Class: File

Inherits:
Object show all
Defined in:
lib/epitools/core_ext/file.rb

Instance Method Summary collapse

Instance Method Details

#reverse_each(&block) ⇒ Object

A streaming ‘reverse_each` implementation. (For large files, it’s faster and uses less memory.)



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# File 'lib/epitools/core_ext/file.rb', line 13

def reverse_each(&block)
  return to_enum(:reverse_each) unless block_given?

  seek_end
  reverse_each_from_current_pos(&block)
end

#reverse_each_from_current_pos {|fragment| ... } ⇒ Object

Read each line of file backwards (from the current position.)

Yields:

  • (fragment) 


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# File 'lib/epitools/core_ext/file.rb', line 54

def reverse_each_from_current_pos
  return to_enum(:reverse_each_from_current_pos) unless block_given?

  # read the rest of the current line, in case we started in the middle of a line
  start_pos = pos
  fragment = readline rescue ""
  seek(start_pos)

  while data = reverse_read(4096)
    lines = data.each_line.to_a
    lines.last << fragment unless lines.last[-1] == "\n"

    fragment = lines.first

    lines[1..-1].reverse_each { |line| yield line }
  end

  yield fragment
end

#reverse_read(length, block_aligned = false) ⇒ Object

Read the previous ‘length` bytes. After the read, `pos` will be at the beginning of the region that you just read. Returns `nil` when the beginning of the file is reached.

If the ‘block_aligned` argument is `true`, reads will always be aligned to file positions which are multiples of 512 bytes. (This should increase performance slightly.)



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# File 'lib/epitools/core_ext/file.rb', line 27

def reverse_read(length, block_aligned=false)
  raise "length must be a multiple of 512" if block_aligned and length % 512 != 0

  end_pos = pos
  return nil if end_pos == 0

  if block_aligned
    misalignment = end_pos % length
    length      += misalignment
  end

  if length >= end_pos # this read will take us to the beginning of the file
    seek(0)
  else
    seek(-length, IO::SEEK_CUR)
  end

  start_pos = pos
  data      = read(end_pos - start_pos)
  seek(start_pos)

  data
end

#reverse_readline ⇒ Object

Read the previous line (leaving ‘pos` at the beginning of the string that was read.)

Raises:



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# File 'lib/epitools/core_ext/file.rb', line 91

def reverse_readline
  raise BOFError.new("beginning of file reached") if pos == 0

  seek_backwards_to("\n", 512, -2)
  new_pos = pos
  data = readline
  seek(new_pos)
  data
end

#seek_backwards_to(string, blocksize = 512, rindex_end = -1)) ⇒ Object

Scan backwards in the file until ‘string` is found, and set the IO’s pos to the first character after the matched string.



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# File 'lib/epitools/core_ext/file.rb', line 104

def seek_backwards_to(string, blocksize=512, rindex_end=-1)
  loop do
    data = reverse_read(blocksize)

    if index = data.rindex(string, rindex_end)
      seek(index+string.size, IO::SEEK_CUR)
      break
    elsif pos == 0
      break
    end
  end
end

#seek_end ⇒ Object

Seek to ‘EOF`



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# File 'lib/epitools/core_ext/file.rb', line 77

def seek_end
  seek(0, IO::SEEK_END)
end

#seek_start ⇒ Object

Seek to ‘BOF`



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# File 'lib/epitools/core_ext/file.rb', line 84

def seek_start
  seek(0)
end