get_value(Vips::META_LOADER) fails for gif files

[raimondasv]

Might be the issue with libvips, still, reporting it here. We are using Vips::META_LOADER property to detect file types and correct Content-Type header. Unfortunately, it fails for gifs.

require 'vips'

gif = Vips::Image.new_from_file('image.gif')
puts gif.get_value(Vips::META_LOADER)

produces

.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/ruby-vips-1.0.3/lib/vips/image.rb:699:in `get_value': Field vips-loader not found. (Vips::Error)
	from gif.rb:4:in `<main>'

Gif loader is present in the system and Gif files can be loaded and manipulated. Just accessing vips-loader header value fails.

Same code for jpegs:

require 'vips'

gif = Vips::Image.new_from_file('image.jpg')
puts gif.get_value(Vips::META_LOADER)

produces

jpegload

Maybe there are different means to detect image formats?

[jcupitt]

Hi, I agree, this looks like a libvips bug. I'll have a look.

[jcupitt]

OK, working for me now:

$ irb
irb(main):001:0> require 'vips'
=> true
irb(main):002:0> x = Vips::Image.new_from_file "walk.gif"
=> #<Vips::Image:0x55bfd4bf3e90 ptr=0x55bfd4bb2010>
irb(main):003:0> x.get_value Vips::META_LOADER
=> "gifload"

Thank you for reporting this dumbness!

I'll try to think of a workaround for you in the meantime.

[raimondasv]

Amazing, @jcupitt thank you for doing this!

[jcupitt]

Looks like you can call vips_foreign_find_load() directly:

http://www.vips.ecs.soton.ac.uk/supported/current/doc/html/libvips/VipsForeignSave.html#vips-foreign-find-load

irb(main):001:0> require 'vips'
=> true
irb(main):009:0> Vips::Foreign.find_load("/home/john/pics/k2.jpg")
=> "VipsForeignLoadJpegFile"
irb(main):011:0> Vips::Foreign.find_load("/home/john/pics/walk.gif")
=> "VipsForeignLoadGifFile"

It gives you the canonical name of the loader class rather than the nickname, but it's obvious what it means. It should work on your libvips. There's Vips::Foreign.find_load_buffer() as well, which will sniff the image type from a string.

[raimondasv]

👍

I've tried to avoid this because new_from_buffer would do detection again, no? However, the overhead seems to be small, so we are going to use Vips::Foreign.find_load_buffer for now and later update to and use get_value(Vips::META_LOADER)

[jcupitt]

Yes, it'll detect again, but detection is mostly quick. If you build your libvips without magick support and without support for things like openslide (very slow detection), it should be fast enough, I'd think.

[jcupitt]

I'll close, I think this is done.