[Feature] Session caching

[x1unix]

Changelog

• Introduced caching
  • Added built-in file cache using SessionFileCache
  • Session lifetime supported
  • Custom cache support by implementing SessionAbstractCache interface
• Added client builder as client setup facade. Used with cache.

Checks

API

• [x] Abstract cache interface
• [x] File system cache
• [x] Client builder

Unit tests

• [x] File cache
• [x] Client builder

Example

cache := zabbix.NewSessionFileCache().SetFilePath("./zabbix_session")
session, err := zabbix.CreateClient("http://zabbix/api_jsonrpc.php").
    WithCache(cache).
    WithCredentials("Admin", "zabbix").
    Connect()

fmt.Printf("Connected to Zabbix API v%s", session.Version())

SessionBuilder.Connect() will check the cache for cached sessions. If a valid cached session exists - it will provide it, otherwize will connect to Zabbix and will save a session (if cache was provided).

[x1unix]

@cavaliercoder, thank you for adding me as a repo collaborator!

Can you review this PR, please? This PR is huge and introduces some new API's and approaches.

[cavaliercoder]

You're welcome! Your last few PRs have been really helpful, and I am so slow at responding. Hopefully the community will get value from you being able to fix things faster.

[cavaliercoder]

Thanks for putting the time into this, and running it by me. I'm pretty happy with the session caching logic, but I think the API could maybe be made a little simpler. There are quite a few moving parts for the developer to understand.

Could you achieve the same outcome with two functions, Session.Save(cachePath) and RestoreSession(cachePath, maxAge). So, for the caller:

session, err := zabbix.RestoreSession(cachePath, maxAge)
if err == zabbix.ErrNoSession { // file not found or expired, etc.
    session, err = zabbix.NewSession(.......).WithCache(cachePath)
}
if err != nil {
    // handle
}

WithCache could simple wrap Session.Save and return the underlying session.

I'm not married to the above code - just an example - but I'm keen to avoid introducing new types that might not be needed, like SessionFileCache, SessionAbstractCache, ClientBuilder, etc.

I'd also recommend decoupling file modified date from the session start date. There are other reasons the file date could change and it could break your cache. You could store the session date in the file?

Great feature!

[x1unix]

@cavaliercoder, thank you for the feedback. I've introduced an external session builder to single responsibility principle and to provide a simpler API for custom caching.

It might have some logic overhead (I was inspired by Java approach 😄 ) and might be improved in future.

The default file system cache introduced more as a PoC demo than a production solution, but thank you for the feedback again!

[cavaliercoder]

I suspected .Net actually, but Java has very similar idioms! 🤣Go tends to take a more minimalist approach, with all the associated tradeoffs. Thanks for approaching this so thoughtfully.