problem details in modules

[kliushnichenko]

While was working on problem details support in validation modules the general concept a bit changed.
Enabling the ProblemDetailsHandler moved to the hocon configuration.

1. It greatly simplifies the integration of problem details in modules. Modules can now detect if ProblemDetailsHandler is enabled at an early stage of the module initiation. With the previous approach, it would have been much harder and might have led to implementing awkward solutions.

2. An additional benefit of the new approach is that ProblemDetailsHandler will be automatically registered as the last handler in the error handlers chain, so dev no longer need to worry about that.

So, to enable ProblemDetailsHandler the next config now required:

problem.details {
  enable: true
  muteCodes: [401, 106]
  muteTypes: ['com.example.MyException']
}

@jknack pls share your thoughts, if you are Ok with the new approach I'll continue with docs update and some minor improvements

[jknack]

I have fixed feelings. I like it but then is like we need to add the a new property in Jooby class isn't wrong but wonder if we could do it using an Extension + install call

install(new ProblemsDetailsModule());

Once installed take care of configure everything. The issue here is how to integrate with other error handler like validation

[kliushnichenko]

Just for clarity, there is no new property in Jooby class, just a helper method that reads the config. We can move this helper to any other place, all it needs is access to the config.

Regarding module

install(new ProblemsDetailsModule());

If a new module only sets the same hocon config as it is now(just code-driven approach) it will work. But this module should always be registered before validation modules.

If the module should also register the handler error(new ProblemDetailsHandler()), that's the issue.
Because the global handler should be the last in the chain. Even if we made this module lateinit=true it will fix one issue (global err handler now registered the last), but we introduce another issue - the config properties are set too late, and validation modules won't detect that ProblemDetails is enabled.
So, the last option is to move the detection of ProblemDetails in validation modules to the stage when the first error is thrown - I believe this is the worst option. That's why I ended up with a hocon config.

[jknack]

@kliushnichenko thanks for explaining let's proceed with documentation.

[kliushnichenko]

docs and some minor improvements added.
The major change is the removal of a type property in custom problem errors. Since JSON Pointer spec clearly defines how to point to the whole document(a "" pointer). Ready to merge

[jknack]

rename to from and let's add javadoc

[jknack]

cool

[jknack]

just few minor changes