Error when rendring in :egd (UndefinedFunctionError) function :zlib.crc32/2 is undefined or private

Questions / Help
, ,
1

Hi,

I am going through some tutorials, and I’m trying to generate an Identicon, but Im getting an error when trying to run the program. The program is compiling with no issues, but it looks like it errors when executing :egd.render(image) - when I comment it out there is no error. I had a look at the code and I cannot find anything wrong. EGD has been installed from the git repo.
Error:

09:55:06.606 [error] Process #PID<0.141.0> raised an exception
** (UndefinedFunctionError) function :zlib.crc32/2 is undefined or private
    :zlib.crc32(#Reference<0.1358207439.4254203912.140130>, <<73, 72, 68, 82, 0, 0, 0, 250, 0, 0, 0, 250, 8, 2, 0, 0, 0>>)
    (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd_png.erl:102: :egd_png.create_chunk/2
    (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd_png.erl:72: :egd_png.bitmap2png/4
    (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd_png.erl:62: :egd_png.binary/3
    (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd.erl:240: :egd.loop/1
** (EXIT from #PID<0.140.0>) shell process exited with reason: an exception was raised:
    ** (UndefinedFunctionError) function :zlib.crc32/2 is undefined or private
        :zlib.crc32(#Reference<0.1358207439.4254203912.140130>, <<73, 72, 68, 82, 0, 0, 0, 250, 0, 0, 0, 250, 8, 2, 0, 0, 0>>)
        (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd_png.erl:102: :egd_png.create_chunk/2
        (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd_png.erl:72: :egd_png.bitmap2png/4
        (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd_png.erl:62: :egd_png.binary/3
        (egd 0.10.0) d:/Dropbox/Projects/Programming/Elixir/maps/deps/egd/src/egd.erl:240: :egd.loop/1

Program:

defmodule Maps do
  def main(input) do
    input
    |> hashstring
    |> pick_color
    |> build_grid
    |> filter_odd
    |> build_pixel_map
    |> draw_image
    |> save_image(input)
  end

  def save_image(image, input) do
    File.write("#{input}.png", image)
  end

  def draw_image(%Identicon.Image{color: color, pixel_map: pixel_map}) do
    image = :egd.create(250, 250)
    fill = :egd.color(color)

    Enum.each pixel_map, fn({start, stop}) ->
      :egd.filledRectangle(image, start, stop, fill)
    end

    :egd.render(image)
  end

  def build_pixel_map(%Identicon.Image{grid: grid} = image) do
    pix_map = Enum.map grid, fn({_code, index}) ->
      horizontal = rem(index, 5) *50
      vertical = div(index, 5) *50

      top_left = {horizontal, vertical}
      bottom_right = {horizontal+50, vertical+50}

      {top_left, bottom_right}
    end

    %Identicon.Image{image | pixel_map: pix_map}
  end

  def filter_odd(%Identicon.Image{grid: grid} = image) do
    grid = Enum.filter grid, fn({code, _index}) ->
      rem(code, 2) == 0
    end

    %Identicon.Image{image | grid: grid}
  end

  def build_grid(%Identicon.Image{hex: hex}= image) do
    grid =
      hex
      |> Enum.chunk_every(3, 2, :discard)
      |> Enum.map(&mirror_row/1)
      |> List.flatten
      |> Enum.with_index

    %Identicon.Image{image | grid: grid}
  end

  def mirror_row(row) do
    # [123, 34, 22]
    [first, second | _tail] = row

    # [123, 34, 22, 34, 123]
    row ++ [second, first]
  end

  def pick_color(%Identicon.Image{hex: [red, green, blue | _tail]} = image) do
    %Identicon.Image{image | color: {red, green, blue}}
  end

  def hashstring(string) do
    hex =  :crypto.hash(:md5, string)
    |> :binary.bin_to_list

    %Identicon.Image{hex: hex}
  end
end
'''
Struct:

defmodule Identicon.Image do
defstruct hex: nil, color: nil, grid: nil, pixel_map: nil
end


Thanks.

The :egd
2

Hi @polovy !

I believe the issue you’re facing is due to the fact that the :egd library uses zlib:crc32/2, but that was removed in Erlang/OTP 27. Can you confirm this is a version you’re using (via elixir --version)?

Your code seems to be working as intended when an older version of Erlang/OTP is used, as those versions still retain zlib:crc32/2.

If you “just” want to run your code to see that it is working, you can downgrade your version of Erlang/OTP to below 27. Otherwise, you’ll need to look into either patching the :egd library to use the built-in :erlang.crc32/1, or to look for other ways to perform this part of the job :egd is doing for you.

1 Like
3

It is indeed Erlang/OTP 27. As you can see from the code I’m calling sunctions and I dont quite see why those functions would call zlib:crc32/2. I’m not calling it explicitly, byt I’m calling :egd.render which seams to be using the zlib. I’m not sure why this would be.

In any case I may downgrade to test the code, as I’ve not yet the level of expertise to patch or look for other solutions.

Thanks.

4

I really like the Grider Elixir course on Udemy and there’s a reasonably easy (if not best practices) way around this if you’ve got OTP27 on your machine.

You can change your deps to refer directly to the local copy of EGD, and then change the one line that calls zlib:crc32:

In mix.exs, change {:egd, github: "erlang/egd"} to {:egd, path: "deps/egd"}.

In your project directory (probably identicon), run a mix deps.compile.

Then find deps/egd/src/dgd_png.erl and change Crc = zlib:crc32(Z,Bin), to Crc = erlang:crc32(Bin).

I’ll see about getting a PR opened against EGD when I can figure out how to get the test suite to run properly.

1 Like