mirror of https://github.com/poanetwork/hbbft.git
562 lines
21 KiB
Rust
562 lines
21 KiB
Rust
//! # Broadcast
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//!
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//! The Reliable Broadcast Protocol assumes a network of `N` nodes that send signed messages to
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//! each other, with at most `f` of them faulty, where `3 * f < N`. Handling the networking and
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//! signing is the responsibility of this crate's user; a message is only handed to the Broadcast
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//! instance after it has been verified to be "from node i". One of the nodes is the "proposer"
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//! who sends a value. It needs to be determined beforehand, and all nodes need to know and agree
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//! who it is. Under the above conditions, the protocol guarantees that either all or none
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//! of the correct nodes output a value, and that if the proposer is correct, all correct nodes
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//! output the proposed value.
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//!
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//! ## How it works
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//!
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//! * The proposer uses a Reed-Solomon code to split the value into `N` chunks, `f + 1` of which
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//! suffice to reconstruct the value. These chunks are put into a Merkle tree, so that with the
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//! tree's root hash `h`, branch `bi` and chunk `si`, the `i`-th chunk `si` can be verified by
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//! anyone as belonging to the Merkle tree with root hash `h`. These values are "proof" number `i`:
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//! `pi = (h, bi, si)`.
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//! * The proposer sends `Value(pi)` to node `i`. It translates to: "I am the proposer, and `pi`
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//! contains the `i`-th share of my value."
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//! * Every (correct) node that receives `Value(pi)` from the proposer sends it on to everyone else
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//! as `Echo(pi)`. An `Echo` translates to: "I have received `pi` directly from the proposer." If
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//! the proposer sends another `Value` message it is ignored.
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//! * So every node that receives at least `f + 1` `Echo` messages with the same root hash can
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//! decode a value.
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//! * Every node that has received `N - f` `Echo`s with the same root hash from different nodes
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//! knows that at least `f + 1` _correct_ nodes have sent an `Echo` with that hash to everyone, and
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//! therefore everyone will eventually receive at least `f + 1` of them. So upon receiving `N - f`
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//! `Echo`s, they send a `Ready(h)` to everyone. It translates to: "I know that everyone will
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//! eventually be able to decode the value with root hash `h`." Moreover, since every correct node
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//! only sends one kind of `Echo` message, there is no danger of receiving `N - f` `Echo`s with two
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//! different root hashes.
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//! * Even without enough `Echo` messages, if a node receives `f + 1` `Ready` messages, it knows
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//! that at least one _correct_ node has sent `Ready`. It therefore also knows that everyone will
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//! be able to decode eventually, and multicasts `Ready` itself.
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//! * If a node has received `2 * f + 1` `Ready`s (with matching root hash) from different nodes,
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//! it knows that at least `f + 1` _correct_ nodes have sent it. Therefore, every correct node will
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//! eventually receive `f + 1`, and multicast it itself. Therefore, every correct node will
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//! eventually receive `2 * f + 1` `Ready`s, too. _And_ we know at this point that every correct
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//! node will eventually be able to decode (i.e. receive at least `f + 1` `Echo` messages).
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//! * So a node with `2 * f + 1` `Ready`s and `f + 1` `Echos` will decode and _output_ the value,
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//! knowing that every other correct node will eventually do the same.
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use std::collections::{BTreeMap, VecDeque};
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use std::fmt::{self, Debug};
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use std::iter::once;
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use std::rc::Rc;
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use byteorder::{BigEndian, ByteOrder};
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use merkle::{MerkleTree, Proof};
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use reed_solomon_erasure as rse;
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use reed_solomon_erasure::ReedSolomon;
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use ring::digest;
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use fmt::{HexBytes, HexList, HexProof};
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use messaging::{DistAlgorithm, NetworkInfo, Target, TargetedMessage};
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error_chain!{
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types {
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Error, ErrorKind, ResultExt, BroadcastResult;
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}
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foreign_links {
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ReedSolomon(rse::Error);
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}
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errors {
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InstanceCannotPropose
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NotImplemented
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ProofConstructionFailed
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RootHashMismatch
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Threading
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UnknownSender
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}
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}
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/// The three kinds of message sent during the reliable broadcast stage of the
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/// consensus algorithm.
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#[derive(Serialize, Deserialize, Clone, PartialEq)]
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pub enum BroadcastMessage {
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Value(Proof<Vec<u8>>),
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Echo(Proof<Vec<u8>>),
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Ready(Vec<u8>),
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}
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impl Debug for BroadcastMessage {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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match *self {
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BroadcastMessage::Value(ref v) => write!(f, "Value({:?})", HexProof(&v)),
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BroadcastMessage::Echo(ref v) => write!(f, "Echo({:?})", HexProof(&v)),
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BroadcastMessage::Ready(ref bytes) => write!(f, "Ready({:?})", HexBytes(bytes)),
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}
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}
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}
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/// Reliable Broadcast algorithm instance.
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pub struct Broadcast<NodeUid> {
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/// Shared network data.
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netinfo: Rc<NetworkInfo<NodeUid>>,
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/// The UID of the sending node.
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proposer_id: NodeUid,
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data_shard_num: usize,
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coding: Coding,
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/// Whether we have already multicast `Echo`.
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echo_sent: bool,
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/// Whether we have already multicast `Ready`.
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ready_sent: bool,
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/// Whether we have already output a value.
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decided: bool,
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/// The proofs we have received via `Echo` messages, by sender ID.
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echos: BTreeMap<NodeUid, Proof<Vec<u8>>>,
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/// The root hashes we received via `Ready` messages, by sender ID.
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readys: BTreeMap<NodeUid, Vec<u8>>,
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/// The outgoing message queue.
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messages: VecDeque<TargetedMessage<BroadcastMessage, NodeUid>>,
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/// The output, if any.
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output: Option<Vec<u8>>,
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}
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impl<NodeUid: Debug + Clone + Ord> DistAlgorithm for Broadcast<NodeUid> {
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type NodeUid = NodeUid;
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// TODO: Allow anything serializable and deserializable, i.e. make this a type parameter
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// T: Serialize + DeserializeOwned
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type Input = Vec<u8>;
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type Output = Self::Input;
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type Message = BroadcastMessage;
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type Error = Error;
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fn input(&mut self, input: Self::Input) -> BroadcastResult<()> {
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if *self.netinfo.our_uid() != self.proposer_id {
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return Err(ErrorKind::InstanceCannotPropose.into());
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}
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// Split the value into chunks/shards, encode them with erasure codes.
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// Assemble a Merkle tree from data and parity shards. Take all proofs
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// from this tree and send them, each to its own node.
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let proof = self.send_shards(input)?;
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let our_uid = &self.netinfo.our_uid().clone();
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self.handle_value(our_uid, proof)
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}
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fn handle_message(
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&mut self,
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sender_id: &NodeUid,
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message: Self::Message,
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) -> BroadcastResult<()> {
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if !self.netinfo.all_uids().contains(sender_id) {
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return Err(ErrorKind::UnknownSender.into());
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}
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match message {
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BroadcastMessage::Value(p) => self.handle_value(sender_id, p),
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BroadcastMessage::Echo(p) => self.handle_echo(sender_id, p),
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BroadcastMessage::Ready(ref hash) => self.handle_ready(sender_id, hash),
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}
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}
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fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, NodeUid>> {
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self.messages.pop_front()
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}
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fn next_output(&mut self) -> Option<Self::Output> {
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self.output.take()
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}
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fn terminated(&self) -> bool {
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self.decided
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}
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fn our_id(&self) -> &NodeUid {
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self.netinfo.our_uid()
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}
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}
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impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
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/// Creates a new broadcast instance to be used by node `our_id` which expects a value proposal
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/// from node `proposer_id`.
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pub fn new(netinfo: Rc<NetworkInfo<NodeUid>>, proposer_id: NodeUid) -> BroadcastResult<Self> {
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let parity_shard_num = 2 * netinfo.num_faulty();
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let data_shard_num = netinfo.num_nodes() - parity_shard_num;
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let coding = Coding::new(data_shard_num, parity_shard_num)?;
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Ok(Broadcast {
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netinfo,
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proposer_id,
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data_shard_num,
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coding,
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echo_sent: false,
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ready_sent: false,
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decided: false,
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echos: BTreeMap::new(),
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readys: BTreeMap::new(),
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messages: VecDeque::new(),
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output: None,
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})
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}
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/// Breaks the input value into shards of equal length and encodes them --
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/// and some extra parity shards -- with a Reed-Solomon erasure coding
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/// scheme. The returned value contains the shard assigned to this
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/// node. That shard doesn't need to be sent anywhere. It gets recorded in
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/// the broadcast instance.
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fn send_shards(&mut self, mut value: Vec<u8>) -> BroadcastResult<Proof<Vec<u8>>> {
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let data_shard_num = self.coding.data_shard_count();
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let parity_shard_num = self.coding.parity_shard_count();
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debug!(
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"Data shards: {}, parity shards: {}",
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self.data_shard_num, parity_shard_num
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);
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// Insert the length of `v` so it can be decoded without the padding.
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let payload_len = value.len() as u32;
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value.splice(0..0, 0..4); // Insert four bytes at the beginning.
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BigEndian::write_u32(&mut value[..4], payload_len); // Write the size.
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let value_len = value.len();
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// Size of a Merkle tree leaf value, in bytes.
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let shard_len = if value_len % data_shard_num > 0 {
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value_len / data_shard_num + 1
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} else {
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value_len / data_shard_num
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};
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// Pad the last data shard with zeros. Fill the parity shards with
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// zeros.
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value.resize(shard_len * (data_shard_num + parity_shard_num), 0);
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debug!("value_len {}, shard_len {}", value_len, shard_len);
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// Divide the vector into chunks/shards.
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let shards_iter = value.chunks_mut(shard_len);
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// Convert the iterator over slices into a vector of slices.
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let mut shards: Vec<&mut [u8]> = shards_iter.collect();
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debug!("Shards before encoding: {:?}", HexList(&shards));
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// Construct the parity chunks/shards
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self.coding
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.encode(&mut shards)
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.expect("the size and number of shards is correct");
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debug!("Shards: {:?}", HexList(&shards));
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// TODO: `MerkleTree` generates the wrong proof if a leaf occurs more than once, so we
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// prepend an "index byte" to each shard. Consider using the `merkle_light` crate instead.
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let shards_t: Vec<Vec<u8>> = shards
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.into_iter()
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.enumerate()
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.map(|(i, s)| once(i as u8).chain(s.iter().cloned()).collect())
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.collect();
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// Convert the Merkle tree into a partial binary tree for later
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// deconstruction into compound branches.
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let mtree = MerkleTree::from_vec(&digest::SHA256, shards_t);
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// Default result in case of `gen_proof` error.
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let mut result = Err(ErrorKind::ProofConstructionFailed.into());
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assert_eq!(self.netinfo.num_nodes(), mtree.iter().count());
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// Send each proof to a node.
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for (leaf_value, uid) in mtree.iter().zip(self.netinfo.all_uids()) {
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let proof = mtree
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.gen_proof(leaf_value.to_vec())
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.ok_or(ErrorKind::ProofConstructionFailed)?;
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if *uid == *self.netinfo.our_uid() {
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// The proof is addressed to this node.
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result = Ok(proof);
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} else {
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// Rest of the proofs are sent to remote nodes.
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let msg = Target::Node(uid.clone()).message(BroadcastMessage::Value(proof));
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self.messages.push_back(msg);
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}
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}
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result
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}
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/// Handles a received echo and verifies the proof it contains.
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fn handle_value(&mut self, sender_id: &NodeUid, p: Proof<Vec<u8>>) -> BroadcastResult<()> {
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// If the sender is not the proposer, this is not the first `Value` or the proof is invalid,
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// ignore.
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if *sender_id != self.proposer_id {
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info!(
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"Node {:?} received Value from {:?} instead of {:?}.",
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self.netinfo.our_uid(),
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sender_id,
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self.proposer_id
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);
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return Ok(());
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}
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if self.echo_sent {
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info!(
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"Node {:?} received multiple Values.",
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self.netinfo.our_uid()
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);
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return Ok(());
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}
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if !self.validate_proof(&p, &self.netinfo.our_uid()) {
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return Ok(());
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}
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// Otherwise multicast the proof in an `Echo` message, and handle it ourselves.
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self.send_echo(p)
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}
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/// Handles a received `Echo` message.
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fn handle_echo(&mut self, sender_id: &NodeUid, p: Proof<Vec<u8>>) -> BroadcastResult<()> {
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// If the proof is invalid or the sender has already sent `Echo`, ignore.
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if self.echos.contains_key(sender_id) {
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info!(
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"Node {:?} received multiple Echos from {:?}.",
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self.netinfo.our_uid(),
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sender_id,
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);
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return Ok(());
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}
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if !self.validate_proof(&p, sender_id) {
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return Ok(());
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}
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let hash = p.root_hash.clone();
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// Save the proof for reconstructing the tree later.
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self.echos.insert(sender_id.clone(), p);
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if self.ready_sent
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|| self.count_echos(&hash) < self.netinfo.num_nodes() - self.netinfo.num_faulty()
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{
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return self.compute_output(&hash);
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}
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// Upon receiving `N - f` `Echo`s with this root hash, multicast `Ready`.
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self.send_ready(&hash)
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}
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/// Handles a received `Ready` message.
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fn handle_ready(&mut self, sender_id: &NodeUid, hash: &[u8]) -> BroadcastResult<()> {
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// If the sender has already sent a `Ready` before, ignore.
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if self.readys.contains_key(sender_id) {
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info!(
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"Node {:?} received multiple Readys from {:?}.",
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self.netinfo.our_uid(),
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sender_id
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);
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return Ok(());
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}
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self.readys.insert(sender_id.clone(), hash.to_vec());
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// Upon receiving f + 1 matching Ready(h) messages, if Ready
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// has not yet been sent, multicast Ready(h).
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if self.count_readys(hash) == self.netinfo.num_faulty() + 1 && !self.ready_sent {
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// Enqueue a broadcast of a Ready message.
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self.send_ready(hash)?;
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}
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self.compute_output(hash)
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}
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/// Sends an `Echo` message and handles it. Does nothing if we are only an observer.
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fn send_echo(&mut self, p: Proof<Vec<u8>>) -> BroadcastResult<()> {
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self.echo_sent = true;
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if !self.netinfo.is_validator() {
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return Ok(());
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}
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let echo_msg = Target::All.message(BroadcastMessage::Echo(p.clone()));
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self.messages.push_back(echo_msg);
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let our_uid = &self.netinfo.our_uid().clone();
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self.handle_echo(our_uid, p)
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}
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/// Sends a `Ready` message and handles it. Does nothing if we are only an observer.
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fn send_ready(&mut self, hash: &[u8]) -> BroadcastResult<()> {
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self.ready_sent = true;
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if !self.netinfo.is_validator() {
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return Ok(());
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}
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let ready_msg = Target::All.message(BroadcastMessage::Ready(hash.to_vec()));
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self.messages.push_back(ready_msg);
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let our_uid = &self.netinfo.our_uid().clone();
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self.handle_ready(our_uid, hash)
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}
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/// Checks whether the condition for output are met for this hash, and if so, sets the output
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/// value.
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fn compute_output(&mut self, hash: &[u8]) -> BroadcastResult<()> {
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if self.decided
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|| self.count_readys(hash) <= 2 * self.netinfo.num_faulty()
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|| self.count_echos(hash) <= self.netinfo.num_faulty()
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{
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return Ok(());
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}
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// Upon receiving 2f + 1 matching Ready(h) messages, wait for N − 2f Echo messages.
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let mut leaf_values: Vec<Option<Box<[u8]>>> = self
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.netinfo
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.all_uids()
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.iter()
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.map(|id| {
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self.echos.get(id).and_then(|p| {
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if p.root_hash.as_slice() == hash {
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Some(p.value.clone().into_boxed_slice())
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} else {
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None
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}
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})
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})
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.collect();
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let value = decode_from_shards(&mut leaf_values, &self.coding, self.data_shard_num, hash);
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self.decided = value.is_some();
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self.output = value;
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Ok(())
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}
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/// Returns `i` if `node_id` is the `i`-th ID among all participating nodes.
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fn index_of_node(&self, node_id: &NodeUid) -> Option<usize> {
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self.netinfo.all_uids().iter().position(|id| id == node_id)
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}
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/// Returns `true` if the proof is valid and has the same index as the node ID. Otherwise
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/// logs an info message.
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fn validate_proof(&self, p: &Proof<Vec<u8>>, id: &NodeUid) -> bool {
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if !p.validate(&p.root_hash) {
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info!(
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"Node {:?} received invalid proof: {:?}",
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self.netinfo.our_uid(),
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HexProof(&p)
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);
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false
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} else if self.index_of_node(id) != Some(p.value[0] as usize)
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|| p.index(self.netinfo.num_nodes()) != p.value[0] as usize
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{
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info!(
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"Node {:?} received proof for wrong position: {:?}.",
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self.netinfo.our_uid(),
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HexProof(&p)
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);
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false
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} else {
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true
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}
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}
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/// Returns the number of nodes that have sent us an `Echo` message with this hash.
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fn count_echos(&self, hash: &[u8]) -> usize {
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self.echos
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.values()
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.filter(|p| p.root_hash.as_slice() == hash)
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.count()
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}
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/// Returns the number of nodes that have sent us a `Ready` message with this hash.
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fn count_readys(&self, hash: &[u8]) -> usize {
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self.readys
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.values()
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.filter(|h| h.as_slice() == hash)
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.count()
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}
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}
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/// A wrapper for `ReedSolomon` that doesn't panic if there are no parity shards.
|
||
enum Coding {
|
||
/// A `ReedSolomon` instance with at least one parity shard.
|
||
ReedSolomon(Box<ReedSolomon>),
|
||
/// A no-op replacement that doesn't encode or decode anything.
|
||
Trivial(usize),
|
||
}
|
||
|
||
impl Coding {
|
||
/// Creates a new `Coding` instance with the given number of shards.
|
||
fn new(data_shard_num: usize, parity_shard_num: usize) -> BroadcastResult<Self> {
|
||
Ok(if parity_shard_num > 0 {
|
||
let rs = ReedSolomon::new(data_shard_num, parity_shard_num)?;
|
||
Coding::ReedSolomon(Box::new(rs))
|
||
} else {
|
||
Coding::Trivial(data_shard_num)
|
||
})
|
||
}
|
||
|
||
/// Returns the number of data shards.
|
||
fn data_shard_count(&self) -> usize {
|
||
match *self {
|
||
Coding::ReedSolomon(ref rs) => rs.data_shard_count(),
|
||
Coding::Trivial(dsc) => dsc,
|
||
}
|
||
}
|
||
|
||
/// Returns the number of parity shards.
|
||
fn parity_shard_count(&self) -> usize {
|
||
match *self {
|
||
Coding::ReedSolomon(ref rs) => rs.parity_shard_count(),
|
||
Coding::Trivial(_) => 0,
|
||
}
|
||
}
|
||
|
||
/// Constructs (and overwrites) the parity shards.
|
||
fn encode(&self, slices: &mut [&mut [u8]]) -> BroadcastResult<()> {
|
||
match *self {
|
||
Coding::ReedSolomon(ref rs) => rs.encode(slices)?,
|
||
Coding::Trivial(_) => (),
|
||
}
|
||
Ok(())
|
||
}
|
||
|
||
/// If enough shards are present, reconstructs the missing ones.
|
||
fn reconstruct_shards(&self, shards: &mut [Option<Box<[u8]>>]) -> BroadcastResult<()> {
|
||
match *self {
|
||
Coding::ReedSolomon(ref rs) => rs.reconstruct_shards(shards)?,
|
||
Coding::Trivial(_) => {
|
||
if shards.iter().any(Option::is_none) {
|
||
return Err(rse::Error::TooFewShardsPresent.into());
|
||
}
|
||
}
|
||
}
|
||
Ok(())
|
||
}
|
||
}
|
||
|
||
fn decode_from_shards(
|
||
leaf_values: &mut [Option<Box<[u8]>>],
|
||
coding: &Coding,
|
||
data_shard_num: usize,
|
||
root_hash: &[u8],
|
||
) -> Option<Vec<u8>> {
|
||
// Try to interpolate the Merkle tree using the Reed-Solomon erasure coding scheme.
|
||
if let Err(err) = coding.reconstruct_shards(leaf_values) {
|
||
debug!("Shard reconstruction failed: {:?}", err); // Faulty proposer
|
||
return None;
|
||
}
|
||
|
||
// Recompute the Merkle tree root.
|
||
|
||
// Collect shards for tree construction.
|
||
let shards: Vec<Vec<u8>> = leaf_values
|
||
.iter()
|
||
.filter_map(|l| l.as_ref().map(|v| v.to_vec()))
|
||
.collect();
|
||
|
||
debug!("Reconstructed shards: {:?}", HexList(&shards));
|
||
|
||
// Construct the Merkle tree.
|
||
let mtree = MerkleTree::from_vec(&digest::SHA256, shards);
|
||
// If the root hash of the reconstructed tree does not match the one
|
||
// received with proofs then abort.
|
||
if &mtree.root_hash()[..] != root_hash {
|
||
None // The proposer is faulty.
|
||
} else {
|
||
// Reconstruct the value from the data shards.
|
||
glue_shards(mtree, data_shard_num)
|
||
}
|
||
}
|
||
|
||
/// Concatenates the first `n` leaf values of a Merkle tree `m` in one value of
|
||
/// type `T`. This is useful for reconstructing the data value held in the tree
|
||
/// and forgetting the leaves that contain parity information.
|
||
fn glue_shards(m: MerkleTree<Vec<u8>>, n: usize) -> Option<Vec<u8>> {
|
||
// Create an iterator over the shard payload, drop the index bytes.
|
||
let mut bytes = m.into_iter().take(n).flat_map(|s| s.into_iter().skip(1));
|
||
let payload_len = match (bytes.next(), bytes.next(), bytes.next(), bytes.next()) {
|
||
(Some(b0), Some(b1), Some(b2), Some(b3)) => BigEndian::read_u32(&[b0, b1, b2, b3]) as usize,
|
||
_ => return None, // The proposing node is faulty: no payload size.
|
||
};
|
||
let payload: Vec<u8> = bytes.take(payload_len).collect();
|
||
debug!("Glued data shards {:?}", HexBytes(&payload));
|
||
Some(payload)
|
||
}
|