Use ZIO to manage Rudder result type

[fanf]

Ready for review!

The intersting part is com.normation.errors which defines the main error types for rudder, along with two main result types:

• PureResult[A] is a no effect result that can fail with a RudderError (for example because of business logic) or succeed with a A value. Under the hood it's a Either[RudderError, A].
• IOResult[A] is a value describing a result with effects that can fail with a RudderError (for ex because an exception happened. Under the hood, it's a ZIO[Any, RudderError, A].
  Plus theres some generic mapping from/to Option (notOptional), Box, and exceptions.

ZIO short presentation.

ZIO parameters

ZIO[R,E,A] =>

• R == context, it is always Any for now but can be use for method-level dependency injection (to do. A big one).
• E == error type. In our case, it's always a subtype of RudderError.
• A == the return value.

There is 2 alias of ZIO:

• IO[A] == ZIO[Any,Throwable,A] when your errors are exception (ie: java)
• UIO[A] == ZIO[Any,Nothin,A] for effectful programs that can't fail (for ex, Ssytem.currentTimeMillis neither fail).

And so IOResult[A] if one more alias.

Importing effectful code

ZIO has the very clean notion of importing an effectful code into a ZIO value. It is the clear limit between the two world, and the step you need to do each time you deal with effectuf (java) code.

I added a IORestult variant, so that we (almost) always use it to be consistant in our types.
Ex: val hello = IOResult.effect(println("hello!"))
You can also import an other effectful prog, for ex is some logic is needed:

val hello = IOResult.effectM {
  if(isAlice) IOResult.effect(println("hello Alice!")) 
  else Unexpected("it's not Alice!").fail
}

There is variant of IOResult.effect/effectM that takes an error message in case the imported code throws an exception. The message is used to build a RudderError.System(message, exception) error.

Combinators

There is a lot of wonderful combinators in ZIO. You can work as easely on the success value (map, etc) than on the error one (mapError, catchAll) or on both (fold, foldM). The xxxMvariant of these combinators tells that the arguments is also an effect (aZIO[R, E, A]`)

The most interesting ones for use are:

• ZIO.foreach: it's traverse, renamad. ZIO.foreach(iterable){ elt => doStuff(elt) } with doStuff:ZIO. The first errors stop the traversal.
• ZIO.bracket(get resources)(release resource)(use resource) which ensure that the resource release code is always executed whatever happen in use resource code. No more leak!

(... to be contnued...)

[ncharles]

sounds like an eager replace :)

[VinceMacBuche]

I can't find com.normation.errors package in code change through github UI ... I'll look in the branch directly

[VinceMacBuche]

OK ! found it here! webapp/sources/utils/src/main/scala/com/normation/ZioCommons.scala

[VinceMacBuche]

is.readAllBytes does not compile with Java8

[fanf]

Superseeded by #2218