maelstrom-rust-node

Yet another one Rust crate for implementing nodes for https://github.com/jepsen-io/maelstrom and solve https://fly.io/dist-sys/ challenges.

What is Maelstrom?

Maelstrom is a platform for learning distributed systems. It is build around Jepsen and Elle to ensure no properties are violated. With maelstrom you build nodes that form distributed system that can process different workloads.

Features

• async (tokio)
• multi-threading
• simple API - single trait fn to implement
• response types auto-deduction, extra data available via Value()
• unknown message types handling
• a/sync RPC() support + timeout / context
• lin/seq/lww kv storage
• transparent error handling
• TODO: thiserror + error parsing/ser causes

Examples

Echo workload

$ cargo build --examples
$ maelstrom test -w echo --bin ./target/debug/examples/echo --node-count 1 --time-limit 10 --log-stderr

implementation:

use async_trait::async_trait;
use maelstrom::protocol::Message;
use maelstrom::{Node, Result, Runtime};
use std::sync::Arc;

pub(crate) fn main() -> Result<()> {
    Runtime::init(try_main())
}

async fn try_main() -> Result<()> {
    let handler = Arc::new(Handler::default());
    Runtime::new().with_handler(handler).run().await
}

#[derive(Clone, Default)]
struct Handler {}

#[async_trait]
impl Node for Handler {
    async fn process(&self, runtime: Runtime, req: Message) -> Result<()> {
        if req.get_type() == "echo" {
            let echo = req.body.clone().with_type("echo_ok");
            return runtime.reply(req, echo).await;
        }

        done(runtime, message)
    }
}

spec:

receiving

{
  "src": "c1",
  "dest": "n1",
  "body": {
    "type": "echo",
    "msg_id": 1,
    "echo": "Please echo 35"
  }
}

send back the same msg with body.type == echo_ok.

{
  "src": "n1",
  "dest": "c1",
  "body": {
    "type": "echo_ok",
    "msg_id": 1,
    "in_reply_to": 1,
    "echo": "Please echo 35"
  }
}

Broadcast workload

$ cargo build --examples
$ RUST_LOG=debug maelstrom test -w broadcast --bin ./target/debug/examples/broadcast --node-count 2 --time-limit 20 --rate 10 --log-stderr

implementation:

#[async_trait]
impl Node for Handler {
    async fn process(&self, runtime: Runtime, req: Message) -> Result<()> {
        let msg: Result<Request> = req.body.as_obj();
        match msg {
            Ok(Request::Read {}) => {
                let data = self.snapshot();
                let msg = Request::ReadOk { messages: data };
                return runtime.reply(req, msg).await;
            }
            Ok(Request::Broadcast { message: element }) => {
                if self.try_add(element) {
                    info!("messages now {}", element);
                    for node in runtime.neighbours() {
                        runtime.call_async(node, Request::Broadcast { message: element });
                    }
                }

                return runtime.reply_ok(req).await;
            }
            Ok(Request::Topology { topology }) => {
                let neighbours = topology.get(runtime.node_id()).unwrap();
                self.inner.lock().unwrap().t = neighbours.clone();
                info!("My neighbors are {:?}", neighbours);
                return runtime.reply_ok(req).await;
            }
            _ => done(runtime, req),
        }
    }
}

lin-kv workload

$ cargo build --examples
$ RUST_LOG=debug ~/Projects/maelstrom/maelstrom test -w lin-kv --bin ./target/debug/examples/lin_kv --node-count 4 --concurrency 2n --time-limit 10 --rate 100 --log-stderr

implementation:

#[async_trait]
impl Node for Handler {
    async fn process(&self, runtime: Runtime, req: Message) -> Result<()> {
        let (ctx, _handler) = Context::new();
        let msg: Result<Request> = req.body.as_obj();
        match msg {
            Ok(Request::Read { key }) => {
                let value = self.s.get(ctx, key.to_string()).await?;
                return runtime.reply(req, Request::ReadOk { value }).await;
            }
            Ok(Request::Write { key, value }) => {
                self.s.put(ctx, key.to_string(), value).await?;
                return runtime.reply(req, Request::WriteOk {}).await;
            }
            Ok(Request::Cas { key, from, to, put }) => {
                self.s.cas(ctx, key.to_string(), from, to, put).await?;
                return runtime.reply(req, Request::CasOk {}).await;
            }
            _ => done(runtime, req),
        }
    }
}

fn handler(runtime: Runtime) -> Handler {
    Handler { s: lin_kv(runtime) }
}

g-set workload

$ cargo build --examples
$ RUST_LOG=debug ~/Projects/maelstrom/maelstrom test -w g-set --bin ./target/debug/examples/g_set --node-count 2 --concurrency 2n --time-limit 20 --rate 10 --log-stderr

implementation:

#[async_trait]
impl Node for Handler {
    async fn process(&self, runtime: Runtime, req: Message) -> Result<()> {
        let msg: Result<Request> = req.body.as_obj();
        match msg {
            Ok(Request::Read {}) => {
                let data = to_seq(&self.s.lock().unwrap());
                return runtime.reply(req, Request::ReadOk { value: data }).await;
            }
            Ok(Request::Add { element }) => {
                self.s.lock().unwrap().insert(element);
                return runtime.reply(req, Request::AddOk {}).await;
            }
            Ok(Request::ReplicateOne { element }) => {
                self.s.lock().unwrap().insert(element);
                return Ok(());
            }
            Ok(Request::ReplicateFull { value }) => {
                let mut s = self.s.lock().unwrap();
                for v in value {
                    s.insert(v);
                }
                return Ok(());
            }
            Ok(Request::Init {}) => {
                // spawn into tokio (instead of runtime) to not to wait
                // until it is completed, as it will never be.
                let (r0, h0) = (runtime.clone(), self.clone());
                tokio::spawn(async move {
                    loop {
                        tokio::time::sleep(Duration::from_secs(5)).await;
                        debug!("emit replication signal");
                        let s = h0.s.lock().unwrap();
                        for n in r0.neighbours() {
                            let msg = Request::ReplicateFull { value: to_seq(&s) };
                            drop(r0.send_async(n.to_string(), msg));
                        }
                    }
                });
                return Ok(());
            }
            _ => done(runtime, req),
        }
    }
}

API

Key-Value storage

use async_trait::async_trait;
use maelstrom::kv::{lin_kv, Storage, KV};
use maelstrom::protocol::Message;
use maelstrom::{done, Node, Result, Runtime};
use tokio_context::context::Context;

#[derive(Clone)]
struct Handler {
    s: Storage,
}

#[async_trait]
impl Node for Handler {
    async fn process(&self, runtime: Runtime, req: Message) -> Result<()> {
        let (ctx, _handler) = Context::new();
        let msg: Result<Request> = req.body.as_obj();
        match msg {
            Ok(Request::Read { key }) => {
                let value = self.s.get(ctx, key.to_string()).await?;
                return runtime.reply(req, Request::ReadOk { value }).await;
            }
            Ok(Request::Write { key, value }) => {
                self.s.put(ctx, key.to_string(), value).await?;
                return runtime.reply(req, Request::WriteOk {}).await;
            }
            Ok(Request::Cas { key, from, to, put }) => {
                self.s.cas(ctx, key.to_string(), from, to, put).await?;
                return runtime.reply(req, Request::CasOk {}).await;
            }
            _ => done(runtime, req),
        }
    }
}

fn handler(runtime: Runtime) -> Handler {
    Handler { s: lin_kv(runtime) }
}

RPC

use async_trait::async_trait;
use maelstrom::protocol::Message;
use maelstrom::{Node, Result, Runtime};
use serde::{Deserialize, Serialize};
use std::sync::{Arc, Mutex};

#[derive(Clone, Default)]
struct Handler {}

#[async_trait]
impl Node for Handler {
    async fn process(&self, runtime: Runtime, req: Message) -> Result<()> {
        let (mut ctx, _handler) = Context::with_timeout(Duration::from_secs(1));
        
        // 1.
        runtime.call_async(node, msg.clone());
        
        // 2. put it into runtime.spawn(async move { ... }) if needed
        let res: RPCResult = runtime.rpc(node, msg.clone()).await?;
        let msg: Result<Message> = res.await;
        
        // 3. put it into runtime.spawn(async move { ... }) if needed
        let mut res: RPCResult = runtime.rpc(node, msg.clone()).await?;
        let msg: Message = res.done_with(ctx).await?;

        // 4. put it into runtime.spawn(async move { ... }) if needed
        let msg = runtime.call(ctx, node, msg.clone()).await?;
        
        // 5. async send variant
        //    spawn into tokio (instead of runtime) to not to wait
        //    until it is completed, as it will never be.
        let (r0, h0) = (runtime.clone(), self.clone());
        tokio::spawn(async move {
            loop {
                tokio::time::sleep(Duration::from_secs(5)).await;
                debug!("emit replication signal");
                let s = h0.s.lock().unwrap();
                for n in r0.neighbours() {
                    let msg = Request::ReplicateFull { value: to_seq(&s) };
                    drop(r0.send_async(n, msg));
                }
            }
        });
    
        return runtime.reply_ok(req).await;
    }
}

Requests

use serde::{Deserialize, Serialize};

#[derive(Deserialize)]
struct TopologyRequest {
    topology: HashMap<String, Vec<String>>,
}

// or

#[derive(Serialize, Deserialize)]
#[serde(rename_all = "snake_case", tag = "type")]
pub enum Message {
    Topology {
        topology: HashMap<String, Vec<String>>,
    },
    Broadcast {
        message: u64,
    },
    ReadOk {
        messages: Vec<u64>,
    },
}

Responses

use async_trait::async_trait;
use log::info;
use maelstrom::protocol::Message;
use maelstrom::{done, Node, Result, Runtime};
use serde::{Deserialize, Serialize};
use serde_json::Value;
use std::sync::{Arc, Mutex};

#[derive(Clone, Default)]
struct Handler { /* ... */ }

#[async_trait]
impl Node for Handler {
    async fn process(&self, runtime: Runtime, req: Message) -> Result<()> {
        if req.get_type() == "echo" {
            let echo = req.body.clone().with_type("echo_ok");
            return runtime.reply(req, echo).await;
        }

        if req.get_type() == "echo" {
            let echo = format!("Another echo {}", message.body.msg_id);
            let msg = Value::Object(Map::from_iter([("echo".to_string(), Value::String(echo))]));
            return runtime.reply(message, msg).await;
        }

        if req.get_type() == "echo" {
            let err = maelstrom::Error::TemporarilyUnavailable {};
            let body = ErrorMessageBody::from_error(err);
            return runtime.reply(message, body).await;
        }

        if req.get_type() == "echo" {
            let body = MessageBody::default().with_type("echo_ok").with_reply_to(req.body.msg_id);
            // send: no response type auto-deduction and no reply_to
            return runtime.send(message, body).await;
        }

        if req.get_type() == "echo" {
            return runtime.reply(message, EchoResponse { echo: "blah".to_string() }).await;
        }

        if req.get_type() == "read" {
            let data = self.inner.lock().unwrap().clone();
            let msg = ReadResponse { messages: data };
            return runtime.reply(req, msg).await;
        }

        if req.get_type() == "broadcast" {
            let raw = Value::Object(req.body.extra.clone());

            let mut msg = serde_json::from_value::<BroadcastRequest>(raw)?;
            msg.typ = req.body.typ.clone();

            return runtime.reply(req, msg).await;
        }

        if req.get_type() == "broadcast" {
            let mut msg = serde_json::from_value::<BroadcastRequest>(req.body.raw())?;
            msg.typ = req.body.typ.clone();

            return runtime.reply(req, msg).await;
        }

        if req.get_type() == "broadcast" {
            let mut msg = req.body.as_obj::<BroadcastRequest>()?;
            msg.typ = req.body.typ.clone();

            return runtime.reply(req, msg).await;
        }

        if req.get_type() == "topology" {
            info!("new topology {:?}", req.body.extra.get("topology").unwrap());
            return runtime.reply_ok(req).await;
        }

        done(runtime, message)
    }
}

Why

Because I am learning Rust and I liked Maelstrom and fly.io pretty much. I wanted to play with different aspects of the language and ecosystem and build an API that will be somewhat convenient and short. I am sorry for my ego.

Thanks Aphyr and guys a lot.

Where

GitHub