Dispute spam protection (#4134)

* Mostly notes.

* Better error messages.

* Introduce Fatal/NonFatal + drop back channel participation

- Fatal/NonFatal - in order to make it easier to use utility functions.
- We drop the back channel in dispute participation as it won't be
needed any more.

* Better error messages.

* Utility function for receiving `CandidateEvent`s.

* Ordering module typechecks.

* cargo fmt

* Prepare spam slots module.

* Implement SpamSlots mechanism.

* Implement queues.

* cargo fmt

* Participation.

* Participation taking shape.

* Finish participation.

* cargo fmt

* Cleanup.

* WIP: Cleanup + Integration.

* Make `RollingSessionWindow` initialized by default.

* Make approval voting typecheck.

* Get rid of lazy_static & fix approval voting tests

* Move `SessionWindowSize` to node primitives.

* Implement dispute coordinator initialization.

* cargo fmt

* Make queues return error instead of boolean.

* Initialized: WIP

* Introduce chain api for getting finalized block.

* Fix ordering to only prune candidates on finalized events.

* Pruning of old sessions in spam slots.

* New import logic.

* Make everything typecheck.

* Fix warnings.

* Get rid of obsolete dispute-participation.

* Fixes.

* Add back accidentelly deleted Cargo.lock

* Deliver disputes in an ordered fashion.

* Add module docs for errors

* Use type synonym.

* hidden docs.

* Fix overseer tests.

* Ordering provider taking `CandidateReceipt`.

... To be kicked on one next commit.

* Fix ordering to use relay_parent

as included block is not unique per candidate.

* Add comment in ordering.rs.

* Take care of duplicate entries in queues.

* Better spam slots.

* Review remarks + docs.

* Fix db tests.

* Participation tests.

* Also scrape votes on first leaf for good measure.

* Make tests typecheck.

* Spelling.

* Only participate in actual disputes, not on every import.

* Don't account backing votes to spam slots.

* Fix more tests.

* Don't participate if we don't have keys.

* Fix tests, typos and warnings.

* Fix merge error.

* Spelling fixes.

* Add missing docs.

* Queue tests.

* More tests.

* Add metrics + don't short circuit import.

* Basic test for ordering provider.

* Import fix.

* Remove dead link.

* One more dead link.

Co-authored-by: Lldenaurois <Ljdenaurois@gmail.com>

polkadot/node/primitives/src/lib.rs

@@ -65,12 +65,6 @@ pub const VALIDATION_CODE_BOMB_LIMIT: usize = (MAX_CODE_SIZE * 4u32) as usize;
 /// The bomb limit for decompressing PoV blobs.
 pub const POV_BOMB_LIMIT: usize = (MAX_POV_SIZE * 4u32) as usize;
 
-/// It would be nice to draw this from the chain state, but we have no tools for it right now.
-/// On Polkadot this is 1 day, and on Kusama it's 6 hours.
-///
-/// Number of sessions we want to consider in disputes.
-pub const DISPUTE_WINDOW: SessionIndex = 6;
-
 /// The amount of time to spend on execution during backing.
 pub const BACKING_EXECUTION_TIMEOUT: Duration = Duration::from_secs(2);
 
@@ -82,6 +76,59 @@ pub const BACKING_EXECUTION_TIMEOUT: Duration = Duration::from_secs(2);
 /// dispute participants.
 pub const APPROVAL_EXECUTION_TIMEOUT: Duration = Duration::from_secs(6);
 
+/// Type of a session window size.
+///
+/// We are not using `NonZeroU32` here because `expect` and `unwrap` are not yet const, so global
+/// constants of `SessionWindowSize` would require `lazy_static` in that case.
+///
+/// See: https://github.com/rust-lang/rust/issues/67441
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub struct SessionWindowSize(SessionIndex);
+
+#[macro_export]
+/// Create a new checked `SessionWindowSize`
+///
+/// which cannot be 0.
+macro_rules! new_session_window_size {
+	(0) => {
+		compile_error!("Must be non zero");
+	};
+	(0_u32) => {
+		compile_error!("Must be non zero");
+	};
+	(0 as u32) => {
+		compile_error!("Must be non zero");
+	};
+	(0 as _) => {
+		compile_error!("Must be non zero");
+	};
+	($l:literal) => {
+		SessionWindowSize::unchecked_new($l as _)
+	};
+}
+
+/// It would be nice to draw this from the chain state, but we have no tools for it right now.
+/// On Polkadot this is 1 day, and on Kusama it's 6 hours.
+///
+/// Number of sessions we want to consider in disputes.
+pub const DISPUTE_WINDOW: SessionWindowSize = new_session_window_size!(6);
+
+impl SessionWindowSize {
+	/// Get the value as `SessionIndex` for doing comparisons with those.
+	pub fn get(self) -> SessionIndex {
+		self.0
+	}
+
+	/// Helper function for `new_session_window_size`.
+	///
+	/// Don't use it. The only reason it is public, is because otherwise the
+	/// `new_session_window_size` macro would not work outside of this module.
+	#[doc(hidden)]
+	pub const fn unchecked_new(size: SessionIndex) -> Self {
+		Self(size)
+	}
+}
+
 /// The cumulative weight of a block in a fork-choice rule.
 pub type BlockWeight = u32;