Magick::Image::write outputs empty files on Windows

[joankaradimov]

My environment is:

JRuby 9.1.10.0 through 9.1.15.0 Java 8 Windows 10

I initially encountered this using jnormington/dotdiff. After some debugging I came up with a straightforward way to reproduce it in a jirb. Here's what a reproduction looks like:

irb(main):001:0> require 'rmagick'
=> true
irb(main):002:0> image = Magick::Image.read('C:\somewhere\in.png').first
=> #<Magick::Image:0x5c7933ad @image=#<Java::Magick4j::MagickImage:0x57bc27f5>>
irb(main):003:0> image.write('C:\somewhere\out1.png')
=> #<Magick::Image:0x5c7933ad @image=#<Java::Magick4j::MagickImage:0x57bc27f5>>

At this point the file C:\somewhere\out1.png gets generated and it's empty.

What is interesting is that this works correctly:

irb(main):004:0> File.open('C:\somewhere\out2.png', 'wb') { |file| file.write(image.to_blob) }
=> 1654

Both of these end up calling MagickImage::writeImage. So I am assuming that the problem is somewhere in MagickImage::write. I don't have a fix for this, but the obvious workaround is to monkeypatch the write method:

module Magick
  class Image
    def write(file, &add)
      File.open(file, 'wb') { |file| file.write(to_blob) }
      self
    end
  end
end

... still a proper fix would be welcome.

[Serabe]

This project is unmaintained, though PRs are welcome.

[Serabe]

Quite likely, the problem is here https://github.com/Serabe/RMagick4J/blob/master/Magick4J/src/magick4j/MagickImage.java#L988-L995

Cannot test in a Windows machine.

The thing is there is a behaviour for settings filetype with a prefix of type jpeg:filename, so it is taking C as a filetype.

A fix is not trivial.

[joankaradimov]

This project is unmaintained, though PRs are welcome.

Thanks for taking the time to answer even though this is no longer maintained.

Quite likely, the problem is here

Yes, I think I see the problem.

I won't have the time now, but I am definitely interested in writing the fix and doing a PR. Maybe you can keep the issue open for now.