Class: Kaitai::Struct::SubIO

Inherits:
Object
  • Object
show all
Defined in:
lib/kaitai/struct/struct.rb

Overview

Substream IO implementation: a IO object which wraps existing IO object and provides similar byte/bytes reading functionality, but only for a limited set of bytes starting from specified offset and spanning up to specified length.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(parent_io, parent_start, size) ⇒ SubIO

Returns a new instance of SubIO.



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# File 'lib/kaitai/struct/struct.rb', line 618

def initialize(parent_io, parent_start, size)
  @parent_io = parent_io
  @parent_start = parent_start
  @size = size
  @pos = 0
  @closed = false
end

Instance Attribute Details

#parent_io ⇒ Object (readonly)

Parent IO object that this substream is projecting data from.



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# File 'lib/kaitai/struct/struct.rb', line 602

def parent_io
  @parent_io
end

#parent_start ⇒ Object (readonly)

Offset of start of substream in coordinates of parent stream. In coordinates of substream itself start will be always 0.



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# File 'lib/kaitai/struct/struct.rb', line 607

def parent_start
  @parent_start
end

#pos ⇒ Object (readonly)

Current position in a substream. Independent from a position in a parent IO.



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# File 'lib/kaitai/struct/struct.rb', line 616

def pos
  @pos
end

#size ⇒ Object (readonly)

Size of substream in bytes.



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# File 'lib/kaitai/struct/struct.rb', line 611

def size
  @size
end

Instance Method Details

#close ⇒ Object 



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# File 'lib/kaitai/struct/struct.rb', line 701

def close
  @closed = true
  nil
end

#closed? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/kaitai/struct/struct.rb', line 706

def closed?
  @closed
end

#eof? ⇒ Boolean

Returns:

  • (Boolean)

Raises:

  • (IOError) 


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# File 'lib/kaitai/struct/struct.rb', line 626

def eof?
  raise IOError.new('not opened for reading') if @closed

  @pos >= @size
end

#getc ⇒ Object

Raises:

  • (IOError) 


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# File 'lib/kaitai/struct/struct.rb', line 642

def getc
  raise IOError.new('not opened for reading') if @closed

  return nil if @pos >= @size

  # remember position in parent IO
  old_pos = @parent_io.pos
  @parent_io.seek(@parent_start + @pos)
  begin
    res = @parent_io.getc
    @pos += 1
  ensure
    # restore position in parent IO
    @parent_io.seek(old_pos)
  end

  res
end

#read(len = nil) ⇒ Object

Raises:

  • (IOError) 


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# File 'lib/kaitai/struct/struct.rb', line 661

def read(len = nil)
  raise IOError.new('not opened for reading') if @closed

  # read until the end of substream
  if len.nil?
    len = @size - @pos
    return String.new if len <= 0
  elsif len.respond_to?(:to_int)
    len = len.to_int
    # special case for requesting exactly 0 bytes
    return String.new if len == 0

    if len > 0
      # cap intent to read if going beyond substream boundary
      left = @size - @pos

      # if actually requested reading and we're beyond the boundary, return nil
      return nil if left <= 0

      # otherwise, still return something, but less than requested
      len = left if len > left
    end
  end

  # remember position in parent IO
  old_pos = @parent_io.pos

  @parent_io.seek(@parent_start + @pos)
  begin
    res = @parent_io.read(len)
    read_len = res.bytesize
    @pos += read_len
  ensure
    # restore position in parent IO
    @parent_io.seek(old_pos)
  end

  res
end

#seek(offset, whence = IO::SEEK_SET) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/kaitai/struct/struct.rb', line 632

def seek(offset, whence = IO::SEEK_SET)
  raise ArgumentError.new('only IO::SEEK_SET is supported by SubIO#seek') unless whence == IO::SEEK_SET

  offset = Internal.num2long(offset)
  raise IOError.new('closed stream') if @closed
  raise Errno::EINVAL if offset < 0
  @pos = offset.to_int
  return 0
end