[Xamarin.Android.Build.Tasks] Fix issues with Library Resource Extraction

[dellis1972]

Since the switch to System.IO.Compression we have a few
issues when dealing with resource extraction.

1. It was not ignoring __MACOSX or .DS_Store during extraction.
2. It was not correctly detecting duplicate zip entries.

This commit updates the code to correctly filter __MACOSX and
.DS_Store entries. It also changes the way we check if an entry
exists in the zip already. And finally it updates
ResolveLibraryProjectImports to use the Files.ExtractAll method.
This is because the standard ZipFile.ExtractToDirectory has no
way of filtering the output (so it includes __MACOSX and .DS_Store).

[jonpryor]

I don't understand how the previous check was "bad", and I'm not fond of the new check as it's locale-sensitive.

The commit message mentions that files named _MACOSX weren't ignored, but this new check still won't support that, as __ != _ -- the .Contains() check is looking for two underscores, not one, just as it originally did, so _MACOSX will still be processed.

Or is the problem that entry.FullName contains directory information, so it could be foo/bar/_MACOSX? If so, then the _MACOSX check should presumably follow the .DS_Store check and use .EndsWith() with StringComparison.OrdinalIgnoreCase.

[jonpryor]

If entry.FullName does contain path information, is the directory separator char at all normalized? The problem with the updated logic is that it'll process my-file.ds_store, which doesn't seem at all correct. Perhaps this should instead check for entry.FullName.EndsWith("/.DS_Store", StringComparison.OrdinalIgnoreCase)?

[dellis1972]

The _MACOSX stuff appears like

'foo/bar/_MACOSX/.classes.jar'

hence the use of Contains :(

[jonpryor]

On the one hand, I'm wrong in saying that .Contains() is locale-sensitive. It isn't:

This method performs an ordinal (case-sensitive and culture-insensitive) comparison

Alas, that means it's case sensitive. Hopefully that won't break anything.

That said, it'll accept with some_file_name_that_contains_MACOSX.class, so if you happen to have some resource that you want that contains _MACOSX, you're screwed.

I would thus suggest two checks for _MACOSX, for a total of three:

if (entry.FullName.Contains ("/__MACOSX/") ||
        entry.FullName.EndsWith ("/__MACOSX", StringComparison.OrdinalIgnoreCase)) ||
        entry.FullName.EndsWith ("/.DS_Store", StringComparison.OrdinalIgnoreCase)))
    continue;

Additionally, the commit message should be updated to use two _s to be consistent with the code.