Contents

# frozen_string_literal: true

# A simple stateful class for keeping track of a CRC32 value through multiple writes
class ZipTricks::StreamCRC32
  BUFFER_SIZE = 1024 * 1024 * 5

  # Compute a CRC32 value from an IO object. The object should respond to `read` and `eof?`
  #
  # @param io[IO] the IO to read the data from
  # @return [Fixnum] the computed CRC32 value
  def self.from_io(io)
    crc = new
    crc << io.read(BUFFER_SIZE) until io.eof?
    crc.to_i
  end

  # Creates a new streaming CRC32 calculator
  def initialize
    @buf = StringIO.new
    @crc = Zlib.crc32('')
  end

  # Append data to the CRC32. Updates the contained CRC32 value in place.
  #
  # @param blob[String] the string to compute the CRC32 from
  # @return [self]
  def <<(blob)
    @buf << blob
    buf_flush if @buf.size > BUFFER_SIZE
    self
  end

  # Returns the CRC32 value computed so far
  #
  # @return [Fixnum] the updated CRC32 value for all the blobs so far
  def to_i
    buf_flush if @buf.size > 0
    @crc
  end

  # Appends a known CRC32 value to the current one, and combines the
  # contained CRC32 value in-place.
  #
  # @param crc32[Fixnum] the CRC32 value to append
  # @param blob_size[Fixnum] the size of the daata the `crc32` is computed from
  # @return [Fixnum] the updated CRC32 value for all the blobs so far
  def append(crc32, blob_size)
    buf_flush if @buf.size > 0
    @crc = Zlib.crc32_combine(@crc, crc32, blob_size)
  end

  private

  def buf_flush
    @crc = Zlib.crc32_combine(@crc, Zlib.crc32(@buf.string), @buf.size)
    @buf.truncate(0)
    @buf.rewind
  end
end

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
zip_tricks-4.5.2	lib/zip_tricks/stream_crc32.rb
zip_tricks-4.5.1	lib/zip_tricks/stream_crc32.rb