#[macro_use]
extern crate slog;
use slog::Drain;
use std::collections::{HashMap, VecDeque};
use std::sync::mpsc::{self, Receiver, Sender, SyncSender, TryRecvError};
use std::sync::{Arc, Mutex};
use std::time::{Duration, Instant};
use std::{str, thread};
use protobuf::Message as PbMessage;
use raft::eraftpb::ConfState;
use raft::storage::MemStorage;
use raft::{prelude::*, StateRole};
use regex::Regex;
fn main() {
    let decorator = slog_term::TermDecorator::new().build();
    let drain = slog_term::FullFormat::new(decorator).build().fuse();
    let drain = slog_async::Async::new(drain)
        .chan_size(4096)
        .overflow_strategy(slog_async::OverflowStrategy::Block)
        .build()
        .fuse();
    let logger = slog::Logger::root(drain, o!());
    const NUM_NODES: u32 = 5;
    // Create 5 mailboxes to send/receive messages. Every node holds a `Receiver` to receive
    // messages from others, and uses the respective `Sender` to send messages to others.
    let (mut tx_vec, mut rx_vec) = (Vec::new(), Vec::new());
    for _ in 0..NUM_NODES {
        let (tx, rx) = mpsc::channel();
        tx_vec.push(tx);
        rx_vec.push(rx);
    }
    let (tx_stop, rx_stop) = mpsc::channel();
    let rx_stop = Arc::new(Mutex::new(rx_stop));
    // A global pending proposals queue. New proposals will be pushed back into the queue, and
    // after it's committed by the raft cluster, it will be poped from the queue.
    let proposals = Arc::new(Mutex::new(VecDeque::<Proposal>::new()));
    let mut handles = Vec::new();
    for (i, rx) in rx_vec.into_iter().enumerate() {
        // A map[peer_id -> sender]. In the example we create 5 nodes, with ids in [1, 5].
        let mailboxes = (1..6u64).zip(tx_vec.iter().cloned()).collect();
        let mut node = match i {
            // Peer 1 is the leader.
            0 => Node::create_raft_leader(1, rx, mailboxes, &logger),
            // Other peers are followers.
            _ => Node::create_raft_follower(rx, mailboxes),
        };
        let proposals = Arc::clone(&proposals);
        // Tick the raft node per 100ms. So use an `Instant` to trace it.
        let mut t = Instant::now();
        // Clone the stop receiver
        let rx_stop_clone = Arc::clone(&rx_stop);
        let logger = logger.clone();
        // Here we spawn the node on a new thread and keep a handle so we can join on them later.
        let handle = thread::spawn(move || loop {
            thread::sleep(Duration::from_millis(10));
            loop {
                // Step raft messages.
                match node.my_mailbox.try_recv() {
                    Ok(msg) => node.step(msg, &logger),
                    Err(TryRecvError::Empty) => break,
                    Err(TryRecvError::Disconnected) => return,
                }
            }
            let raft_group = match node.raft_group {
                Some(ref mut r) => r,
                // When Node::raft_group is `None` it means the node is not initialized.
                _ => continue,
            };
            if t.elapsed() >= Duration::from_millis(100) {
                // Tick the raft.
                raft_group.tick();
                t = Instant::now();
            }
            // Let the leader pick pending proposals from the global queue.
            if raft_group.raft.state == StateRole::Leader {
                // Handle new proposals.
                let mut proposals = proposals.lock().unwrap();
                for p in proposals.iter_mut().skip_while(|p| p.proposed > 0) {
                    propose(raft_group, p);
                }
            }
            // Handle readies from the raft.
            on_ready(
                raft_group,
                &mut node.kv_pairs,
                &node.mailboxes,
                &proposals,
                &logger,
            );
            // Check control signals from
            if check_signals(&rx_stop_clone) {
                return;
            };
        });
        handles.push(handle);
    }
    // Propose some conf changes so that followers can be initialized.
    add_all_followers(proposals.as_ref());
    // Put 100 key-value pairs.
    info!(
        logger,
        "We get a 5 nodes Raft cluster now, now propose 100 proposals"
    );
    (0..100u16)
        .filter(|i| {
            let (proposal, rx) = Proposal::normal(*i, "hello, world".to_owned());
            proposals.lock().unwrap().push_back(proposal);
            // After we got a response from `rx`, we can assume the put succeeded and following
            // `get` operations can find the key-value pair.
            rx.recv().unwrap()
        })
        .count();
    info!(logger, "Propose 100 proposals success!");
    // Send terminate signals
    for _ in 0..NUM_NODES {
        tx_stop.send(Signal::Terminate).unwrap();
    }
    // Wait for the thread to finish
    for th in handles {
        th.join().unwrap();
    }
}
enum Signal {
    Terminate,
}
fn check_signals(receiver: &Arc<Mutex<mpsc::Receiver<Signal>>>) -> bool {
    match receiver.lock().unwrap().try_recv() {
        Ok(Signal::Terminate) => true,
        Err(TryRecvError::Empty) => false,
        Err(TryRecvError::Disconnected) => true,
    }
}
struct Node {
    // None if the raft is not initialized.
    raft_group: Option<RawNode<MemStorage>>,
    my_mailbox: Receiver<Message>,
    mailboxes: HashMap<u64, Sender<Message>>,
    // Key-value pairs after applied. `MemStorage` only contains raft logs,
    // so we need an additional storage engine.
    kv_pairs: HashMap<u16, String>,
}
impl Node {
    // Create a raft leader only with itself in its configuration.
    fn create_raft_leader(
        id: u64,
        my_mailbox: Receiver<Message>,
        mailboxes: HashMap<u64, Sender<Message>>,
        logger: &slog::Logger,
    ) -> Self {
        let mut cfg = example_config();
        cfg.id = id;
        let logger = logger.new(o!("tag" => format!("peer_{}", id)));
        let storage = MemStorage::new_with_conf_state(ConfState::from((vec![id], vec![])));
        let raft_group = Some(RawNode::new(&cfg, storage, &logger).unwrap());
        Node {
            raft_group,
            my_mailbox,
            mailboxes,
            kv_pairs: Default::default(),
        }
    }
    // Create a raft follower.
    fn create_raft_follower(
        my_mailbox: Receiver<Message>,
        mailboxes: HashMap<u64, Sender<Message>>,
    ) -> Self {
        Node {
            raft_group: None,
            my_mailbox,
            mailboxes,
            kv_pairs: Default::default(),
        }
    }
    // Initialize raft for followers.
    fn initialize_raft_from_message(&mut self, msg: &Message, logger: &slog::Logger) {
        if !is_initial_msg(msg) {
            return;
        }
        let mut cfg = example_config();
        cfg.id = msg.to;
        let logger = logger.new(o!("tag" => format!("peer_{}", msg.to)));
        let storage = MemStorage::new();
        self.raft_group = Some(RawNode::new(&cfg, storage, &logger).unwrap());
    }
    // Step a raft message, initialize the raft if need.
    fn step(&mut self, msg: Message, logger: &slog::Logger) {
        if self.raft_group.is_none() {
            if is_initial_msg(&msg) {
                self.initialize_raft_from_message(&msg, &logger);
            } else {
                return;
            }
        }
        let raft_group = self.raft_group.as_mut().unwrap();
        let _ = raft_group.step(msg);
    }
}
fn on_ready(
    raft_group: &mut RawNode<MemStorage>,
    kv_pairs: &mut HashMap<u16, String>,
    mailboxes: &HashMap<u64, Sender<Message>>,
    proposals: &Mutex<VecDeque<Proposal>>,
    logger: &slog::Logger,
) {
    if !raft_group.has_ready() {
        return;
    }
    let store = raft_group.raft.raft_log.store.clone();
    // Get the `Ready` with `RawNode::ready` interface.
    let mut ready = raft_group.ready();
    // Persistent raft logs. It's necessary because in `RawNode::advance` we stabilize
    // raft logs to the latest position.
    if let Err(e) = store.wl().append(ready.entries()) {
        error!(
            logger,
            "persist raft log fail: {:?}, need to retry or panic", e
        );
        return;
    }
    // Apply the snapshot. It's necessary because in `RawNode::advance` we stabilize the snapshot.
    if *ready.snapshot() != Snapshot::default() {
        let s = ready.snapshot().clone();
        if let Err(e) = store.wl().apply_snapshot(s) {
            error!(
                logger,
                "apply snapshot fail: {:?}, need to retry or panic", e
            );
            return;
        }
    }
    // Send out the messages come from the node.
    for msg in ready.messages.drain(..) {
        let to = msg.to;
        if mailboxes[&to].send(msg).is_err() {
            error!(
                logger,
                "send raft message to {} fail, let Raft retry it", to
            );
        }
    }
    // Apply all committed proposals.
    if let Some(committed_entries) = ready.committed_entries.take() {
        for entry in &committed_entries {
            if entry.data.is_empty() {
                // From new elected leaders.
                continue;
            }
            if let EntryType::EntryConfChange = entry.get_entry_type() {
                // For conf change messages, make them effective.
                let mut cc = ConfChange::default();
                cc.merge_from_bytes(&entry.data).unwrap();
                let node_id = cc.node_id;
                match cc.get_change_type() {
                    ConfChangeType::AddNode => raft_group.raft.add_node(node_id).unwrap(),
                    ConfChangeType::RemoveNode => raft_group.raft.remove_node(node_id).unwrap(),
                    ConfChangeType::AddLearnerNode => raft_group.raft.add_learner(node_id).unwrap(),
                }
                let cs = raft_group.raft.prs().configuration().to_conf_state();
                store.wl().set_conf_state(cs);
            } else {
                // For normal proposals, extract the key-value pair and then
                // insert them into the kv engine.
                let data = str::from_utf8(&entry.data).unwrap();
                let reg = Regex::new("put ([0-9]+) (.+)").unwrap();
                if let Some(caps) = reg.captures(&data) {
                    kv_pairs.insert(caps[1].parse().unwrap(), caps[2].to_string());
                }
            }
            if raft_group.raft.state == StateRole::Leader {
                // The leader should response to the clients, tell them if their proposals
                // succeeded or not.
                let proposal = proposals.lock().unwrap().pop_front().unwrap();
                proposal.propose_success.send(true).unwrap();
            }
        }
        if let Some(last_committed) = committed_entries.last() {
            let mut s = store.wl();
            s.mut_hard_state().commit = last_committed.index;
            s.mut_hard_state().term = last_committed.term;
        }
    }
    // Call `RawNode::advance` interface to update position flags in the raft.
    raft_group.advance(ready);
}
fn example_config() -> Config {
    Config {
        election_tick: 10,
        heartbeat_tick: 3,
        ..Default::default()
    }
}
// The message can be used to initialize a raft node or not.
fn is_initial_msg(msg: &Message) -> bool {
    let msg_type = msg.get_msg_type();
    msg_type == MessageType::MsgRequestVote
        || msg_type == MessageType::MsgRequestPreVote
        || (msg_type == MessageType::MsgHeartbeat && msg.commit == 0)
}
struct Proposal {
    normal: Option<(u16, String)>, // key is an u16 integer, and value is a string.
    conf_change: Option<ConfChange>, // conf change.
    transfer_leader: Option<u64>,
    // If it's proposed, it will be set to the index of the entry.
    proposed: u64,
    propose_success: SyncSender<bool>,
}
impl Proposal {
    fn conf_change(cc: &ConfChange) -> (Self, Receiver<bool>) {
        let (tx, rx) = mpsc::sync_channel(1);
        let proposal = Proposal {
            normal: None,
            conf_change: Some(cc.clone()),
            transfer_leader: None,
            proposed: 0,
            propose_success: tx,
        };
        (proposal, rx)
    }
    fn normal(key: u16, value: String) -> (Self, Receiver<bool>) {
        let (tx, rx) = mpsc::sync_channel(1);
        let proposal = Proposal {
            normal: Some((key, value)),
            conf_change: None,
            transfer_leader: None,
            proposed: 0,
            propose_success: tx,
        };
        (proposal, rx)
    }
}
fn propose(raft_group: &mut RawNode<MemStorage>, proposal: &mut Proposal) {
    let last_index1 = raft_group.raft.raft_log.last_index() + 1;
    if let Some((ref key, ref value)) = proposal.normal {
        let data = format!("put {} {}", key, value).into_bytes();
        let _ = raft_group.propose(vec![], data);
    } else if let Some(ref cc) = proposal.conf_change {
        let _ = raft_group.propose_conf_change(vec![], cc.clone());
    } else if let Some(_transferee) = proposal.transfer_leader {
        // TODO: implement transfer leader.
        unimplemented!();
    }
    let last_index2 = raft_group.raft.raft_log.last_index() + 1;
    if last_index2 == last_index1 {
        // Propose failed, don't forget to respond to the client.
        proposal.propose_success.send(false).unwrap();
    } else {
        proposal.proposed = last_index1;
    }
}
// Proposes some conf change for peers [2, 5].
fn add_all_followers(proposals: &Mutex<VecDeque<Proposal>>) {
    for i in 2..6u64 {
        let mut conf_change = ConfChange::default();
        conf_change.node_id = i;
        conf_change.set_change_type(ConfChangeType::AddNode);
        loop {
            let (proposal, rx) = Proposal::conf_change(&conf_change);
            proposals.lock().unwrap().push_back(proposal);
            if rx.recv().unwrap() {
                break;
            }
            thread::sleep(Duration::from_millis(100));
        }
    }
}

# ϩⲟⲩⲣⲁⲧⲉ
/hɔwratɛ/, Sadhidic Coptic for *guardians*.
## A distributed uptime notification system
There are certainly many tools to identify uptime of systems out there, although I'd prefer one that worked completely in house and was pretty minimal, but smart.
Additionally, I want to learn about consensus protocols and gRPC, so this seemed to make a good deal of sense for a little project.
---
The aim is simple: a microservice that runs on all of my VPS's, my NAS and any other machines in my network (some of which are acceptable to be down at any point in time, but can be a part of the collective when up).
Everyone knows who should be awake and when, if that isn't the case, make sure everyone agrees and send me a notification.
If there is no consensus, then attempt to trace any connectivity issue and alert me of what is known.

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[package]
name = "howrate"
version = "0.1.0"
authors = ["Tim DuBois <tim@neophilus.net>"]
edition = "2018"
[dependencies]
raft = { version = "0.6.0-alpha", features = ["default"] }
protobuf = "2"
regex = "1.1"
slog = "2.2"
slog-stdlog = "4"
slog-envlogger = "2.1.0"
slog-term = "2.4.0"
slog-async = "2.3.0"
[patch.crates-io]
raft = { git = 'https://github.com/tikv/raft-rs' }