Do not allow any crowdloan contributions during the VRF period (#3346)

* patch `is_ending` logic for sampling * Create AuctionStatus abstraction * clean up apis * fix docs * Add check for contributions during vrf * custom error for this * fix benchmark * opening -> starting * Apply suggestions from code review Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com> * Update runtime/common/src/auctions.rs * avoid divide by zero stuff Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
2026-06-14 02:51:08 +00:00 · 2021-06-24 22:24:37 +01:00
parent 3827f6e6f8
commit 9e641ba187
4 changed files with 238 additions and 111 deletions
@@ -27,7 +27,7 @@ use frame_support::{
 };
 use primitives::v1::Id as ParaId;
 use crate::slot_range::SlotRange;
-use crate::traits::{Leaser, LeaseError, Auctioneer, Registrar};
+use crate::traits::{Leaser, LeaseError, Auctioneer, Registrar, AuctionStatus};
 use parity_scale_codec::Decode;
 pub use pallet::*;

@@ -201,7 +201,7 @@ pub mod pallet {
 			// If the current auction was in its ending period last block, then ensure that the (sub-)range
 			// winner information is duplicated from the previous block in case no bids happened in the
 			// last block.
-			if let Some(offset) = Self::is_ending(n) {
+			if let AuctionStatus::EndingPeriod(offset, _sub_sample) = Self::auction_status(n) {
 				weight = weight.saturating_add(T::DbWeight::get().reads(1));
 				if !Winning::<T>::contains_key(&offset) {
 					weight = weight.saturating_add(T::DbWeight::get().writes(1));
@@ -241,19 +241,7 @@ pub mod pallet {
 			#[pallet::compact] lease_period_index: LeasePeriodOf<T>,
 		) -> DispatchResult {
 			T::InitiateOrigin::ensure_origin(origin)?;
-
-			ensure!(!Self::is_in_progress(), Error::<T>::AuctionInProgress);
-			ensure!(lease_period_index >= T::Leaser::lease_period_index(), Error::<T>::LeasePeriodInPast);
-
-			// Bump the counter.
-			let n = AuctionCounter::<T>::mutate(|n| { *n += 1; *n });
-
-			// Set the information.
-			let ending = frame_system::Pallet::<T>::block_number().saturating_add(duration);
-			AuctionInfo::<T>::put((lease_period_index, ending));
-
-			Self::deposit_event(Event::<T>::AuctionStarted(n, lease_period_index, ending));
-			Ok(())
+			Self::do_new_auction(duration, lease_period_index)
 		}

 		/// Make a new bid from an account (including a parachain account) for deploying a new
@@ -316,16 +304,28 @@ impl<T: Config> Auctioneer for Pallet<T> {
 		Self::do_new_auction(duration, lease_period_index)
 	}

-	// Returns whether the auction is ending, and which sample number we are on.
-	fn is_ending(now: Self::BlockNumber) -> Option<Self::BlockNumber> {
-		if let Some((_, early_end)) = AuctionInfo::<T>::get() {
-			if let Some(after_early_end) = now.checked_sub(&early_end) {
-				if after_early_end < T::EndingPeriod::get() {
-					return Some(after_early_end / T::SampleLength::get())
-				}
-			}
+	// Returns the status of the auction given the current block number.
+	fn auction_status(now: Self::BlockNumber) -> AuctionStatus<Self::BlockNumber> {
+		let early_end = match AuctionInfo::<T>::get() {
+			Some((_, early_end)) => early_end,
+			None => return AuctionStatus::NotStarted,
+		};
+
+		let after_early_end = match now.checked_sub(&early_end) {
+			Some(after_early_end) => after_early_end,
+			None => return AuctionStatus::StartingPeriod,
+		};
+
+		let ending_period = T::EndingPeriod::get();
+		if after_early_end < ending_period {
+			let sample_length = T::SampleLength::get().max(One::one());
+			let sample = after_early_end / sample_length;
+			let sub_sample = after_early_end % sample_length;
+			return AuctionStatus::EndingPeriod(sample, sub_sample)
+		} else {
+			// This is safe because of the comparison operator above
+			return AuctionStatus::VrfDelay(after_early_end - ending_period)
 		}
-		None
 	}

 	fn place_bid(
@@ -355,17 +355,6 @@ impl<T: Config> Pallet<T> {
 	// A trick to allow me to initialize large arrays with nothing in them.
 	const EMPTY: Option<(<T as frame_system::Config>::AccountId, ParaId, BalanceOf<T>)> = None;

-	/// True if an auction is in progress.
-	pub fn is_in_progress() -> bool {
-		AuctionInfo::<T>::get().map_or(false, |(_, early_end)| {
-			let late_end = early_end.saturating_add(T::EndingPeriod::get());
-			// We need to check that the auction isn't in the period where it has definitely ended, but yeah we keep the
-			// info around because we haven't yet decided *exactly* when in the `EndingPeriod` that it ended.
-			let now = frame_system::Pallet::<T>::block_number();
-			now < late_end
-		})
-	}
-
 	/// Create a new auction.
 	///
 	/// This can only happen when there isn't already an auction in progress. Accepts the `duration`
@@ -375,7 +364,8 @@ impl<T: Config> Pallet<T> {
 		duration: T::BlockNumber,
 		lease_period_index: LeasePeriodOf<T>,
 	) -> DispatchResult {
-		ensure!(!Self::is_in_progress(), Error::<T>::AuctionInProgress);
+		let maybe_auction = AuctionInfo::<T>::get();
+		ensure!(maybe_auction.is_none(), Error::<T>::AuctionInProgress);
 		ensure!(lease_period_index >= T::Leaser::lease_period_index(), Error::<T>::LeasePeriodInPast);

 		// Bump the counter.
@@ -410,21 +400,24 @@ impl<T: Config> Pallet<T> {
 		// Bidding on latest auction.
 		ensure!(auction_index == AuctionCounter::<T>::get(), Error::<T>::NotCurrentAuction);
 		// Assume it's actually an auction (this should never fail because of above).
-		let (first_lease_period, early_end) = AuctionInfo::<T>::get().ok_or(Error::<T>::NotAuction)?;
-		let late_end = early_end.saturating_add(T::EndingPeriod::get());
+		let (first_lease_period, _) = AuctionInfo::<T>::get().ok_or(Error::<T>::NotAuction)?;

-		// We need to check that the auction isn't in the period where it has definitely ended, but yeah we keep the
-		// info around because we haven't yet decided *exactly* when in the `EndingPeriod` that it ended.
-		let now = frame_system::Pallet::<T>::block_number();
-		ensure!(now < late_end, Error::<T>::AuctionEnded);
+		// Get the auction status and the current sample block. For the starting period, the sample
+		// block is zero.
+		let auction_status = Self::auction_status(frame_system::Pallet::<T>::block_number());
+		// The offset into the ending samples of the auction.
+		let offset = match auction_status {
+			AuctionStatus::NotStarted => return Err(Error::<T>::AuctionEnded.into()),
+			AuctionStatus::StartingPeriod => Zero::zero(),
+			AuctionStatus::EndingPeriod(o, _) => o,
+			AuctionStatus::VrfDelay(_) => return Err(Error::<T>::AuctionEnded.into()),
+		};

 		// Our range.
 		let range = SlotRange::new_bounded(first_lease_period, first_slot, last_slot)?;
 		// Range as an array index.
 		let range_index = range as u8 as usize;
-		let is_ending = Self::is_ending(frame_system::Pallet::<T>::block_number());
-		// The offset into the ending samples of the auction.
-		let offset = is_ending.unwrap_or_default();
+
 		// The current winning ranges.
 		let mut current_winning = Winning::<T>::get(offset)
 			.or_else(|| offset.checked_sub(&One::one()).and_then(Winning::<T>::get))
@@ -463,7 +456,7 @@ impl<T: Config> Pallet<T> {
 			let mut outgoing_winner = Some((bidder.clone(), para, amount));
 			swap(&mut current_winning[range_index], &mut outgoing_winner);
 			if let Some((who, para, _amount)) = outgoing_winner {
-				if !is_ending.is_some() && current_winning.iter()
+				if auction_status.is_starting() && current_winning.iter()
 					.filter_map(Option::as_ref)
 					.all(|&(ref other, other_para, _)| other != &who || other_para != para)
 				{
@@ -504,7 +497,7 @@ impl<T: Config> Pallet<T> {
 					// Our random seed was known only after the auction ended. Good to use.
 					let raw_offset_block_number = <T::BlockNumber>::decode(&mut raw_offset.as_ref())
 						.expect("secure hashes should always be bigger than the block number; qed");
-					let offset = (raw_offset_block_number % ending_period) / T::SampleLength::get();
+					let offset = (raw_offset_block_number % ending_period) / T::SampleLength::get().max(One::one());

 					let auction_counter = AuctionCounter::<T>::get();
 					Self::deposit_event(Event::<T>::WinningOffset(auction_counter, offset));
@@ -835,15 +828,13 @@ mod tests {
 		new_test_ext().execute_with(|| {
 			assert_eq!(AuctionCounter::<Test>::get(), 0);
 			assert_eq!(TestLeaser::deposit_held(0u32.into(), &1), 0);
-			assert_eq!(Auctions::is_in_progress(), false);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::NotStarted);

 			run_to_block(10);

 			assert_eq!(AuctionCounter::<Test>::get(), 0);
 			assert_eq!(TestLeaser::deposit_held(0u32.into(), &1), 0);
-			assert_eq!(Auctions::is_in_progress(), false);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::NotStarted);
 		});
 	}

@@ -856,8 +847,7 @@ mod tests {
 			assert_ok!(Auctions::new_auction(Origin::signed(6), 5, 1));

 			assert_eq!(AuctionCounter::<Test>::get(), 1);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);
 		});
 	}

@@ -918,40 +908,31 @@ mod tests {
 			assert_ok!(Auctions::new_auction(Origin::signed(6), 5, 1));

 			assert_eq!(AuctionCounter::<Test>::get(), 1);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);

 			run_to_block(2);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);

 			run_to_block(3);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);

 			run_to_block(4);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);

 			run_to_block(5);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);

 			run_to_block(6);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(0));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(0, 0));

 			run_to_block(7);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(1));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(1, 0));

 			run_to_block(8);
-			assert_eq!(Auctions::is_in_progress(), true);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(2));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(2, 0));

 			run_to_block(9);
-			assert_eq!(Auctions::is_in_progress(), false);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::NotStarted);
 		});
 	}

@@ -983,19 +964,19 @@ mod tests {
 			assert_ok!(Auctions::bid(Origin::signed(1), 0.into(), 1, 1, 4, 1));
 			assert_eq!(Balances::reserved_balance(1), 1);
 			assert_eq!(Balances::free_balance(1), 9);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);
 			run_to_block(8);
 			// Auction has not yet ended.
 			assert_eq!(leases(), vec![]);
-			assert!(Auctions::is_in_progress());
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(2, 0));
 			// This will prevent the auction's winner from being decided in the next block, since the random
 			// seed was known before the final bids were made.
 			set_last_random(H256::zero(), 8);
 			// Auction definitely ended now, but we don't know exactly when in the last 3 blocks yet since
 			// no randomness available yet.
 			run_to_block(9);
-			// Auction has now ended...
-			assert!(!Auctions::is_in_progress());
-			// ...But auction winner still not yet decided, so no leases yet.
+			// Auction has now ended... But auction winner still not yet decided, so no leases yet.
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::VrfDelay(0));
 			assert_eq!(leases(), vec![]);

 			// Random seed now updated to a value known at block 9, when the auction ended. This means
@@ -1003,7 +984,7 @@ mod tests {
 			set_last_random(H256::zero(), 9);
 			run_to_block(10);
 			// Auction ended and winner selected
-			assert!(!Auctions::is_in_progress());
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::NotStarted);
 			assert_eq!(leases(), vec![
 				((0.into(), 1), LeaseData { leaser: 1, amount: 1 }),
 				((0.into(), 2), LeaseData { leaser: 1, amount: 1 }),
@@ -1289,26 +1270,26 @@ mod tests {
 			assert_ok!(Auctions::bid(Origin::signed(1), para_1, 1, 1, 4, 10));
 			assert_ok!(Auctions::bid(Origin::signed(2), para_2, 1, 3, 4, 20));

-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);
 			let mut winning = [None; SlotRange::SLOT_RANGE_COUNT];
 			winning[SlotRange::ZeroThree as u8 as usize] = Some((1, para_1, 10));
 			winning[SlotRange::TwoThree as u8 as usize] = Some((2, para_2, 20));
 			assert_eq!(Auctions::winning(0), Some(winning));

 			run_to_block(9);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);

 			run_to_block(10);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(0));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(0, 0));
 			assert_eq!(Auctions::winning(0), Some(winning));

 			run_to_block(11);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(1));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(1, 0));
 			assert_eq!(Auctions::winning(1), Some(winning));
 			assert_ok!(Auctions::bid(Origin::signed(3), para_3, 1, 3, 4, 30));

 			run_to_block(12);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(2));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(2, 0));
 			winning[SlotRange::TwoThree as u8 as usize] = Some((3, para_3, 30));
 			assert_eq!(Auctions::winning(2), Some(winning));
 		});
@@ -1342,17 +1323,17 @@ mod tests {
 			assert_ok!(Auctions::bid(Origin::signed(1), para_1, 1, 11, 14, 10));
 			assert_ok!(Auctions::bid(Origin::signed(2), para_2, 1, 13, 14, 20));

-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);
 			let mut winning = [None; SlotRange::SLOT_RANGE_COUNT];
 			winning[SlotRange::ZeroThree as u8 as usize] = Some((1, para_1, 10));
 			winning[SlotRange::TwoThree as u8 as usize] = Some((2, para_2, 20));
 			assert_eq!(Auctions::winning(0), Some(winning));

 			run_to_block(9);
-			assert_eq!(Auctions::is_ending(System::block_number()), None);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);

 			run_to_block(10);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(0));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(0, 0));
 			assert_eq!(Auctions::winning(0), Some(winning));

 			// New bids update the current winning
@@ -1361,7 +1342,7 @@ mod tests {
 			assert_eq!(Auctions::winning(0), Some(winning));

 			run_to_block(20);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(1));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(1, 0));
 			assert_eq!(Auctions::winning(1), Some(winning));
 			run_to_block(25);
 			// Overbid mid sample
@@ -1370,13 +1351,13 @@ mod tests {
 			assert_eq!(Auctions::winning(1), Some(winning));

 			run_to_block(30);
-			assert_eq!(Auctions::is_ending(System::block_number()), Some(2));
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(2, 0));
 			assert_eq!(Auctions::winning(2), Some(winning));

 			set_last_random(H256::from([254; 32]), 40);
 			run_to_block(40);
 			// Auction ended and winner selected
-			assert!(!Auctions::is_in_progress());
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::NotStarted);
 			assert_eq!(leases(), vec![
 				((3.into(), 13), LeaseData { leaser: 3, amount: 30 }),
 				((3.into(), 14), LeaseData { leaser: 3, amount: 30 }),
@@ -1384,6 +1365,54 @@ mod tests {
 		});
 	}

+	#[test]
+	fn auction_status_works() {
+		new_test_ext().execute_with(|| {
+			EndingPeriod::set(30);
+			SampleLength::set(10);
+			set_last_random(Default::default(), 0);
+
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::NotStarted);
+
+			run_to_block(1);
+			assert_ok!(Auctions::new_auction(Origin::signed(6), 9, 11));
+
+			run_to_block(9);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::StartingPeriod);
+
+			run_to_block(10);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(0, 0));
+
+			run_to_block(11);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(0, 1));
+
+			run_to_block(19);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(0, 9));
+
+			run_to_block(20);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(1, 0));
+
+			run_to_block(25);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(1, 5));
+
+			run_to_block(30);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(2, 0));
+
+			run_to_block(39);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::EndingPeriod(2, 9));
+
+			run_to_block(40);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::VrfDelay(0));
+
+			run_to_block(44);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::VrfDelay(4));
+
+			set_last_random(Default::default(), 45);
+			run_to_block(45);
+			assert_eq!(Auctions::auction_status(System::block_number()), AuctionStatus::<u32>::NotStarted);
+		});
+	}
+
 	#[test]
 	fn can_cancel_auction() {
 		new_test_ext().execute_with(|| {
@@ -289,14 +289,17 @@ pub mod pallet {
 		/// The provided memo is too large.
 		MemoTooLarge,
 		/// The fund is already in NewRaise
-		AlreadyInNewRaise
+		AlreadyInNewRaise,
+		/// No contributions allowed during the VRF delay
+		VrfDelayInProgress,
 	}

 	#[pallet::hooks]
 	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
-		fn on_initialize(n: T::BlockNumber) -> frame_support::weights::Weight {
-			if let Some(n) = T::Auctioneer::is_ending(n) {
-				if n.is_zero() {
+		fn on_initialize(num: T::BlockNumber) -> frame_support::weights::Weight {
+			if let Some((sample, sub_sample)) = T::Auctioneer::auction_status(num).is_ending() {
+				// This is the very first block in the ending period
+				if sample.is_zero() && sub_sample.is_zero() {
 					// first block of ending period.
 					EndingsCount::<T>::mutate(|c| *c += 1);
 				}
@@ -413,6 +416,10 @@ pub mod pallet {
 			let fund_account = Self::fund_account_id(index);
 			ensure!(!T::Auctioneer::has_won_an_auction(index, &fund_account), Error::<T>::BidOrLeaseActive);

+			// We disallow any crowdloan contributions during the VRF Period, so that people do not sneak their
+			// contributions into the auction when it would not impact the outcome.
+			ensure!(!T::Auctioneer::auction_status(now).is_vrf(), Error::<T>::VrfDelayInProgress);
+
 			let (old_balance, memo) = Self::contribution_get(fund.trie_index, &who);

 			if let Some(ref verifier) = fund.verifier {
@@ -427,7 +434,7 @@ pub mod pallet {
 			let balance = old_balance.saturating_add(value);
 			Self::contribution_put(fund.trie_index, &who, &balance, &memo);

-			if T::Auctioneer::is_ending(now).is_some() {
+			if T::Auctioneer::auction_status(now).is_ending().is_some() {
 				match fund.last_contribution {
 					// In ending period; must ensure that we are in NewRaise.
 					LastContribution::Ending(n) if n == now => {
@@ -758,7 +765,7 @@ mod tests {
 	};
 	use crate::{
 		mock::TestRegistrar,
-		traits::OnSwap,
+		traits::{OnSwap, AuctionStatus},
 		crowdloan,
 	};
 	use sp_keystore::{KeystoreExt, testing::KeyStore};
@@ -837,6 +844,7 @@ mod tests {
 	}
 	thread_local! {
 		static AUCTION: RefCell<Option<(u64, u64)>> = RefCell::new(None);
+		static VRF_DELAY: RefCell<u64> = RefCell::new(0);
 		static ENDING_PERIOD: RefCell<u64> = RefCell::new(5);
 		static BIDS_PLACED: RefCell<Vec<BidPlaced>> = RefCell::new(Vec::new());
 		static HAS_WON: RefCell<BTreeMap<(ParaId, u64), bool>> = RefCell::new(BTreeMap::new());
@@ -855,6 +863,12 @@ mod tests {
 	fn bids() -> Vec<BidPlaced> {
 		BIDS_PLACED.with(|p| p.borrow().clone())
 	}
+	fn vrf_delay() -> u64 {
+		VRF_DELAY.with(|p| p.borrow().clone())
+	}
+	fn set_vrf_delay(delay: u64) {
+		VRF_DELAY.with(|p| *p.borrow_mut() = delay);
+	}
 	// Emulate what would happen if we won an auction:
 	// balance is reserved and a deposit_held is recorded
 	fn set_winner(para: ParaId, who: u64, winner: bool) {
@@ -884,15 +898,29 @@ mod tests {
 			Ok(())
 		}

-		fn is_ending(now: u64) -> Option<u64> {
-			if let Some((_, early_end)) = auction() {
-				if let Some(after_early_end) = now.checked_sub(early_end) {
-					if after_early_end < ending_period() {
-						return Some(after_early_end)
-					}
+		fn auction_status(now: u64) -> AuctionStatus<u64> {
+			let early_end = match auction() {
+				Some((_, early_end)) => early_end,
+				None => return AuctionStatus::NotStarted,
+			};
+			let after_early_end = match now.checked_sub(early_end) {
+				Some(after_early_end) => after_early_end,
+				None => return AuctionStatus::StartingPeriod,
+			};
+
+			let ending_period = ending_period();
+			if after_early_end < ending_period {
+				return AuctionStatus::EndingPeriod(after_early_end, 0)
+			} else {
+				let after_end = after_early_end - ending_period;
+				// Optional VRF delay
+				if after_end < vrf_delay() {
+					return AuctionStatus::VrfDelay(after_end);
+				} else {
+					// VRF delay is done, so we just end the auction
+					return AuctionStatus::NotStarted;
 				}
 			}
-			None
 		}

 		fn place_bid(
@@ -997,10 +1025,10 @@ mod tests {
 			assert_ok!(TestAuctioneer::place_bid(1, 2.into(), 0, 3, 6));
 			let b = BidPlaced { height: 0, bidder: 1, para: 2.into(), first_period: 0, last_period: 3, amount: 6 };
 			assert_eq!(bids(), vec![b]);
-			assert_eq!(TestAuctioneer::is_ending(4), None);
-			assert_eq!(TestAuctioneer::is_ending(5), Some(0));
-			assert_eq!(TestAuctioneer::is_ending(9), Some(4));
-			assert_eq!(TestAuctioneer::is_ending(11), None);
+			assert_eq!(TestAuctioneer::auction_status(4), AuctionStatus::<u64>::StartingPeriod);
+			assert_eq!(TestAuctioneer::auction_status(5), AuctionStatus::<u64>::EndingPeriod(0, 0));
+			assert_eq!(TestAuctioneer::auction_status(9), AuctionStatus::<u64>::EndingPeriod(4, 0));
+			assert_eq!(TestAuctioneer::auction_status(11), AuctionStatus::<u64>::NotStarted);
 		});
 	}

@@ -1209,11 +1237,41 @@ mod tests {
 		});
 	}

+	#[test]
+	fn cannot_contribute_during_vrf() {
+		new_test_ext().execute_with(|| {
+			set_vrf_delay(5);
+
+			let para = new_para();
+			let first_period = 1;
+			let last_period = 4;
+
+			assert_ok!(TestAuctioneer::new_auction(5, 0));
+
+			// Set up a crowdloan
+			assert_ok!(Crowdloan::create(Origin::signed(1), para, 1000, first_period, last_period, 20, None));
+
+			run_to_block(8);
+			// Can def contribute when auction is running.
+			assert!(TestAuctioneer::auction_status(System::block_number()).is_ending().is_some());
+			assert_ok!(Crowdloan::contribute(Origin::signed(2), para, 250, None));
+
+			run_to_block(10);
+			// Can't contribute when auction is in the VRF delay period.
+			assert!(TestAuctioneer::auction_status(System::block_number()).is_vrf());
+			assert_noop!(Crowdloan::contribute(Origin::signed(2), para, 250, None), Error::<Test>::VrfDelayInProgress);
+
+			run_to_block(15);
+			// Its fine to contribute when no auction is running.
+			assert!(!TestAuctioneer::auction_status(System::block_number()).is_in_progress());
+			assert_ok!(Crowdloan::contribute(Origin::signed(2), para, 250, None));
+		})
+	}
+
 	#[test]
 	fn bidding_works() {
 		new_test_ext().execute_with(|| {
 			let para = new_para();
-
 			let first_period = 1;
 			let last_period = 4;

@@ -1811,7 +1869,7 @@ mod benchmarking {
 				.ok_or("duration of auction less than zero")?;
 			T::Auctioneer::new_auction(duration, lease_period_index)?;

-			assert_eq!(T::Auctioneer::is_ending(end_block), Some(0u32.into()));
+			assert_eq!(T::Auctioneer::auction_status(end_block).is_ending(), Some((0u32.into(), 0u32.into())));
 			assert_eq!(NewRaise::<T>::get().len(), n as usize);
 			let old_endings_count = EndingsCount::<T>::get();
 		}: {
@@ -41,7 +41,7 @@ use crate::{
 	auctions, crowdloan, slots, paras_registrar,
 	slot_range::SlotRange,
 	traits::{
-		Registrar as RegistrarT, Auctioneer,
+		Registrar as RegistrarT, Auctioneer, AuctionStatus,
 	},
 };

@@ -868,7 +868,7 @@ fn crowdloan_ending_period_bid() {
 		// Go to beginning of ending period
 		run_to_block(100);

-		assert_eq!(Auctions::is_ending(100), Some(0));
+		assert_eq!(Auctions::auction_status(100), AuctionStatus::<u32>::EndingPeriod(0, 0));
 		let mut winning = [None; SlotRange::SLOT_RANGE_COUNT];
 		winning[SlotRange::ZeroOne as u8 as usize] = Some((2, ParaId::from(2001), 900));
 		winning[SlotRange::ZeroThree as u8 as usize] = Some((crowdloan_account, ParaId::from(2000), total));
@@ -137,6 +137,47 @@ pub trait Leaser {
 	fn lease_period_index() -> Self::LeasePeriod;
 }

+/// An enum which tracks the status of the auction system, and which phase it is in.
+#[derive(PartialEq, Debug)]
+pub enum AuctionStatus<BlockNumber> {
+	/// An auction has not started yet.
+	NotStarted,
+	/// We are in the starting period of the auction, collecting initial bids.
+	StartingPeriod,
+	/// We are in the ending period of the auction, where we are taking snapshots of the winning
+	/// bids. This state supports "sampling", where we may only take a snapshot every N blocks.
+	/// In this case, the first number is the current sample number, and the second number
+	/// is the sub-sample. i.e. for sampling every 20 blocks, the 25th block in the ending period
+	/// will be `EndingPeriod(1, 5)`.
+	EndingPeriod(BlockNumber, BlockNumber),
+	/// We have completed the bidding process and are waiting for the VRF to return some acceptable
+	/// randomness to select the winner. The number represents how many blocks we have been waiting.
+	VrfDelay(BlockNumber),
+}
+
+impl<BlockNumber> AuctionStatus<BlockNumber> {
+	/// Returns true if the auction is in any state other than `NotStarted`.
+	pub fn is_in_progress(&self) -> bool {
+		!matches!(self, Self::NotStarted)
+	}
+	/// Return true if the auction is in the starting period.
+	pub fn is_starting(&self) -> bool {
+		matches!(self, Self::StartingPeriod)
+	}
+	/// Returns `Some(sample, sub_sample)` if the auction is in the `EndingPeriod`,
+	/// otherwise returns `None`.
+	pub fn is_ending(self) -> Option<(BlockNumber, BlockNumber)> {
+		match self {
+			Self::EndingPeriod(sample, sub_sample) => Some((sample, sub_sample)),
+			_ => None,
+		}
+	}
+	/// Returns true if the auction is in the `VrfDelay` period.
+	pub fn is_vrf(&self) -> bool {
+		matches!(self, Self::VrfDelay(_))
+	}
+}
+
 pub trait Auctioneer {
 	/// An account identifier for a leaser.
 	type AccountId;
@@ -157,9 +198,8 @@ pub trait Auctioneer {
 	/// are to be auctioned.
 	fn new_auction(duration: Self::BlockNumber, lease_period_index: Self::LeasePeriod) -> DispatchResult;

-	/// Returns `Some(n)` if the `now` block is part of the ending period of an auction, where `n`
-	/// represents how far into the ending period this block is. Otherwise, returns `None`.
-	fn is_ending(now: Self::BlockNumber) -> Option<Self::BlockNumber>;
+	/// Given the current block number, return the current auction status.
+	fn auction_status(now: Self::BlockNumber) -> AuctionStatus<Self::BlockNumber>;

 	/// Place a bid in the current auction.
 	///