Method listing supported "foreign" extensions

[aleksandrs-ledovskis]

This is a feature request.

Would it be possible to add class method to Vips that would return an array of supported file formats akin to $ vips -l foreign does? Having such introspection would allow to programmatically decide if for example Vips supports any given format for transformation operation.

If there already exists a way how to get list of Vips' supported extensions, I'm all ears.

[jcupitt]

Hello @aleksandrs-ledovskis,

You can do this now, though it's a little painful. Have a look at:

https://github.com/libvips/ruby-vips/blob/master/lib/vips/image.rb#L1341

The generate_yard method that makes the ruby-vips docs.

You would use GObject::g_type_from_name("VipsForeign") to get the GType for the base class of the file load/save operations (it's just an int), then walk all the subclasses recursively with Vips::vips_type_map looking for non-abstract types. You can instantiate an object of that type and get the text description, a list of the arguments, and the properties of each argument.

You can get things like supported suffixes too, though you'd need to add a little more ffi for that.

[aleksandrs-ledovskis]

Spent some time digging in ruby-vips/libvips and managed to get some PoC code

require "vips"
require "set"

module Vips
  attach_function :vips_class_find, [:string, :string], :pointer
  attach_function :vips_object_summary_class, [:pointer, :pointer], :void

  class BufStruct < FFI::Struct
    layout :base, :pointer,
           :mx, :int,
           :i, :int,
           :full, :bool,
           :lasti, :int,
           :dynamic, :bool
  end
end

nicknames = []

generate_class = lambda do |gtype, _|
  nickname = Vips.nickname_find(gtype)
  nicknames << nickname if nickname

  Vips.vips_type_map(gtype, generate_class, nil)
end

generate_class.call(
  GObject.g_type_from_name("VipsForeign"),
  nil
)

extensions = Set.new

nicknames.each do |nickname|
  foreign_class = Vips.vips_class_find("VipsForeignLoad", nickname)
  next if foreign_class.null?

  buf_struct = Vips::BufStruct.new
  buf_struct_string = FFI::MemoryPointer.new(:char, 2048)
  buf_struct[:base] = buf_struct_string
  buf_struct[:mx] = 2048

  Vips.vips_object_summary_class(foreign_class, buf_struct.pointer)

  class_summary = buf_struct_string.read_string
  extensions.merge(class_summary.scan(/\.\w+\.?\w+/))
end

puts extensions

On my machine/libvips configuration outputs:

#<Set: {".csv", ".mat", ".vips", ".img", ".hdr", ".ppm", ".pgm", ".pbm", ".pfm", ".pdf", ".svg", ".svgz", ".svg.gz", ".gif", ".png", ".jpg", ".jpeg", ".jpe", ".webp", ".tif", ".tiff"}>

---

I couldn't make access to foreign_class->suffs work via FFI. There isn't existing ForeignClass mapping in ruby-vips and making a simplistic pointer-to-struct didn't work.

  class ForeignClassStruct < FFI::Struct
    layout :parent, GObject::GObject::Struct,
       :constructed, :int,
       :static_object, :int,
       :argument_table, :pointer,
       :nickname, :string,
       :description, :string,
       :preclose, :int,
       :close, :int,
       :postclose, :int,
       :local_memory, :size_t,
       :priority, :int,
       :chars, :pointer
  end

  # Junk
  ForeignClassStruct.new(Vips.vips_class_find("VipsForeignLoad", "pngload"))[:nickname]
  ForeignClassStruct.new(Vips.vips_class_find("VipsForeignLoad", "pngload"))[:priority]

[tomasc]

@aleksandrs-ledovskis I am using this method here through command-line:

https://github.com/tomasc/dragonfly_libvips/blob/master/lib/dragonfly_libvips.rb#L19

But indeed, would be great to have a method of ruby-vips that outputs such list.

[jcupitt]

I had a quick hack and added get_suffixes:

$ irb
irb(main):001:0> require 'vips'
=> true
irb(main):002:0> Vips::get_suffixes
=> [".csv", ".mat", ".v", ".vips", ".ppm", ".pgm", ".pbm", ".pfm", ".hdr", ".dz", ".png", ".jpg", ".jpeg", ".jpe", ".webp", ".tif", ".tiff", ".fits", ".fit", ".fts", ".nii", ".nii.gz", ".hdr.gz", ".img", ".img.gz", ".nia", ".nia.gz", ".heic", ".gif", ".bmp"]
irb(main):003:0> 

Does that look reasonable? I'll add some tests as well.

[tomasc]

Fabulous!

[aleksandrs-ledovskis]

@jcupitt I see that you are basing the output on VipsForeignSave. If I compare "save" vs. "load" class extensions, there are some differences (e.g. SVG/PDFs are only supported as input and BMP as output).

As I use Vips for image processing I would be (more) interested in seeing a way to determine what extensions can be processed by Vips at the intake for purpose of populating texts visible to end-user ("Please upload image in ".jpg", ".jpeg" or ".png" formats)/doing pre-emptive validations based on file name.

@tomasc's case also seems to require both "load" and "save" extensions.

[jcupitt]

Hi @aleksandrs-ledovskis, yes, that's true. libvips uses the suffix to pick savers, so there's a simple relationship between filetype and extension. But loaders are picked by sniffing the first few bytes of the file, so a list of extensions won't always be complete.

I tried swapping it for VipsForeignLoad and I see:

irb(main):004:0> Vips::get_suffixes
=> [".v", ".vips", ".ppm", ".pgm", ".pbm", ".pfm", ".png", ".exr", ".svs", ".vms", 
".vmu", ".ndpi", ".scn", ".mrxs", ".svslide", ".tif", ".bif", ".jpg", ".jpeg", ".jpe", 
".tiff", ".csv", ".pdf", ".svg", ".svgz", ".svg.gz", ".gif", ".mat", ".webp", ".img", 
".hdr", ".fits", ".fit", ".fts", ".nii", ".nii.gz", ".hdr.gz", ".img.gz", ".nia", ".nia.gz"]

I don't know how useful that is. It's missing .ico and .bmp; .jpg is there three times, etc.

If you want a list of the available loaders, just walking the types below VipsForeignLoad might be simpler.

(libvips will load BMP, btw)