ffdev-info/signature-development-utility

Max Offset and Variable

Opened this issue · 4 comments

gleporeNARA commented

Should it be possible to assign a Signature Anchor as Variable, and also assign a Max Offset? It does not seem to work, the Max Offset value is only written to the XML file when the Anchor is Beginning of File or End of File.

In other words, how would I say "find this fragment somewhere in the first 500 bytes of the file"? Would that be Beginning of File, Max Offset of 500?

My understanding is that Beginning of File is absolutely tied to the very first bytes of the file.

Thanks.

ross-spencer commented

Hi @gleporeNARA it's not possible within the utility - and I was pretty sure DROID couldn't handle that, but maybe @richardlehane can confirm whether Siegfried can?

I can't recall if there's a technical limitation here (performance maybe?) or it's just the way DROID was first written? It would be fairly easy to write a signature file to specify this too if it was desired.

Also, there should be some references somewhere about this, but I had a quick look at the droid-list and droid repo and couldn't find anything initially. We also used to have a mailing list on Sourceforge for DROID but (one of my regrets is) i think it was removed before it was archived. (We live and learn). The information may have been there. I'll keep pondering.

richardlehane commented

to say "find this fragment somewhere in the first 500 bytes of the file" I think you should use a Beginning of File anchor with a max offset of 500.

@ross-spencer : I think your utility should re-label the "offset" field to "min offset" as that is more accurate. Could you also just hide the offset fields if Variable is selected as the anchor?

richardlehane commented

Droid 6 technical documentation is linked from here: https://github.com/digital-preservation/droid/wiki

ross-spencer commented

I think your utility should re-label the "offset" field to "min offset" as that is more accurate.

👍

Could you also just hide the offset fields if Variable is selected as the anchor?

That's a really nice idea. It would help guide folks a little more as well. I've some maintenance work to do on this, including adding the technical docs above to the UI - I'll try wrapping that in!