This is a rust library implementing weighted BPCon consensus.
Library is documented with rustdoc
.
Compiled documentation for main
branch is available at GitBook.
[dependencies]
bpcon = {version = "0.1.0", git = "https://github.com/distributed-lab/bpcon"}
Implement Value trait
This is a core trait, which defines what type are you selecting in your consensus. It may be the next block in blockchain, or leader for some operation, or anything else you need.
Below is a simple example, where we will operate on selection for u64
type.
Using it you may interpret ID
for leader of distributed operation, for instance.
...
use bpcon::value::Value;
#[derive(Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize, Debug, Hash)]
pub(crate) struct MyValue(u64);
impl Value for MyValue {}
Implement ValueSelector trait
BPCon
allows you to define specific conditions how proposer (leader) will select value
and how other members will verify its selection.
Here is a simple example:
...
use bpcon::value::ValueSelector;
#[derive(Clone)]
pub struct MyValueSelector;
impl ValueSelector<MyValue> for MyValueSelector {
/// Verifies if the given value `v` has been correctly selected according to the protocol rules.
///
/// In this basic implementation, we'll consider a value as "correctly selected" if it matches
/// the majority of the values in the provided `HashMap`.
fn verify(&self, v: &MyValue, m: &HashMap<u64, Option<MyValue>>) -> bool {
// Count how many times the value `v` appears in the `HashMap`
let count = m.values().filter(|&val| val.as_ref() == Some(v)).count();
// For simplicity, consider the value verified if it appears in more than half of the entries
count > m.len() / 2
}
/// Selects a value based on the provided `HashMap` of party votes.
///
/// This implementation selects the value that appears most frequently in the `HashMap`.
/// If there is a tie, it selects the smallest value (as per the natural ordering of `u64`).
fn select(&self, m: &HashMap<u64, Option<MyValue>>) -> MyValue {
let mut frequency_map = HashMap::new();
// Count the frequency of each value in the `HashMap`
for value in m.values().flatten() {
*frequency_map.entry(value).or_insert(0) += 1;
}
// Find the value with the highest frequency. In case of a tie, select the smallest value.
frequency_map
.into_iter()
.max_by_key(|(value, count)| (*count, value.0))
.map(|(value, _)| value.clone())
.expect("No valid value found")
}
}
Decide on a LeaderElector
LeaderElector
trait allows you to define specific conditions, how to select leader for consensus.
NOTE: it is important to provide deterministic mechanism, because each participant will compute leader for itself and in case it is not deterministic, state divergence occurs.
We also provide ready-to-use DefaultLeaderElector which is using weighted randomization.
As a next step, you need to decide on parameters for your ballot:
- Amount of parties and their weight.
- Threshold weight.
- Time bounds.
Example:
use bpcon::config::BPConConfig;
let cfg = BPConConfig::with_default_timeouts(vec![1, 1, 1, 1, 1, 1], 4);
Feel free to explore config.rs for more information.
Having BPConConfig
, ValueSelector
and LeaderElector
defined, instantiate your parties.
Check out new
method on a Party
struct.
Each party interfaces communication with external system via channels. In a way, you shall propagate outgoing messages to other parties like:
- Listen for outgoing message using
msg_out_receiver
. - Forward it to other parties using
msg_in_sender
.
We welcome you to check test_end_to_end_ballot
in party.rs
for example.