Packmatic.Field.Central.FileHeader (Packmatic v2.0.0)

Represents the Central Directory File Header, which is part of the Central Directory at the end of the archive.

The Central Directory is emitted after all successfully encoded files have been incorporated into the Zip stream. It contains one Central Directory File Header for each encoded file and a single End of Central Directory record.

Structure

Central Directory File Header

Size	Content
4 bytes	Signature
1 byte	Version made by - Zip Specification Version
1 byte	Version made by - Environment
2 bytes	Version needed to extract
2 bytes	General Purpose Flag
2 bytes	Compression Method (0 = No Compression; 8 = Deflated)
2 bytes	Modification Time (DOS Format)
2 bytes	Modification Date (DOS Format)
4 bytes	Checksum (CRC-32)
4 bytes	Compressed Size (Placeholder to force Zip64)
4 bytes	Original Size (Placeholder to force Zip64)
2 bytes	File Path Length (Bytes)
2 bytes	Extra Fields Length (Bytes)
2 bytes	File Comment Length (Bytes)
2 bytes	Starting Disk Number for File
2 bytes	Internal Attrbutes
4 bytes	External Attrbutes
4 bytes	Offset of Local File Header (Placeholder to force Zip64)
Variable	File Path
Variable	Extra Fields
Variable	File Comment

Notes

The General Purpose Flag has the following bits set.
- Bit 3: Indicating a Streaming Archive; Data Descriptor is used, and the Local File Header has no Size or CRC information.
- Bit 11: Language encoding flag, indicating that the Filename and Comment are both already in UTF-8. As per APPNOTE, the presence of this flag obviates the need to emit a separate Info-ZIP Unicode Path Extra Field.
The Compressed Size and Original Size fields are both 4-byte fields, meaning the maximum value is 0xFF 0xFF 0xFF 0xFF in case of overflow, however we will not use these fields, because the Zip version 4.5 is already required, which implies that the client must support Zip64. The real sizes are always set again in the Zip64 Extended Information Extra Field, which uses 8-byte fields, as provided by Packmatic.Field.Shared.ExtendedInformation.
If the Entry has both the UID and GID attributes set then this will be emitted in an Extra Field, otherwise said field will not be emitted.
The following Extra Fields are emitted:
- Extended Timestamp, see Packmatic.Field.Shared.ExtendedTimestamp
- Zip64 Extended Information, see Packmatic.Field.Shared.ExtendedInformation
- UNIX UID/GID Information, see Packmatic.Field.Shared.Unix
File comments are not emitted by Packmatic.

Summary

Types

t()

Types

t()

@type t() :: %Packmatic.Field.Central.FileHeader{
  attributes: Packmatic.Manifest.Entry.Attributes.t(),
  checksum: non_neg_integer(),
  method: Packmatic.Manifest.Entry.method(),
  offset: non_neg_integer(),
  path: Path.t(),
  size: non_neg_integer(),
  size_compressed: non_neg_integer(),
  timestamp: DateTime.t()
}