Use most up-to-date FileHandle APIs

[dfed]

When iOS 13 / tvOS 13 / watchOS 6 / macOS 10.15 were released, Apple deprecated the readData(ofLength:) and the write(_:) methods, but did not replace them with any new documented methods. The only available, non-deprecated replacements for these methods were __readDataUp(toLength:) and __write(_:, error:), but neither were documented.

Then in iOS 13.4 / tvOS 13.4 / watchOS 6.2 / macOS 10.15.4 Apple fixed their mistake, introducing the APIs read(upToCount:) and write(contentsOf:). This PR adopts these newer methods.

It is expected that this PR will lower our code coverage, since we do not have CI running on iOS 13.0<=13.4 / tvOS 13.0<=13.4 / watchOS 6<=6.2 / macOS 10.15.0<=10.15.4

[codecov]

Codecov Report

Merging #74 (7e6962e) into main (26a1c97) will increase coverage by 2.47%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #74      +/-   ##
==========================================
+ Coverage   96.44%   98.92%   +2.47%     
==========================================
  Files          14       13       -1     
  Lines         591      556      -35     
==========================================
- Hits          570      550      -20     
+ Misses         21        6      -15     

Impacted Files	Coverage Δ
Sources/CacheAdvance/FileHandleExtensions.swift

[dfed]

Ignoring this file because due to limitations of Github Actions we can't test most of the branches in this file.

[bachand]

Can we add a comment to this effect?

[dfed]

done!

[bachand]

Can we add a comment to this effect?

[bachand]

It's interesting that the method both throws and returns a nullable result. I wonder how you could end up with nil? In any case, do you think we should throw our own error if the data is nil?

[dfed]

Oh we end up with nil when the data is empty. I tried throwing here instead of returning Data() and I broke a ton of tests. Returning Data() here preserves existing behavior.