Class: FormatParser::ZIPParser::FileReader

Inherits:

Object

Object
FormatParser::ZIPParser::FileReader

show all

Defined in:: lib/parsers/zip_parser/file_reader.rb

Overview

A very barebones ZIP file reader

Defined Under Namespace

Classes: ZipEntry

Constant Summary collapse

Error =

Class.new(StandardError)

ReadError =

Class.new(Error)

UnsupportedFeature =

Class.new(Error)

InvalidStructure =

Class.new(Error)

LocalHeaderPending =

Class.new(Error) do
  def message
    'The compressed data offset is not available (local header has not been read)'
  end
end

MissingEOCD =

Class.new(Error) do
  def message
    'Could not find the EOCD signature in the buffer - maybe a malformed ZIP file'
  end
end

Instance Method Summary collapse

#read_zip_structure(io:) ⇒ Array<ZipEntry>

Parse an IO handle to a ZIP archive into an array of Entry objects.
#zip?(io) ⇒ Boolean

Tells whether the given IO is likely to be a ZIP file without performing too many detailed reads.

Instance Method Details

#read_zip_structure(io:) ⇒ `Array<ZipEntry>`

Parse an IO handle to a ZIP archive into an array of Entry objects.

Parameters:

io (#tell, #seek, #read, #size) —

an IO-ish object

Returns:

(Array<ZipEntry>) —

an array of entries within the ZIP being parsed

# File 'lib/parsers/zip_parser/file_reader.rb', line 159

def read_zip_structure(io:)
  zip_file_size = io.size
  eocd_offset = get_eocd_offset(io, zip_file_size)
  zip64_end_of_cdir_location = get_zip64_eocd_location(io, eocd_offset)
  num_files, cdir_location, cdir_size =
    if zip64_end_of_cdir_location
      num_files_and_central_directory_offset_zip64(io, zip64_end_of_cdir_location)
    else
      num_files_and_central_directory_offset(io, eocd_offset)
    end

  log { format('Located the central directory start at %d', cdir_location) }
  seek(io, cdir_location)

  # In zip_tricks we read the entire central directory _and_ enything behind it.
  # Strictly speaking, we should be able to read `cdir_size` bytes and not a byte more.
  # BUT! in format_parser we avoid unbounded reads, as a matter of fact they are forbidden.
  # So we will again limit ouselves to cdir_size, and we will take cushion of 1 KB.
  central_directory_str = io.read(cdir_size + 1024)
  central_directory_io = StringIO.new(central_directory_str)
  log do
    format(
      'Read %d bytes with central directory + EOCD record and locator',
      central_directory_str.bytesize)
  end

  entries = (0...num_files).map do |entry_n|
    offset_location = cdir_location + central_directory_io.pos
    log do
      format(
        'Reading the central directory entry %d starting at offset %d',
        entry_n, offset_location)
    end
    read_cdir_entry(central_directory_io)
  end

  entries
end

#zip?(io) ⇒ `Boolean`

Tells whether the given IO is likely to be a ZIP file without performing too many detailed reads