Parachain auctions (#239)

* Slots module

* Integrate slots

* More drafting

* Minor updates

* Update parachains to use trati

* More build fixes

* Full code now compiles

* Add renew bid function

* Implement calculate_winner

* Warning remove

* Update gitignore

* Test framework

* Tests

* Further testing

* More tests, new parameterisation.

* Fix and new test

* Thread-safe tests

* Test off-boarding and a fix.

* Test onboarding

* Allow late onboarding.

* Another test and fix

* Avoid println in nostd

* Compact representation of paraids

* Introduce documentation.

* Introduce events.

* Additional test and fix

* Additional test

* Tidy up line lengths.

* Remove printlns

* Use later substrate utils.

* Fix build/test

* Make slots work with latest substrate

* Update runtime/src/slot_range.rs

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

* Update runtime/src/slots.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update runtime/src/slots.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Polish logic

* Rewind to earlier substrate master

* Remove dead code.

Cargo.lock

@@ -1362,10 +1362,10 @@ dependencies = [
  "libp2p-ping 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-plaintext 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-ratelimit 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "libp2p-secio 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libp2p-secio 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-tcp 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-uds 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "libp2p-wasm-ext 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libp2p-wasm-ext 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-websocket 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-yamux 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "parity-multiaddr 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1603,7 +1603,7 @@ dependencies = [
 
 [[package]]
 name = "libp2p-secio"
-version = "0.8.0"
+version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "aes-ctr 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1616,11 +1616,11 @@ dependencies = [
  "lazy_static 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-core 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parity-send-wrapper 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "protobuf 2.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "ring 0.14.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rw-stream-sink 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "send_wrapper 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "sha2 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tokio-io 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "twofish 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1658,13 +1658,13 @@ dependencies = [
 
 [[package]]
 name = "libp2p-wasm-ext"
-version = "0.1.0"
+version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "futures 0.1.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "js-sys 0.3.20 (registry+https://github.com/rust-lang/crates.io-index)",
  "libp2p-core 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "send_wrapper 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parity-send-wrapper 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tokio-io 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "wasm-bindgen 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
  "wasm-bindgen-futures 0.3.20 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2095,6 +2095,11 @@ dependencies = [
  "unsigned-varint 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "parity-send-wrapper"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "parity-wasm"
 version = "0.31.3"
@@ -5120,10 +5125,10 @@ dependencies = [
 "checksum libp2p-ping 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3b3bb3328d206ad3061e863f179a211fc978d7bce05f90440ed6b8a6a9d17ced"
 "checksum libp2p-plaintext 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "4b23a8ece138f448572c5ff781d62323a954f1f681c303e6553368026764b0ae"
 "checksum libp2p-ratelimit 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "55918f058f118d72d83f9a976f12e02e54c8616ddfc795c779c4801a5042a44f"
-"checksum libp2p-secio 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "9bff57806e0f71832cc02b5dea1010e5f1a9d16393fd104a4b64e4aaae40d885"
+"checksum libp2p-secio 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "ea5c0636053e01575d6269b6112f9239e9d35ca861e3e5c7d6970a07f9e1682a"
 "checksum libp2p-tcp 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3629f9a667d9f5acb5876df59cf3b547250e340131c47587f9ace7c517f21327"
 "checksum libp2p-uds 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d65c15f89c0607d4a334664d759e54e847e1856a73ea78e7bb6a75e6f4039010"
-"checksum libp2p-wasm-ext 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "dff6c81d0f46261a6327219349753aefd3a92021a1e6102185fa112cfcddca97"
+"checksum libp2p-wasm-ext 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "318d727d5e8e0fe3bb70aacbf99bde57334eae9559deff447edd993422dc0f03"
 "checksum libp2p-websocket 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "04451aa166aa2040293f44c1c27144b65500e4a2ebbb723dfe732f39436eccbd"
 "checksum libp2p-yamux 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5369165359bea84e7ebe73f37b6240f31f8d924ce6710be3d8e1fa678985c9b8"
 "checksum librocksdb-sys 5.17.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7dfb546562f9b450237bb8df7a31961849ee9fb1186d9e356db1d7a6b7609ff2"
@@ -5170,6 +5175,7 @@ dependencies = [
 "checksum parity-codec-derive 3.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "00a486fd383382ddcb2de928364b1f82571c1e48274fc43b7667a4738ee4056c"
 "checksum parity-multiaddr 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "18a130a727008cfcd1068a28439fe939897ccad28664422aeca65b384d6de6d0"
 "checksum parity-multihash 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3e8eab0287ccde7821e337a124dc5a4f1d6e4c25d10cc91e3f9361615dd95076"
+"checksum parity-send-wrapper 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "aa9777aa91b8ad9dd5aaa04a9b6bcb02c7f1deb952fca5a66034d5e63afc5c6f"
 "checksum parity-wasm 0.31.3 (registry+https://github.com/rust-lang/crates.io-index)" = "511379a8194230c2395d2f5fa627a5a7e108a9f976656ce723ae68fca4097bfc"
 "checksum parity-ws 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "2fec5048fba72a2e01baeb0d08089db79aead4b57e2443df172fb1840075a233"
 "checksum parking_lot 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)" = "d4d05f1349491390b1730afba60bb20d55761bef489a954546b58b4b34e1e2ac"

parachain/Cargo.toml

@@ -5,8 +5,8 @@ authors = ["Parity Technologies <admin@parity.io>"]
 description = "Types and utilities for creating and working with parachains"
 
 [dependencies]
-parity-codec = { version = "3.0", default-features = false }
-parity-codec-derive = { version = "3.0", default-features = false }
+parity-codec = { version = "3.5", default-features = false }
+parity-codec-derive = { version = "3.3", default-features = false }
 wasmi = { version = "0.4.3", optional = true }
 error-chain = { version = "0.12", optional = true }
 serde = { version = "1.0", default-features = false }

parachain/src/lib.rs

@@ -77,6 +77,21 @@ pub mod wasm_executor;
 #[cfg(feature = "wasm-api")]
 pub mod wasm_api;
 
+use codec::{Encode, Decode};
+
+struct TrailingZeroInput<'a>(&'a [u8]);
+impl<'a> codec::Input for TrailingZeroInput<'a> {
+	fn read(&mut self, into: &mut [u8]) -> usize {
+		let len = into.len().min(self.0.len());
+		into[..len].copy_from_slice(&self.0[..len]);
+		for i in &mut into[len..] {
+			*i = 0;
+		}
+		self.0 = &self.0[len..];
+		len
+	}
+}
+
 /// Validation parameters for evaluating the parachain validity function.
 // TODO: balance downloads (https://github.com/paritytech/polkadot/issues/220)
 #[derive(PartialEq, Eq, Decode)]
@@ -100,10 +115,56 @@ pub struct ValidationResult {
 }
 
 /// Unique identifier of a parachain.
-#[derive(PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy, Encode, Decode)]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Hash, Default, Clone, Copy, Encode, Decode)]
 #[cfg_attr(feature = "std", derive(Serialize, Deserialize, Debug))]
 pub struct Id(u32);
 
+impl codec::CompactAs for Id {
+	type As = u32;
+	fn encode_as(&self) -> &u32 {
+		&self.0
+	}
+	fn decode_from(x: u32) -> Self {
+		Self(x)
+	}
+}
+impl From<codec::Compact<Id>> for Id {
+	fn from(x: codec::Compact<Id>) -> Id {
+		x.0
+	}
+}
+
+/// This type can be converted into and possibly from an AccountId (which itself is generic).
+pub trait AccountIdConversion<AccountId>: Sized {
+	/// Convert into an account ID. This is infallible.
+	fn into_account(&self) -> AccountId;
+
+	/// Try to convert an account ID into this type. Might not succeed.
+	fn try_from_account(a: &AccountId) -> Option<Self>;
+}
+
+/// Format is b"para" ++ encode(parachain ID) ++ 00.... where 00... is indefinite trailing zeroes to fill AccountId.
+impl<T: Encode + Decode + Default> AccountIdConversion<T> for Id {
+	fn into_account(&self) -> T {
+		(b"para", self).using_encoded(|b|
+			T::decode(&mut TrailingZeroInput(b))
+		).unwrap_or_default()
+	}
+
+	fn try_from_account(x: &T) -> Option<Self> {
+		x.using_encoded(|d| {
+			if &d[0..4] != b"para" { return None }
+			let mut cursor = &d[4..];
+			let result = Decode::decode(&mut cursor)?;
+			if cursor.iter().all(|x| *x == 0) {
+				Some(result)
+			} else {
+				None
+			}
+		})
+	}
+}
+
 impl From<Id> for u32 {
 	fn from(x: Id) -> Self { x.0 }
 }

primitives/src/parachain.rs

@@ -24,7 +24,7 @@ use super::Hash;
 use primitives::bytes;
 use primitives::ed25519;
 
-pub use polkadot_parachain::Id;
+pub use polkadot_parachain::{Id, AccountIdConversion};
 
 /// Identity that collators use.
 pub type CollatorId = ed25519::Public;

runtime/src/claims.rs

@@ -50,6 +50,7 @@ impl EcdsaSignature {
 		r[64] = self.2 as u8;
 		r
 	}
+	#[cfg(test)]
 	pub fn from_blob(blob: &[u8; 65]) -> Self {
 		let mut r = Self([0u8; 32], [0u8; 32], 0);
 		r.0[..].copy_from_slice(&blob[0..32]);
@@ -148,7 +149,7 @@ mod tests {
 	use tiny_keccak::keccak256;
 	use super::*;
 
-	use sr_io::{self as runtime_io, with_externalities};
+	use sr_io::with_externalities;
 	use substrate_primitives::{H256, Blake2Hasher};
 	use codec::{Decode, Encode};
 	// The testing primitives are very useful for avoiding having to work with signatures

runtime/src/lib.rs

@@ -76,6 +76,8 @@ extern crate substrate_trie;
 mod curated_grandpa;
 mod parachains;
 mod claims;
+mod slot_range;
+mod slots;
 
 use rstd::prelude::*;
 use substrate_primitives::u32_trait::{_2, _4};
@@ -252,6 +254,19 @@ impl grandpa::Trait for Runtime {
 
 impl parachains::Trait for Runtime {}
 
+parameter_types!{
+	pub const LeasePeriod: BlockNumber = 100000;
+	pub const EndingPeriod: BlockNumber = 1000;
+}
+
+impl slots::Trait for Runtime {
+	type Event = Event;
+	type Currency = balances::Module<Self>;
+	type Parachains = parachains::Module<Self>;
+	type LeasePeriod = LeasePeriod;
+	type EndingPeriod = EndingPeriod;
+}
+
 impl curated_grandpa::Trait for Runtime { }
 
 impl sudo::Trait for Runtime {
@@ -283,6 +298,7 @@ construct_runtime!(
 		CouncilSeats: council_seats::{Config<T>},
 		Treasury: treasury,
 		Parachains: parachains::{Module, Call, Storage, Config<T>, Inherent},
+		Slots: slots::{Module, Call, Storage, Event<T>},
 		Sudo: sudo,
 	}
 );

runtime/src/parachains.rs

@@ -17,16 +17,16 @@
 //! Main parachains logic. For now this is just the determination of which validators do what.
 
 use rstd::prelude::*;
-use codec::Decode;
+use codec::{Decode, HasCompact};
 
 use bitvec::BigEndian;
-use sr_primitives::traits::{Hash as HashT, BlakeTwo256};
-use primitives::Hash;
-use primitives::parachain::{Id as ParaId, Chain, DutyRoster, AttestedCandidate, Statement};
+use sr_primitives::traits::{Hash as HashT, BlakeTwo256, Member};
+use primitives::{Hash, parachain::{Id as ParaId, Chain, DutyRoster, AttestedCandidate, Statement, AccountIdConversion}};
 use {system, session};
 
-use srml_support::{StorageValue, StorageMap, storage::hashed::generator};
-use srml_support::dispatch::Result;
+use srml_support::{StorageValue, StorageMap, Parameter, dispatch::Result};
+#[cfg(feature = "std")]
+use srml_support::storage::hashed::generator;
 
 use inherents::{ProvideInherent, InherentData, RuntimeString, MakeFatalError, InherentIdentifier};
 
@@ -38,7 +38,64 @@ use rstd::marker::PhantomData;
 
 use system::ensure_none;
 
-pub trait Trait: session::Trait {}
+/// Parachain registration API.
+pub trait ParachainRegistrar<AccountId> {
+	/// An identifier for a parachain.
+	type ParaId: Member + Parameter + Default + AccountIdConversion<AccountId> + Copy + HasCompact;
+
+	/// Create a new unique parachain identity for later registration.
+	fn new_id() -> Self::ParaId;
+
+	/// Register a parachain with given `code` and `initial_head_data`. `id` must not yet be registered or it will
+	/// result in a error.
+	fn register_parachain(id: Self::ParaId, code: Vec<u8>, initial_head_data: Vec<u8>) -> Result;
+
+	/// Deregister a parachain with given `id`. If `id` is not currently registered, an error is returned.
+	fn deregister_parachain(id: Self::ParaId) -> Result;
+}
+
+impl<T: Trait> ParachainRegistrar<T::AccountId> for Module<T> {
+	type ParaId = ParaId;
+	fn new_id() -> ParaId {
+		<NextFreeId<T>>::mutate(|n| { let r = *n; *n = ParaId::from(u32::from(*n) + 1); r })
+	}
+	fn register_parachain(id: ParaId, code: Vec<u8>, initial_head_data: Vec<u8>) -> Result {
+		let mut parachains = Self::active_parachains();
+		match parachains.binary_search(&id) {
+			Ok(_) => fail!("Parachain already exists"),
+			Err(idx) => parachains.insert(idx, id),
+		}
+
+		<Code<T>>::insert(id, code);
+		<Parachains<T>>::put(parachains);
+		<Heads<T>>::insert(id, initial_head_data);
+
+		Ok(())
+	}
+	fn deregister_parachain(id: ParaId) -> Result {
+		let mut parachains = Self::active_parachains();
+		match parachains.binary_search(&id) {
+			Ok(idx) => { parachains.remove(idx); }
+			Err(_) => return Ok(()),
+		}
+
+		<Code<T>>::remove(id);
+		<Heads<T>>::remove(id);
+
+		// clear all routing entries to and from other parachains.
+		for other in parachains.iter().cloned() {
+			<Routing<T>>::remove((id, other));
+			<Routing<T>>::remove((other, id));
+		}
+
+		<Parachains<T>>::put(parachains);
+
+		Ok(())
+	}
+}
+
+pub trait Trait: session::Trait {
+}
 
 // result of <NodeCodec<Blake2Hasher> as trie_db::NodeCodec<Blake2Hasher>>::hashed_null_node()
 const EMPTY_TRIE_ROOT: [u8; 32] = [
@@ -59,6 +116,9 @@ decl_storage! {
 
 		// Did the parachain heads get updated in this block?
 		DidUpdate: bool;
+
+		/// The next unused ParaId value.
+		NextFreeId: ParaId;
 	}
 	add_extra_genesis {
 		config(parachains): Vec<(ParaId, Vec<u8>, Vec<u8>)>;
@@ -137,39 +197,12 @@ decl_module! {
 		/// Register a parachain with given code.
 		/// Fails if given ID is already used.
 		pub fn register_parachain(id: ParaId, code: Vec<u8>, initial_head_data: Vec<u8>) -> Result {
-			let mut parachains = Self::active_parachains();
-			match parachains.binary_search(&id) {
-				Ok(_) => fail!("Parachain already exists"),
-				Err(idx) => parachains.insert(idx, id),
-			}
-
-			<Code<T>>::insert(id, code);
-			<Parachains<T>>::put(parachains);
-			<Heads<T>>::insert(id, initial_head_data);
-
-			Ok(())
+			<Self as ParachainRegistrar<T::AccountId>>::register_parachain(id, code, initial_head_data)
 		}
 
 		/// Deregister a parachain with given id
 		pub fn deregister_parachain(id: ParaId) -> Result {
-			let mut parachains = Self::active_parachains();
-			match parachains.binary_search(&id) {
-				Ok(idx) => { parachains.remove(idx); }
-				Err(_) => return Ok(()),
-			}
-
-			<Code<T>>::remove(id);
-			<Heads<T>>::remove(id);
-
-			// clear all routing entries to and from other parachains.
-			for other in parachains.iter().cloned() {
-				<Routing<T>>::remove((id, other));
-				<Routing<T>>::remove((other, id));
-			}
-
-			<Parachains<T>>::put(parachains);
-
-			Ok(())
+			<Self as ParachainRegistrar<T::AccountId>>::deregister_parachain(id)
 		}
 
 		fn on_finalize(_n: T::BlockNumber) {

runtime/src/slot_range.rs

+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! The SlotRange struct which succinctly handles the ten values that
+//! represent all sub ranges between 0 and 3 inclusive.
+
+use rstd::{result, ops::Add, convert::{TryFrom, TryInto}};
+use sr_primitives::traits::CheckedSub;
+
+/// Total number of possible sub ranges of slots.
+pub const SLOT_RANGE_COUNT: usize = 10;
+
+/// A compactly represented sub-range from the series (0, 1, 2, 3).
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Encode, Decode)]
+#[repr(u8)]
+pub enum SlotRange {
+	/// Sub range from index 0 to index 0 inclusive.
+	ZeroZero = 0,
+	/// Sub range from index 0 to index 1 inclusive.
+	ZeroOne = 1,
+	/// Sub range from index 0 to index 2 inclusive.
+	ZeroTwo = 2,
+	/// Sub range from index 0 to index 3 inclusive.
+	ZeroThree = 3,
+	/// Sub range from index 1 to index 1 inclusive.
+	OneOne = 4,
+	/// Sub range from index 1 to index 2 inclusive.
+	OneTwo = 5,
+	/// Sub range from index 1 to index 3 inclusive.
+	OneThree = 6,
+	/// Sub range from index 2 to index 2 inclusive.
+	TwoTwo = 7,
+	/// Sub range from index 2 to index 3 inclusive.
+	TwoThree = 8,
+	/// Sub range from index 3 to index 3 inclusive.
+	ThreeThree = 9,     // == SLOT_RANGE_COUNT - 1
+}
+
+#[cfg(feature = "std")]
+impl std::fmt::Debug for SlotRange {
+	fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+		let p = self.as_pair();
+		write!(fmt, "[{}..{}]", p.0, p.1)
+	}
+}
+
+impl SlotRange {
+	pub fn new_bounded<
+		Index: Add<Output=Index> + CheckedSub + Copy + Ord + From<u32> + TryInto<u32>
+	>(
+		initial: Index,
+		first: Index,
+		last: Index
+	) -> result::Result<Self, &'static str> {
+		if first > last || first < initial || last > initial + 3.into() {
+			return Err("Invalid range for this auction")
+		}
+		let count: u32 = last.checked_sub(&first)
+			.ok_or("range ends before it begins")?
+			.try_into()
+			.map_err(|_| "range too big")?;
+		let first: u32 = first.checked_sub(&initial)
+			.ok_or("range begins too early")?
+			.try_into()
+			.map_err(|_| "start too far")?;
+		match first {
+			0 => match count {
+				0 => Some(SlotRange::ZeroZero),
+				1 => Some(SlotRange::ZeroOne),
+				2 => Some(SlotRange::ZeroTwo),
+				3 => Some(SlotRange::ZeroThree),
+				_ => None,
+			},
+			1 => match count {
+				0 => Some(SlotRange::OneOne),
+				1 => Some(SlotRange::OneTwo),
+				2 => Some(SlotRange::OneThree),
+				_ => None
+			},
+			2 => match count { 0 => Some(SlotRange::TwoTwo), 1 => Some(SlotRange::TwoThree), _ => None },
+			3 => match count { 0 => Some(SlotRange::ThreeThree), _ => None },
+			_ => return Err("range begins too late"),
+		}.ok_or("range ends too late")
+	}
+
+	pub fn as_pair(&self) -> (u8, u8) {
+		match self {
+			SlotRange::ZeroZero => (0, 0),
+			SlotRange::ZeroOne => (0, 1),
+			SlotRange::ZeroTwo => (0, 2),
+			SlotRange::ZeroThree => (0, 3),
+			SlotRange::OneOne => (1, 1),
+			SlotRange::OneTwo => (1, 2),
+			SlotRange::OneThree => (1, 3),
+			SlotRange::TwoTwo => (2, 2),
+			SlotRange::TwoThree => (2, 3),
+			SlotRange::ThreeThree => (3, 3),
+		}
+	}
+
+	pub fn intersects(&self, other: SlotRange) -> bool {
+		let a = self.as_pair();
+		let b = other.as_pair();
+		b.0 <= a.1 && a.0 <= b.1
+//		== !(b.0 > a.1 || a.0 > b.1)
+	}
+
+	pub fn len(&self) -> usize {
+		match self {
+			SlotRange::ZeroZero => 1,
+			SlotRange::ZeroOne => 2,
+			SlotRange::ZeroTwo => 3,
+			SlotRange::ZeroThree => 4,
+			SlotRange::OneOne => 1,
+			SlotRange::OneTwo => 2,
+			SlotRange::OneThree => 3,
+			SlotRange::TwoTwo => 1,
+			SlotRange::TwoThree => 2,
+			SlotRange::ThreeThree => 1,
+		}
+	}
+}
+
+impl TryFrom<usize> for SlotRange {
+	type Error = ();
+	fn try_from(x: usize) -> Result<SlotRange, ()> {
+		Ok(match x {
+			0 => SlotRange::ZeroZero,
+			1 => SlotRange::ZeroOne,
+			2 => SlotRange::ZeroTwo,
+			3 => SlotRange::ZeroThree,
+			4 => SlotRange::OneOne,
+			5 => SlotRange::OneTwo,
+			6 => SlotRange::OneThree,
+			7 => SlotRange::TwoTwo,
+			8 => SlotRange::TwoThree,
+			9 => SlotRange::ThreeThree,
+			_ => return Err(()),
+		})
+	}
+}

test-parachains/adder/Cargo.toml

@@ -6,6 +6,6 @@ description = "Test parachain which adds to a number as its state transition"
 
 [dependencies]
 polkadot-parachain = { path = "../../parachain/", default-features = false }
-parity-codec = { version = "3.0", default-features = false }
-parity-codec-derive = { version = "3.0", default-features = false }
+parity-codec = { version = "3.5", default-features = false }
+parity-codec-derive = { version = "3.3", default-features = false }
 tiny-keccak = "1.4"