Mixnet PoC base branch (#316)

* Add `mixnode` and `mixnet-client` crate (#302)

* Add `mixnode` binary (#317)

* Integrate mixnet with libp2p network backend (#318)

* Fix #312: proper delays (#321)

* proper delays

* add missing duration param

* tiny fix: compilation error caused by `rand` 0.8 -> 0.7

* use `get_available_port()` for mixnet integration tests (#333)

* add missing comments

* Overwatch mixnet node (#339)

* Add mixnet service and overwatch app

* remove #[tokio::main]

---------

Co-authored-by: Youngjoon Lee <taxihighway@gmail.com>

* fix tests for the overwatch mixnode (#342)

* fix panic when corner case happen in RandomDelayIter (#335)

* Use `log` service for `mixnode` bin (#341)

* Use `wire` for MixnetMessage in libp2p (#347)

* Prevent tmixnet tests from running forever (#363)

* Use random delay when sending msgs to mixnet (#362)

* fix a minor compilation error caused by the latest master

* Fix run output fd (#343)

* add a connection pool

* Exp backoff (#332)

* move mixnet listening into separate task

* add exponential retry for insufficient peers in libp2p

* fix logging

* Fix MutexGuard across await (#373)

* Fix MutexGuard across await

Holding a MutexGuard across an await point is not a good idea.
Removing that solves the issues we had with the mixnet test

* Make mixnode handle bodies coming from the same source concurrently (#372)

---------

Co-authored-by: Youngjoon Lee <taxihighway@gmail.com>

* Move wait at network startup (#338)

We now wait after the call to 'subscribe' to give the network
the time to register peers in the mesh before starting to
publish messages

* Remove unused functions from mixnet connpool (#374)

* Mixnet benchmark (#375)

* merge fixes

* add `connection_pool_size` field to `config.yaml`

* Simplify mixnet topology (#393)

* Simplify bytes and duration range ser/de (#394)

* optimize bytes serde and duration serde

---------

Co-authored-by: Al Liu <scygliu1@gmail.com>
Co-authored-by: Daniel Sanchez <sanchez.quiros.daniel@gmail.com>
Co-authored-by: Giacomo Pasini <Zeegomo@users.noreply.github.com>

Cargo.toml

@@ -14,8 +14,13 @@ members = [
     "nomos-da/kzg",
     "nomos-da/full-replication",
     "nodes/nomos-node",
+    "nodes/mixnode",
     "simulations",
     "consensus-engine",
     "tests",
+    "mixnet/node",
+    "mixnet/client",
+    "mixnet/protocol",
+    "mixnet/topology",
 ]
 resolver = "2"

mixnet/client/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "mixnet-client"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+serde = { version = "1.0", features = ["derive"] }
+tracing = "0.1.37"
+tokio = { version = "1.29.1", features = ["net"] }
+sphinx-packet = "0.1.0"
+nym-sphinx = { package = "nym-sphinx", git = "https://github.com/nymtech/nym", tag = "v1.1.22" }
+# Using an older version, since `nym-sphinx` depends on `rand` v0.7.3.
+rand = "0.7.3"
+mixnet-protocol = { path = "../protocol" }
+mixnet-topology = { path = "../topology" }
+mixnet-util = { path = "../util" }
+futures = "0.3.28"
+thiserror = "1"

mixnet/client/src/config.rs

@@ -0,0 +1,31 @@
+use std::net::SocketAddr;
+
+use futures::{stream, StreamExt};
+use mixnet_topology::MixnetTopology;
+use serde::{Deserialize, Serialize};
+
+use crate::{receiver::Receiver, MessageStream, MixnetClientError};
+
+#[derive(Serialize, Deserialize, Clone, Debug)]
+pub struct MixnetClientConfig {
+    pub mode: MixnetClientMode,
+    pub topology: MixnetTopology,
+    pub connection_pool_size: usize,
+}
+
+#[derive(Serialize, Deserialize, Clone, Debug)]
+pub enum MixnetClientMode {
+    Sender,
+    SenderReceiver(SocketAddr),
+}
+
+impl MixnetClientMode {
+    pub(crate) async fn run(&self) -> Result<MessageStream, MixnetClientError> {
+        match self {
+            Self::Sender => Ok(stream::empty().boxed()),
+            Self::SenderReceiver(node_address) => {
+                Ok(Receiver::new(*node_address).run().await?.boxed())
+            }
+        }
+    }
+}

mixnet/client/src/lib.rs

@@ -0,0 +1,56 @@
+pub mod config;
+mod receiver;
+mod sender;
+
+use std::error::Error;
+use std::time::Duration;
+
+pub use config::MixnetClientConfig;
+pub use config::MixnetClientMode;
+use futures::stream::BoxStream;
+use mixnet_util::ConnectionPool;
+use rand::Rng;
+use sender::Sender;
+use thiserror::Error;
+
+// A client for sending packets to Mixnet and receiving packets from Mixnet.
+pub struct MixnetClient<R: Rng> {
+    mode: MixnetClientMode,
+    sender: Sender<R>,
+}
+
+pub type MessageStream = BoxStream<'static, Result<Vec<u8>, MixnetClientError>>;
+
+impl<R: Rng> MixnetClient<R> {
+    pub fn new(config: MixnetClientConfig, rng: R) -> Self {
+        let cache = ConnectionPool::new(config.connection_pool_size);
+        Self {
+            mode: config.mode,
+            sender: Sender::new(config.topology, cache, rng),
+        }
+    }
+
+    pub async fn run(&self) -> Result<MessageStream, MixnetClientError> {
+        self.mode.run().await
+    }
+
+    pub fn send(
+        &mut self,
+        msg: Vec<u8>,
+        total_delay: Duration,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        self.sender.send(msg, total_delay)
+    }
+}
+
+#[derive(Error, Debug)]
+pub enum MixnetClientError {
+    #[error("mixnet node connect error")]
+    MixnetNodeConnectError,
+    #[error("mixnode stream has been closed")]
+    MixnetNodeStreamClosed,
+    #[error("unexpected stream body received")]
+    UnexpectedStreamBody,
+    #[error("invalid payload")]
+    InvalidPayload,
+}

mixnet/client/src/receiver.rs

@@ -0,0 +1,139 @@
+use std::{error::Error, net::SocketAddr};
+
+use futures::{stream, Stream, StreamExt};
+use mixnet_protocol::Body;
+use nym_sphinx::{
+    chunking::{fragment::Fragment, reconstruction::MessageReconstructor},
+    message::{NymMessage, PaddedMessage},
+    Payload,
+};
+use tokio::net::TcpStream;
+
+use crate::MixnetClientError;
+
+// Receiver accepts TCP connections to receive incoming payloads from the Mixnet.
+pub struct Receiver {
+    node_address: SocketAddr,
+}
+
+impl Receiver {
+    pub fn new(node_address: SocketAddr) -> Self {
+        Self { node_address }
+    }
+
+    pub async fn run(
+        &self,
+    ) -> Result<
+        impl Stream<Item = Result<Vec<u8>, MixnetClientError>> + Send + 'static,
+        MixnetClientError,
+    > {
+        let Ok(socket) = TcpStream::connect(self.node_address).await else {
+            return Err(MixnetClientError::MixnetNodeConnectError);
+        };
+
+        Ok(Self::message_stream(Box::pin(Self::fragment_stream(
+            socket,
+        ))))
+    }
+
+    fn fragment_stream(
+        socket: TcpStream,
+    ) -> impl Stream<Item = Result<Fragment, MixnetClientError>> + Send + 'static {
+        stream::unfold(socket, |mut socket| async move {
+            let Ok(body) = Body::read(&mut socket).await else {
+                // TODO: Maybe this is a hard error and the stream is corrupted? In that case stop the stream
+                return Some((Err(MixnetClientError::MixnetNodeStreamClosed), socket));
+            };
+
+            match body {
+                Body::SphinxPacket(_) => {
+                    Some((Err(MixnetClientError::UnexpectedStreamBody), socket))
+                }
+                Body::FinalPayload(payload) => Some((Self::fragment_from_payload(payload), socket)),
+            }
+        })
+    }
+
+    fn message_stream(
+        fragment_stream: impl Stream<Item = Result<Fragment, MixnetClientError>>
+            + Send
+            + Unpin
+            + 'static,
+    ) -> impl Stream<Item = Result<Vec<u8>, MixnetClientError>> + Send + 'static {
+        // MessageReconstructor buffers all received fragments
+        // and eventually returns reconstructed messages.
+        let message_reconstructor: MessageReconstructor = Default::default();
+
+        stream::unfold(
+            (fragment_stream, message_reconstructor),
+            |(mut fragment_stream, mut message_reconstructor)| async move {
+                let result =
+                    Self::reconstruct_message(&mut fragment_stream, &mut message_reconstructor)
+                        .await;
+                Some((result, (fragment_stream, message_reconstructor)))
+            },
+        )
+    }
+
+    fn fragment_from_payload(payload: Payload) -> Result<Fragment, MixnetClientError> {
+        let Ok(payload_plaintext) = payload.recover_plaintext() else {
+            return Err(MixnetClientError::InvalidPayload);
+        };
+        let Ok(fragment) = Fragment::try_from_bytes(&payload_plaintext) else {
+            return Err(MixnetClientError::InvalidPayload);
+        };
+        Ok(fragment)
+    }
+
+    async fn reconstruct_message(
+        fragment_stream: &mut (impl Stream<Item = Result<Fragment, MixnetClientError>>
+                  + Send
+                  + Unpin
+                  + 'static),
+        message_reconstructor: &mut MessageReconstructor,
+    ) -> Result<Vec<u8>, MixnetClientError> {
+        // Read fragments until at least one message is fully reconstructed.
+        while let Some(next) = fragment_stream.next().await {
+            match next {
+                Ok(fragment) => {
+                    if let Some(message) =
+                        Self::try_reconstruct_message(fragment, message_reconstructor)
+                    {
+                        return Ok(message);
+                    }
+                }
+                Err(e) => {
+                    return Err(e);
+                }
+            }
+        }
+
+        // fragment_stream closed before messages are fully reconstructed
+        Err(MixnetClientError::MixnetNodeStreamClosed)
+    }
+
+    fn try_reconstruct_message(
+        fragment: Fragment,
+        message_reconstructor: &mut MessageReconstructor,
+    ) -> Option<Vec<u8>> {
+        let reconstruction_result = message_reconstructor.insert_new_fragment(fragment);
+        match reconstruction_result {
+            Some((padded_message, _)) => {
+                let message = Self::remove_padding(padded_message).unwrap();
+                Some(message)
+            }
+            None => None,
+        }
+    }
+
+    fn remove_padding(msg: Vec<u8>) -> Result<Vec<u8>, Box<dyn Error>> {
+        let padded_message = PaddedMessage::new_reconstructed(msg);
+        // we need this because PaddedMessage.remove_padding requires it for other NymMessage types.
+        let dummy_num_mix_hops = 0;
+
+        match padded_message.remove_padding(dummy_num_mix_hops)? {
+            NymMessage::Plain(msg) => Ok(msg),
+            _ => todo!("return error"),
+        }
+    }
+}

mixnet/client/src/sender.rs

@@ -0,0 +1,200 @@
+use std::{error::Error, net::SocketAddr, time::Duration};
+
+use mixnet_protocol::Body;
+use mixnet_topology::MixnetTopology;
+use mixnet_util::ConnectionPool;
+use nym_sphinx::{
+    addressing::nodes::NymNodeRoutingAddress, chunking::fragment::Fragment, message::NymMessage,
+    params::PacketSize, Delay, Destination, DestinationAddressBytes, NodeAddressBytes,
+    IDENTIFIER_LENGTH, PAYLOAD_OVERHEAD_SIZE,
+};
+use rand::{distributions::Uniform, prelude::Distribution, Rng};
+use sphinx_packet::{route, SphinxPacket, SphinxPacketBuilder};
+
+// Sender splits messages into Sphinx packets and sends them to the Mixnet.
+pub struct Sender<R: Rng> {
+    //TODO: handle topology update
+    topology: MixnetTopology,
+    pool: ConnectionPool,
+    rng: R,
+}
+
+impl<R: Rng> Sender<R> {
+    pub fn new(topology: MixnetTopology, pool: ConnectionPool, rng: R) -> Self {
+        Self {
+            topology,
+            rng,
+            pool,
+        }
+    }
+
+    pub fn send(
+        &mut self,
+        msg: Vec<u8>,
+        total_delay: Duration,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        let destination = self.topology.random_destination(&mut self.rng)?;
+        let destination = Destination::new(
+            DestinationAddressBytes::from_bytes(destination.address.as_bytes()),
+            [0; IDENTIFIER_LENGTH], // TODO: use a proper SURBIdentifier if we need SURB
+        );
+
+        self.pad_and_split_message(msg)
+            .into_iter()
+            .map(|fragment| self.build_sphinx_packet(fragment, &destination, total_delay))
+            .collect::<Result<Vec<_>, _>>()?
+            .into_iter()
+            .for_each(|(packet, first_node)| {
+                let pool = self.pool.clone();
+                tokio::spawn(async move {
+                    if let Err(e) =
+                        Self::send_packet(&pool, Box::new(packet), first_node.address).await
+                    {
+                        tracing::error!("failed to send packet to the first node: {e}");
+                    }
+                });
+            });
+
+        Ok(())
+    }
+
+    fn pad_and_split_message(&mut self, msg: Vec<u8>) -> Vec<Fragment> {
+        let nym_message = NymMessage::new_plain(msg);
+
+        // TODO: add PUBLIC_KEY_SIZE for encryption for the destination,
+        //       if we're going to encrypt final payloads for the destination.
+        // TODO: add ACK_OVERHEAD if we need SURB-ACKs.
+        // https://github.com/nymtech/nym/blob/3748ab77a132143d5fd1cd75dd06334d33294815/common/nymsphinx/src/message.rs#L181-L181
+        let plaintext_size_per_packet = PacketSize::RegularPacket.plaintext_size();
+
+        nym_message
+            .pad_to_full_packet_lengths(plaintext_size_per_packet)
+            .split_into_fragments(&mut self.rng, plaintext_size_per_packet)
+    }
+
+    fn build_sphinx_packet(
+        &mut self,
+        fragment: Fragment,
+        destination: &Destination,
+        total_delay: Duration,
+    ) -> Result<(sphinx_packet::SphinxPacket, route::Node), Box<dyn Error + Send + Sync + 'static>>
+    {
+        let route = self.topology.random_route(&mut self.rng)?;
+
+        let delays: Vec<Delay> =
+            RandomDelayIterator::new(&mut self.rng, route.len() as u64, total_delay)
+                .map(|d| Delay::new_from_millis(d.as_millis() as u64))
+                .collect();
+
+        // TODO: encrypt the payload for the destination, if we want
+        // https://github.com/nymtech/nym/blob/3748ab77a132143d5fd1cd75dd06334d33294815/common/nymsphinx/src/preparer/payload.rs#L70
+        let payload = fragment.into_bytes();
+
+        let packet = SphinxPacketBuilder::new()
+            .with_payload_size(payload.len() + PAYLOAD_OVERHEAD_SIZE)
+            .build_packet(payload, &route, destination, &delays)?;
+
+        let first_mixnode = route.first().cloned().expect("route is not empty");
+
+        Ok((packet, first_mixnode))
+    }
+
+    async fn send_packet(
+        pool: &ConnectionPool,
+        packet: Box<SphinxPacket>,
+        addr: NodeAddressBytes,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        let addr = SocketAddr::try_from(NymNodeRoutingAddress::try_from(addr)?)?;
+        tracing::debug!("Sending a Sphinx packet to the node: {addr:?}");
+
+        let mu: std::sync::Arc<tokio::sync::Mutex<tokio::net::TcpStream>> =
+            pool.get_or_init(&addr).await?;
+        let mut socket = mu.lock().await;
+        let body = Body::new_sphinx(packet);
+        body.write(&mut *socket).await?;
+
+        tracing::debug!("Sent a Sphinx packet successuflly to the node: {addr:?}");
+
+        Ok(())
+    }
+}
+
+struct RandomDelayIterator<R> {
+    rng: R,
+    remaining_delays: u64,
+    remaining_time: u64,
+    avg_delay: u64,
+}
+
+impl<R> RandomDelayIterator<R> {
+    fn new(rng: R, total_delays: u64, total_time: Duration) -> Self {
+        let total_time = total_time.as_millis() as u64;
+        RandomDelayIterator {
+            rng,
+            remaining_delays: total_delays,
+            remaining_time: total_time,
+            avg_delay: total_time / total_delays,
+        }
+    }
+}
+
+impl<R> Iterator for RandomDelayIterator<R>
+where
+    R: Rng,
+{
+    type Item = Duration;
+
+    fn next(&mut self) -> Option<Duration> {
+        if self.remaining_delays == 0 {
+            return None;
+        }
+
+        self.remaining_delays -= 1;
+
+        if self.remaining_delays == 1 {
+            return Some(Duration::from_millis(self.remaining_time));
+        }
+
+        // Calculate bounds to avoid extreme values
+        let upper_bound = (self.avg_delay as f64 * 1.5)
+            // guarantee that we don't exceed the remaining time and promise the delay we return is
+            // at least 1ms.
+            .min(self.remaining_time.saturating_sub(self.remaining_delays) as f64);
+        let lower_bound = (self.avg_delay as f64 * 0.5).min(upper_bound);
+
+        let delay = Uniform::new_inclusive(lower_bound, upper_bound).sample(&mut self.rng) as u64;
+        self.remaining_time = self.remaining_time.saturating_sub(delay);
+
+        Some(Duration::from_millis(delay))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::Duration;
+
+    use super::RandomDelayIterator;
+
+    const TOTAL_DELAYS: u64 = 3;
+
+    #[test]
+    fn test_random_delay_iter_zero_total_time() {
+        let mut delays = RandomDelayIterator::new(rand::thread_rng(), TOTAL_DELAYS, Duration::ZERO);
+        for _ in 0..TOTAL_DELAYS {
+            assert!(delays.next().is_some());
+        }
+        assert!(delays.next().is_none());
+    }
+
+    #[test]
+    fn test_random_delay_iter_small_total_time() {
+        let mut delays =
+            RandomDelayIterator::new(rand::thread_rng(), TOTAL_DELAYS, Duration::from_millis(1));
+        let mut d = Duration::ZERO;
+        for _ in 0..TOTAL_DELAYS {
+            d += delays.next().unwrap();
+        }
+        assert!(delays.next().is_none());
+        assert_eq!(d, Duration::from_millis(1));
+    }
+}

mixnet/node/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "mixnet-node"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+serde = { version = "1.0", features = ["derive"] }
+tracing = "0.1.37"
+tokio = { version = "1.32", features = ["net", "time"] }
+sphinx-packet = "0.1.0"
+nym-sphinx = { package = "nym-sphinx", git = "https://github.com/nymtech/nym", tag = "v1.1.22" }
+mixnet-protocol = { path = "../protocol" }
+mixnet-topology = { path = "../topology" }
+mixnet-util = { path = "../util" }
+
+[dev-dependencies]
+tokio = {version = "1.32", features =["full"]}

mixnet/node/src/client_notifier.rs

@@ -0,0 +1,47 @@
+use std::{error::Error, net::SocketAddr};
+
+use mixnet_protocol::Body;
+use tokio::{
+    net::{TcpListener, TcpStream},
+    sync::mpsc,
+};
+
+pub struct ClientNotifier {}
+
+impl ClientNotifier {
+    pub async fn run(
+        listen_address: SocketAddr,
+        mut rx: mpsc::Receiver<Body>,
+    ) -> Result<(), Box<dyn Error>> {
+        let listener = TcpListener::bind(listen_address).await?;
+        tracing::info!("Listening mixnet client connections: {listen_address}");
+
+        // Currently, handling only a single incoming connection
+        // TODO: consider handling multiple clients
+        loop {
+            match listener.accept().await {
+                Ok((socket, remote_addr)) => {
+                    tracing::debug!("Accepted incoming client connection from {remote_addr:?}");
+
+                    if let Err(e) = Self::handle_connection(socket, &mut rx).await {
+                        tracing::error!("failed to handle conn: {e}");
+                    }
+                }
+                Err(e) => tracing::warn!("Failed to accept incoming client connection: {e}"),
+            }
+        }
+    }
+
+    async fn handle_connection(
+        mut socket: TcpStream,
+        rx: &mut mpsc::Receiver<Body>,
+    ) -> Result<(), Box<dyn Error>> {
+        while let Some(body) = rx.recv().await {
+            if let Err(e) = body.write(&mut socket).await {
+                return Err(format!("error from client conn: {e}").into());
+            }
+        }
+        tracing::debug!("body receiver closed");
+        Ok(())
+    }
+}

mixnet/node/src/config.rs

@@ -0,0 +1,37 @@
+use std::net::{Ipv4Addr, SocketAddr, SocketAddrV4};
+
+use nym_sphinx::{PrivateKey, PublicKey};
+use serde::{Deserialize, Serialize};
+use sphinx_packet::crypto::{PRIVATE_KEY_SIZE, PUBLIC_KEY_SIZE};
+
+#[derive(Serialize, Deserialize, Clone, Debug)]
+pub struct MixnetNodeConfig {
+    /// A listen address for receiving Sphinx packets
+    pub listen_address: SocketAddr,
+    /// An listen address fro communicating with mixnet clients
+    pub client_listen_address: SocketAddr,
+    /// A key for decrypting Sphinx packets
+    pub private_key: [u8; PRIVATE_KEY_SIZE],
+    /// The size of the connection pool.
+    pub connection_pool_size: usize,
+}
+
+impl Default for MixnetNodeConfig {
+    fn default() -> Self {
+        Self {
+            listen_address: SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 7777)),
+            client_listen_address: SocketAddr::V4(SocketAddrV4::new(
+                Ipv4Addr::new(127, 0, 0, 1),
+                7778,
+            )),
+            private_key: PrivateKey::new().to_bytes(),
+            connection_pool_size: 255,
+        }
+    }
+}
+
+impl MixnetNodeConfig {
+    pub fn public_key(&self) -> [u8; PUBLIC_KEY_SIZE] {
+        *PublicKey::from(&PrivateKey::from(self.private_key)).as_bytes()
+    }
+}

mixnet/node/src/lib.rs

@@ -0,0 +1,191 @@
+mod client_notifier;
+pub mod config;
+
+use std::{error::Error, net::SocketAddr};
+
+use client_notifier::ClientNotifier;
+pub use config::MixnetNodeConfig;
+use mixnet_protocol::Body;
+use mixnet_topology::MixnetNodeId;
+use mixnet_util::ConnectionPool;
+use nym_sphinx::{
+    addressing::nodes::NymNodeRoutingAddress, Delay, DestinationAddressBytes, NodeAddressBytes,
+    Payload, PrivateKey,
+};
+pub use sphinx_packet::crypto::PRIVATE_KEY_SIZE;
+use sphinx_packet::{crypto::PUBLIC_KEY_SIZE, ProcessedPacket, SphinxPacket};
+use tokio::{
+    net::{TcpListener, TcpStream},
+    sync::mpsc,
+};
+
+// A mix node that routes packets in the Mixnet.
+pub struct MixnetNode {
+    config: MixnetNodeConfig,
+    pool: ConnectionPool,
+}
+
+impl MixnetNode {
+    pub fn new(config: MixnetNodeConfig) -> Self {
+        let pool = ConnectionPool::new(config.connection_pool_size);
+        Self { config, pool }
+    }
+
+    pub fn id(&self) -> MixnetNodeId {
+        self.public_key()
+    }
+
+    pub fn public_key(&self) -> [u8; PUBLIC_KEY_SIZE] {
+        self.config.public_key()
+    }
+
+    const CLIENT_NOTI_CHANNEL_SIZE: usize = 100;
+
+    pub async fn run(self) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        tracing::info!("Public key: {:?}", self.public_key());
+
+        // Spawn a ClientNotifier
+        let (client_tx, client_rx) = mpsc::channel(Self::CLIENT_NOTI_CHANNEL_SIZE);
+        tokio::spawn(async move {
+            if let Err(e) = ClientNotifier::run(self.config.client_listen_address, client_rx).await
+            {
+                tracing::error!("failed to run client notifier: {e}");
+            }
+        });
+
+        //TODO: Accepting ad-hoc TCP conns for now. Improve conn handling.
+        //TODO: Add graceful shutdown
+        let listener = TcpListener::bind(self.config.listen_address).await?;
+        tracing::info!(
+            "Listening mixnet node connections: {}",
+            self.config.listen_address
+        );
+
+        loop {
+            match listener.accept().await {
+                Ok((socket, remote_addr)) => {
+                    tracing::debug!("Accepted incoming connection from {remote_addr:?}");
+
+                    let client_tx = client_tx.clone();
+                    let private_key = self.config.private_key;
+                    let pool = self.pool.clone();
+                    tokio::spawn(async move {
+                        if let Err(e) =
+                            Self::handle_connection(socket, pool, private_key, client_tx).await
+                        {
+                            tracing::error!("failed to handle conn: {e}");
+                        }
+                    });
+                }
+                Err(e) => tracing::warn!("Failed to accept incoming connection: {e}"),
+            }
+        }
+    }
+
+    async fn handle_connection(
+        mut socket: TcpStream,
+        pool: ConnectionPool,
+        private_key: [u8; PRIVATE_KEY_SIZE],
+        client_tx: mpsc::Sender<Body>,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        loop {
+            let body = Body::read(&mut socket).await?;
+
+            let pool = pool.clone();
+            let private_key = PrivateKey::from(private_key);
+            let client_tx = client_tx.clone();
+
+            tokio::spawn(async move {
+                if let Err(e) = Self::handle_body(body, &pool, &private_key, &client_tx).await {
+                    tracing::error!("failed to handle body: {e}");
+                }
+            });
+        }
+    }
+
+    async fn handle_body(
+        body: Body,
+        pool: &ConnectionPool,
+        private_key: &PrivateKey,
+        client_tx: &mpsc::Sender<Body>,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        match body {
+            Body::SphinxPacket(packet) => {
+                Self::handle_sphinx_packet(pool, private_key, packet).await
+            }
+            _body @ Body::FinalPayload(_) => {
+                Self::forward_body_to_client_notifier(private_key, client_tx, _body).await
+            }
+        }
+    }
+
+    async fn handle_sphinx_packet(
+        pool: &ConnectionPool,
+        private_key: &PrivateKey,
+        packet: Box<SphinxPacket>,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        match packet.process(private_key)? {
+            ProcessedPacket::ForwardHop(packet, next_node_addr, delay) => {
+                Self::forward_packet_to_next_hop(pool, packet, next_node_addr, delay).await
+            }
+            ProcessedPacket::FinalHop(destination_addr, _, payload) => {
+                Self::forward_payload_to_destination(pool, payload, destination_addr).await
+            }
+        }
+    }
+
+    async fn forward_body_to_client_notifier(
+        _private_key: &PrivateKey,
+        client_tx: &mpsc::Sender<Body>,
+        body: Body,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        // TODO: Decrypt the final payload using the private key, if it's encrypted
+
+        // Do not wait when the channel is full or no receiver exists
+        client_tx.try_send(body)?;
+        Ok(())
+    }
+
+    async fn forward_packet_to_next_hop(
+        pool: &ConnectionPool,
+        packet: Box<SphinxPacket>,
+        next_node_addr: NodeAddressBytes,
+        delay: Delay,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        tracing::debug!("Delaying the packet for {delay:?}");
+        tokio::time::sleep(delay.to_duration()).await;
+
+        Self::forward(
+            pool,
+            Body::new_sphinx(packet),
+            NymNodeRoutingAddress::try_from(next_node_addr)?,
+        )
+        .await
+    }
+
+    async fn forward_payload_to_destination(
+        pool: &ConnectionPool,
+        payload: Payload,
+        destination_addr: DestinationAddressBytes,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        tracing::debug!("Forwarding final payload to destination mixnode");
+
+        Self::forward(
+            pool,
+            Body::new_final_payload(payload),
+            NymNodeRoutingAddress::try_from_bytes(&destination_addr.as_bytes())?,
+        )
+        .await
+    }
+
+    async fn forward(
+        pool: &ConnectionPool,
+        body: Body,
+        to: NymNodeRoutingAddress,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        let addr = SocketAddr::try_from(to)?;
+        body.write(&mut *pool.get_or_init(&addr).await?.lock().await)
+            .await?;
+        Ok(())
+    }
+}

mixnet/protocol/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "mixnet-protocol"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+tokio = "1.29.1"
+sphinx-packet = "0.1.0"
+futures = "0.3"
+tokio-util = {version  = "0.7", features = ["io", "io-util"] }

mixnet/protocol/src/lib.rs

@@ -0,0 +1,101 @@
+use sphinx_packet::{payload::Payload, SphinxPacket};
+use std::error::Error;
+
+use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
+
+pub enum Body {
+    SphinxPacket(Box<SphinxPacket>),
+    FinalPayload(Payload),
+}
+
+impl Body {
+    pub fn new_sphinx(packet: Box<SphinxPacket>) -> Self {
+        Self::SphinxPacket(packet)
+    }
+
+    pub fn new_final_payload(payload: Payload) -> Self {
+        Self::FinalPayload(payload)
+    }
+
+    fn variant_as_u8(&self) -> u8 {
+        match self {
+            Self::SphinxPacket(_) => 0,
+            Self::FinalPayload(_) => 1,
+        }
+    }
+
+    pub async fn read<R>(reader: &mut R) -> Result<Body, Box<dyn Error + Send + Sync + 'static>>
+    where
+        R: AsyncRead + Unpin,
+    {
+        let id = reader.read_u8().await?;
+        match id {
+            0 => Self::read_sphinx_packet(reader).await,
+            1 => Self::read_final_payload(reader).await,
+            _ => Err("Invalid body type".into()),
+        }
+    }
+
+    fn sphinx_packet_from_bytes(
+        data: &[u8],
+    ) -> Result<Self, Box<dyn Error + Send + Sync + 'static>> {
+        let packet = SphinxPacket::from_bytes(data)?;
+        Ok(Self::new_sphinx(Box::new(packet)))
+    }
+
+    async fn read_sphinx_packet<R>(
+        reader: &mut R,
+    ) -> Result<Body, Box<dyn Error + Send + Sync + 'static>>
+    where
+        R: AsyncRead + Unpin,
+    {
+        let size = reader.read_u64().await?;
+        let mut buf = vec![0; size as usize];
+        reader.read_exact(&mut buf).await?;
+        Self::sphinx_packet_from_bytes(&buf)
+    }
+
+    pub fn final_payload_from_bytes(
+        data: &[u8],
+    ) -> Result<Self, Box<dyn Error + Send + Sync + 'static>> {
+        let payload = Payload::from_bytes(data)?;
+        Ok(Self::new_final_payload(payload))
+    }
+
+    async fn read_final_payload<R>(
+        reader: &mut R,
+    ) -> Result<Body, Box<dyn Error + Send + Sync + 'static>>
+    where
+        R: AsyncRead + Unpin,
+    {
+        let size = reader.read_u64().await?;
+        let mut buf = vec![0; size as usize];
+        reader.read_exact(&mut buf).await?;
+
+        Self::final_payload_from_bytes(&buf)
+    }
+
+    pub async fn write<W>(
+        self,
+        writer: &mut W,
+    ) -> Result<(), Box<dyn Error + Send + Sync + 'static>>
+    where
+        W: AsyncWrite + Unpin + ?Sized,
+    {
+        let variant = self.variant_as_u8();
+        writer.write_u8(variant).await?;
+        match self {
+            Body::SphinxPacket(packet) => {
+                let data = packet.to_bytes();
+                writer.write_u64(data.len() as u64).await?;
+                writer.write_all(&data).await?;
+            }
+            Body::FinalPayload(payload) => {
+                let data = payload.as_bytes();
+                writer.write_u64(data.len() as u64).await?;
+                writer.write_all(data).await?;
+            }
+        }
+        Ok(())
+    }
+}

mixnet/topology/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "mixnet-topology"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+hex = "0.4"
+# Using an older version, since `nym-sphinx` depends on `rand` v0.7.3.
+rand = "0.7.3"
+serde = { version = "1.0", features = ["derive"] }
+sphinx-packet = "0.1.0"
+nym-sphinx = { package = "nym-sphinx", git = "https://github.com/nymtech/nym", tag = "v1.1.22" }

mixnet/topology/src/lib.rs

@@ -0,0 +1,112 @@
+use std::{error::Error, net::SocketAddr};
+
+use nym_sphinx::addressing::nodes::{NymNodeRoutingAddress, NymNodeRoutingAddressError};
+use rand::{seq::IteratorRandom, Rng};
+use serde::{Deserialize, Serialize};
+use sphinx_packet::{crypto::PUBLIC_KEY_SIZE, route};
+
+pub type MixnetNodeId = [u8; PUBLIC_KEY_SIZE];
+
+#[derive(Serialize, Deserialize, Clone, Debug, Default)]
+pub struct MixnetTopology {
+    pub layers: Vec<Layer>,
+}
+
+#[derive(Serialize, Deserialize, Clone, Debug)]
+pub struct Layer {
+    pub nodes: Vec<Node>,
+}
+
+#[derive(Serialize, Deserialize, Clone, Debug)]
+pub struct Node {
+    pub address: SocketAddr,
+    #[serde(with = "hex_serde")]
+    pub public_key: [u8; PUBLIC_KEY_SIZE],
+}
+
+mod hex_serde {
+    use super::PUBLIC_KEY_SIZE;
+    use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+    pub fn serialize<S: Serializer>(
+        pk: &[u8; PUBLIC_KEY_SIZE],
+        serializer: S,
+    ) -> Result<S::Ok, S::Error> {
+        if serializer.is_human_readable() {
+            hex::encode(pk).serialize(serializer)
+        } else {
+            serializer.serialize_bytes(pk)
+        }
+    }
+
+    pub fn deserialize<'de, D: Deserializer<'de>>(
+        deserializer: D,
+    ) -> Result<[u8; PUBLIC_KEY_SIZE], D::Error> {
+        if deserializer.is_human_readable() {
+            let hex_str = String::deserialize(deserializer)?;
+            hex::decode(hex_str)
+                .map_err(serde::de::Error::custom)
+                .and_then(|v| v.as_slice().try_into().map_err(serde::de::Error::custom))
+        } else {
+            <[u8; PUBLIC_KEY_SIZE]>::deserialize(deserializer)
+        }
+    }
+}
+
+impl MixnetTopology {
+    pub fn random_route<R: Rng>(
+        &self,
+        rng: &mut R,
+    ) -> Result<Vec<route::Node>, Box<dyn Error + Send + Sync + 'static>> {
+        let num_hops = self.layers.len();
+
+        let route: Vec<route::Node> = self
+            .layers
+            .iter()
+            .take(num_hops)
+            .map(|layer| {
+                layer
+                    .random_node(rng)
+                    .expect("layer is not empty")
+                    .clone()
+                    .try_into()
+                    .unwrap()
+            })
+            .collect();
+
+        Ok(route)
+    }
+
+    // Choose a destination mixnet node randomly from the last layer.
+    pub fn random_destination<R: Rng>(
+        &self,
+        rng: &mut R,
+    ) -> Result<route::Node, Box<dyn Error + Send + Sync + 'static>> {
+        Ok(self
+            .layers
+            .last()
+            .expect("topology is not empty")
+            .random_node(rng)
+            .expect("layer is not empty")
+            .clone()
+            .try_into()
+            .unwrap())
+    }
+}
+
+impl Layer {
+    pub fn random_node<R: Rng>(&self, rng: &mut R) -> Option<&Node> {
+        self.nodes.iter().choose(rng)
+    }
+}
+
+impl TryInto<route::Node> for Node {
+    type Error = NymNodeRoutingAddressError;
+
+    fn try_into(self) -> Result<route::Node, Self::Error> {
+        Ok(route::Node {
+            address: NymNodeRoutingAddress::from(self.address).try_into()?,
+            pub_key: self.public_key.into(),
+        })
+    }
+}

mixnet/util/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "mixnet-util"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+tokio = { version = "1.32", default-features = false, features = ["sync", "net"] }
+parking_lot = { version = "0.12", features = ["send_guard"] }  

mixnet/util/src/lib.rs

@@ -0,0 +1,29 @@
+use std::{collections::HashMap, net::SocketAddr, sync::Arc};
+
+use tokio::net::TcpStream;
+use tokio::sync::Mutex;
+
+#[derive(Clone)]
+pub struct ConnectionPool {
+    pool: Arc<Mutex<HashMap<SocketAddr, Arc<Mutex<TcpStream>>>>>,
+}
+
+impl ConnectionPool {
+    pub fn new(size: usize) -> Self {
+        Self {
+            pool: Arc::new(Mutex::new(HashMap::with_capacity(size))),
+        }
+    }
+
+    pub async fn get_or_init(&self, addr: &SocketAddr) -> std::io::Result<Arc<Mutex<TcpStream>>> {
+        let mut pool = self.pool.lock().await;
+        match pool.get(addr).cloned() {
+            Some(tcp) => Ok(tcp),
+            None => {
+                let tcp = Arc::new(Mutex::new(TcpStream::connect(addr).await?));
+                pool.insert(*addr, tcp.clone());
+                Ok(tcp)
+            }
+        }
+    }
+}

nodes/mixnode/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "mixnode"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+async-trait = "0.1"
+mixnet-node = { path = "../../mixnet/node" }
+nomos-log = { path = "../../nomos-services/log" }
+clap = { version = "4", features = ["derive"] }
+color-eyre = "0.6.0"
+overwatch-rs = { git = "https://github.com/logos-co/Overwatch", branch = "main" }
+overwatch-derive = { git = "https://github.com/logos-co/Overwatch", branch = "main" }
+serde = "1"
+serde_yaml = "0.9"
+tracing = "0.1"
+tracing-subscriber = "0.3"
+tokio = "1.29.1"

nodes/mixnode/config.yaml

@@ -0,0 +1,9 @@
+mixnode:
+  listen_address: 127.0.0.1:7777
+  client_listen_address: 127.0.0.1:7778
+  private_key: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
+  connection_pool_size: 255
+log:
+  backend: "Stdout"
+  format: "Json"
+  level: "debug"

nodes/mixnode/src/lib.rs

@@ -0,0 +1,20 @@
+mod services;
+
+use nomos_log::Logger;
+use overwatch_derive::Services;
+use overwatch_rs::services::handle::ServiceHandle;
+use overwatch_rs::services::ServiceData;
+use serde::{Deserialize, Serialize};
+use services::mixnet::MixnetNodeService;
+
+#[derive(Deserialize, Debug, Clone, Serialize)]
+pub struct Config {
+    pub mixnode: <MixnetNodeService as ServiceData>::Settings,
+    pub log: <Logger as ServiceData>::Settings,
+}
+
+#[derive(Services)]
+pub struct MixNode {
+    node: ServiceHandle<MixnetNodeService>,
+    logging: ServiceHandle<Logger>,
+}

nodes/mixnode/src/main.rs

@@ -0,0 +1,29 @@
+mod services;
+
+use clap::Parser;
+use color_eyre::eyre::Result;
+use mixnode::{Config, MixNode, MixNodeServiceSettings};
+use overwatch_rs::overwatch::OverwatchRunner;
+use overwatch_rs::DynError;
+
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about = None)]
+struct Args {
+    /// Path for a yaml-encoded mixnet-node config file
+    config: std::path::PathBuf,
+}
+
+fn main() -> Result<(), DynError> {
+    let Args { config } = Args::parse();
+    let config = serde_yaml::from_reader::<_, Config>(std::fs::File::open(config)?)?;
+
+    let app = OverwatchRunner::<MixNode>::run(
+        MixNodeServiceSettings {
+            node: config.mixnode,
+            logging: config.log,
+        },
+        None,
+    )?;
+    app.wait_finished();
+    Ok(())
+}

nodes/mixnode/src/services/mixnet.rs

@@ -0,0 +1,31 @@
+use mixnet_node::{MixnetNode, MixnetNodeConfig};
+use overwatch_rs::services::handle::ServiceStateHandle;
+use overwatch_rs::services::relay::NoMessage;
+use overwatch_rs::services::state::{NoOperator, NoState};
+use overwatch_rs::services::{ServiceCore, ServiceData, ServiceId};
+use overwatch_rs::DynError;
+
+pub struct MixnetNodeService(MixnetNode);
+
+impl ServiceData for MixnetNodeService {
+    const SERVICE_ID: ServiceId = "mixnet-node";
+    type Settings = MixnetNodeConfig;
+    type State = NoState<Self::Settings>;
+    type StateOperator = NoOperator<Self::State>;
+    type Message = NoMessage;
+}
+
+#[async_trait::async_trait]
+impl ServiceCore for MixnetNodeService {
+    fn init(service_state: ServiceStateHandle<Self>) -> Result<Self, DynError> {
+        let settings: Self::Settings = service_state.settings_reader.get_updated_settings();
+        Ok(Self(MixnetNode::new(settings)))
+    }
+
+    async fn run(self) -> Result<(), DynError> {
+        if let Err(_e) = self.0.run().await {
+            todo!("Errors should match");
+        }
+        Ok(())
+    }
+}

nodes/mixnode/src/services/mod.rs

@@ -0,0 +1 @@
+pub mod mixnet;

nodes/nomos-node/config.yaml

@@ -19,6 +19,18 @@ network:
     discV5BootstrapNodes: []
     initial_peers: []
     relayTopics: []
+    mixnet_client:
+      mode: Sender
+      topology:
+        layers:
+         - nodes:
+            - address: 127.0.0.1:7777
+              public_key: "0000000000000000000000000000000000000000000000000000000000000000"
+      connection_pool_size: 255
+    mixnet_delay:
+      start: "0ms"
+      end: "0ms"
+
 http:
   backend:
     address: 0.0.0.0:8080

nodes/nomos-node/src/config.rs

@@ -214,22 +214,23 @@ impl Config {
         } = network_args;
 
         if let Some(IpAddr::V4(h)) = host {
-            self.network.backend.host = h;
+            self.network.backend.inner.host = h;
         } else if host.is_some() {
             return Err(eyre!("Unsupported ip version"));
         }
 
         if let Some(port) = port {
-            self.network.backend.port = port as u16;
+            self.network.backend.inner.port = port as u16;
         }
 
         if let Some(node_key) = node_key {
             let mut key_bytes = hex::decode(node_key)?;
-            self.network.backend.node_key = SecretKey::try_from_bytes(key_bytes.as_mut_slice())?;
+            self.network.backend.inner.node_key =
+                SecretKey::try_from_bytes(key_bytes.as_mut_slice())?;
         }
 
         if let Some(peers) = initial_peers {
-            self.network.backend.initial_peers = peers;
+            self.network.backend.inner.initial_peers = peers;
         }
 
         Ok(self)

nomos-core/Cargo.toml

@@ -14,14 +14,12 @@ blake2 = { version = "0.10" }
 bytes = "1.3"
 consensus-engine = { path = "../consensus-engine", features = ["serde"]}
 futures = "0.3"
-nomos-network = { path = "../nomos-services/network", optional = true }
 raptorq = { version = "1.7", optional = true }
 serde = { version = "1.0", features = ["derive"] }
 thiserror = "1.0"
 bincode = "1.3"
 once_cell = "1.0"
 indexmap = { version = "1.9", features = ["serde"] }
-serde_json = { version = "1", optional = true }
 
 [dev-dependencies]
 rand = "0.8"
@@ -31,5 +29,4 @@ tokio = { version = "1.23", features = ["macros", "rt"] }
 [features]
 default = []
 raptor = ["raptorq"]
-mock = ["nomos-network/mock", "serde_json"]
-waku = ["nomos-network/waku", "serde_json"]
+mock = []

nomos-core/src/tx/mock.rs

@@ -6,21 +6,21 @@ use blake2::{
     Blake2bVar,
 };
 use bytes::{Bytes, BytesMut};
-use nomos_network::backends::mock::MockMessage;
+use serde::Serialize;
 
 #[derive(Debug, Clone, Eq, PartialEq, Hash, serde::Serialize, serde::Deserialize)]
-pub struct MockTransaction {
+pub struct MockTransaction<M> {
     id: MockTxId,
-    content: MockMessage,
+    content: M,
 }
 
-impl MockTransaction {
-    pub fn new(content: MockMessage) -> Self {
-        let id = MockTxId::from(content.clone());
+impl<M: Serialize> MockTransaction<M> {
+    pub fn new(content: M) -> Self {
+        let id = MockTxId::from(serialize(&content).unwrap().as_slice());
         Self { id, content }
     }
 
-    pub fn message(&self) -> &MockMessage {
+    pub fn message(&self) -> &M {
         &self.content
     }
 
@@ -37,7 +37,7 @@ impl MockTransaction {
     }
 }
 
-impl Transaction for MockTransaction {
+impl<M: Serialize> Transaction for MockTransaction<M> {
     const HASHER: TransactionHasher<Self> = MockTransaction::id;
     type Hash = MockTxId;
 
@@ -46,9 +46,9 @@ impl Transaction for MockTransaction {
     }
 }
 
-impl From<nomos_network::backends::mock::MockMessage> for MockTransaction {
-    fn from(msg: nomos_network::backends::mock::MockMessage) -> Self {
-        let id = MockTxId::from(msg.clone());
+impl<M: Serialize> From<M> for MockTransaction<M> {
+    fn from(msg: M) -> Self {
+        let id = MockTxId::from(serialize(&msg).unwrap().as_slice());
         Self { id, content: msg }
     }
 }
@@ -84,18 +84,18 @@ impl MockTxId {
     }
 }
 
-impl From<nomos_network::backends::mock::MockMessage> for MockTxId {
-    fn from(msg: nomos_network::backends::mock::MockMessage) -> Self {
+impl From<&[u8]> for MockTxId {
+    fn from(msg: &[u8]) -> Self {
         let mut hasher = Blake2bVar::new(32).unwrap();
-        hasher.update(&serialize(&msg).unwrap());
+        hasher.update(msg);
         let mut id = [0u8; 32];
         hasher.finalize_variable(&mut id).unwrap();
         Self(id)
     }
 }
 
-impl From<&MockTransaction> for MockTxId {
-    fn from(msg: &MockTransaction) -> Self {
+impl<M> From<&MockTransaction<M>> for MockTxId {
+    fn from(msg: &MockTransaction<M>) -> Self {
         msg.id
     }
 }

nomos-services/consensus/src/network/adapters/libp2p.rs

@@ -231,6 +231,11 @@ impl NetworkAdapter for Libp2pAdapter {
         let cache = message_cache.clone();
         let relay = network_relay.clone();
         Self::subscribe(&relay, TOPIC).await;
+        tracing::debug!("Starting up...");
+        // this wait seems to be helpful in some cases since we give the time
+        // to the network to establish connections before we start sending messages
+        tokio::time::sleep(std::time::Duration::from_secs(1)).await;
+
         // TODO: maybe we need the runtime handle here?
         tokio::spawn(async move {
             let (sender, receiver) = tokio::sync::oneshot::channel();

nomos-services/mempool/Cargo.toml

@@ -30,6 +30,6 @@ blake2 = "0.10"
 
 [features]
 default = []
-waku = ["nomos-network/waku", "nomos-core/waku", "waku-bindings"]
+waku = ["nomos-network/waku", "waku-bindings"]
 mock = ["linked-hash-map", "nomos-network/mock", "rand", "nomos-core/mock"]
 libp2p = ["nomos-network/libp2p"]

nomos-services/mempool/src/network/adapters/mock.rs

@@ -4,7 +4,7 @@
 use futures::{Stream, StreamExt};
 use nomos_core::tx::mock::MockTransaction;
 use nomos_network::backends::mock::{
-    EventKind, Mock, MockBackendMessage, MockContentTopic, NetworkEvent,
+    EventKind, Mock, MockBackendMessage, MockContentTopic, MockMessage, NetworkEvent,
 };
 use nomos_network::{NetworkMsg, NetworkService};
 use overwatch_rs::services::relay::OutboundRelay;
@@ -25,7 +25,7 @@ pub struct MockAdapter {
 #[async_trait::async_trait]
 impl NetworkAdapter for MockAdapter {
     type Backend = Mock;
-    type Tx = MockTransaction;
+    type Tx = MockTransaction<MockMessage>;
 
     async fn new(
         network_relay: OutboundRelay<<NetworkService<Self::Backend> as ServiceData>::Message>,

nomos-services/mempool/tests/mock.rs

@@ -17,7 +17,7 @@ use nomos_mempool::{
 struct MockPoolNode {
     logging: ServiceHandle<Logger>,
     network: ServiceHandle<NetworkService<Mock>>,
-    mockpool: ServiceHandle<MempoolService<MockAdapter, MockPool<MockTransaction>>>,
+    mockpool: ServiceHandle<MempoolService<MockAdapter, MockPool<MockTransaction<MockMessage>>>>,
 }
 
 #[test]
@@ -67,7 +67,7 @@ fn test_mockmempool() {
     let network = app.handle().relay::<NetworkService<Mock>>();
     let mempool = app
         .handle()
-        .relay::<MempoolService<MockAdapter, MockPool<MockTransaction>>>();
+        .relay::<MempoolService<MockAdapter, MockPool<MockTransaction<MockMessage>>>>();
 
     app.spawn(async move {
         let network_outbound = network.connect().await.unwrap();

nomos-services/network/Cargo.toml

@@ -9,6 +9,7 @@ edition = "2021"
 async-trait = "0.1"
 bytes = "1.2"
 chrono = { version = "0.4", optional = true }
+humantime-serde = { version = "1", optional = true }
 overwatch-rs = { git = "https://github.com/logos-co/Overwatch", branch = "main" }
 multiaddr = "0.15"
 serde = { version = "1.0", features = ["derive"] }
@@ -18,14 +19,16 @@ tokio = { version = "1", features = ["sync"] }
 tokio-stream = "0.1"
 thiserror = "1.0"
 tracing = "0.1"
-rand = { version = "0.8", optional = true }
+rand = { version = "0.7.3", optional = true }
 waku-bindings = { version = "0.1.1", optional = true }
 tracing-appender = "0.2"
 tracing-subscriber = { version = "0.3", features = ["json"] }
 tracing-gelf = "0.7"
 futures = "0.3"
 parking_lot = "0.12"
+nomos-core = { path = "../../nomos-core" }
 nomos-libp2p = { path = "../../nomos-libp2p", optional = true }
+mixnet-client = { path = "../../mixnet/client" }
 
 [dev-dependencies]
 tokio = { version = "1", features = ["full"] }
@@ -33,5 +36,5 @@ tokio = { version = "1", features = ["full"] }
 [features]
 default = []
 waku = ["waku-bindings"]
-libp2p = ["nomos-libp2p"]
+libp2p = ["nomos-libp2p", "rand", "humantime-serde"]
 mock = ["rand", "chrono"]

nomos-services/network/src/backends/libp2p.rs

@@ -1,7 +1,9 @@
 // std
-use std::error::Error;
+use std::{error::Error, ops::Range, time::Duration};
 // internal
 use super::NetworkBackend;
+use mixnet_client::{MixnetClient, MixnetClientConfig};
+use nomos_core::wire;
 pub use nomos_libp2p::libp2p::gossipsub::{Message, TopicHash};
 use nomos_libp2p::{
     libp2p::{gossipsub, Multiaddr, PeerId},
@@ -9,8 +11,10 @@ use nomos_libp2p::{
 };
 // crates
 use overwatch_rs::{overwatch::handle::OverwatchHandle, services::state::NoState};
+use rand::{rngs::OsRng, thread_rng, Rng};
 use serde::{Deserialize, Serialize};
 use tokio::sync::{broadcast, mpsc, oneshot};
+use tokio_stream::StreamExt;
 
 macro_rules! log_error {
     ($e:expr) => {
@@ -25,6 +29,55 @@ pub struct Libp2p {
     commands_tx: mpsc::Sender<Command>,
 }
 
+#[derive(Serialize, Deserialize, Clone, Debug)]
+pub struct Libp2pConfig {
+    #[serde(flatten)]
+    pub inner: SwarmConfig,
+    pub mixnet_client: MixnetClientConfig,
+    #[serde(with = "humantime")]
+    pub mixnet_delay: Range<Duration>,
+}
+
+mod humantime {
+    use serde::{Deserialize, Deserializer, Serialize, Serializer};
+    use std::{ops::Range, time::Duration};
+
+    #[derive(Serialize, Deserialize)]
+    struct DurationRangeHelper {
+        #[serde(with = "humantime_serde")]
+        start: Duration,
+        #[serde(with = "humantime_serde")]
+        end: Duration,
+    }
+
+    pub fn serialize<S: Serializer>(
+        val: &Range<Duration>,
+        serializer: S,
+    ) -> Result<S::Ok, S::Error> {
+        if serializer.is_human_readable() {
+            DurationRangeHelper {
+                start: val.start,
+                end: val.end,
+            }
+            .serialize(serializer)
+        } else {
+            val.serialize(serializer)
+        }
+    }
+
+    pub fn deserialize<'de, D: Deserializer<'de>>(
+        deserializer: D,
+    ) -> Result<Range<Duration>, D::Error> {
+        if deserializer.is_human_readable() {
+            let DurationRangeHelper { start, end } =
+                DurationRangeHelper::deserialize(deserializer)?;
+            Ok(start..end)
+        } else {
+            Range::<Duration>::deserialize(deserializer)
+        }
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Libp2pInfo {
     pub listen_addresses: Vec<Multiaddr>,
@@ -39,14 +92,29 @@ pub enum EventKind {
 }
 
 const BUFFER_SIZE: usize = 64;
+const BACKOFF: u64 = 5;
+const MAX_RETRY: usize = 3;
 
 #[derive(Debug)]
+#[non_exhaustive]
 pub enum Command {
     Connect(PeerId, Multiaddr),
-    Broadcast { topic: Topic, message: Box<[u8]> },
+    Broadcast {
+        topic: Topic,
+        message: Box<[u8]>,
+    },
     Subscribe(Topic),
     Unsubscribe(Topic),
-    Info { reply: oneshot::Sender<Libp2pInfo> },
+    Info {
+        reply: oneshot::Sender<Libp2pInfo>,
+    },
+    #[doc(hidden)]
+    // broadcast a message directly through gossipsub without mixnet
+    DirectBroadcastAndRetry {
+        topic: Topic,
+        message: Box<[u8]>,
+        retry: usize,
+    },
 }
 
 pub type Topic = String;
@@ -58,24 +126,73 @@ pub enum Event {
     Message(Message),
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize)]
+struct MixnetMessage {
+    topic: Topic,
+    message: Box<[u8]>,
+}
+
+impl MixnetMessage {
+    pub fn as_bytes(&self) -> Vec<u8> {
+        wire::serialize(self).expect("Couldn't serialize MixnetMessage")
+    }
+    pub fn from_bytes(data: &[u8]) -> Result<Self, wire::Error> {
+        wire::deserialize(data)
+    }
+}
+
 #[async_trait::async_trait]
 impl NetworkBackend for Libp2p {
-    type Settings = SwarmConfig;
-    type State = NoState<SwarmConfig>;
+    type Settings = Libp2pConfig;
+    type State = NoState<Libp2pConfig>;
     type Message = Command;
     type EventKind = EventKind;
     type NetworkEvent = Event;
 
     fn new(config: Self::Settings, overwatch_handle: OverwatchHandle) -> Self {
+        let mixnet_client = MixnetClient::new(config.mixnet_client.clone(), OsRng);
         let (commands_tx, mut commands_rx) = tokio::sync::mpsc::channel(BUFFER_SIZE);
         let (events_tx, _) = tokio::sync::broadcast::channel(BUFFER_SIZE);
-        let libp2p = Self {
-            events_tx: events_tx.clone(),
-            commands_tx,
-        };
+
+        let cmd_tx = commands_tx.clone();
         overwatch_handle.runtime().spawn(async move {
-            use tokio_stream::StreamExt;
-            let mut swarm = Swarm::build(&config).unwrap();
+            let Ok(mut stream) = mixnet_client.run().await else {
+                tracing::error!("Could not quickstart mixnet stream");
+                return;
+            };
+
+            while let Some(result) = stream.next().await {
+                match result {
+                    Ok(msg) => {
+                        tracing::debug!("receiving message from mixnet client");
+                        let Ok(MixnetMessage { topic, message }) = MixnetMessage::from_bytes(&msg)
+                        else {
+                            tracing::error!(
+                                "failed to deserialize json received from mixnet client"
+                            );
+                            continue;
+                        };
+
+                        cmd_tx
+                            .send(Command::DirectBroadcastAndRetry {
+                                topic,
+                                message,
+                                retry: 0,
+                            })
+                            .await
+                            .unwrap_or_else(|_| tracing::error!("could not schedule broadcast"));
+                    }
+                    Err(e) => {
+                        todo!("Handle mixclient error: {e}");
+                    }
+                }
+            }
+        });
+        let cmd_tx = commands_tx.clone();
+        let notify = events_tx.clone();
+        overwatch_handle.runtime().spawn(async move {
+            let mut swarm = Swarm::build(&config.inner).unwrap();
+            let mut mixnet_client = MixnetClient::new(config.mixnet_client, OsRng);
             loop {
                 tokio::select! {
                     Some(event) = swarm.next() => {
@@ -86,7 +203,7 @@ impl NetworkBackend for Libp2p {
                                 message,
                             })) => {
                                 tracing::debug!("Got message with id: {id} from peer: {peer_id}");
-                                log_error!(events_tx.send(Event::Message(message)));
+                                log_error!(notify.send(Event::Message(message)));
                             }
                             SwarmEvent::ConnectionEstablished {
                                 peer_id,
@@ -121,23 +238,10 @@ impl NetworkBackend for Libp2p {
                                 log_error!(swarm.connect(peer_id, peer_addr));
                             }
                             Command::Broadcast { topic, message } => {
-                                match swarm.broadcast(&topic, message.to_vec()) {
-                                    Ok(id) => {
-                                        tracing::debug!("broadcasted message with id: {id} tp topic: {topic}");
-                                    }
-                                    Err(e) => {
-                                        tracing::error!("failed to broadcast message to topic: {topic} {e:?}");
-                                    }
-                                }
-
-                                if swarm.is_subscribed(&topic) {
-                                    log_error!(events_tx.send(Event::Message(Message {
-                                        source: None,
-                                        data: message.into(),
-                                        sequence_number: None,
-                                        topic: Swarm::topic_hash(&topic),
-                                    })));
-                                }
+                                tracing::debug!("sending message to mixnet client");
+                                let msg = MixnetMessage { topic, message };
+                                let delay = random_delay(&config.mixnet_delay);
+                                log_error!(mixnet_client.send(msg.as_bytes(), delay));
                             }
                             Command::Subscribe(topic) => {
                                 tracing::debug!("subscribing to topic: {topic}");
@@ -159,12 +263,18 @@ impl NetworkBackend for Libp2p {
                                 };
                                 log_error!(reply.send(info));
                             }
+                            Command::DirectBroadcastAndRetry { topic, message, retry } => {
+                               broadcast_and_retry(topic, message, retry, cmd_tx.clone(), &mut swarm, notify.clone()).await;
+                            }
                         };
                     }
                 }
             }
         });
-        libp2p
+        Self {
+            events_tx,
+            commands_tx,
+        }
     }
 
     async fn process(&self, msg: Self::Message) {
@@ -185,3 +295,75 @@ impl NetworkBackend for Libp2p {
         }
     }
 }
+
+fn random_delay(range: &Range<Duration>) -> Duration {
+    if range.start == range.end {
+        return range.start;
+    }
+    thread_rng().gen_range(range.start, range.end)
+}
+
+async fn broadcast_and_retry(
+    topic: Topic,
+    message: Box<[u8]>,
+    retry: usize,
+    commands_tx: mpsc::Sender<Command>,
+    swarm: &mut Swarm,
+    events_tx: broadcast::Sender<Event>,
+) {
+    tracing::debug!("broadcasting message to topic: {topic}");
+
+    let wait = BACKOFF.pow(retry as u32);
+
+    match swarm.broadcast(&topic, message.to_vec()) {
+        Ok(id) => {
+            tracing::debug!("broadcasted message with id: {id} tp topic: {topic}");
+            // self-notification because libp2p doesn't do it
+            if swarm.is_subscribed(&topic) {
+                log_error!(events_tx.send(Event::Message(Message {
+                    source: None,
+                    data: message.into(),
+                    sequence_number: None,
+                    topic: Swarm::topic_hash(&topic),
+                })));
+            }
+        }
+        Err(gossipsub::PublishError::InsufficientPeers) if retry < MAX_RETRY => {
+            tracing::error!("failed to broadcast message to topic due to insufficient peers, trying again in {wait:?}");
+
+            tokio::spawn(async move {
+                tokio::time::sleep(std::time::Duration::from_secs(wait)).await;
+                commands_tx
+                    .send(Command::DirectBroadcastAndRetry {
+                        topic,
+                        message,
+                        retry: retry + 1,
+                    })
+                    .await
+                    .unwrap_or_else(|_| tracing::error!("could not schedule retry"));
+            });
+        }
+        Err(e) => {
+            tracing::error!("failed to broadcast message to topic: {topic} {e:?}");
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::Duration;
+
+    use super::random_delay;
+
+    #[test]
+    fn test_random_delay() {
+        assert_eq!(
+            random_delay(&(Duration::ZERO..Duration::ZERO)),
+            Duration::ZERO
+        );
+
+        let range = Duration::from_millis(10)..Duration::from_millis(100);
+        let delay = random_delay(&range);
+        assert!(range.start <= delay && delay < range.end);
+    }
+}

nomos-services/network/src/lib.rs

@@ -83,12 +83,6 @@ where
     }
 
     async fn run(mut self) -> Result<(), overwatch_rs::DynError> {
-        tracing::debug!("Starting up...");
-        // this wait seems to be helpful in some cases for waku, where it reports
-        // to be connected to peers but does not seem to be able to send messages
-        // to them
-        tokio::time::sleep(std::time::Duration::from_secs(1)).await;
-
         let Self {
             service_state: ServiceStateHandle {
                 mut inbound_relay, ..

tests/Cargo.toml

@@ -14,9 +14,14 @@ overwatch-rs = { git = "https://github.com/logos-co/Overwatch", branch = "main"
 nomos-core = { path = "../nomos-core" }
 consensus-engine = { path = "../consensus-engine", features = ["serde"] }
 nomos-mempool = { path = "../nomos-services/mempool", features = ["mock"] }
-rand = "0.8"
+mixnode = { path = "../nodes/mixnode" }
+mixnet-node = { path = "../mixnet/node" }
+mixnet-client = { path = "../mixnet/client" }
+mixnet-topology = { path = "../mixnet/topology" }
+# Using older versions, since `mixnet-*` crates depend on `rand` v0.7.3.
+rand = "0.7.3"
+rand_xoshiro = "0.4"
 once_cell = "1"
-rand_xoshiro = "0.6"
 secp256k1 = { version = "0.26", features = ["rand"] }
 waku-bindings = { version = "0.1.1", optional = true }
 reqwest = { version = "0.11", features = ["json"] }
@@ -27,6 +32,8 @@ tokio = "1"
 futures = "0.3"
 async-trait = "0.1"
 fraction = "0.13"
+ntest = "0.9.0"
+criterion = { version = "0.5", features = ["async_tokio"] }
 
 [[test]]
 name = "test_consensus_happy_path"
@@ -36,6 +43,15 @@ path = "src/tests/happy.rs"
 name = "test_consensus_unhappy_path"
 path = "src/tests/unhappy.rs"
 
+[[test]]
+name = "test_mixnet"
+path = "src/tests/mixnet.rs"
+
+[[bench]]
+name = "mixnet"
+path = "src/benches/mixnet.rs"
+harness = false
+
 
 [features]
 metrics = ["nomos-node/metrics"]

tests/src/benches/mixnet.rs

@@ -0,0 +1,78 @@
+use std::time::Duration;
+
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use futures::StreamExt;
+use mixnet_client::{MessageStream, MixnetClient, MixnetClientConfig, MixnetClientMode};
+use rand::{rngs::OsRng, Rng, RngCore};
+use tests::MixNode;
+use tokio::time::Instant;
+
+pub fn mixnet(c: &mut Criterion) {
+    c.bench_function("mixnet", |b| {
+        b.to_async(tokio::runtime::Runtime::new().unwrap())
+            .iter_custom(|iters| async move {
+                let (_mixnodes, mut sender_client, mut destination_stream, msg) =
+                    setup(100 * 1024).await;
+
+                let start = Instant::now();
+                for _ in 0..iters {
+                    black_box(
+                        send_receive_message(&msg, &mut sender_client, &mut destination_stream)
+                            .await,
+                    );
+                }
+                start.elapsed()
+            })
+    });
+}
+
+async fn setup(msg_size: usize) -> (Vec<MixNode>, MixnetClient<OsRng>, MessageStream, Vec<u8>) {
+    let (mixnodes, node_configs, topology) = MixNode::spawn_nodes(3).await;
+
+    let sender_client = MixnetClient::new(
+        MixnetClientConfig {
+            mode: MixnetClientMode::Sender,
+            topology: topology.clone(),
+            connection_pool_size: 255,
+        },
+        OsRng,
+    );
+    let destination_client = MixnetClient::new(
+        MixnetClientConfig {
+            mode: MixnetClientMode::SenderReceiver(
+                // Connect with the MixnetNode in the exit layer
+                // According to the current implementation,
+                // one of mixnodes the exit layer always will be selected as a destination.
+                node_configs.last().unwrap().client_listen_address,
+            ),
+            topology,
+            connection_pool_size: 255,
+        },
+        OsRng,
+    );
+    let destination_stream = destination_client.run().await.unwrap();
+
+    let mut msg = vec![0u8; msg_size];
+    rand::thread_rng().fill_bytes(&mut msg);
+
+    (mixnodes, sender_client, destination_stream, msg)
+}
+
+async fn send_receive_message<R: Rng>(
+    msg: &[u8],
+    sender_client: &mut MixnetClient<R>,
+    destination_stream: &mut MessageStream,
+) {
+    let res = sender_client.send(msg.to_vec(), Duration::ZERO);
+    assert!(res.is_ok());
+
+    let received = destination_stream.next().await.unwrap().unwrap();
+    assert_eq!(msg, received.as_slice());
+}
+
+criterion_group!(
+  name = benches;
+  config = Criterion::default().sample_size(10).measurement_time(Duration::from_secs(180));
+  targets = mixnet
+);
+criterion_main!(benches);

tests/src/lib.rs

@@ -1,4 +1,7 @@
 mod nodes;
+use mixnet_node::MixnetNodeConfig;
+use mixnet_topology::MixnetTopology;
+pub use nodes::MixNode;
 pub use nodes::NomosNode;
 use once_cell::sync::Lazy;
 
@@ -11,7 +14,7 @@ use std::{fmt::Debug, sync::Mutex};
 use fraction::Fraction;
 use rand::{thread_rng, Rng};
 
-static NET_PORT: Lazy<Mutex<u16>> = Lazy::new(|| Mutex::new(thread_rng().gen_range(8000..10000)));
+static NET_PORT: Lazy<Mutex<u16>> = Lazy::new(|| Mutex::new(thread_rng().gen_range(8000, 10000)));
 
 pub fn get_available_port() -> u16 {
     let mut port = NET_PORT.lock().unwrap();
@@ -30,11 +33,13 @@ pub trait Node: Sized {
     fn stop(&mut self);
 }
 
-#[derive(Clone, Copy)]
+#[derive(Clone)]
 pub enum SpawnConfig {
     Star {
         n_participants: usize,
         threshold: Fraction,
         timeout: Duration,
+        mixnet_node_configs: Vec<MixnetNodeConfig>,
+        mixnet_topology: MixnetTopology,
     },
 }

tests/src/nodes/mixnode.rs

@@ -0,0 +1,105 @@
+use std::{
+    net::{Ipv4Addr, SocketAddr, SocketAddrV4},
+    process::{Child, Command, Stdio},
+    time::Duration,
+};
+
+use mixnet_node::{MixnetNodeConfig, PRIVATE_KEY_SIZE};
+use mixnet_topology::{Layer, MixnetTopology, Node};
+use rand::{thread_rng, RngCore};
+use tempfile::NamedTempFile;
+
+use crate::get_available_port;
+
+const MIXNODE_BIN: &str = "../target/debug/mixnode";
+
+pub struct MixNode {
+    child: Child,
+}
+
+impl Drop for MixNode {
+    fn drop(&mut self) {
+        self.child.kill().unwrap();
+    }
+}
+
+impl MixNode {
+    pub async fn spawn(config: MixnetNodeConfig) -> Self {
+        let config = mixnode::Config {
+            mixnode: config,
+            log: Default::default(),
+        };
+
+        let mut file = NamedTempFile::new().unwrap();
+        let config_path = file.path().to_owned();
+        serde_yaml::to_writer(&mut file, &config).unwrap();
+
+        let child = Command::new(std::env::current_dir().unwrap().join(MIXNODE_BIN))
+            .arg(&config_path)
+            .stdout(Stdio::null())
+            .spawn()
+            .unwrap();
+
+        //TODO: use a sophisticated way to wait until the node is ready
+        tokio::time::sleep(Duration::from_secs(1)).await;
+
+        Self { child }
+    }
+
+    pub async fn spawn_nodes(
+        num_nodes: usize,
+    ) -> (Vec<Self>, Vec<MixnetNodeConfig>, MixnetTopology) {
+        let mut configs = Vec::<MixnetNodeConfig>::new();
+        for _ in 0..num_nodes {
+            let mut private_key = [0u8; PRIVATE_KEY_SIZE];
+            thread_rng().fill_bytes(&mut private_key);
+
+            let config = MixnetNodeConfig {
+                listen_address: SocketAddr::V4(SocketAddrV4::new(
+                    Ipv4Addr::new(127, 0, 0, 1),
+                    get_available_port(),
+                )),
+                client_listen_address: SocketAddr::V4(SocketAddrV4::new(
+                    Ipv4Addr::new(127, 0, 0, 1),
+                    get_available_port(),
+                )),
+                private_key,
+                connection_pool_size: 255,
+            };
+            configs.push(config);
+        }
+
+        let mut nodes = Vec::<MixNode>::new();
+        for config in &configs {
+            nodes.push(Self::spawn(config.clone()).await);
+        }
+
+        // We need to return configs as well, to configure mixclients accordingly
+        (nodes, configs.clone(), Self::build_topology(configs))
+    }
+
+    fn build_topology(configs: Vec<MixnetNodeConfig>) -> MixnetTopology {
+        // Build three empty layers first
+        let mut layers = vec![Layer { nodes: Vec::new() }; 3];
+        let mut layer_id = 0;
+
+        // Assign nodes to each layer in round-robin
+        for config in &configs {
+            let public_key = config.public_key();
+            layers.get_mut(layer_id).unwrap().nodes.push(Node {
+                address: config.listen_address,
+                public_key,
+            });
+            layer_id = (layer_id + 1) % layers.len();
+        }
+
+        // Exclude empty layers
+        MixnetTopology {
+            layers: layers
+                .iter()
+                .filter(|layer| !layer.nodes.is_empty())
+                .cloned()
+                .collect(),
+        }
+    }
+}

tests/src/nodes/mod.rs

@@ -1,3 +1,5 @@
+mod mixnode;
 mod nomos;
 
+pub use self::mixnode::MixNode;
 pub use nomos::NomosNode;

tests/src/nodes/nomos.rs

@@ -6,13 +6,17 @@ use std::time::Duration;
 use crate::{get_available_port, Node, SpawnConfig};
 use consensus_engine::overlay::{FlatOverlaySettings, RoundRobin};
 use consensus_engine::NodeId;
+#[cfg(feature = "libp2p")]
+use mixnet_client::{MixnetClientConfig, MixnetClientMode};
+use mixnet_node::MixnetNodeConfig;
+use mixnet_topology::MixnetTopology;
 use nomos_consensus::{CarnotInfo, CarnotSettings};
 use nomos_http::backends::axum::AxumBackendSettings;
 #[cfg(feature = "libp2p")]
 use nomos_libp2p::{Multiaddr, SwarmConfig};
 use nomos_log::{LoggerBackend, LoggerFormat};
 #[cfg(feature = "libp2p")]
-use nomos_network::backends::libp2p::Libp2pInfo;
+use nomos_network::backends::libp2p::{Libp2pConfig, Libp2pInfo};
 #[cfg(feature = "waku")]
 use nomos_network::backends::waku::{WakuConfig, WakuInfo};
 use nomos_network::NetworkConfig;
@@ -171,6 +175,8 @@ impl Node for NomosNode {
                 n_participants,
                 threshold,
                 timeout,
+                mut mixnet_node_configs,
+                mixnet_topology,
             } => {
                 let mut ids = vec![[0; 32]; n_participants];
                 for id in &mut ids {
@@ -184,16 +190,27 @@ impl Node for NomosNode {
                             *id,
                             threshold,
                             timeout,
+                            mixnet_node_configs.pop(),
+                            mixnet_topology.clone(),
                         )
                     })
                     .collect::<Vec<_>>();
                 let mut nodes = vec![Self::spawn(configs.swap_remove(0)).await];
                 let listening_addr = nodes[0].get_listening_address().await;
                 for mut conf in configs {
+                    #[cfg(feature = "waku")]
                     conf.network
                         .backend
                         .initial_peers
                         .push(listening_addr.clone());
+                    #[cfg(feature = "libp2p")]
+                    // TODO: Consider having `initial_peers` outside of `inner`, as WakuConfig does
+                    conf.network
+                        .backend
+                        .inner
+                        .initial_peers
+                        .push(listening_addr.clone());
+
                     nodes.push(Self::spawn(conf).await);
                 }
                 nodes
@@ -220,7 +237,17 @@ fn create_node_config(
     private_key: [u8; 32],
     threshold: Fraction,
     timeout: Duration,
+    #[cfg(feature = "libp2p")] mixnet_node_config: Option<MixnetNodeConfig>,
+    #[cfg(feature = "waku")] _mixnet_node_config: Option<MixnetNodeConfig>,
+    #[cfg(feature = "libp2p")] mixnet_topology: MixnetTopology,
+    #[cfg(feature = "waku")] _mixnet_topology: MixnetTopology,
 ) -> Config {
+    #[cfg(feature = "libp2p")]
+    let mixnet_client_mode = match mixnet_node_config {
+        Some(node_config) => MixnetClientMode::SenderReceiver(node_config.client_listen_address),
+        None => MixnetClientMode::Sender,
+    };
+
     let mut config = Config {
         network: NetworkConfig {
             #[cfg(feature = "waku")]
@@ -229,10 +256,18 @@ fn create_node_config(
                 inner: Default::default(),
             },
             #[cfg(feature = "libp2p")]
-            backend: SwarmConfig {
+            backend: Libp2pConfig {
+                inner: SwarmConfig {
                     initial_peers: vec![],
                     ..Default::default()
                 },
+                mixnet_client: MixnetClientConfig {
+                    mode: mixnet_client_mode,
+                    topology: mixnet_topology,
+                    connection_pool_size: 255,
+                },
+                mixnet_delay: Duration::ZERO..Duration::from_millis(10),
+            },
         },
         consensus: CarnotSettings {
             private_key,
@@ -265,7 +300,7 @@ fn create_node_config(
     }
     #[cfg(feature = "libp2p")]
     {
-        config.network.backend.port = get_available_port();
+        config.network.backend.inner.port = get_available_port();
     }
 
     config

tests/src/tests/happy.rs

@@ -3,7 +3,7 @@ use fraction::{Fraction, One};
 use futures::stream::{self, StreamExt};
 use std::collections::HashSet;
 use std::time::Duration;
-use tests::{Node, NomosNode, SpawnConfig};
+use tests::{MixNode, Node, NomosNode, SpawnConfig};
 
 const TARGET_VIEW: View = View::new(20);
 
@@ -48,10 +48,13 @@ async fn happy_test(nodes: Vec<NomosNode>) {
 
 #[tokio::test]
 async fn two_nodes_happy() {
+    let (_mixnodes, mixnet_node_configs, mixnet_topology) = MixNode::spawn_nodes(2).await;
     let nodes = NomosNode::spawn_nodes(SpawnConfig::Star {
         n_participants: 2,
         threshold: Fraction::one(),
         timeout: Duration::from_secs(10),
+        mixnet_node_configs,
+        mixnet_topology,
     })
     .await;
     happy_test(nodes).await;
@@ -59,10 +62,13 @@ async fn two_nodes_happy() {
 
 #[tokio::test]
 async fn ten_nodes_happy() {
+    let (_mixnodes, mixnet_node_configs, mixnet_topology) = MixNode::spawn_nodes(3).await;
     let nodes = NomosNode::spawn_nodes(SpawnConfig::Star {
         n_participants: 10,
         threshold: Fraction::one(),
         timeout: Duration::from_secs(10),
+        mixnet_node_configs,
+        mixnet_topology,
     })
     .await;
     happy_test(nodes).await;

tests/src/tests/mixnet.rs

@@ -0,0 +1,135 @@
+use std::{
+    net::{Ipv4Addr, SocketAddr, SocketAddrV4},
+    time::Duration,
+};
+
+use futures::{Stream, StreamExt};
+use mixnet_client::{MixnetClient, MixnetClientConfig, MixnetClientError, MixnetClientMode};
+use mixnet_node::{MixnetNode, MixnetNodeConfig};
+use mixnet_topology::{Layer, MixnetTopology, Node};
+use rand::{rngs::OsRng, RngCore};
+use tests::get_available_port;
+
+#[tokio::test]
+// Set timeout since the test won't stop even if mixnodes (spawned asynchronously) panic.
+#[ntest::timeout(5000)]
+async fn mixnet() {
+    let (topology, mut destination_stream) = run_nodes_and_destination_client().await;
+
+    let mut msg = [0u8; 100 * 1024];
+    rand::thread_rng().fill_bytes(&mut msg);
+
+    let mut sender_client = MixnetClient::new(
+        MixnetClientConfig {
+            mode: MixnetClientMode::Sender,
+            topology: topology.clone(),
+            connection_pool_size: 255,
+        },
+        OsRng,
+    );
+
+    let res = sender_client.send(msg.to_vec(), Duration::from_millis(500));
+    assert!(res.is_ok());
+
+    let received = destination_stream.next().await.unwrap().unwrap();
+    assert_eq!(msg, received.as_slice());
+}
+
+async fn run_nodes_and_destination_client() -> (
+    MixnetTopology,
+    impl Stream<Item = Result<Vec<u8>, MixnetClientError>> + Send,
+) {
+    let config1 = MixnetNodeConfig {
+        listen_address: SocketAddr::V4(SocketAddrV4::new(
+            Ipv4Addr::new(127, 0, 0, 1),
+            get_available_port(),
+        )),
+        client_listen_address: SocketAddr::V4(SocketAddrV4::new(
+            Ipv4Addr::new(127, 0, 0, 1),
+            get_available_port(),
+        )),
+        ..Default::default()
+    };
+    let config2 = MixnetNodeConfig {
+        listen_address: SocketAddr::V4(SocketAddrV4::new(
+            Ipv4Addr::new(127, 0, 0, 1),
+            get_available_port(),
+        )),
+        client_listen_address: SocketAddr::V4(SocketAddrV4::new(
+            Ipv4Addr::new(127, 0, 0, 1),
+            get_available_port(),
+        )),
+        ..Default::default()
+    };
+    let config3 = MixnetNodeConfig {
+        listen_address: SocketAddr::V4(SocketAddrV4::new(
+            Ipv4Addr::new(127, 0, 0, 1),
+            get_available_port(),
+        )),
+        client_listen_address: SocketAddr::V4(SocketAddrV4::new(
+            Ipv4Addr::new(127, 0, 0, 1),
+            get_available_port(),
+        )),
+        ..Default::default()
+    };
+
+    let mixnode1 = MixnetNode::new(config1.clone());
+    let mixnode2 = MixnetNode::new(config2.clone());
+    let mixnode3 = MixnetNode::new(config3.clone());
+
+    let topology = MixnetTopology {
+        layers: vec![
+            Layer {
+                nodes: vec![Node {
+                    address: config1.listen_address,
+                    public_key: mixnode1.public_key(),
+                }],
+            },
+            Layer {
+                nodes: vec![Node {
+                    address: config2.listen_address,
+                    public_key: mixnode2.public_key(),
+                }],
+            },
+            Layer {
+                nodes: vec![Node {
+                    address: config3.listen_address,
+                    public_key: mixnode3.public_key(),
+                }],
+            },
+        ],
+    };
+
+    // Run all MixnetNodes
+    tokio::spawn(async move {
+        let res = mixnode1.run().await;
+        assert!(res.is_ok());
+    });
+    tokio::spawn(async move {
+        let res = mixnode2.run().await;
+        assert!(res.is_ok());
+    });
+    tokio::spawn(async move {
+        let res = mixnode3.run().await;
+        assert!(res.is_ok());
+    });
+
+    // Wait until mixnodes are ready
+    // TODO: use a more sophisticated way
+    tokio::time::sleep(Duration::from_secs(1)).await;
+
+    // Run a MixnetClient only for the MixnetNode in the exit layer.
+    // According to the current implementation,
+    // one of mixnodes the exit layer always will be selected as a destination.
+    let client = MixnetClient::new(
+        MixnetClientConfig {
+            mode: MixnetClientMode::SenderReceiver(config3.client_listen_address),
+            topology: topology.clone(),
+            connection_pool_size: 255,
+        },
+        OsRng,
+    );
+    let client_stream = client.run().await.unwrap();
+
+    (topology, client_stream)
+}

tests/src/tests/unhappy.rs

@@ -2,16 +2,19 @@ use consensus_engine::View;
 use fraction::Fraction;
 use futures::stream::{self, StreamExt};
 use std::collections::HashSet;
-use tests::{Node, NomosNode, SpawnConfig};
+use tests::{MixNode, Node, NomosNode, SpawnConfig};
 
 const TARGET_VIEW: View = View::new(20);
 
 #[tokio::test]
 async fn ten_nodes_one_down() {
+    let (_mixnodes, mixnet_node_configs, mixnet_topology) = MixNode::spawn_nodes(3).await;
     let mut nodes = NomosNode::spawn_nodes(SpawnConfig::Star {
         n_participants: 10,
         threshold: Fraction::new(9u32, 10u32),
         timeout: std::time::Duration::from_secs(5),
+        mixnet_node_configs,
+        mixnet_topology,
     })
     .await;
     let mut failed_node = nodes.pop().unwrap();