Gitlab Target Reconciliation

[puffitos]

Motivation

Addresses #30.

Changes

This PR introduces two new Interfaces:

• TargetManager: this serves as a handler for the GlobalTargets struct. It is responsible for updating the local globalTargets state of the Sparrow, by periodically getting the new targets and also registering the Sparrow as a GlobalTarget in the configured remote backend. The TargetManager should also be able to return the current state (AKA the list of GlobalTargets).

• Gitlab: this is an Interface to handle the interaction with the Gitlab API (mostly the Files API of Gitlab). Its responsiblities are to get the current globalTargets from a remote gitlab repository and update the file containing the registration of the Sparrow itself. The next step is implementing a DeleteFile function to handle de-registration.

The implementation of those interfaces handle the interaction of the Sparrow with the remote Gitlab repository holding all the targets.

Tests done

• A buttload of unittests for almost all functions.
• I've tested the file creation and update via cURL, no real E2E tests done yet, to see if the sparrow works.

Concerns

We still need to handle where the config for the TargetManager should be parsed. Currently, we need the base gitlab URL, the project ID (could be merged into one variable) and the gitlab token to access the repo. Also, some durations:

• check interval for new targets
• registration interval (how often to update own registration)
• unhealthy interval (when to ignore a global target - maybe we could even remove this and "dumb down" our Sparrow.

The PutFile, PostFile and FetchFiles functions are similar, which introduce some code duplication. As those functions won't need to be updated significantly for the foreseeable future, we can just refactor them some time down the line to reduce the codebase and simplify testing and usage of the Gitlab interface. A solution would be to use a builder Pattern (`Gitlab().Files().List(), Gitlab().Files().Get("filename") and so on), a la k8s go-client.

TODO

• I've assigned this PR to myself
• I've labeled this PR correctly
• Build and run the sparrow locally to test whether it all really works :)

[puffitos]

1300 lines added. It's all tests and some repetitive and hopefully easy to read code :)

[niklastreml]

LGTM, as discussed I'm going to ignore the hardcoded values, since config and docs will be added in a separate pr

[puffitos]

Did manual E2E testing. The instance can register and update itself:

• registration
• update

The sparrow is also sucessfully grabing the global targets (it-self included) from Gitlab:

{"time":"2023-12-15T15:23:48.106570143+01:00","level":"INFO","msg":"Successfully fetched all target files","sparrow":{"files":3}}
{"time":"2023-12-15T15:23:58.550772143+01:00","level":"INFO","msg":"Successfully fetched all target files","sparrow":{"files":3}}
{"time":"2023-12-15T15:24:09.118347133+01:00","level":"INFO","msg":"Successfully fetched all target files","sparrow":{"files":3}}
{"time":"2023-12-15T15:24:12.413958783+01:00","level":"INFO","msg":"Successfully updated registration"}

[lvlcn-t]

Just a few notes here and there, but LGTM overall. Great job!

[y-eight]

First review

[y-eight]

Well done @puffitos. Readability is on point

[y-eight]

The name (domain name) needs to be configurable as well

[puffitos]

Will resolve in separate Issue

[y-eight]

LGTM as discussed