[luatex] Prevent stop when tiff file loads

[Reinhard Kotucha]

On 2016-01-21 at 18:08:32 +0100, Patrick Gundlach wrote:

 > Hello all,
 > 
 > I am using LuaTeX 0.79.1 and use
 > 
 >     local foo = img.scan({filename = "foo.tiff"})
 > 
 > but this fails with 
 > 
 > !LuaTeX error: internal error: unknown image type (2)
 >  ==> Fatal error occurred, no output PDF file produced!
 > 
 > 
 > Is there a way to prevent LuaTeX from stopping the whole process? Is there a function like 
 > 
 > can_you_handle_this_imagetype(filename="foo.tiff")

Luigi suggested to mimic file(1).  Since the number of graphic file
formats supported by pdftex/luatex is quite small I'm wondering
whether img.scan() can't check itself whether the magic number is
appropriate and return false otherwise.

Then one could write

  local foo = img.scan({filename = "foo.tiff"})

  if foo then
    ...
  end

Regards,
  Reinhard

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