Helm from Java, Part 4

I’ve created a UML class diagram to help me decipher the main structures in the Go code of Helm around chart repositories and their related concepts:

For the most part I stayed true to UML notation.  Similarly-colored boxes are from the same source files:

• pkg/repo/repo.go: a source file dealing with RepoFile structures.
• pkg/repo/chartrepo.go: a source file dealing with ChartRepository and Entry structures.
• pkg/repo/index.go: a source file dealing with ChartVersion and IndexFile structures.

A few interesting things stand out here.

First, from a conceptual standpoint, a ChartRepository is basically a glorified wrapper around an IndexFile, which is, in turn, a glorified wrapper around a set of ChartVersions.  A ChartVersion, in turn, is also a Metadata, which is a gRPC/Protocol Buffers object you’ve seen before (I didn’t indicate that relationship here on this diagram, but probably should have).  ChartVersions are stored (well, should be stored) within their containing IndexFile sorted by their version.  Go maybe doesn’t have the same concept as Java’s sorted collections and Comparators, so there’s some additional sorting logic that really you don’t need in the IndexFile concept.

ChartRepository instances are notionally “stored” in a RepoFile, but really what the RepoFile stores is a “pointer” to a ChartRepository—a primary key, of sorts—called, confusingly, an Entry.  More confusingly, a ChartRepository refers to its identifying Entry as its Config!  But if you think of an Entry as a primary key of a ChartRepository you should do OK.  A RepoFile is basically a pile of Entry instances, so, again, notionally, a collection of ChartRepository pointers.  (There is some question about why this data structure permits duplicate Entry instances (i.e. with the same Name but different contents); see Helm issue #2606 for details.)

I’m in the process of translating this to Java, and I think the resulting object model is going to look a lot cleaner, while delivering the same functionality, and permitting alternate implementations of chart storage and discovery.  Stay tuned.

Advertisements