1/4 TIFF processing simplification by 'shifting' base of random access reader

[don-vip]

This is the first step towards solving #278

Port of this commit: drewnoakes/metadata-extractor-dotnet@2281cea

[don-vip]

(not ready yet, I got test failures to fix)

[drewnoakes]

Looking good so far. The best way to validate correctness is to clone https://github.com/drewnoakes/metadata-extractor-images and run your updated code against all those files to check for regressions. It's not a process I've documented, sorry, so I can do that for you if you like, but doing it yourself would give you a tighter feedback loop.

[don-vip]

@drewnoakes thank you! I'll do it :) And probably create a PR to improve the documentation as well :)

[drewnoakes]

Here's an overview of the process.

• There is a .NET program here: https://github.com/drewnoakes/metadata-extractor-images/tree/master/src/dotnet
• It assumes you have sibling repositories for metadata-extractor, metadata-extractor-dotnet and metadata-extractor-images
• That .NET solution references the source from metadata-extractor-dotnet (here), so it'll build the .NET code as part of its build. You must currently manually build the Java code separately however.
• Running that .NET application will update all the metadata/*.txt files, and compute updated diffs.

[don-vip]

thank you! now the PR is ready for review :)

[drewnoakes]

Looks good! Thanks very much for these nicely structured PRs. It makes them very easy to review, which I appreciate.

I'm adding some comments with initial thoughts to your PRs. Don't feel you have to take any action on them, especially as changes to the first PR require rebasing other PRs etc. I'm going to pull down all your changes locally and try them out. I can make small tweaks in an additional commit at the end if needed. The comments on your PRs are just my notes and thoughts rather than requests of you.

[drewnoakes]

Suggested change

	extract(new ByteArrayReader(segmentBytes).withShiftedBaseOffset(JPEG_SEGMENT_PREAMBLE.length()), metadata);
	extract(new ByteArrayReader(segmentBytes, JPEG_SEGMENT_PREAMBLE.length()), metadata);