Class: ZPNG::Chunk

Inherits:
Object
  • Object
show all
Includes:
DeepCopyable
Defined in:
lib/zpng/chunk.rb,
lib/zpng/text_chunk.rb

Direct Known Subclasses

BMP::BmpPseudoChunk, CHRM, GAMA, IDAT, IEND, IHDR, PHYS, PLTE, SRGB, TIME, TRNS, TextChunk

Defined Under Namespace

Classes: CHRM, GAMA, IDAT, IEND, IHDR, ITXT, PHYS, PLTE, SRGB, TEXT, TIME, TRNS, ZTXT

Constant Summary collapse

KNOWN_TYPES = 
%w'IHDR PLTE IDAT IEND cHRM gAMA iCCP sBIT sRGB bKGD hIST tRNS pHYs sPLT tIME iTXt tEXt zTXt'
VALID_SIZE_RANGE = 
0..((2**31)-1)

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from DeepCopyable

#deep_copy

Constructor Details

#initialize(x = {}) ⇒ Chunk

Returns a new instance of Chunk.



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# File 'lib/zpng/chunk.rb', line 26

def initialize x = {}
  if x.respond_to?(:read)
    # IO
    @offset = x.tell
    @size, @type = x.read(8).unpack('Na4')
    begin
      @data = x.read(size)
    rescue Errno::EINVAL
      # TODO: show warning?
      @data = x.read if size > VALID_SIZE_RANGE.end
    end
    @crc         = x.read(4).to_s.unpack('N').first
  elsif x.respond_to?(:[])
    # Hash
    %w'size type data crc'.each do |k|
      instance_variable_set "@#{k}", x[k.to_sym]
    end
    if !@type && self.class.superclass == ZPNG::Chunk
      # guess @type from self class name, e.g. ZPNG::Chunk::IHDR => "IHDR"
      @type = self.class.to_s.split("::").last
    end
    if !@size && @data
      # guess @size from @data
      @size = @data.size
    end
  end
end

Instance Attribute Details

#crc ⇒ Object

Returns the value of attribute crc.



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# File 'lib/zpng/chunk.rb', line 3

def crc
  @crc
end

#data ⇒ Object

Returns the value of attribute data.



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# File 'lib/zpng/chunk.rb', line 3

def data
  @data
end

#idx ⇒ Object

Returns the value of attribute idx.



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# File 'lib/zpng/chunk.rb', line 3

def idx
  @idx
end

#offset ⇒ Object

Returns the value of attribute offset.



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# File 'lib/zpng/chunk.rb', line 3

def offset
  @offset
end

#size ⇒ Object

Returns the value of attribute size.



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# File 'lib/zpng/chunk.rb', line 3

def size
  @size
end

#type ⇒ Object

Returns the value of attribute type.



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# File 'lib/zpng/chunk.rb', line 3

def type
  @type
end

Class Method Details

.from_stream(io) ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 10

def self.from_stream io
  size, type = io.read(8).unpack('Na4')
  io.seek(-8,IO::SEEK_CUR)
  begin
    if const_defined?(type.upcase)
      klass = const_get(type.upcase)
      return klass.new(io)
    end
  rescue NameError
    # invalid chunk type?
  end
  # putting this out of rescue makes better non-confusing exception messages
  # if exception occurs somewhere in Chunk.new
  Chunk.new(io)
end

Instance Method Details

#check(checks = {type: true, crc: true, size: true}) ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 78

def check checks = {type: true, crc: true, size: true}
  checks.each do |check_type, check_mode|
    case check_type
    when :type
      return false if check_mode != KNOWN_TYPES.include?(self.type)
    when :crc
      return false if check_mode != crc_ok?
    when :size
      return false if check_mode != VALID_SIZE_RANGE.include?(self.size)
    end
  end
  true
end

#crc_ok? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zpng/chunk.rb', line 73

def crc_ok?
  expected_crc = Zlib.crc32(data, Zlib.crc32(type))
  expected_crc == crc
end

#export(fix_crc: true) ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 54

def export( fix_crc: true )
  @data = self.export_data # virtual
  @size = @data.size # XXX hmm.. is it always is?
  fix_crc! if fix_crc
  [@size,@type].pack('Na4') + @data + [@crc].pack('N')
end

#export_data ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 61

def export_data
  #STDERR.puts "[!] Chunk::#{type} must realize 'export_data' virtual method".yellow if @size != 0
  @data || ''
end

#fix_crc! ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 94

def fix_crc!
  @crc = Zlib.crc32(data, Zlib.crc32(type))
end

#inspect(verbosity = 10) ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 66

def inspect verbosity = 10
  size = @size ? sprintf("%6d",@size) : sprintf("%6s","???")
  crc  = @crc  ? sprintf("%08x",@crc) : sprintf("%8s","???")
  type = @type.to_s.gsub(/[^0-9a-z]/i){ |x| sprintf("\\x%02X",x.ord) }
  sprintf "<Chunk #%02d %4s size=%s, crc=%s >", idx.to_i, type, size, crc
end

#valid? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zpng/chunk.rb', line 92

def valid?; check; end