Class: Omnizip::Formats::Tar::Header

Inherits:
Object
  • Object
show all
Includes:
Constants
Defined in:
lib/omnizip/formats/tar/header.rb

Overview

TAR header parser (POSIX ustar format)

Handles reading and writing 512-byte TAR headers

Constant Summary

Constants included from Constants

Constants::BLOCK_SIZE, Constants::CHECKSUM_OFFSET, Constants::CHECKSUM_SIZE, Constants::DEVMAJOR_OFFSET, Constants::DEVMAJOR_SIZE, Constants::DEVMINOR_OFFSET, Constants::DEVMINOR_SIZE, Constants::GID_OFFSET, Constants::GID_SIZE, Constants::GNAME_OFFSET, Constants::GNAME_SIZE, Constants::HEADER_SIZE, Constants::LINKNAME_OFFSET, Constants::LINKNAME_SIZE, Constants::MAGIC_OFFSET, Constants::MAGIC_SIZE, Constants::MAX_FILE_SIZE, Constants::MODE_OFFSET, Constants::MODE_SIZE, Constants::MTIME_OFFSET, Constants::MTIME_SIZE, Constants::NAME_OFFSET, Constants::NAME_SIZE, Constants::PREFIX_OFFSET, Constants::PREFIX_SIZE, Constants::SIZE_OFFSET, Constants::SIZE_SIZE, Constants::TYPEFLAG_OFFSET, Constants::TYPEFLAG_SIZE, Constants::TYPE_BLOCK_DEVICE, Constants::TYPE_CHAR_DEVICE, Constants::TYPE_CONTIGUOUS, Constants::TYPE_DIRECTORY, Constants::TYPE_EXTENDED, Constants::TYPE_FIFO, Constants::TYPE_GLOBAL_EXTENDED, Constants::TYPE_GNU_LONGLINK, Constants::TYPE_GNU_LONGNAME, Constants::TYPE_HARD_LINK, Constants::TYPE_REGULAR, Constants::TYPE_SYMLINK, Constants::UID_OFFSET, Constants::UID_SIZE, Constants::UNAME_OFFSET, Constants::UNAME_SIZE, Constants::USTAR_MAGIC, Constants::USTAR_VERSION, Constants::VERSION_OFFSET, Constants::VERSION_SIZE

Class Method Summary collapse

Class Method Details

.build(entry) ⇒ String

Build a TAR header from an entry

Parameters:

  • entry (Entry) —

    Entry to build header for

Returns:

  • (String) —

    512 bytes of header data



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# File 'lib/omnizip/formats/tar/header.rb', line 68

def self.build(entry)
  header = "\0" * HEADER_SIZE

  # Write fields to header
  write_string(header, entry.name, NAME_OFFSET, NAME_SIZE)
  write_octal(header, entry.mode, MODE_OFFSET, MODE_SIZE)
  write_octal(header, entry.uid, UID_OFFSET, UID_SIZE)
  write_octal(header, entry.gid, GID_OFFSET, GID_SIZE)
  write_octal(header, entry.size, SIZE_OFFSET, SIZE_SIZE)
  write_octal(
    header, entry.mtime.to_i, MTIME_OFFSET, MTIME_SIZE
  )
  header[TYPEFLAG_OFFSET] = entry.typeflag || TYPE_REGULAR
  write_string(header, entry.linkname, LINKNAME_OFFSET, LINKNAME_SIZE)

  # Write ustar magic and version
  write_string(header, USTAR_MAGIC, MAGIC_OFFSET, MAGIC_SIZE)
  write_string(header, USTAR_VERSION, VERSION_OFFSET, VERSION_SIZE)
  write_string(header, entry.uname, UNAME_OFFSET, UNAME_SIZE)
  write_string(header, entry.gname, GNAME_OFFSET, GNAME_SIZE)
  write_octal(header, entry.devmajor, DEVMAJOR_OFFSET, DEVMAJOR_SIZE)
  write_octal(header, entry.devminor, DEVMINOR_OFFSET, DEVMINOR_SIZE)
  write_string(header, entry.prefix, PREFIX_OFFSET, PREFIX_SIZE)

  # Calculate and write checksum
  checksum = Entry.calculate_checksum(header)
  write_octal(header, checksum, CHECKSUM_OFFSET, CHECKSUM_SIZE)

  header
end

.parse(header_data) ⇒ Entry?

Parse a TAR header from binary data

Parameters:

  • header_data (String) —

    512 bytes of header data

Returns:

  • (Entry, nil) —

    Parsed entry or nil if end of archive



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# File 'lib/omnizip/formats/tar/header.rb', line 16

def self.parse(header_data)
  return nil if header_data.nil? || header_data.bytesize < HEADER_SIZE
  return nil if all_zeros?(header_data)

  entry = Entry.new("")

  # Extract fields from header
  entry.name = extract_string(header_data, NAME_OFFSET, NAME_SIZE)
  entry.mode = extract_octal(header_data, MODE_OFFSET, MODE_SIZE)
  entry.uid = extract_octal(header_data, UID_OFFSET, UID_SIZE)
  entry.gid = extract_octal(header_data, GID_OFFSET, GID_SIZE)
  entry.size = extract_octal(header_data, SIZE_OFFSET, SIZE_SIZE)
  entry.mtime = Time.at(
    extract_octal(header_data, MTIME_OFFSET, MTIME_SIZE),
  )
  entry.typeflag = header_data[TYPEFLAG_OFFSET]
  entry.linkname = extract_string(
    header_data, LINKNAME_OFFSET, LINKNAME_SIZE
  )

  # Check for ustar format
  magic = extract_string(header_data, MAGIC_OFFSET, MAGIC_SIZE)
  if magic == USTAR_MAGIC
    entry.uname = extract_string(header_data, UNAME_OFFSET, UNAME_SIZE)
    entry.gname = extract_string(header_data, GNAME_OFFSET, GNAME_SIZE)
    entry.devmajor = extract_octal(
      header_data, DEVMAJOR_OFFSET, DEVMAJOR_SIZE
    )
    entry.devminor = extract_octal(
      header_data, DEVMINOR_OFFSET, DEVMINOR_SIZE
    )
    entry.prefix = extract_string(
      header_data, PREFIX_OFFSET, PREFIX_SIZE
    )
  end

  # Verify checksum
  checksum = extract_octal(
    header_data, CHECKSUM_OFFSET, CHECKSUM_SIZE
  )
  calculated = Entry.calculate_checksum(header_data)
  unless checksum == calculated
    raise Error, "TAR header checksum mismatch"
  end

  entry
end