libp3p 0.0.0

libp3p
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// Copyright 2019 Stichting Organism
// Copyright (c) 2018-2019 Prime Type Ltd
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.


use rand_core::RngCore;
use std::collections::BTreeMap;

use crate::{topology::Module, Id, NodeData};

pub const CYCLON_MAX_GOSSIPING_LENGTH: usize = 128;

/// this module is responsible for randomly selecting Nodes
/// to be gossiped to another node.
///
/// It also make sure we contact the least contacted node for the next
/// gossiping round.
#[derive(Clone, Debug)]
pub struct Cyclon;
impl Cyclon {
    fn select_random_gossips<'a, Rng>(
        &self,
        rng: &mut Rng,
        known_nodes: &'a BTreeMap<Id, NodeData>,
    ) -> Vec<(&'a Id, &'a NodeData)>
    where
        Rng: RngCore,
    {
        let mut randomly_ordered_nodes: Vec<_> = known_nodes.iter().collect();
        randomly_ordered_nodes.sort_by(|_, _| match rng.next_u32() % 3 {
            0 => std::cmp::Ordering::Less,
            1 => std::cmp::Ordering::Equal,
            _ => std::cmp::Ordering::Greater,
        });

        randomly_ordered_nodes
    }
}

impl Default for Cyclon {
    fn default() -> Self {
        Cyclon
    }
}

impl Module for Cyclon {
    fn name(&self) -> &'static str {
        "cyclon"
    }

    fn select_gossips(
        &self,
        _our_node: &NodeData,
        gossip_recipient: &NodeData,
        known_nodes: &BTreeMap<Id, NodeData>,
    ) -> BTreeMap<Id, NodeData> {
        let mut candidates = BTreeMap::new();
        let mut rng = rand_os::OsRng::new().unwrap();

        candidates.extend(
            self.select_random_gossips(&mut rng, known_nodes)
                .into_iter()
                .filter(|(k, _)| k != &gossip_recipient.id())
                .take(CYCLON_MAX_GOSSIPING_LENGTH)
                .map(|(k, v)| (*k, v.clone())),
        );

        candidates
    }

    fn update(&mut self, _: &NodeData, _: &BTreeMap<Id, NodeData>) {
        /* nothing to update here, because we take all the known_nodes for the cyclon module */
    }

    fn view(&self, known_nodes: &BTreeMap<Id, NodeData>, view: &mut BTreeMap<Id, NodeData>) {
        let mut node_iterator = known_nodes.values();
        let candidate = if let Some(candidate) = node_iterator.next() {
            candidate
        } else {
            return;
        };

        let candidate = node_iterator.fold(candidate, |candidate, prospect| {
            if candidate.last_gossip < prospect.last_gossip {
                candidate
            } else {
                prospect
            }
        });
        view.insert(*candidate.id(), candidate.clone());
    }
}