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//! # Queueing Honey Badger //! //! This works exactly like Dynamic Honey Badger, but it has a transaction queue built in. Whenever //! an epoch is output, it will automatically select a list of pending transactions and propose it //! for the next one. The user can continuously add more pending transactions to the queue. //! //! If there are no pending transactions, no validators in the process of being added or //! removed and not enough other nodes have proposed yet, no automatic proposal will be made: The //! network then waits until at least _f + 1_ have any content for the next epoch. //! //! ## How it works //! //! Queueing Honey Badger runs a Dynamic Honey Badger internally, and automatically inputs a list //! of pending transactions as its contribution at the beginning of each epoch. These are selected //! by making a random choice of _B / N_ out of the first _B_ entries in the queue, where _B_ is the //! configurable `batch_size` parameter, and _N_ is the current number of validators. //! //! After each output, the transactions that made it into the new batch are removed from the queue. //! //! The random choice of transactions is made to reduce redundancy even if all validators have //! roughly the same entries in their queues. By selecting a random fraction of the first _B_ //! entries, any two nodes will likely make almost disjoint contributions instead of proposing //! the same transaction multiple times. use std::marker::PhantomData; use std::{cmp, iter}; use derivative::Derivative; use failure::Fail; use rand::distributions::{Distribution, Standard}; use rand::Rng; use serde::{de::DeserializeOwned, Serialize}; use crate::crypto::{PublicKey, SecretKey}; use crate::dynamic_honey_badger::{ self, Batch as DhbBatch, DynamicHoneyBadger, FaultKind, JoinPlan, Message, Step as DhbStep, }; use crate::transaction_queue::TransactionQueue; use crate::{ConsensusProtocol, Contribution, NetworkInfo, NodeIdT}; pub use crate::dynamic_honey_badger::{Change, ChangeState, Input}; /// Queueing honey badger error variants. #[derive(Debug, Fail)] pub enum Error { /// Failed to handle input. #[fail(display = "Input error: {}", _0)] Input(dynamic_honey_badger::Error), /// Failed to handle a message. #[fail(display = "Handle message error: {}", _0)] HandleMessage(dynamic_honey_badger::Error), /// Failed to propose a contribution. #[fail(display = "Propose error: {}", _0)] Propose(dynamic_honey_badger::Error), /// Failed to create a Dynamic Honey Badger instance according to a join plan. #[fail(display = "New joining error: {}", _0)] NewJoining(dynamic_honey_badger::Error), } /// The result of `QueueingHoneyBadger` handling an input or message. pub type Result<T> = ::std::result::Result<T, Error>; /// A Queueing Honey Badger builder, to configure the parameters and create new instances of /// `QueueingHoneyBadger`. pub struct QueueingHoneyBadgerBuilder<T, N, Q> where T: Contribution + Serialize + DeserializeOwned + Clone, N: NodeIdT + Serialize + DeserializeOwned, { /// Shared network data. dyn_hb: DynamicHoneyBadger<Vec<T>, N>, /// The target number of transactions to be included in each batch. batch_size: usize, /// The queue of pending transactions that haven't been output in a batch yet. queue: Q, /// The initial step of the managed `DynamicHoneyBadger` instance. step: Option<DhbStep<Vec<T>, N>>, _phantom: PhantomData<T>, } type QueueingHoneyBadgerWithStep<T, N, Q> = (QueueingHoneyBadger<T, N, Q>, Step<T, N>); impl<T, N, Q> QueueingHoneyBadgerBuilder<T, N, Q> where T: Contribution + Serialize + DeserializeOwned + Clone, N: NodeIdT + Serialize + DeserializeOwned, Q: TransactionQueue<T>, Standard: Distribution<N>, { /// Returns a new `QueueingHoneyBadgerBuilder` wrapping the given instance of /// `DynamicHoneyBadger`. pub fn new(dyn_hb: DynamicHoneyBadger<Vec<T>, N>) -> Self { // TODO: Use the defaults from `HoneyBadgerBuilder`. QueueingHoneyBadgerBuilder { dyn_hb, batch_size: 100, queue: Default::default(), step: None, _phantom: PhantomData, } } /// Sets the initial step of the `DynamicHoneyBadger` instance. pub fn step(mut self, step: DhbStep<Vec<T>, N>) -> Self { self.step = Some(step); self } /// Sets the target number of transactions per batch. pub fn batch_size(mut self, batch_size: usize) -> Self { self.batch_size = batch_size; self } /// Sets the transaction queue object. pub fn queue(mut self, queue: Q) -> Self { self.queue = queue; self } /// Creates a new Queueing Honey Badger instance with an empty buffer. pub fn build<R: Rng>(self, rng: &mut R) -> Result<QueueingHoneyBadgerWithStep<T, N, Q>> { self.build_with_transactions(None, rng) } /// Returns a new Queueing Honey Badger instance that starts with the given transactions in its /// buffer. pub fn build_with_transactions<TI, R>( mut self, txs: TI, rng: &mut R, ) -> Result<QueueingHoneyBadgerWithStep<T, N, Q>> where TI: IntoIterator<Item = T>, R: Rng, { self.queue.extend(txs); let mut qhb = QueueingHoneyBadger { dyn_hb: self.dyn_hb, batch_size: self.batch_size, queue: self.queue, }; let mut step = qhb.propose(rng)?; if let Some(dhb_step) = self.step { step.extend(dhb_step); } Ok((qhb, step)) } } /// A Honey Badger instance that can handle adding and removing nodes and manages a transaction /// queue. #[derive(Derivative)] #[derivative(Debug)] pub struct QueueingHoneyBadger<T, N: Ord, Q> { /// The target number of transactions to be included in each batch. batch_size: usize, /// The internal managed `DynamicHoneyBadger` instance. dyn_hb: DynamicHoneyBadger<Vec<T>, N>, /// The queue of pending transactions that haven't been output in a batch yet. queue: Q, } /// A `QueueingHoneyBadger` step, possibly containing multiple outputs. pub type Step<T, N> = crate::Step<Message<N>, Batch<T, N>, N, FaultKind>; impl<T, N, Q> ConsensusProtocol for QueueingHoneyBadger<T, N, Q> where T: Contribution + Serialize + DeserializeOwned + Clone, N: NodeIdT + Serialize + DeserializeOwned, Q: TransactionQueue<T>, Standard: Distribution<N>, { type NodeId = N; type Input = Input<T, N>; type Output = Batch<T, N>; type Message = Message<N>; type Error = Error; type FaultKind = FaultKind; fn handle_input<R: Rng>(&mut self, input: Self::Input, rng: &mut R) -> Result<Step<T, N>> { // User transactions are forwarded to `HoneyBadger` right away. Internal messages are // in addition signed and broadcast. match input { Input::User(tx) => self.push_transaction(tx, rng), Input::Change(change) => self.vote_for(change, rng), } } fn handle_message<R: Rng>( &mut self, sender_id: &N, message: Self::Message, rng: &mut R, ) -> Result<Step<T, N>> { self.handle_message(sender_id, message, rng) } fn terminated(&self) -> bool { false } fn our_id(&self) -> &N { self.dyn_hb.our_id() } } impl<T, N, Q> QueueingHoneyBadger<T, N, Q> where T: Contribution + Serialize + DeserializeOwned + Clone, N: NodeIdT + Serialize + DeserializeOwned, Q: TransactionQueue<T>, Standard: Distribution<N>, { /// Returns a new `QueueingHoneyBadgerBuilder` configured to use the node IDs and cryptographic /// keys specified by `netinfo`. pub fn builder(dyn_hb: DynamicHoneyBadger<Vec<T>, N>) -> QueueingHoneyBadgerBuilder<T, N, Q> { QueueingHoneyBadgerBuilder::new(dyn_hb) } /// Creates a new `QueueingHoneyBadgerBuilder` for joining the network specified in the /// `JoinPlan`. /// /// Returns a `QueueingHoneyBadgerBuilder` or an error if creation of the managed /// `DynamicHoneyBadger` instance has failed. pub fn builder_joining<R: Rng>( our_id: N, secret_key: SecretKey, join_plan: JoinPlan<N>, rng: &mut R, ) -> Result<QueueingHoneyBadgerBuilder<T, N, Q>> { let (dhb, step) = DynamicHoneyBadger::new_joining(our_id, secret_key, join_plan, rng) .map_err(Error::NewJoining)?; Ok(QueueingHoneyBadgerBuilder::new(dhb).step(step)) } /// Adds a transaction to the queue. /// /// This can be called at any time to append to the transaction queue. The new transaction will /// be proposed in some future epoch. /// /// If no proposal has yet been made for the current epoch, this may trigger one. In this case, /// a nonempty step will returned, with the corresponding messages. (Or, if we are the only /// validator, even with the completed batch as an output.) pub fn push_transaction<R: Rng>(&mut self, tx: T, rng: &mut R) -> Result<Step<T, N>> { self.queue.extend(iter::once(tx)); self.propose(rng) } /// Casts a vote to change the set of validators. /// /// This stores a pending vote for the change. It will be included in some future batch, and /// once enough validators have been voted for the same change, it will take effect. pub fn vote_for<R: Rng>(&mut self, change: Change<N>, rng: &mut R) -> Result<Step<T, N>> { self.apply(|dyn_hb, _| dyn_hb.vote_for(change), rng) } /// Casts a vote to add a node as a validator. /// /// This stores a pending vote for the change. It will be included in some future batch, and /// once enough validators have been voted for the same change, it will take effect. pub fn vote_to_add<R: Rng>( &mut self, node_id: N, pub_key: PublicKey, rng: &mut R, ) -> Result<Step<T, N>> { self.apply(|dyn_hb, _| dyn_hb.vote_to_add(node_id, pub_key), rng) } /// Casts a vote to demote a validator to observer. /// /// This stores a pending vote for the change. It will be included in some future batch, and /// once enough validators have been voted for the same change, it will take effect. pub fn vote_to_remove<R: Rng>(&mut self, node_id: &N, rng: &mut R) -> Result<Step<T, N>> { self.apply(|dyn_hb, _| dyn_hb.vote_to_remove(node_id), rng) } /// Handles a message received from `sender_id`. /// /// This must be called with every message we receive from another node. pub fn handle_message<R: Rng>( &mut self, sender_id: &N, message: Message<N>, rng: &mut R, ) -> Result<Step<T, N>> { self.apply( |dyn_hb, rng| dyn_hb.handle_message(sender_id, message, rng), rng, ) } /// Returns a reference to the internal managed `DynamicHoneyBadger` instance. pub fn dyn_hb(&self) -> &DynamicHoneyBadger<Vec<T>, N> { &self.dyn_hb } /// Returns the information about the node IDs in the network, and the cryptographic keys. pub fn netinfo(&self) -> &NetworkInfo<N> { self.dyn_hb.netinfo() } /// Returns the current queue of the `QueueingHoneyBadger`. pub fn queue(&self) -> &Q { &self.queue } /// Applies a function `f` to the `DynamicHoneyBadger` instance and processes the step. fn apply<R, F>(&mut self, f: F, rng: &mut R) -> Result<Step<T, N>> where F: FnOnce( &mut DynamicHoneyBadger<Vec<T>, N>, &mut R, ) -> dynamic_honey_badger::Result<Step<T, N>>, R: Rng, { let step = f(&mut self.dyn_hb, rng).map_err(Error::Input)?; self.queue .remove_multiple(step.output.iter().flat_map(Batch::iter)); Ok(step.join(self.propose(rng)?)) } /// Returns the epoch of the next batch that will be output. pub fn next_epoch(&self) -> u64 { self.dyn_hb.next_epoch() } /// Returns `true` if we are ready to propose our contribution for the next epoch, i.e. if the /// previous epoch has completed and we have either pending transactions or we are required to /// make a proposal to avoid stalling the network. fn can_propose(&self) -> bool { if self.dyn_hb.has_input() { return false; // Previous epoch is still in progress. } !self.queue.is_empty() || self.dyn_hb.should_propose() } /// Initiates the next epoch by proposing a batch from the queue. fn propose<R: Rng>(&mut self, rng: &mut R) -> Result<Step<T, N>> { let mut step = Step::default(); while self.can_propose() { let amount = cmp::max(1, self.batch_size / self.dyn_hb.netinfo().num_nodes()); let proposal = self.queue.choose(rng, amount, self.batch_size); step.extend( self.dyn_hb .handle_input(Input::User(proposal), rng) .map_err(Error::Propose)?, ); } Ok(step) } } /// A batch containing a list of transactions from at least two thirds of the validators. pub type Batch<T, N> = DhbBatch<Vec<T>, N>;