[luatex] Prevent stop when tiff file loads

[luigi scarso]

On Sat, Jan 23, 2016 at 12:23 AM, Hans Hagen <pragma at wxs.nl> wrote:

> Hi Patrick,
>
> In practice, identifying all image files formats (tiff, png, pdf...)
>>> *should* work with the first 4 bytes of the file (they were designed this
>>> way).
>>>
>>
>> I think I'll go that way, but I still wish (feature request) that LuaTeX
>> does not fail with a fatal error if an unknown file format is encountered,
>> instead it would be nice to have something like "return nil, errormessage".
>>
>
> In addition to L's remark ...
>
> Concerning img in luatex: when an image is needed (can be a delayed
> action) the backend will create objects that keep some states (e.g.
> requirements and later identified properties). Then at some point there is
> some checking of filename and preamble, then when it's a known format the
> datastructures are checked .. at any point luatex can quit on error
> (recovering is no option due to the many dependencies or maybe overflows).
> For instance changing the error in a warning (i tested it to be sure)
> aborts luatex.
>
> Now, we could reshuffle code of course (and for instance check first) but
> then we have a chicken-egg issue: we have callbacks for locating files and
> these can decide to choose for instance to report back a jpg instead of a
> gif when present. Think of:
>
> - scan requested
>   - image objects made (anchored in other backend mechanisms)
>   - image scan happens
>     - file is looked up based on info stored in object (1)
>     - when known type detailed scan happens (2)
>     - extended object is available
>    - a valid object is required (contains partially parsed image data +
> properties now)
>
> moving 1 up in the chain could probably work but then we still can't be
> too sure about success later on anyway where we still would need to abort
> the run.
>
> Anyway, I made a catch for an unknown type but beware: you need to check
> the dimensions (zero) in order to figure out that was ignored. Basically an
> image object is still present but with zero dimensions (after all it was
> not scanned).
>
> From the upcoming 0.89 manual:
>
> You can use \type {pdf.setignoreunknownimages(1)} (or at the \TEX\ end
> the \type {\pdfvariable} \type {ignoreunknownimages}) to get around a
> quit when no known image type is found (based on name or preamble).
> Beware: this will not catch invalid images and we cannot guarantee side
> effects. A zero dimension image is still included when requested. No
> special flags are set. A proper workflow will not rely in such a catch
> but make sure that images are valid.
>
> (Fwiw: personally i'd not rely on such a catch in a workflow.)




on trunk now.
-- 
luigi
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