Emitting :key_deleted when key is purged

[lsxliron]

• Now :key_deleted event is emitted when wither purging or deleting a key
• Moved operations module attributes to KV module for better readability

Fixes #156

[mmmries]

Do you think there will ever be a case where someone cares about the difference between delete vs purge? I don't use the KV functionality much, so I'm not sure about the semantics of this API

[mmmries]

I don't know go very well, but I think this bit of the go-client is exposing purge events separately from delete events? https://github.com/nats-io/nats.go/blob/9d4b227179d60d6996c32b4b889d4e325ee06f78/kv.go#L982-L989

[lsxliron]

@mmmries i just started using the KV so I’m not an expert. The end result is the same, the key is removed from the bucket (history stays when using del and removed when using purge).

However, when the watcher process starts, you will still get historical events for a key that was deleted but not for a key that was purged.

Edit
It shouldn’t be hard to add a purge event if needed though

[davydog187]

Suggested change

	headers
	|> Enum.filter(fn {k, v} ->
	k == @operation_header and (v == @operation_del or v == @operation_purge)
	end)
	|> length() > 0
	Enum.any?(headers, fn {k, v} ->
	k == @operation_header and (v == @operation_del or v == @operation_purge)
	end)

In practice this probably isn't a huge issue as written since the size of headers is probably small, but this is equivalent. At worst it makes a full pass once, at best it short-circuits early

[davydog187]

Suggested change

	headers
	|> Enum.filter(fn {k, v} ->
	k == @operation_header and (v == @operation_del or v == @operation_purge)
	end)
	|> length() > 0
	Enum.any?(headers, fn {k, v} ->
	k == @operation_header and (v == @operation_del or v == @operation_purge)
	end)

In practice this probably isn't a huge issue as written since the size of headers is probably small, but this is equivalent. At worst it makes a full pass once, at best it short-circuits early

[davydog187]

Suggested change

	@spec is_delete_operation?(headers :: Gnat.headers()) :: boolean()
	def is_delete_operation?(headers) do
	@spec delete_operation?(headers :: Gnat.headers()) :: boolean()
	def delete_operation?(headers) do

As an Elixir convention, using the ? is correct for a function that returns a boolean, but the is_ prefix is reserved for guards. See https://hexdocs.pm/elixir/naming-conventions.html#trailing-question-mark-foo