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more clear randomness API for BABE (#8180)

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* more clear randomness API for BABE

* babe: move randomness utilities to its own file

* node: use babe::RandomnessFromOneEpochAgo in random_seed implementation

* frame-support: annotate randomness trait with block number

* pallet-randomness-collective-flip: fix for new randomness trait

* pallet-society: fix randomness usage

* pallet-lottery: fix randomness usage

* pallet-contracts: fix randomness usage

* pallet-babe: fix randomness usage

we need to track when the current and previous epoch started so that we
know the block number by each existing on-chain was known

* node: fix random_seed

* node-template: fix random_seed

* frame-support: extend docs

* babe: add test for epoch starting block number tracking

* babe: fix epoch randomness docs

* frame: add todos for dealing with randomness api changes

Co-authored-by: André Silva <andrerfosilva@gmail.com>
This commit is contained in:
Robert Habermeier
2021-03-10 10:31:49 -06:00
committed by GitHub
parent f3d4355a20
commit e2960c383e
18 changed files with 286 additions and 78 deletions
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substrate/frame/support/src/traits.rs
+32 -28
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@@ -23,13 +23,13 @@ use sp_std::{prelude::*, result, marker::PhantomData, ops::Div, fmt::Debug};
use codec::{FullCodec, Codec, Encode, Decode, EncodeLike};
use sp_core::u32_trait::Value as U32;
use sp_runtime::{
RuntimeAppPublic, RuntimeDebug, BoundToRuntimeAppPublic,
ConsensusEngineId, DispatchResult, DispatchError,
traits::{
MaybeSerializeDeserialize, AtLeast32Bit, Saturating, TrailingZeroInput, Bounded, Zero,
BadOrigin, AtLeast32BitUnsigned, Convert, UniqueSaturatedFrom, UniqueSaturatedInto,
SaturatedConversion, StoredMapError, Block as BlockT,
AtLeast32Bit, AtLeast32BitUnsigned, BadOrigin, Block as BlockT, Bounded, Convert,
MaybeSerializeDeserialize, SaturatedConversion, Saturating, StoredMapError,
UniqueSaturatedFrom, UniqueSaturatedInto, Zero,
},
BoundToRuntimeAppPublic, ConsensusEngineId, DispatchError, DispatchResult, RuntimeAppPublic,
RuntimeDebug,
};
use sp_staking::SessionIndex;
use crate::dispatch::Parameter;
@@ -1413,38 +1413,42 @@ impl<T> InitializeMembers<T> for () {
fn initialize_members(_: &[T]) {}
}
// A trait that is able to provide randomness.
pub trait Randomness<Output> {
/// Get a "random" value
/// A trait that is able to provide randomness.
///
/// Being a deterministic blockchain, real randomness is difficult to come by, different
/// implementations of this trait will provide different security guarantees. At best,
/// this will be randomness which was hard to predict a long time ago, but that has become
/// easy to predict recently.
pub trait Randomness<Output, BlockNumber> {
/// Get the most recently determined random seed, along with the time in the past
/// since when it was determinable by chain observers.
///
/// Being a deterministic blockchain, real randomness is difficult to come by. This gives you
/// something that approximates it. At best, this will be randomness which was
/// hard to predict a long time ago, but that has become easy to predict recently.
/// `subject` is a context identifier and allows you to get a different result to
/// other callers of this function; use it like `random(&b"my context"[..])`.
///
/// `subject` is a context identifier and allows you to get a
/// different result to other callers of this function; use it like
/// `random(&b"my context"[..])`.
fn random(subject: &[u8]) -> Output;
/// NOTE: The returned seed should only be used to distinguish commitments made before
/// the returned block number. If the block number is too early (i.e. commitments were
/// made afterwards), then ensure no further commitments may be made and repeatedly
/// call this on later blocks until the block number returned is later than the latest
/// commitment.
fn random(subject: &[u8]) -> (Output, BlockNumber);
/// Get the basic random seed.
///
/// In general you won't want to use this, but rather `Self::random` which allows you to give a
/// subject for the random result and whose value will be independently low-influence random
/// from any other such seeds.
fn random_seed() -> Output {
/// In general you won't want to use this, but rather `Self::random` which allows
/// you to give a subject for the random result and whose value will be
/// independently low-influence random from any other such seeds.
///
/// NOTE: The returned seed should only be used to distinguish commitments made before
/// the returned block number. If the block number is too early (i.e. commitments were
/// made afterwards), then ensure no further commitments may be made and repeatedly
/// call this on later blocks until the block number returned is later than the latest
/// commitment.
fn random_seed() -> (Output, BlockNumber) {
Self::random(&[][..])
}
}
/// Provides an implementation of [`Randomness`] that should only be used in tests!
pub struct TestRandomness;
impl<Output: Decode + Default> Randomness<Output> for TestRandomness {
fn random(subject: &[u8]) -> Output {
Output::decode(&mut TrailingZeroInput::new(subject)).unwrap_or_default()
}
}
/// Trait to be used by block producing consensus engine modules to determine
/// how late the current block is (e.g. in a slot-based proposal mechanism how
/// many slots were skipped since the previous block).