sbctl bundle splash image should detect if it's a valid bitmap file

[Foxboron]

Currently we accept any file and it's not clear why the image isn't displayed. We should probably inspect the file and ensure it's valid before we include it.

Some details of the format can be found here.

https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/boot-screen-components#add-the-logo-to-the-bgrt

[igo95862]

Probably magick identify is a good tool for this.

[Foxboron]

I'd prefer if we managed to write some Go code for this :) I dislike shelling out for tools and this could either be it's own library, find something already implemented or we make it a thing in go-uefi.

https://github.com/Foxboron/go-uefi

[igo95862]

Go based BMP decoder/encoder:

https://pkg.go.dev/golang.org/x/image/bmp

I dislike shelling out for tools

I also dislike spawning processes when a complex output parser is required but image magick exact output can be specified which makes parsing trivial.

[igo95862]

@Foxboron what do you think about temporary solution with magick identify.

It can be an optional dependency. If its not found on the system when a warning will be printed that splash image could not be verified.

[Foxboron]

If we are only detecting the filetype pulling imagemagick is a bit much I think, we only really need to peek at 2 bytes in the file to see if it's a BMP (Example). But if you want to try and use more of the output to check towards the accepted image format then It's probably fine :)

[igo95862]

But if you want to try and use more of the output to check towards the accepted image format then It's probably fine

I will do that.

Imagemagick also verifies that the image is valid.

When should image check happen? In GenerateBundle ?

Should it instantly return error or just skip image?

[igo95862]

Maybe also check in bundle command?

[Foxboron]

I think we can just do a hard failure in the bundle command when there is a file passed there :) No need for one in GenerateBundle as we should probably assume the values have been validated.

[igo95862]

How should lack of image magick be handled? Maybe print a warning that image could not be verified but proceed?

[Foxboron]

If the file extension is not ".bmp" just say it can't be verified. Good enough I think

[igo95862]

I mean the magick command not the magic numbers.

[Foxboron]

Yep, I got that :) But a simple fil extension check if fine if imagemagick is not available I think.

[igo95862]

I made initial check function but it far from finished: https://github.com/igo95862/sbctl/commit/577c1828bd2f726bcd2096773d22fb7980f7379c