move paras inherent filtering to runtime

node/core/parachains-inherent/src/lib.rs

@@ -28,7 +28,7 @@ use futures::{select, FutureExt};
 use polkadot_node_subsystem::{
 	errors::SubsystemError, messages::ProvisionerMessage, overseer::Handle,
 };
-use polkadot_primitives::v1::{Block, Hash, InherentData as ParachainsInherentData};
+use polkadot_primitives::v1::{Block, SeedEntropy, Hash, InherentData as ParachainsInherentData};
 use sp_blockchain::HeaderBackend;
 use sp_runtime::generic::BlockId;
 use std::time;
@@ -97,6 +97,7 @@ impl ParachainsInherentDataProvider {
 					backed_candidates: Vec::new(),
 					disputes: Vec::new(),
 					parent_header,
+					entropy: SeedEntropy::draw(),
 				}
 			},
 		};

primitives/Cargo.toml

@@ -28,7 +28,9 @@ bitvec = { version = "0.20.1", default-features = false, features = ["alloc"] }
 frame-system = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 hex-literal = "0.3.3"
 parity-util-mem = { version = "0.10.0", default-features = false, optional = true }
-
+rand = { version = "0.8.4", optional = true }
+rand_chacha = { version = "0.3.1", optional = true }
+lazy_static = { version = "1.4", optional = true }
 
 [features]
 default = ["std"]
@@ -55,4 +57,7 @@ std = [
 	"polkadot-core-primitives/std",
 	"bitvec/std",
 	"frame-system/std",
+	"rand_chacha",
+	"rand/std",
+	"lazy_static",
 ]

primitives/src/v1/mod.rs

@@ -1344,6 +1344,43 @@ pub struct DisputeState<N = BlockNumber> {
 	pub concluded_at: Option<N>,
 }
 
+/// Type abstraction to provide entropy for seeding a `crng`
+#[derive(Clone, Encode, Decode, PartialEq, RuntimeDebug, TypeInfo)]
+pub struct SeedEntropy(pub [u8; 16]);
+
+impl AsRef<[u8]> for SeedEntropy {
+	fn as_ref(&self) -> &[u8] {
+		&self.0[..]
+	}
+}
+
+#[cfg(feature = "std")]
+impl SeedEntropy {
+	/// Collect a random entropy.
+	pub fn draw() -> Self {
+		let mut bytes = [0u8; 16];
+
+		use rand::RngCore;
+
+		#[cfg(not(fuzzing))]
+		{
+
+			let mut rng = rand::thread_rng();
+			rng.fill_bytes(&mut bytes[..]);
+		}
+
+		#[cfg(fuzzing)]
+		{
+			lazy_static::lazy_static!{
+				static ref RNG: rand_chacha::ChaChaRng = rand_chacha::ChaChaRng::from_seed(b"polkadot_on_chain_selection_seed");
+			}
+			RNG.fill_bytes(&mut bytes[..])
+		}
+
+
+		Self(bytes)
+	}
+}
 /// Parachains inherent-data passed into the runtime by a block author
 #[derive(Encode, Decode, Clone, PartialEq, RuntimeDebug, TypeInfo)]
 pub struct InherentData<HDR: HeaderT = Header> {
@@ -1355,6 +1392,9 @@ pub struct InherentData<HDR: HeaderT = Header> {
 	pub disputes: MultiDisputeStatementSet,
 	/// The parent block header. Used for checking state proofs.
 	pub parent_header: HDR,
+	/// Entropy source to initialize a `cprng`, for usage
+	/// in the decimation process of overweight blocks.
+	pub entropy: SeedEntropy,
 }
 
 /// The maximum number of validators `f` which may safely be faulty.