitField length; mismatches indicate a corrupt or malformed archive.

Semantics:

Bit set = entry has no data (empty file or directory)
Bit clear = entry has data in SubStreamsInfo

Index mapping: Empty stream entries are skipped when indexing into SubStreamsInfo.

EmptyFile Property (0x0F)

Distinguishes empty files from directories among EmptyStream entries.

EmptyFile ::= 0x0F Size BitField

Only applies to entries where EmptyStream bit is set.

Semantics:

Bit set = empty file (0 bytes)
Bit clear = directory

BitField size: (NumEmptyStreams + 7) / 8

Anti Property (0x10)

Marks entries for deletion in incremental backups.

Anti ::= 0x10 Size BitField

Only applies to entries where EmptyStream bit is set.

Semantics:

Bit set = anti-item (delete this file/directory)
Bit clear = normal entry

Anti-items indicate that a previously archived file should be removed when applying the archive.

Extraction behavior: When extracting an archive containing anti-items:

If the target path exists, implementations SHOULD delete it (file or directory)
If the target path does not exist, implementations SHOULD ignore the anti-item (no error)
Implementations MAY prompt the user before deleting files
Directory anti-items SHOULD only delete empty directories; non-empty directories MAY be skipped with a warning

Security consideration: Anti-items can be used maliciously to delete files outside the intended extraction scope. Path validation (see [17-SECURITY](/7z/17-security)) MUST be applied to anti-item paths.

Name Property (0x11)

File and directory names.

Name ::= 0x11 Size External [DataIndex | Names]

External ::= BYTE  # 0x00 = inline, 0x01 = external
DataIndex ::= NUMBER
Names ::= Name[NumFiles]
Name ::= UTF16LE_Char* 0x0000

Encoding: UTF-16-LE with null terminator (2 zero bytes).

Path format:

Path separator: / (forward slash)
Paths MUST be relative (no leading /)
Paths MUST NOT contain .. components
Directory entries SHOULD end with /

Examples:

"file.txt"          →  66 00 69 00 6C 00 65 00 2E 00 74 00 78 00 74 00 00 00
"dir/"              →  64 00 69 00 72 00 2F 00 00 00
"dir/subfile.txt"   →  64 00 69 00 72 00 2F 00 73 00 ... 00 00

Time Properties (0x12, 0x13, 0x14)

Creation, access, and modification times.

TimeProperty ::= PropertyID Size AllAreDefined [BitField] External [DataIndex | Times]

PropertyID ::= 0x12 | 0x13 | 0x14
AllAreDefined ::= BYTE
External ::= BYTE
Times ::= FILETIME[NumDefined]
FILETIME ::= UINT64  # 100-nanosecond intervals since 1601-01-01

AllAreDefined:

0x01: All files have this time, no BitField
0x00: BitField indicates which files have times

External:

0x00: Times stored inline
0x01: Times stored in external stream

See [16-TIMESTAMPS-ATTRIBUTES](/7z/16-timestamps-attributes) for FILETIME details.

Attributes Property (0x15)

Windows and Unix file attributes.

Attributes ::= 0x15 Size AllAreDefined [BitField] External [DataIndex | Attrs]

Attrs ::= UINT32[NumDefined]

Attribute format:

Bits	Description
0-15	Windows attributes
16-31	Unix mode (when bit 15 set)

Windows attributes (bits 0-15):

Bit	Value	Name
0	0x0001	FILE_ATTRIBUTE_READONLY
1	0x0002	FILE_ATTRIBUTE_HIDDEN
2	0x0004	FILE_ATTRIBUTE_SYSTEM
4	0x0010	FILE_ATTRIBUTE_DIRECTORY
5	0x0020	FILE_ATTRIBUTE_ARCHIVE
10	0x0400	FILE_ATTRIBUTE_REPARSE_POINT
11	0x0800	FILE_ATTRIBUTE_COMPRESSED
15	0x8000	Unix extension flag

Unix mode (bits 16-31, when bit 15 set):

Bits	Mask	Description
16-18	0x0007 << 16	Other permissions (rwx)
19-21	0x0038 << 16	Group permissions
22-24	0x01C0 << 16	Owner permissions
25	0x0200 << 16	Sticky bit
26	0x0400 << 16	Set GID
27	0x0800 << 16	Set UID
28-31	0xF000 << 16	File type

Unix file types (bits 28-31):

Value	Type
0x1	FIFO
0x2	Character device
0x4	Directory
0x6	Block device
0x8	Regular file
0xA	Symbolic link
0xC	Socket

See [16-TIMESTAMPS-ATTRIBUTES](/7z/16-timestamps-attributes) for complete attribute details.

Comment Property (0x16)

Archive comment (rarely used).

Comment ::= 0x16 Size External [DataIndex | CommentText]
CommentText ::= UTF16LE_Char* 0x0000

Dummy Property (0x19)

Padding for alignment.

Dummy ::= 0x19 Size Zeros
Zeros ::= 0x00[Size]

Used to align subsequent data to word boundaries when needed.

Complete Example

Archive with 3 entries:

readme.txt (100 bytes)
src/ (directory)
src/main.rs (500 bytes)

05                      # FilesInfo
03                      # NumFiles = 3

0E                      # EmptyStream
  01                    # Size = 1
  40                    # BitField: 01000000 (entry 1 is empty)

0F                      # EmptyFile
  01                    # Size = 1
  00                    # BitField: 00000000 (not empty file, so directory)

11                      # Name
  36                    # Size = 54 bytes
  00                    # External = inline
  # "readme.txt\0"
  72 00 65 00 61 00 64 00 6D 00 65 00 2E 00 74 00 78 00 74 00 00 00
  # "src/\0"
  73 00 72 00 63 00 2F 00 00 00
  # "src/main.rs\0"
  73 00 72 00 63 00 2F 00 6D 00 61 00 69 00 6E 00 2E 00 72 00 73 00 00 00

14                      # MTime
  03                    # Size
  01                    # AllAreDefined = true
  00                    # External = inline
  # 3 FILETIME values (8 bytes each)
  00 80 3E D5 DE B1 9D 01  # readme.txt mtime
  00 80 3E D5 DE B1 9D 01  # src/ mtime
  00 80 3E D5 DE B1 9D 01  # src/main.rs mtime

15                      # Attributes
  0E                    # Size
  01                    # AllAreDefined = true
  00                    # External = inline
  20 00 00 00           # readme.txt: ARCHIVE
  10 00 00 00           # src/: DIRECTORY
  20 00 00 00           # src/main.rs: ARCHIVE

00                      # End FilesInfo

Entry Type Determination

To determine entry type:

function get_entry_type(file_index):
    is_empty_stream = empty_stream_bits[file_index]

    if not is_empty_stream:
        return FILE_WITH_DATA

    empty_stream_index = count_preceding_empty_streams(file_index)
    is_empty_file = empty_file_bits[empty_stream_index]
    is_anti = anti_bits[empty_stream_index]

    if is_anti:
        return ANTI_ITEM
    if is_empty_file:
        return EMPTY_FILE
    return DIRECTORY

Symbolic Links

Symbolic links are stored as:

EmptyStream = false (has data)
Data = link target path in UTF-8
Attributes = Unix symlink type (0xA000 in bits 28-31) OR Windows reparse point

See [16-TIMESTAMPS-ATTRIBUTES](/7z/16-timestamps-attributes) "Symbolic Links" section.

Validation

Implementations MUST verify:

Name uniqueness: Implementations MUST reject archives containing byte-identical duplicate paths. Additionally, on case-insensitive filesystems, implementations MUST reject archives where multiple entries would resolve to the same path after case normalization. On case-sensitive filesystems, paths differing only in case are permitted.
Path safety: No .. components or absolute paths
BitField sizes: Match expected number of entries
External indices: Reference valid streams
UTF-16 validity: Names are valid UTF-16

Files Info ​

Overview ​

Structure ​

Property Order ​

EmptyStream Property (0x0E) ​

EmptyFile Property (0x0F) ​

Anti Property (0x10) ​

Name Property (0x11) ​

Time Properties (0x12, 0x13, 0x14) ​

Attributes Property (0x15) ​

Comment Property (0x16) ​

Dummy Property (0x19) ​

Complete Example ​

Entry Type Determination ​

Symbolic Links ​

Validation ​

See Also ​

Files Info

Overview

Structure

Property Order

EmptyStream Property (0x0E)

EmptyFile Property (0x0F)

Anti Property (0x10)

Name Property (0x11)

Time Properties (0x12, 0x13, 0x14)

Attributes Property (0x15)

Comment Property (0x16)

Dummy Property (0x19)

Complete Example

Entry Type Determination

Symbolic Links

Validation

See Also