Merge pull request #150 from poanetwork/vk-api-messages66

Outgoing message API refactoring

examples/network/node.rs

@@ -144,8 +144,8 @@ impl<T: Clone + Debug + AsRef<[u8]> + PartialEq + Send + Sync + From<Vec<u8>> +
 
                 if let Some(v) = value {
                     // FIXME: Use the output.
-                    let _ = broadcast.input(v.clone().into()).expect("propose value");
+                    let step = broadcast.input(v.clone().into()).expect("propose value");
-                    for msg in broadcast.message_iter() {
+                    for msg in step.messages {
                         tx_from_algo.send(msg).expect("send from algo");
                     }
                 }
@@ -158,7 +158,7 @@ impl<T: Clone + Debug + AsRef<[u8]> + PartialEq + Send + Sync + From<Vec<u8>> +
                     let step = broadcast
                         .handle_message(&i, message)
                         .expect("handle broadcast message");
-                    for msg in broadcast.message_iter() {
+                    for msg in step.messages {
                         debug!("{} sending to {:?}: {:?}", our_id, msg.target, msg.message);
                         tx_from_algo.send(msg).expect("send from algo");
                     }

examples/simulation.rs

@@ -137,20 +137,40 @@ pub struct TestNode<D: DistAlgorithm> {
     hw_quality: HwQuality,
 }
 
+type TestNodeStepResult<D> = Step<D>;
+
 impl<D: DistAlgorithm> TestNode<D>
 where
     D::Message: Serialize + DeserializeOwned,
 {
     /// Creates a new test node with the given broadcast instance.
-    fn new(algo: D, hw_quality: HwQuality) -> TestNode<D> {
+    fn new((algo, step): (D, Step<D>), hw_quality: HwQuality) -> TestNode<D> {
+        let out_queue = step
+            .messages
+            .into_iter()
+            .map(|msg| {
+                let ser_msg = bincode::serialize(&msg.message).expect("serialize");
+                TimestampedMessage {
+                    time: Duration::default(),
+                    sender_id: algo.our_id().clone(),
+                    target: msg.target,
+                    message: ser_msg,
+                }
+            })
+            .collect();
+        let outputs = step
+            .output
+            .into_iter()
+            .map(|out| (Duration::default(), out))
+            .collect();
         let mut node = TestNode {
             id: algo.our_id().clone(),
             algo,
             time: Duration::default(),
             sent_time: Duration::default(),
             in_queue: VecDeque::new(),
-            out_queue: VecDeque::new(),
+            out_queue,
-            outputs: Vec::new(),
+            outputs,
             message_count: 0,
             message_size: 0,
             hw_quality,
@@ -176,19 +196,14 @@ where
     }
 
     /// Handles the algorithm's output and messages.
-    fn send_output_and_msgs(
+    fn send_output_and_msgs(&mut self, step: TestNodeStepResult<D>) {
-        &mut self,
-        step: Step<<D as DistAlgorithm>::NodeUid, <D as DistAlgorithm>::Output>,
-    ) {
         let start = Instant::now();
-        let out_msgs: Vec<_> = self
+        let out_msgs: Vec<_> = step
-            .algo
+            .messages
-            .message_iter()
+            .into_iter()
             .map(|msg| {
-                (
+                let ser_msg = bincode::serialize(&msg.message).expect("serialize");
-                    msg.target,
+                (msg.target, ser_msg)
-                    bincode::serialize(&msg.message).expect("serialize"),
-                )
             })
             .collect();
         self.time += start.elapsed() * self.hw_quality.cpu_factor / 100;
@@ -251,7 +266,7 @@ where
         hw_quality: HwQuality,
     ) -> TestNetwork<D>
     where
-        F: Fn(NetworkInfo<NodeUid>) -> D,
+        F: Fn(NetworkInfo<NodeUid>) -> (D, Step<D>),
     {
         let netinfos = NetworkInfo::generate_map((0..(good_num + adv_num)).map(NodeUid));
         let new_node = |(uid, netinfo): (NodeUid, NetworkInfo<_>)| {
@@ -431,9 +446,7 @@ fn main() {
     let num_good_nodes = args.flag_n - args.flag_f;
     let txs = (0..args.flag_txs).map(|_| Transaction::new(args.flag_tx_size));
     let new_honey_badger = |netinfo: NetworkInfo<NodeUid>| {
-        let dyn_hb = DynamicHoneyBadger::builder(netinfo)
+        let dyn_hb = DynamicHoneyBadger::builder().build(netinfo);
-            .build()
-            .expect("instantiate DynamicHoneyBadger");
         QueueingHoneyBadger::builder(dyn_hb)
             .batch_size(args.flag_b)
             .build_with_transactions(txs.clone())

src/agreement/mod.rs

@@ -74,20 +74,15 @@ use std::sync::Arc;
 use itertools::Itertools;
 
 use agreement::bin_values::BinValues;
-use common_coin;
+use common_coin::{self, CommonCoin, CommonCoinMessage};
-use common_coin::{CommonCoin, CommonCoinMessage, CommonCoinStep};
 use fault_log::FaultLog;
-use messaging::{DistAlgorithm, NetworkInfo, Step, Target, TargetedMessage};
+use messaging::{self, DistAlgorithm, NetworkInfo, Target, TargetedMessage};
 
 error_chain!{
     links {
         CommonCoin(common_coin::Error, common_coin::ErrorKind);
     }
 
-    types {
-        Error, ErrorKind, ResultExt, AgreementResult;
-    }
-
     errors {
         UnknownProposer {
             description("unknown proposer")
@@ -208,7 +203,7 @@ pub struct Agreement<NodeUid> {
     coin_schedule: CoinSchedule,
 }
 
-pub type AgreementStep<NodeUid> = Step<NodeUid, bool>;
+pub type Step<NodeUid> = messaging::Step<Agreement<NodeUid>>;
 
 impl<NodeUid: Clone + Debug + Ord> DistAlgorithm for Agreement<NodeUid> {
     type NodeUid = NodeUid;
@@ -217,7 +212,7 @@ impl<NodeUid: Clone + Debug + Ord> DistAlgorithm for Agreement<NodeUid> {
     type Message = AgreementMessage;
     type Error = Error;
 
-    fn input(&mut self, input: Self::Input) -> AgreementResult<AgreementStep<NodeUid>> {
+    fn input(&mut self, input: Self::Input) -> Result<Step<NodeUid>> {
         let fault_log = self.set_input(input)?;
         self.step(fault_log)
     }
@@ -227,7 +222,7 @@ impl<NodeUid: Clone + Debug + Ord> DistAlgorithm for Agreement<NodeUid> {
         &mut self,
         sender_id: &Self::NodeUid,
         message: Self::Message,
-    ) -> AgreementResult<AgreementStep<NodeUid>> {
+    ) -> Result<Step<NodeUid>> {
         let fault_log = if self.terminated || message.epoch < self.epoch {
             // Message is obsolete: We are already in a later epoch or terminated.
             FaultLog::new()
@@ -247,13 +242,6 @@ impl<NodeUid: Clone + Debug + Ord> DistAlgorithm for Agreement<NodeUid> {
         self.step(fault_log)
     }
 
-    /// Take the next Agreement message for multicast to all other nodes.
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, Self::NodeUid>> {
-        self.messages
-            .pop_front()
-            .map(|msg| Target::All.message(msg))
-    }
-
     /// Whether the algorithm has terminated.
     fn terminated(&self) -> bool {
         self.terminated
@@ -269,7 +257,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         netinfo: Arc<NetworkInfo<NodeUid>>,
         session_id: u64,
         proposer_id: NodeUid,
-    ) -> AgreementResult<Self> {
+    ) -> Result<Self> {
         let invocation_id = netinfo.invocation_id();
         if let Some(proposer_i) = netinfo.node_index(&proposer_id) {
             Ok(Agreement {
@@ -301,15 +289,19 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         }
     }
 
-    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> AgreementResult<AgreementStep<NodeUid>> {
+    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> Result<Step<NodeUid>> {
         Ok(Step::new(
             self.output.take().into_iter().collect(),
             fault_log,
+            self.messages
+                .drain(..)
+                .map(|msg| Target::All.message(msg))
+                .collect(),
         ))
     }
 
     /// Sets the input value for agreement.
-    fn set_input(&mut self, input: bool) -> AgreementResult<FaultLog<NodeUid>> {
+    fn set_input(&mut self, input: bool) -> Result<FaultLog<NodeUid>> {
         if self.epoch != 0 || self.estimated.is_some() {
             return Err(ErrorKind::InputNotAccepted.into());
         }
@@ -331,7 +323,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         self.epoch == 0 && self.estimated.is_none()
     }
 
-    fn handle_bval(&mut self, sender_id: &NodeUid, b: bool) -> AgreementResult<FaultLog<NodeUid>> {
+    fn handle_bval(&mut self, sender_id: &NodeUid, b: bool) -> Result<FaultLog<NodeUid>> {
         self.received_bval
             .entry(sender_id.clone())
             .or_insert_with(BTreeSet::new)
@@ -369,7 +361,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
 
     /// Called when `bin_values` changes as a result of receiving a `BVal` message. Tries to update
     /// the epoch.
-    fn on_bin_values_changed(&mut self) -> AgreementResult<FaultLog<NodeUid>> {
+    fn on_bin_values_changed(&mut self) -> Result<FaultLog<NodeUid>> {
         match self.coin_schedule {
             CoinSchedule::False => {
                 let (aux_count, aux_vals) = self.count_aux();
@@ -395,7 +387,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         }
     }
 
-    fn send_bval(&mut self, b: bool) -> AgreementResult<FaultLog<NodeUid>> {
+    fn send_bval(&mut self, b: bool) -> Result<FaultLog<NodeUid>> {
         if !self.netinfo.is_validator() {
             return Ok(FaultLog::new());
         }
@@ -409,7 +401,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         self.handle_bval(our_uid, b)
     }
 
-    fn send_conf(&mut self) -> AgreementResult<FaultLog<NodeUid>> {
+    fn send_conf(&mut self) -> Result<FaultLog<NodeUid>> {
         if self.conf_round {
             // Only one `Conf` message is allowed in an epoch.
             return Ok(FaultLog::new());
@@ -436,7 +428,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
     /// bin_values (note that bin_values_r may continue to change as `BVal`
     /// messages are received, thus this condition may be triggered upon arrival
     /// of either an `Aux` or a `BVal` message).
-    fn handle_aux(&mut self, sender_id: &NodeUid, b: bool) -> AgreementResult<FaultLog<NodeUid>> {
+    fn handle_aux(&mut self, sender_id: &NodeUid, b: bool) -> Result<FaultLog<NodeUid>> {
         // Perform the `Aux` message round only if a `Conf` round hasn't started yet.
         if self.conf_round {
             return Ok(FaultLog::new());
@@ -462,11 +454,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         }
     }
 
-    fn handle_conf(
+    fn handle_conf(&mut self, sender_id: &NodeUid, v: BinValues) -> Result<FaultLog<NodeUid>> {
-        &mut self,
-        sender_id: &NodeUid,
-        v: BinValues,
-    ) -> AgreementResult<FaultLog<NodeUid>> {
         self.received_conf.insert(sender_id.clone(), v);
         self.try_finish_conf_round()
     }
@@ -474,7 +462,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
     /// Receives a `Term(v)` message. If we haven't yet decided on a value and there are more than
     /// `num_faulty` such messages with the same value from different nodes, performs expedite
     /// termination: decides on `v`, broadcasts `Term(v)` and terminates the instance.
-    fn handle_term(&mut self, sender_id: &NodeUid, b: bool) -> AgreementResult<FaultLog<NodeUid>> {
+    fn handle_term(&mut self, sender_id: &NodeUid, b: bool) -> Result<FaultLog<NodeUid>> {
         self.received_term.insert(sender_id.clone(), b);
         // Check for the expedite termination condition.
         if self.decision.is_none()
@@ -492,20 +480,26 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         &mut self,
         sender_id: &NodeUid,
         msg: CommonCoinMessage,
-    ) -> AgreementResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         let coin_step = self.common_coin.handle_message(sender_id, msg)?;
-        self.extend_common_coin();
         self.on_coin_step(coin_step)
     }
 
     fn on_coin_step(
         &mut self,
-        coin_step: CommonCoinStep<NodeUid>,
+        coin_step: common_coin::Step<NodeUid, Nonce>,
-    ) -> AgreementResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
-        let Step {
+        let common_coin::Step {
             output,
             mut fault_log,
+            messages,
         } = coin_step;
+        let epoch = self.epoch;
+        self.messages.extend(messages.into_iter().map(
+            |msg: TargetedMessage<CommonCoinMessage, NodeUid>| {
+                AgreementContent::Coin(Box::new(msg.message)).with_epoch(epoch)
+            },
+        ));
         if let Some(coin) = output.into_iter().next() {
             let def_bin_value = self.count_conf().1.definite();
             fault_log.extend(self.on_coin(coin, def_bin_value)?);
@@ -515,11 +509,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
 
     /// When the common coin has been computed, tries to decide on an output value, updates the
     /// `Agreement` epoch and handles queued messages for the new epoch.
-    fn on_coin(
+    fn on_coin(&mut self, coin: bool, def_bin_value: Option<bool>) -> Result<FaultLog<NodeUid>> {
-        &mut self,
-        coin: bool,
-        def_bin_value: Option<bool>,
-    ) -> AgreementResult<FaultLog<NodeUid>> {
         let mut fault_log = FaultLog::new();
         if self.terminated {
             // Avoid an infinite regression without making an Agreement step.
@@ -562,16 +552,6 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         }
     }
 
-    /// Propagates Common Coin messages to the top level.
-    fn extend_common_coin(&mut self) {
-        let epoch = self.epoch;
-        self.messages.extend(self.common_coin.message_iter().map(
-            |msg: TargetedMessage<CommonCoinMessage, NodeUid>| {
-                AgreementContent::Coin(Box::new(msg.message)).with_epoch(epoch)
-            },
-        ));
-    }
-
     /// Decides on a value and broadcasts a `Term` message with that value.
     fn decide(&mut self, b: bool) {
         if self.terminated {
@@ -596,13 +576,12 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         self.terminated = true;
     }
 
-    fn try_finish_conf_round(&mut self) -> AgreementResult<FaultLog<NodeUid>> {
+    fn try_finish_conf_round(&mut self) -> Result<FaultLog<NodeUid>> {
         if self.conf_round
             && self.count_conf().0 >= self.netinfo.num_nodes() - self.netinfo.num_faulty()
         {
             // Invoke the common coin.
             let coin_step = self.common_coin.input(())?;
-            self.extend_common_coin();
             self.on_coin_step(coin_step)
         } else {
             // Continue waiting for (N - f) `Conf` messages
@@ -610,7 +589,7 @@ impl<NodeUid: Clone + Debug + Ord> Agreement<NodeUid> {
         }
     }
 
-    fn send_aux(&mut self, b: bool) -> AgreementResult<FaultLog<NodeUid>> {
+    fn send_aux(&mut self, b: bool) -> Result<FaultLog<NodeUid>> {
         if !self.netinfo.is_validator() {
             return Ok(FaultLog::new());
         }

src/broadcast.rs

@@ -141,13 +141,9 @@ use ring::digest;
 
 use fault_log::{FaultKind, FaultLog};
 use fmt::{HexBytes, HexList, HexProof};
-use messaging::{DistAlgorithm, NetworkInfo, Step, Target, TargetedMessage};
+use messaging::{self, DistAlgorithm, NetworkInfo, Target, TargetedMessage};
 
 error_chain!{
-    types {
-        Error, ErrorKind, ResultExt, BroadcastResult;
-    }
-
     foreign_links {
         ReedSolomon(rse::Error);
     }
@@ -228,7 +224,7 @@ pub struct Broadcast<NodeUid> {
     output: Option<Vec<u8>>,
 }
 
-pub type BroadcastStep<N> = Step<N, Vec<u8>>;
+pub type Step<NodeUid> = messaging::Step<Broadcast<NodeUid>>;
 
 impl<NodeUid: Debug + Clone + Ord> DistAlgorithm for Broadcast<NodeUid> {
     type NodeUid = NodeUid;
@@ -239,7 +235,7 @@ impl<NodeUid: Debug + Clone + Ord> DistAlgorithm for Broadcast<NodeUid> {
     type Message = BroadcastMessage;
     type Error = Error;
 
-    fn input(&mut self, input: Self::Input) -> BroadcastResult<BroadcastStep<NodeUid>> {
+    fn input(&mut self, input: Self::Input) -> Result<Step<NodeUid>> {
         if *self.netinfo.our_uid() != self.proposer_id {
             return Err(ErrorKind::InstanceCannotPropose.into());
         }
@@ -256,7 +252,7 @@ impl<NodeUid: Debug + Clone + Ord> DistAlgorithm for Broadcast<NodeUid> {
         &mut self,
         sender_id: &NodeUid,
         message: Self::Message,
-    ) -> BroadcastResult<BroadcastStep<NodeUid>> {
+    ) -> Result<Step<NodeUid>> {
         if !self.netinfo.is_node_validator(sender_id) {
             return Err(ErrorKind::UnknownSender.into());
         }
@@ -270,10 +266,6 @@ impl<NodeUid: Debug + Clone + Ord> DistAlgorithm for Broadcast<NodeUid> {
         self.step(fault_log)
     }
 
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, NodeUid>> {
-        self.messages.pop_front()
-    }
-
     fn terminated(&self) -> bool {
         self.decided
     }
@@ -286,7 +278,7 @@ impl<NodeUid: Debug + Clone + Ord> DistAlgorithm for Broadcast<NodeUid> {
 impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
     /// Creates a new broadcast instance to be used by node `our_id` which expects a value proposal
     /// from node `proposer_id`.
-    pub fn new(netinfo: Arc<NetworkInfo<NodeUid>>, proposer_id: NodeUid) -> BroadcastResult<Self> {
+    pub fn new(netinfo: Arc<NetworkInfo<NodeUid>>, proposer_id: NodeUid) -> Result<Self> {
         let parity_shard_num = 2 * netinfo.num_faulty();
         let data_shard_num = netinfo.num_nodes() - parity_shard_num;
         let coding = Coding::new(data_shard_num, parity_shard_num)?;
@@ -306,10 +298,11 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
         })
     }
 
-    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> BroadcastResult<BroadcastStep<NodeUid>> {
+    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> Result<Step<NodeUid>> {
         Ok(Step::new(
             self.output.take().into_iter().collect(),
             fault_log,
+            self.messages.drain(..).collect(),
         ))
     }
 
@@ -318,7 +311,7 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
     /// scheme. The returned value contains the shard assigned to this
     /// node. That shard doesn't need to be sent anywhere. It gets recorded in
     /// the broadcast instance.
-    fn send_shards(&mut self, mut value: Vec<u8>) -> BroadcastResult<Proof<Vec<u8>>> {
+    fn send_shards(&mut self, mut value: Vec<u8>) -> Result<Proof<Vec<u8>>> {
         let data_shard_num = self.coding.data_shard_count();
         let parity_shard_num = self.coding.parity_shard_count();
 
@@ -396,7 +389,7 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
         &mut self,
         sender_id: &NodeUid,
         p: Proof<Vec<u8>>,
-    ) -> BroadcastResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         // If the sender is not the proposer or if this is not the first `Value`, ignore.
         if *sender_id != self.proposer_id {
             info!(
@@ -428,11 +421,7 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
     }
 
     /// Handles a received `Echo` message.
-    fn handle_echo(
+    fn handle_echo(&mut self, sender_id: &NodeUid, p: Proof<Vec<u8>>) -> Result<FaultLog<NodeUid>> {
-        &mut self,
-        sender_id: &NodeUid,
-        p: Proof<Vec<u8>>,
-    ) -> BroadcastResult<FaultLog<NodeUid>> {
         let mut fault_log = FaultLog::new();
         // If the sender has already sent `Echo`, ignore.
         if self.echos.contains_key(sender_id) {
@@ -468,7 +457,7 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
     }
 
     /// Handles a received `Ready` message.
-    fn handle_ready(&mut self, sender_id: &NodeUid, hash: &[u8]) -> BroadcastResult<()> {
+    fn handle_ready(&mut self, sender_id: &NodeUid, hash: &[u8]) -> Result<()> {
         // If the sender has already sent a `Ready` before, ignore.
         if self.readys.contains_key(sender_id) {
             info!(
@@ -491,7 +480,7 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
     }
 
     /// Sends an `Echo` message and handles it. Does nothing if we are only an observer.
-    fn send_echo(&mut self, p: Proof<Vec<u8>>) -> BroadcastResult<FaultLog<NodeUid>> {
+    fn send_echo(&mut self, p: Proof<Vec<u8>>) -> Result<FaultLog<NodeUid>> {
         self.echo_sent = true;
         if !self.netinfo.is_validator() {
             return Ok(FaultLog::new());
@@ -503,7 +492,7 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
     }
 
     /// Sends a `Ready` message and handles it. Does nothing if we are only an observer.
-    fn send_ready(&mut self, hash: &[u8]) -> BroadcastResult<()> {
+    fn send_ready(&mut self, hash: &[u8]) -> Result<()> {
         self.ready_sent = true;
         if !self.netinfo.is_validator() {
             return Ok(());
@@ -516,7 +505,7 @@ impl<NodeUid: Debug + Clone + Ord> Broadcast<NodeUid> {
 
     /// Checks whether the condition for output are met for this hash, and if so, sets the output
     /// value.
-    fn compute_output(&mut self, hash: &[u8]) -> BroadcastResult<()> {
+    fn compute_output(&mut self, hash: &[u8]) -> Result<()> {
         if self.decided
             || self.count_readys(hash) <= 2 * self.netinfo.num_faulty()
             || self.count_echos(hash) <= self.netinfo.num_faulty()
@@ -595,7 +584,7 @@ enum Coding {
 
 impl Coding {
     /// Creates a new `Coding` instance with the given number of shards.
-    fn new(data_shard_num: usize, parity_shard_num: usize) -> BroadcastResult<Self> {
+    fn new(data_shard_num: usize, parity_shard_num: usize) -> Result<Self> {
         Ok(if parity_shard_num > 0 {
             let rs = ReedSolomon::new(data_shard_num, parity_shard_num)?;
             Coding::ReedSolomon(Box::new(rs))
@@ -621,7 +610,7 @@ impl Coding {
     }
 
     /// Constructs (and overwrites) the parity shards.
-    fn encode(&self, slices: &mut [&mut [u8]]) -> BroadcastResult<()> {
+    fn encode(&self, slices: &mut [&mut [u8]]) -> Result<()> {
         match *self {
             Coding::ReedSolomon(ref rs) => rs.encode(slices)?,
             Coding::Trivial(_) => (),
@@ -630,7 +619,7 @@ impl Coding {
     }
 
     /// If enough shards are present, reconstructs the missing ones.
-    fn reconstruct_shards(&self, shards: &mut [Option<Box<[u8]>>]) -> BroadcastResult<()> {
+    fn reconstruct_shards(&self, shards: &mut [Option<Box<[u8]>>]) -> Result<()> {
         match *self {
             Coding::ReedSolomon(ref rs) => rs.reconstruct_shards(shards)?,
             Coding::Trivial(_) => {

src/common_coin.rs

@@ -28,7 +28,7 @@ use std::sync::Arc;
 use crypto::error as cerror;
 use crypto::{Signature, SignatureShare};
 use fault_log::{FaultKind, FaultLog};
-use messaging::{DistAlgorithm, NetworkInfo, Step, Target, TargetedMessage};
+use messaging::{self, DistAlgorithm, NetworkInfo, Target};
 
 error_chain! {
     links {
@@ -78,7 +78,7 @@ pub struct CommonCoin<NodeUid, T> {
     terminated: bool,
 }
 
-pub type CommonCoinStep<NodeUid> = Step<NodeUid, bool>;
+pub type Step<NodeUid, T> = messaging::Step<CommonCoin<NodeUid, T>>;
 
 impl<NodeUid, T> DistAlgorithm for CommonCoin<NodeUid, T>
 where
@@ -92,7 +92,7 @@ where
     type Error = Error;
 
     /// Sends our threshold signature share if not yet sent.
-    fn input(&mut self, _input: Self::Input) -> Result<CommonCoinStep<NodeUid>> {
+    fn input(&mut self, _input: Self::Input) -> Result<Step<NodeUid, T>> {
         let fault_log = if !self.had_input {
             self.had_input = true;
             self.get_coin()?
@@ -107,7 +107,7 @@ where
         &mut self,
         sender_id: &Self::NodeUid,
         message: Self::Message,
-    ) -> Result<CommonCoinStep<NodeUid>> {
+    ) -> Result<Step<NodeUid, T>> {
         let fault_log = if !self.terminated {
             let CommonCoinMessage(share) = message;
             self.handle_share(sender_id, share)?
@@ -117,13 +117,6 @@ where
         self.step(fault_log)
     }
 
-    /// Takes the next share of a threshold signature message for multicasting to all other nodes.
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, Self::NodeUid>> {
-        self.messages
-            .pop_front()
-            .map(|msg| Target::All.message(msg))
-    }
-
     /// Whether the algorithm has terminated.
     fn terminated(&self) -> bool {
         self.terminated
@@ -151,10 +144,14 @@ where
         }
     }
 
-    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> Result<CommonCoinStep<NodeUid>> {
+    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> Result<Step<NodeUid, T>> {
         Ok(Step::new(
             self.output.take().into_iter().collect(),
             fault_log,
+            self.messages
+                .drain(..)
+                .map(|msg| Target::All.message(msg))
+                .collect(),
         ))
     }
 

src/common_subset.rs

@@ -25,20 +25,17 @@
 
 use std::collections::{BTreeMap, BTreeSet, VecDeque};
 use std::fmt::Debug;
+use std::result;
 use std::sync::Arc;
 
-use agreement::{self, Agreement, AgreementMessage, AgreementStep};
+use agreement::{self, Agreement, AgreementMessage};
-use broadcast::{self, Broadcast, BroadcastMessage, BroadcastStep};
+use broadcast::{self, Broadcast, BroadcastMessage};
 use fault_log::FaultLog;
 use fmt::HexBytes;
-use messaging::{DistAlgorithm, NetworkInfo, Step, TargetedMessage};
+use messaging::{self, DistAlgorithm, NetworkInfo, TargetedMessage};
 use rand::Rand;
 
 error_chain!{
-    types {
-        Error, ErrorKind, ResultExt, CommonSubsetResult;
-    }
-
     links {
         Agreement(agreement::Error, agreement::ErrorKind);
         Broadcast(broadcast::Error, broadcast::ErrorKind);
@@ -70,19 +67,27 @@ struct MessageQueue<NodeUid: Rand>(VecDeque<TargetedMessage<Message<NodeUid>, No
 
 impl<NodeUid: Clone + Debug + Ord + Rand> MessageQueue<NodeUid> {
     /// Appends to the queue the messages from `agr`, wrapped with `proposer_id`.
-    fn extend_agreement(&mut self, proposer_id: &NodeUid, agr: &mut Agreement<NodeUid>) {
+    fn extend_agreement(
+        &mut self,
+        proposer_id: &NodeUid,
+        msgs: &mut VecDeque<TargetedMessage<AgreementMessage, NodeUid>>,
+    ) {
         let convert = |msg: TargetedMessage<AgreementMessage, NodeUid>| {
             msg.map(|a_msg| Message::Agreement(proposer_id.clone(), a_msg))
         };
-        self.extend(agr.message_iter().map(convert));
+        self.extend(msgs.drain(..).map(convert));
     }
 
     /// Appends to the queue the messages from `bc`, wrapped with `proposer_id`.
-    fn extend_broadcast(&mut self, proposer_id: &NodeUid, bc: &mut Broadcast<NodeUid>) {
+    fn extend_broadcast(
+        &mut self,
+        proposer_id: &NodeUid,
+        msgs: &mut VecDeque<TargetedMessage<BroadcastMessage, NodeUid>>,
+    ) {
         let convert = |msg: TargetedMessage<BroadcastMessage, NodeUid>| {
             msg.map(|b_msg| Message::Broadcast(proposer_id.clone(), b_msg))
         };
-        self.extend(bc.message_iter().map(convert));
+        self.extend(msgs.drain(..).map(convert));
     }
 }
 
@@ -102,7 +107,7 @@ pub struct CommonSubset<NodeUid: Rand> {
     decided: bool,
 }
 
-pub type CommonSubsetStep<NodeUid> = Step<NodeUid, BTreeMap<NodeUid, ProposedValue>>;
+pub type Step<NodeUid> = messaging::Step<CommonSubset<NodeUid>>;
 
 impl<NodeUid: Clone + Debug + Ord + Rand> DistAlgorithm for CommonSubset<NodeUid> {
     type NodeUid = NodeUid;
@@ -111,7 +116,7 @@ impl<NodeUid: Clone + Debug + Ord + Rand> DistAlgorithm for CommonSubset<NodeUid
     type Message = Message<NodeUid>;
     type Error = Error;
 
-    fn input(&mut self, input: Self::Input) -> CommonSubsetResult<CommonSubsetStep<NodeUid>> {
+    fn input(&mut self, input: Self::Input) -> Result<Step<NodeUid>> {
         debug!(
             "{:?} Proposing {:?}",
             self.netinfo.our_uid(),
@@ -125,7 +130,7 @@ impl<NodeUid: Clone + Debug + Ord + Rand> DistAlgorithm for CommonSubset<NodeUid
         &mut self,
         sender_id: &Self::NodeUid,
         message: Self::Message,
-    ) -> CommonSubsetResult<CommonSubsetStep<NodeUid>> {
+    ) -> Result<Step<NodeUid>> {
         let fault_log = match message {
             Message::Broadcast(p_id, b_msg) => self.handle_broadcast(sender_id, &p_id, b_msg)?,
             Message::Agreement(p_id, a_msg) => self.handle_agreement(sender_id, &p_id, a_msg)?,
@@ -133,10 +138,6 @@ impl<NodeUid: Clone + Debug + Ord + Rand> DistAlgorithm for CommonSubset<NodeUid
         self.step(fault_log)
     }
 
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, Self::NodeUid>> {
-        self.messages.pop_front()
-    }
-
     fn terminated(&self) -> bool {
         self.messages.is_empty() && self.agreement_instances.values().all(Agreement::terminated)
     }
@@ -147,7 +148,7 @@ impl<NodeUid: Clone + Debug + Ord + Rand> DistAlgorithm for CommonSubset<NodeUid
 }
 
 impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
-    pub fn new(netinfo: Arc<NetworkInfo<NodeUid>>, session_id: u64) -> CommonSubsetResult<Self> {
+    pub fn new(netinfo: Arc<NetworkInfo<NodeUid>>, session_id: u64) -> Result<Self> {
         // Create all broadcast instances.
         let mut broadcast_instances: BTreeMap<NodeUid, Broadcast<NodeUid>> = BTreeMap::new();
         for proposer_id in netinfo.all_uids() {
@@ -178,22 +179,17 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
         })
     }
 
-    fn step(
+    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> Result<Step<NodeUid>> {
-        &mut self,
-        fault_log: FaultLog<NodeUid>,
-    ) -> CommonSubsetResult<CommonSubsetStep<NodeUid>> {
         Ok(Step::new(
             self.output.take().into_iter().collect(),
             fault_log,
+            self.messages.drain(..).collect(),
         ))
     }
 
     /// Common Subset input message handler. It receives a value for broadcast
     /// and redirects it to the corresponding broadcast instance.
-    pub fn send_proposed_value(
+    pub fn send_proposed_value(&mut self, value: ProposedValue) -> Result<FaultLog<NodeUid>> {
-        &mut self,
-        value: ProposedValue,
-    ) -> CommonSubsetResult<FaultLog<NodeUid>> {
         if !self.netinfo.is_validator() {
             return Ok(FaultLog::new());
         }
@@ -209,7 +205,7 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
         sender_id: &NodeUid,
         proposer_id: &NodeUid,
         bmessage: BroadcastMessage,
-    ) -> CommonSubsetResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         self.process_broadcast(proposer_id, |bc| bc.handle_message(sender_id, bmessage))
     }
 
@@ -220,7 +216,7 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
         sender_id: &NodeUid,
         proposer_id: &NodeUid,
         amessage: AgreementMessage,
-    ) -> CommonSubsetResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         // Send the message to the local instance of Agreement
         self.process_agreement(proposer_id, |agreement| {
             agreement.handle_message(sender_id, amessage)
@@ -229,13 +225,10 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
 
     /// Upon delivery of v_j from RBC_j, if input has not yet been provided to
     /// BA_j, then provide input 1 to BA_j. See Figure 11.
-    fn process_broadcast<F>(
+    fn process_broadcast<F>(&mut self, proposer_id: &NodeUid, f: F) -> Result<FaultLog<NodeUid>>
-        &mut self,
-        proposer_id: &NodeUid,
-        f: F,
-    ) -> CommonSubsetResult<FaultLog<NodeUid>>
     where
-        F: FnOnce(&mut Broadcast<NodeUid>) -> Result<BroadcastStep<NodeUid>, broadcast::Error>,
+        F: FnOnce(&mut Broadcast<NodeUid>)
+            -> result::Result<broadcast::Step<NodeUid>, broadcast::Error>,
     {
         let mut fault_log = FaultLog::new();
         let value = {
@@ -243,9 +236,10 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
                 .broadcast_instances
                 .get_mut(proposer_id)
                 .ok_or(ErrorKind::NoSuchBroadcastInstance)?;
-            let step = f(broadcast)?;
+            let mut step = f(broadcast)?;
             fault_log.extend(step.fault_log);
-            self.messages.extend_broadcast(&proposer_id, broadcast);
+            self.messages
+                .extend_broadcast(&proposer_id, &mut step.messages);
             if let Some(output) = step.output.into_iter().next() {
                 output
             } else {
@@ -257,7 +251,7 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
             if agreement.accepts_input() {
                 agreement.input(true)
             } else {
-                Ok(Step::default())
+                Ok(agreement::Step::default())
             }
         };
         self.process_agreement(proposer_id, set_agreement_input)?
@@ -267,13 +261,10 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
 
     /// Callback to be invoked on receipt of the decision value of the Agreement
     /// instance `uid`.
-    fn process_agreement<F>(
+    fn process_agreement<F>(&mut self, proposer_id: &NodeUid, f: F) -> Result<FaultLog<NodeUid>>
-        &mut self,
-        proposer_id: &NodeUid,
-        f: F,
-    ) -> CommonSubsetResult<FaultLog<NodeUid>>
     where
-        F: FnOnce(&mut Agreement<NodeUid>) -> Result<AgreementStep<NodeUid>, agreement::Error>,
+        F: FnOnce(&mut Agreement<NodeUid>)
+            -> result::Result<agreement::Step<NodeUid>, agreement::Error>,
     {
         let mut fault_log = FaultLog::new();
         let value = {
@@ -284,9 +275,10 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
             if agreement.terminated() {
                 return Ok(fault_log);
             }
-            let step = f(agreement)?;
+            let mut step = f(agreement)?;
             fault_log.extend(step.fault_log);
-            self.messages.extend_agreement(proposer_id, agreement);
+            self.messages
+                .extend_agreement(proposer_id, &mut step.messages);
             if let Some(output) = step.output.into_iter().next() {
                 output
             } else {
@@ -311,9 +303,9 @@ impl<NodeUid: Clone + Debug + Ord + Rand> CommonSubset<NodeUid> {
             // input 0 to each instance of BA that has not yet been provided input.
             for (uid, agreement) in &mut self.agreement_instances {
                 if agreement.accepts_input() {
-                    let step = agreement.input(false)?;
+                    let mut step = agreement.input(false)?;
                     fault_log.extend(step.fault_log);
-                    self.messages.extend_agreement(uid, agreement);
+                    self.messages.extend_agreement(uid, &mut step.messages);
                     if let Some(output) = step.output.into_iter().next() {
                         if self.agreement_results.insert(uid.clone(), output).is_some() {
                             return Err(ErrorKind::MultipleAgreementResults.into());

src/dynamic_honey_badger/builder.rs

@@ -1,4 +1,4 @@
-use std::collections::VecDeque;
+use std::default::Default;
 use std::fmt::Debug;
 use std::hash::Hash;
 use std::iter::once;
@@ -8,7 +8,7 @@ use std::sync::Arc;
 use rand::{self, Rand, Rng};
 use serde::{Deserialize, Serialize};
 
-use super::{ChangeState, DynamicHoneyBadger, JoinPlan, MessageQueue, Result, VoteCounter};
+use super::{ChangeState, DynamicHoneyBadger, JoinPlan, Result, Step, VoteCounter};
 use crypto::{SecretKey, SecretKeySet, SecretKeyShare};
 use honey_badger::HoneyBadger;
 use messaging::NetworkInfo;
@@ -16,15 +16,19 @@ use messaging::NetworkInfo;
 /// A Dynamic Honey Badger builder, to configure the parameters and create new instances of
 /// `DynamicHoneyBadger`.
 pub struct DynamicHoneyBadgerBuilder<C, NodeUid> {
-    /// Shared network data.
-    netinfo: NetworkInfo<NodeUid>,
-    /// The epoch at which to join the network.
-    start_epoch: u64,
-    /// The current change, for which key generation is beginning at `start_epoch`.
-    change: ChangeState<NodeUid>,
     /// The maximum number of future epochs for which we handle messages simultaneously.
     max_future_epochs: usize,
-    _phantom: PhantomData<C>,
+    _phantom: PhantomData<(C, NodeUid)>,
+}
+
+impl<C, NodeUid> Default for DynamicHoneyBadgerBuilder<C, NodeUid> {
+    fn default() -> Self {
+        // TODO: Use the defaults from `HoneyBadgerBuilder`.
+        DynamicHoneyBadgerBuilder {
+            max_future_epochs: 3,
+            _phantom: PhantomData,
+        }
+    }
 }
 
 impl<C, NodeUid> DynamicHoneyBadgerBuilder<C, NodeUid>
@@ -34,51 +38,8 @@ where
 {
     /// Returns a new `DynamicHoneyBadgerBuilder` configured to use the node IDs and cryptographic
     /// keys specified by `netinfo`.
-    pub fn new(netinfo: NetworkInfo<NodeUid>) -> Self {
+    pub fn new() -> Self {
-        // TODO: Use the defaults from `HoneyBadgerBuilder`.
+        Self::default()
-        DynamicHoneyBadgerBuilder {
-            netinfo,
-            start_epoch: 0,
-            change: ChangeState::None,
-            max_future_epochs: 3,
-            _phantom: PhantomData,
-        }
-    }
-
-    /// Returns a new `DynamicHoneyBadgerBuilder` configured to start a new network as a single
-    /// validator.
-    pub fn new_first_node(our_uid: NodeUid) -> Self {
-        let mut rng = rand::thread_rng();
-        let sk_set = SecretKeySet::random(0, &mut rng);
-        let pk_set = sk_set.public_keys();
-        let sks = sk_set.secret_key_share(0);
-        let sk: SecretKey = rng.gen();
-        let pub_keys = once((our_uid.clone(), sk.public_key())).collect();
-        let netinfo = NetworkInfo::new(our_uid, sks, pk_set, sk, pub_keys);
-        DynamicHoneyBadgerBuilder::new(netinfo)
-    }
-
-    /// Returns a new `DynamicHoneyBadgerBuilder` configured to join the network at the epoch
-    /// specified in the `JoinPlan`.
-    pub fn new_joining(
-        our_uid: NodeUid,
-        secret_key: SecretKey,
-        join_plan: JoinPlan<NodeUid>,
-    ) -> Self {
-        let netinfo = NetworkInfo::new(
-            our_uid,
-            SecretKeyShare::default(), // TODO: Should be an option?
-            join_plan.pub_key_set,
-            secret_key,
-            join_plan.pub_keys,
-        );
-        DynamicHoneyBadgerBuilder {
-            netinfo,
-            start_epoch: join_plan.epoch,
-            change: join_plan.change,
-            max_future_epochs: 3,
-            _phantom: PhantomData,
-        }
     }
 
     /// Sets the maximum number of future epochs for which we handle messages simultaneously.
@@ -88,26 +49,68 @@ where
     }
 
     /// Creates a new Dynamic Honey Badger instance with an empty buffer.
-    pub fn build(&self) -> Result<DynamicHoneyBadger<C, NodeUid>> {
+    pub fn build(&self, netinfo: NetworkInfo<NodeUid>) -> DynamicHoneyBadger<C, NodeUid> {
-        let netinfo = Arc::new(self.netinfo.clone());
+        let arc_netinfo = Arc::new(netinfo.clone());
-        let honey_badger = HoneyBadger::builder(netinfo.clone())
+        let honey_badger = HoneyBadger::builder(arc_netinfo.clone())
             .max_future_epochs(self.max_future_epochs)
             .build();
-        let mut dhb = DynamicHoneyBadger {
+        DynamicHoneyBadger {
-            netinfo: self.netinfo.clone(),
+            netinfo,
             max_future_epochs: self.max_future_epochs,
-            start_epoch: self.start_epoch,
+            start_epoch: 0,
-            vote_counter: VoteCounter::new(netinfo, self.start_epoch),
+            vote_counter: VoteCounter::new(arc_netinfo, 0),
             key_gen_msg_buffer: Vec::new(),
             honey_badger,
             key_gen: None,
             incoming_queue: Vec::new(),
-            messages: MessageQueue(VecDeque::new()),
-            output: VecDeque::new(),
-        };
-        if let ChangeState::InProgress(ref change) = self.change {
-            dhb.update_key_gen(self.start_epoch, change)?;
         }
-        Ok(dhb)
+    }
+
+    /// Creates a new `DynamicHoneyBadger` configured to start a new network as a single validator.
+    pub fn build_first_node(&self, our_uid: NodeUid) -> DynamicHoneyBadger<C, NodeUid> {
+        let mut rng = rand::thread_rng();
+        let sk_set = SecretKeySet::random(0, &mut rng);
+        let pk_set = sk_set.public_keys();
+        let sks = sk_set.secret_key_share(0);
+        let sk: SecretKey = rng.gen();
+        let pub_keys = once((our_uid.clone(), sk.public_key())).collect();
+        let netinfo = NetworkInfo::new(our_uid, sks, pk_set, sk, pub_keys);
+        self.build(netinfo)
+    }
+
+    /// Creates a new `DynamicHoneyBadger` configured to join the network at the epoch specified in
+    /// the `JoinPlan`.
+    pub fn build_joining(
+        &self,
+        our_uid: NodeUid,
+        secret_key: SecretKey,
+        join_plan: JoinPlan<NodeUid>,
+    ) -> Result<(DynamicHoneyBadger<C, NodeUid>, Step<C, NodeUid>)> {
+        let netinfo = NetworkInfo::new(
+            our_uid,
+            SecretKeyShare::default(), // TODO: Should be an option?
+            join_plan.pub_key_set,
+            secret_key,
+            join_plan.pub_keys,
+        );
+        let arc_netinfo = Arc::new(netinfo.clone());
+        let honey_badger = HoneyBadger::builder(arc_netinfo.clone())
+            .max_future_epochs(self.max_future_epochs)
+            .build();
+        let mut dhb = DynamicHoneyBadger {
+            netinfo,
+            max_future_epochs: self.max_future_epochs,
+            start_epoch: join_plan.epoch,
+            vote_counter: VoteCounter::new(arc_netinfo, join_plan.epoch),
+            key_gen_msg_buffer: Vec::new(),
+            honey_badger,
+            key_gen: None,
+            incoming_queue: Vec::new(),
+        };
+        let step = match join_plan.change {
+            ChangeState::InProgress(ref change) => dhb.update_key_gen(join_plan.epoch, change)?,
+            ChangeState::None | ChangeState::Complete(..) => Step::default(),
+        };
+        Ok((dhb, step))
     }
 }

src/dynamic_honey_badger/mod.rs

@@ -56,7 +56,7 @@
 //! majority before that happens, key generation resets again, and is attempted for the new change.
 
 use rand::Rand;
-use std::collections::{BTreeMap, VecDeque};
+use std::collections::BTreeMap;
 use std::fmt::Debug;
 use std::hash::Hash;
 use std::mem;
@@ -66,10 +66,10 @@ use bincode;
 use serde::{Deserialize, Serialize};
 
 use self::votes::{SignedVote, VoteCounter};
-use crypto::{PublicKey, PublicKeySet, SecretKey, Signature};
+use crypto::{PublicKey, PublicKeySet, Signature};
 use fault_log::{FaultKind, FaultLog};
-use honey_badger::{HoneyBadger, HoneyBadgerStep, Message as HbMessage};
+use honey_badger::{self, HoneyBadger, Message as HbMessage};
-use messaging::{DistAlgorithm, NetworkInfo, Step, Target, TargetedMessage};
+use messaging::{self, DistAlgorithm, NetworkInfo, Target};
 use sync_key_gen::{Ack, Part, PartOutcome, SyncKeyGen};
 
 pub use self::batch::Batch;
@@ -110,13 +110,9 @@ pub struct DynamicHoneyBadger<C, NodeUid: Rand> {
     key_gen: Option<(SyncKeyGen<NodeUid>, Change<NodeUid>)>,
     /// A queue for messages from future epochs that cannot be handled yet.
     incoming_queue: Vec<(NodeUid, Message<NodeUid>)>,
-    /// The messages that need to be sent to other nodes.
-    messages: MessageQueue<NodeUid>,
-    /// The outputs from completed epochs.
-    output: VecDeque<Batch<C, NodeUid>>,
 }
 
-pub type DynamicHoneyBadgerStep<C, NodeUid> = Step<NodeUid, Batch<C, NodeUid>>;
+pub type Step<C, NodeUid> = messaging::Step<DynamicHoneyBadger<C, NodeUid>>;
 
 impl<C, NodeUid> DistAlgorithm for DynamicHoneyBadger<C, NodeUid>
 where
@@ -129,48 +125,44 @@ where
     type Message = Message<NodeUid>;
     type Error = Error;
 
-    fn input(&mut self, input: Self::Input) -> Result<DynamicHoneyBadgerStep<C, NodeUid>> {
+    fn input(&mut self, input: Self::Input) -> Result<Step<C, NodeUid>> {
         // User contributions are forwarded to `HoneyBadger` right away. Votes are signed and
         // broadcast.
-        let fault_log = match input {
+        match input {
-            Input::User(contrib) => self.propose(contrib)?,
+            Input::User(contrib) => self.propose(contrib),
-            Input::Change(change) => self.vote_for(change).map(|()| FaultLog::new())?,
+            Input::Change(change) => self.vote_for(change),
-        };
+        }
-        self.step(fault_log)
     }
 
     fn handle_message(
         &mut self,
         sender_id: &NodeUid,
         message: Self::Message,
-    ) -> Result<DynamicHoneyBadgerStep<C, NodeUid>> {
+    ) -> Result<Step<C, NodeUid>> {
         let epoch = message.start_epoch();
-        let fault_log = if epoch < self.start_epoch {
+        if epoch < self.start_epoch {
             // Obsolete message.
-            FaultLog::new()
+            Ok(Step::default())
         } else if epoch > self.start_epoch {
             // Message cannot be handled yet. Save it for later.
             let entry = (sender_id.clone(), message);
             self.incoming_queue.push(entry);
-            FaultLog::new()
+            Ok(Step::default())
         } else {
             match message {
                 Message::HoneyBadger(_, hb_msg) => {
-                    self.handle_honey_badger_message(sender_id, hb_msg)?
+                    self.handle_honey_badger_message(sender_id, hb_msg)
                 }
                 Message::KeyGen(_, kg_msg, sig) => {
-                    self.handle_key_gen_message(sender_id, kg_msg, *sig)?
+                    self.handle_key_gen_message(sender_id, kg_msg, *sig)?;
-                }
+                    Ok(Step::default())
-                Message::SignedVote(signed_vote) => {
-                    self.vote_counter.add_pending_vote(sender_id, signed_vote)?
                 }
+                Message::SignedVote(signed_vote) => self
+                    .vote_counter
+                    .add_pending_vote(sender_id, signed_vote)
+                    .map(FaultLog::into),
             }
-        };
+        }
-        self.step(fault_log)
-    }
-
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, NodeUid>> {
-        self.messages.pop_front()
     }
 
     fn terminated(&self) -> bool {
@@ -187,30 +179,9 @@ where
     C: Eq + Serialize + for<'r> Deserialize<'r> + Debug + Hash,
     NodeUid: Eq + Ord + Clone + Debug + Serialize + for<'r> Deserialize<'r> + Hash + Rand,
 {
-    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> Result<DynamicHoneyBadgerStep<C, NodeUid>> {
+    /// Returns a new `DynamicHoneyBadgerBuilder`.
-        Ok(Step::new(self.output.drain(..).collect(), fault_log))
+    pub fn builder() -> DynamicHoneyBadgerBuilder<C, NodeUid> {
-    }
+        DynamicHoneyBadgerBuilder::new()
-
-    /// Returns a new `DynamicHoneyBadgerBuilder` configured to use the node IDs and cryptographic
-    /// keys specified by `netinfo`.
-    pub fn builder(netinfo: NetworkInfo<NodeUid>) -> DynamicHoneyBadgerBuilder<C, NodeUid> {
-        DynamicHoneyBadgerBuilder::new(netinfo)
-    }
-
-    /// Returns a new `DynamicHoneyBadgerBuilder` configured to start a new network as the first
-    /// node.
-    pub fn first_node_builder(our_uid: NodeUid) -> DynamicHoneyBadgerBuilder<C, NodeUid> {
-        DynamicHoneyBadgerBuilder::new_first_node(our_uid)
-    }
-
-    /// Returns a new `DynamicHoneyBadgerBuilder` configured to join the network at the epoch
-    /// specified in the `JoinPlan`.
-    pub fn joining_builder(
-        our_uid: NodeUid,
-        secret_key: SecretKey,
-        join_plan: JoinPlan<NodeUid>,
-    ) -> DynamicHoneyBadgerBuilder<C, NodeUid> {
-        DynamicHoneyBadgerBuilder::new_joining(our_uid, secret_key, join_plan)
     }
 
     /// Returns `true` if input for the current epoch has already been provided.
@@ -219,7 +190,7 @@ where
     }
 
     /// Proposes a contribution in the current epoch.
-    pub fn propose(&mut self, contrib: C) -> Result<FaultLog<NodeUid>> {
+    pub fn propose(&mut self, contrib: C) -> Result<Step<C, NodeUid>> {
         let step = self.honey_badger.input(InternalContrib {
             contrib,
             key_gen_messages: self.key_gen_msg_buffer.clone(),
@@ -229,14 +200,13 @@ where
     }
 
     /// Cast a vote to change the set of validators.
-    pub fn vote_for(&mut self, change: Change<NodeUid>) -> Result<()> {
+    pub fn vote_for(&mut self, change: Change<NodeUid>) -> Result<Step<C, NodeUid>> {
         if !self.netinfo.is_validator() {
-            return Ok(()); // TODO: Return an error?
+            return Ok(Step::default()); // TODO: Return an error?
         }
         let signed_vote = self.vote_counter.sign_vote_for(change)?.clone();
         let msg = Message::SignedVote(signed_vote);
-        self.messages.push_back(Target::All.message(msg));
+        Ok(Target::All.message(msg).into())
-        Ok(())
     }
 
     /// Returns the information about the node IDs in the network, and the cryptographic keys.
@@ -249,12 +219,12 @@ where
         &mut self,
         sender_id: &NodeUid,
         message: HbMessage<NodeUid>,
-    ) -> Result<FaultLog<NodeUid>> {
+    ) -> Result<Step<C, NodeUid>> {
         if !self.netinfo.is_node_validator(sender_id) {
             info!("Unknown sender {:?} of message {:?}", sender_id, message);
             return Err(ErrorKind::UnknownSender.into());
         }
-        // Handle the message and put the outgoing messages into the queue.
+        // Handle the message.
         let step = self.honey_badger.handle_message(sender_id, message)?;
         self.process_output(step)
     }
@@ -266,22 +236,22 @@ where
         sender_id: &NodeUid,
         kg_msg: KeyGenMessage,
         sig: Signature,
-    ) -> Result<FaultLog<NodeUid>> {
+    ) -> Result<()> {
         self.verify_signature(sender_id, &sig, &kg_msg)?;
         let tx = SignedKeyGenMsg(self.start_epoch, sender_id.clone(), kg_msg, sig);
         self.key_gen_msg_buffer.push(tx);
-        Ok(FaultLog::default())
+        Ok(())
     }
 
     /// Processes all pending batches output by Honey Badger.
     fn process_output(
         &mut self,
-        step: HoneyBadgerStep<InternalContrib<C, NodeUid>, NodeUid>,
+        hb_step: honey_badger::Step<InternalContrib<C, NodeUid>, NodeUid>,
-    ) -> Result<FaultLog<NodeUid>> {
+    ) -> Result<Step<C, NodeUid>> {
-        let mut fault_log = FaultLog::new();
+        let mut step: Step<C, NodeUid> = Step::default();
-        fault_log.extend(step.fault_log);
         let start_epoch = self.start_epoch;
-        for hb_batch in step.output {
+        let output = step.extend_with(hb_step, |hb_msg| Message::HoneyBadger(start_epoch, hb_msg));
+        for hb_batch in output {
             // Create the batch we output ourselves. It will contain the _user_ transactions of
             // `hb_batch`, and the current change state.
             let mut batch = Batch::new(hb_batch.epoch + self.start_epoch);
@@ -293,7 +263,8 @@ where
                     key_gen_messages,
                     contrib,
                 } = int_contrib;
-                fault_log.extend(self.vote_counter.add_committed_votes(&id, votes)?);
+                step.fault_log
+                    .extend(self.vote_counter.add_committed_votes(&id, votes)?);
                 batch.contributions.insert(id, contrib);
                 self.key_gen_msg_buffer
                     .retain(|skgm| !key_gen_messages.contains(skgm));
@@ -305,13 +276,13 @@ where
                     if !self.verify_signature(&s_id, &sig, &kg_msg)? {
                         info!("Invalid signature from {:?} for: {:?}.", s_id, kg_msg);
                         let fault_kind = FaultKind::InvalidKeyGenMessageSignature;
-                        fault_log.append(s_id.clone(), fault_kind);
+                        step.fault_log.append(s_id.clone(), fault_kind);
                         continue;
                     }
-                    match kg_msg {
+                    step.extend(match kg_msg {
                         KeyGenMessage::Part(part) => self.handle_part(&s_id, part)?,
-                        KeyGenMessage::Ack(ack) => self.handle_ack(&s_id, ack)?,
+                        KeyGenMessage::Ack(ack) => self.handle_ack(&s_id, ack)?.into(),
-                    }.merge_into(&mut fault_log);
+                    });
                 }
             }
 
@@ -323,30 +294,26 @@ where
                 batch.set_change(ChangeState::Complete(change), &self.netinfo);
             } else if let Some(change) = self.vote_counter.compute_majority().cloned() {
                 // If there is a majority, restart DKG. Inform the user about the current change.
-                self.update_key_gen(batch.epoch + 1, &change)?;
+                step.extend(self.update_key_gen(batch.epoch + 1, &change)?);
                 batch.set_change(ChangeState::InProgress(change), &self.netinfo);
             }
-            self.output.push_back(batch);
+            step.output.push_back(batch);
         }
-        self.messages
-            .extend_with_epoch(self.start_epoch, &mut self.honey_badger);
         // If `start_epoch` changed, we can now handle some queued messages.
         if start_epoch < self.start_epoch {
             let queue = mem::replace(&mut self.incoming_queue, Vec::new());
             for (sender_id, msg) in queue {
-                let rec_step = self.handle_message(&sender_id, msg)?;
+                step.extend(self.handle_message(&sender_id, msg)?);
-                self.output.extend(rec_step.output);
-                fault_log.extend(rec_step.fault_log);
             }
         }
-        Ok(fault_log)
+        Ok(step)
     }
 
     /// If the majority of votes has changed, restarts Key Generation for the set of nodes implied
     /// by the current change.
-    fn update_key_gen(&mut self, epoch: u64, change: &Change<NodeUid>) -> Result<()> {
+    fn update_key_gen(&mut self, epoch: u64, change: &Change<NodeUid>) -> Result<Step<C, NodeUid>> {
         if self.key_gen.as_ref().map(|&(_, ref ch)| ch) == Some(change) {
-            return Ok(()); // The change is the same as before. Continue DKG as is.
+            return Ok(Step::default()); // The change is the same as before. Continue DKG as is.
         }
         debug!("{:?} Restarting DKG for {:?}.", self.our_id(), change);
         // Use the existing key shares - with the change applied - as keys for DKG.
@@ -366,16 +333,14 @@ where
         let (key_gen, part) = SyncKeyGen::new(our_uid, sk, pub_keys, threshold);
         self.key_gen = Some((key_gen, change.clone()));
         if let Some(part) = part {
-            self.send_transaction(KeyGenMessage::Part(part))?;
+            self.send_transaction(KeyGenMessage::Part(part))
+        } else {
+            Ok(Step::default())
         }
-        Ok(())
     }
 
     /// Starts a new `HoneyBadger` instance and resets the vote counter.
     fn restart_honey_badger(&mut self, epoch: u64) {
-        // TODO: Filter out the messages for `epoch` and later.
-        self.messages
-            .extend_with_epoch(self.start_epoch, &mut self.honey_badger);
         self.start_epoch = epoch;
         self.key_gen_msg_buffer.retain(|kg_msg| kg_msg.0 >= epoch);
         let netinfo = Arc::new(self.netinfo.clone());
@@ -387,17 +352,14 @@ where
     }
 
     /// Handles a `Part` message that was output by Honey Badger.
-    fn handle_part(&mut self, sender_id: &NodeUid, part: Part) -> Result<FaultLog<NodeUid>> {
+    fn handle_part(&mut self, sender_id: &NodeUid, part: Part) -> Result<Step<C, NodeUid>> {
         let handle = |&mut (ref mut key_gen, _): &mut (SyncKeyGen<NodeUid>, _)| {
             key_gen.handle_part(&sender_id, part)
         };
         match self.key_gen.as_mut().and_then(handle) {
-            Some(PartOutcome::Valid(ack)) => {
+            Some(PartOutcome::Valid(ack)) => self.send_transaction(KeyGenMessage::Ack(ack)),
-                self.send_transaction(KeyGenMessage::Ack(ack))?;
+            Some(PartOutcome::Invalid(fault_log)) => Ok(fault_log.into()),
-                Ok(FaultLog::new())
+            None => Ok(Step::default()),
-            }
-            Some(PartOutcome::Invalid(fault_log)) => Ok(fault_log),
-            None => Ok(FaultLog::new()),
         }
     }
 
@@ -411,18 +373,17 @@ where
     }
 
     /// Signs and sends a `KeyGenMessage` and also tries to commit it.
-    fn send_transaction(&mut self, kg_msg: KeyGenMessage) -> Result<()> {
+    fn send_transaction(&mut self, kg_msg: KeyGenMessage) -> Result<Step<C, NodeUid>> {
         let ser = bincode::serialize(&kg_msg)?;
         let sig = Box::new(self.netinfo.secret_key().sign(ser));
-        let msg = Message::KeyGen(self.start_epoch, kg_msg.clone(), sig.clone());
+        if self.netinfo.is_validator() {
-        self.messages.push_back(Target::All.message(msg));
+            let our_uid = self.netinfo.our_uid().clone();
-        if !self.netinfo.is_validator() {
+            let signed_msg =
-            return Ok(());
+                SignedKeyGenMsg(self.start_epoch, our_uid, kg_msg.clone(), *sig.clone());
+            self.key_gen_msg_buffer.push(signed_msg);
         }
-        let our_uid = self.netinfo.our_uid().clone();
+        let msg = Message::KeyGen(self.start_epoch, kg_msg, sig);
-        let signed_msg = SignedKeyGenMsg(self.start_epoch, our_uid, kg_msg, *sig);
+        Ok(Target::All.message(msg).into())
-        self.key_gen_msg_buffer.push(signed_msg);
-        Ok(())
     }
 
     /// If the current Key Generation process is ready, returns the `SyncKeyGen`.
@@ -520,26 +481,6 @@ impl<NodeUid: Rand> Message<NodeUid> {
     }
 }
 
-/// The queue of outgoing messages in a `HoneyBadger` instance.
-#[derive(Deref, DerefMut)]
-struct MessageQueue<NodeUid: Rand>(VecDeque<TargetedMessage<Message<NodeUid>, NodeUid>>);
-
-impl<NodeUid> MessageQueue<NodeUid>
-where
-    NodeUid: Eq + Hash + Ord + Clone + Debug + Serialize + for<'r> Deserialize<'r> + Rand,
-{
-    /// Appends to the queue the messages from `hb`, wrapped with `epoch`.
-    fn extend_with_epoch<Tx>(&mut self, epoch: u64, hb: &mut HoneyBadger<Tx, NodeUid>)
-    where
-        Tx: Eq + Serialize + for<'r> Deserialize<'r> + Debug + Hash,
-    {
-        let convert = |msg: TargetedMessage<HbMessage<NodeUid>, NodeUid>| {
-            msg.map(|hb_msg| Message::HoneyBadger(epoch, hb_msg))
-        };
-        self.extend(hb.message_iter().map(convert));
-    }
-}
-
 /// The information a new node requires to join the network as an observer. It contains the state
 /// of voting and key generation after a specific epoch, so that the new node will be in sync if it
 /// joins in the next one.

src/honey_badger.rs

@@ -34,16 +34,12 @@ use bincode;
 use itertools::Itertools;
 use serde::{Deserialize, Serialize};
 
-use common_subset::{self, CommonSubset, CommonSubsetStep};
+use common_subset::{self, CommonSubset};
 use crypto::{Ciphertext, DecryptionShare};
 use fault_log::{FaultKind, FaultLog};
-use messaging::{DistAlgorithm, NetworkInfo, Step, Target, TargetedMessage};
+use messaging::{self, DistAlgorithm, NetworkInfo, Target, TargetedMessage};
 
 error_chain!{
-    types {
-        Error, ErrorKind, ResultExt, HoneyBadgerResult;
-    }
-
     links {
         CommonSubset(common_subset::Error, common_subset::ErrorKind);
     }
@@ -134,7 +130,7 @@ pub struct HoneyBadger<C, NodeUid: Rand> {
     ciphertexts: BTreeMap<u64, BTreeMap<NodeUid, Ciphertext>>,
 }
 
-pub type HoneyBadgerStep<C, NodeUid> = Step<NodeUid, Batch<C, NodeUid>>;
+pub type Step<C, NodeUid> = messaging::Step<HoneyBadger<C, NodeUid>>;
 
 impl<C, NodeUid> DistAlgorithm for HoneyBadger<C, NodeUid>
 where
@@ -147,7 +143,7 @@ where
     type Message = Message<NodeUid>;
     type Error = Error;
 
-    fn input(&mut self, input: Self::Input) -> HoneyBadgerResult<HoneyBadgerStep<C, NodeUid>> {
+    fn input(&mut self, input: Self::Input) -> Result<Step<C, NodeUid>> {
         let fault_log = self.propose(&input)?;
         self.step(fault_log)
     }
@@ -156,7 +152,7 @@ where
         &mut self,
         sender_id: &NodeUid,
         message: Self::Message,
-    ) -> HoneyBadgerResult<HoneyBadgerStep<C, NodeUid>> {
+    ) -> Result<Step<C, NodeUid>> {
         if !self.netinfo.is_node_validator(sender_id) {
             return Err(ErrorKind::UnknownSender.into());
         }
@@ -174,10 +170,6 @@ where
         self.step(fault_log)
     }
 
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, NodeUid>> {
-        self.messages.pop_front()
-    }
-
     fn terminated(&self) -> bool {
         false
     }
@@ -198,15 +190,16 @@ where
         HoneyBadgerBuilder::new(netinfo)
     }
 
-    fn step(
+    fn step(&mut self, fault_log: FaultLog<NodeUid>) -> Result<Step<C, NodeUid>> {
-        &mut self,
+        Ok(Step::new(
-        fault_log: FaultLog<NodeUid>,
+            self.output.drain(..).collect(),
-    ) -> HoneyBadgerResult<HoneyBadgerStep<C, NodeUid>> {
+            fault_log,
-        Ok(Step::new(self.output.drain(..).collect(), fault_log))
+            self.messages.drain(..).collect(),
+        ))
     }
 
     /// Proposes a new item in the current epoch.
-    pub fn propose(&mut self, proposal: &C) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    pub fn propose(&mut self, proposal: &C) -> Result<FaultLog<NodeUid>> {
         if !self.netinfo.is_validator() {
             return Ok(FaultLog::new());
         }
@@ -220,11 +213,9 @@ where
             let ser_prop = bincode::serialize(&proposal)?;
             let ciphertext = self.netinfo.public_key_set().public_key().encrypt(ser_prop);
             self.has_input = true;
-            let step = cs.input(bincode::serialize(&ciphertext).unwrap())?;
+            cs.input(bincode::serialize(&ciphertext).unwrap())?
-            self.messages.extend_with_epoch(self.epoch, cs);
-            step
         };
-        Ok(self.process_output(step)?)
+        Ok(self.process_output(step, None)?)
     }
 
     /// Returns `true` if input for the current epoch has already been provided.
@@ -238,7 +229,7 @@ where
         sender_id: &NodeUid,
         epoch: u64,
         content: MessageContent<NodeUid>,
-    ) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         match content {
             MessageContent::CommonSubset(cs_msg) => {
                 self.handle_common_subset_message(sender_id, epoch, cs_msg)
@@ -255,7 +246,7 @@ where
         sender_id: &NodeUid,
         epoch: u64,
         message: common_subset::Message<NodeUid>,
-    ) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         let mut fault_log = FaultLog::new();
         let step = {
             // Borrow the instance for `epoch`, or create it.
@@ -270,15 +261,9 @@ where
                     }
                 }
             };
-            // Handle the message and put the outgoing messages into the queue.
+            cs.handle_message(sender_id, message)?
-            let cs_step = cs.handle_message(sender_id, message)?;
-            self.messages.extend_with_epoch(epoch, cs);
-            cs_step
         };
-        // If this is the current epoch, the message could cause a new output.
+        fault_log.extend(self.process_output(step, Some(epoch))?);
-        if epoch == self.epoch {
-            fault_log.extend(self.process_output(step)?);
-        }
         self.remove_terminated(epoch);
         Ok(fault_log)
     }
@@ -290,7 +275,7 @@ where
         epoch: u64,
         proposer_id: NodeUid,
         share: DecryptionShare,
-    ) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         let mut fault_log = FaultLog::new();
 
         if let Some(ciphertext) = self
@@ -339,7 +324,7 @@ where
 
     /// When contributions of transactions have been decrypted for all valid proposers in this
     /// epoch, moves those contributions into a batch, outputs the batch and updates the epoch.
-    fn try_output_batch(&mut self) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    fn try_output_batch(&mut self) -> Result<FaultLog<NodeUid>> {
         // Wait until contributions have been successfully decoded for all proposer nodes with correct
         // ciphertext outputs.
         if !self.all_contributions_decrypted() {
@@ -379,7 +364,7 @@ where
     }
 
     /// Increments the epoch number and clears any state that is local to the finished epoch.
-    fn update_epoch(&mut self) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    fn update_epoch(&mut self) -> Result<FaultLog<NodeUid>> {
         // Clear the state of the old epoch.
         self.ciphertexts.remove(&self.epoch);
         self.decrypted_contributions.clear();
@@ -402,7 +387,7 @@ where
     }
 
     /// Tries to decrypt contributions from all proposers and output those in a batch.
-    fn try_decrypt_and_output_batch(&mut self) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    fn try_decrypt_and_output_batch(&mut self) -> Result<FaultLog<NodeUid>> {
         // Return if we don't have ciphertexts yet.
         let proposer_ids: Vec<_> = match self.ciphertexts.get(&self.epoch) {
             Some(cts) => cts.keys().cloned().collect(),
@@ -474,7 +459,7 @@ where
     fn send_decryption_shares(
         &mut self,
         cs_output: BTreeMap<NodeUid, Vec<u8>>,
-    ) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+    ) -> Result<FaultLog<NodeUid>> {
         let mut fault_log = FaultLog::new();
         let mut ciphertexts = BTreeMap::new();
         for (proposer_id, v) in cs_output {
@@ -512,7 +497,7 @@ where
         &mut self,
         proposer_id: &NodeUid,
         ciphertext: &Ciphertext,
-    ) -> HoneyBadgerResult<(bool, FaultLog<NodeUid>)> {
+    ) -> Result<(bool, FaultLog<NodeUid>)> {
         if !self.netinfo.is_validator() {
             return Ok((ciphertext.verify(), FaultLog::new()));
         }
@@ -576,18 +561,27 @@ where
         }
     }
 
-    /// Checks whether the current epoch has output, and if it does, sends out our decryption shares.
+    /// Checks whether the current epoch has output, and if it does, sends out our decryption
+    /// shares.  The `epoch` argument allows to differentiate between calls which produce output in
+    /// all conditions, `epoch == None`, and calls which only produce output in a given epoch,
+    /// `epoch == Some(given_epoch)`.
     fn process_output(
         &mut self,
-        step: CommonSubsetStep<NodeUid>,
+        step: common_subset::Step<NodeUid>,
-    ) -> HoneyBadgerResult<FaultLog<NodeUid>> {
+        epoch: Option<u64>,
-        let Step {
+    ) -> Result<FaultLog<NodeUid>> {
+        let common_subset::Step {
             output,
             mut fault_log,
+            mut messages,
         } = step;
-        for cs_output in output {
+        self.messages.extend_with_epoch(self.epoch, &mut messages);
-            fault_log.extend(self.send_decryption_shares(cs_output)?);
+        // If this is the current epoch, the message could cause a new output.
-            // TODO: May also check that there is no further output from Common Subset.
+        if epoch.is_none() || epoch == Some(self.epoch) {
+            for cs_output in output {
+                fault_log.extend(self.send_decryption_shares(cs_output)?);
+                // TODO: May also check that there is no further output from Common Subset.
+            }
         }
         Ok(fault_log)
     }
@@ -699,10 +693,14 @@ struct MessageQueue<NodeUid: Rand>(VecDeque<TargetedMessage<Message<NodeUid>, No
 
 impl<NodeUid: Clone + Debug + Ord + Rand> MessageQueue<NodeUid> {
     /// Appends to the queue the messages from `cs`, wrapped with `epoch`.
-    fn extend_with_epoch(&mut self, epoch: u64, cs: &mut CommonSubset<NodeUid>) {
+    fn extend_with_epoch(
+        &mut self,
+        epoch: u64,
+        msgs: &mut VecDeque<TargetedMessage<common_subset::Message<NodeUid>, NodeUid>>,
+    ) {
         let convert = |msg: TargetedMessage<common_subset::Message<NodeUid>, NodeUid>| {
             msg.map(|cs_msg| MessageContent::CommonSubset(cs_msg).with_epoch(epoch))
         };
-        self.extend(cs.message_iter().map(convert));
+        self.extend(msgs.drain(..).map(convert));
     }
 }

src/messaging.rs

@@ -1,5 +1,6 @@
 use std::collections::{BTreeMap, BTreeSet, VecDeque};
 use std::fmt::Debug;
+use std::iter::once;
 
 use crypto::{PublicKey, PublicKeySet, PublicKeyShare, SecretKey, SecretKeyShare};
 use fault_log::FaultLog;
@@ -52,32 +53,115 @@ impl<M, N> TargetedMessage<M, N> {
 /// Result of one step of the local state machine of a distributed algorithm. Such a result should
 /// be used and never discarded by the client of the algorithm.
 #[must_use = "The algorithm step result must be used."]
-pub struct Step<N, O>
+pub struct Step<D>
 where
-    N: Clone,
+    D: DistAlgorithm,
+    <D as DistAlgorithm>::NodeUid: Clone,
 {
-    pub output: VecDeque<O>,
+    pub output: VecDeque<D::Output>,
-    pub fault_log: FaultLog<N>,
+    pub fault_log: FaultLog<D::NodeUid>,
+    pub messages: VecDeque<TargetedMessage<D::Message, D::NodeUid>>,
 }
 
-impl<N, O> Default for Step<N, O>
+impl<D> Default for Step<D>
 where
-    N: Clone,
+    D: DistAlgorithm,
+    <D as DistAlgorithm>::NodeUid: Clone,
 {
-    fn default() -> Step<N, O> {
+    fn default() -> Step<D> {
         Step {
-            output: Default::default(),
+            output: VecDeque::default(),
             fault_log: FaultLog::default(),
+            messages: VecDeque::default(),
         }
     }
 }
 
-impl<N, O> Step<N, O>
+impl<D: DistAlgorithm> Step<D>
 where
-    N: Clone,
+    <D as DistAlgorithm>::NodeUid: Clone,
 {
-    pub fn new(output: VecDeque<O>, fault_log: FaultLog<N>) -> Self {
+    /// Creates a new `Step` from the given collections.
-        Step { output, fault_log }
+    pub fn new(
+        output: VecDeque<D::Output>,
+        fault_log: FaultLog<D::NodeUid>,
+        messages: VecDeque<TargetedMessage<D::Message, D::NodeUid>>,
+    ) -> Self {
+        Step {
+            output,
+            fault_log,
+            messages,
+        }
+    }
+
+    /// Converts `self` into a step of another type, given conversion methods for output and
+    /// messages.
+    pub fn map<D2, FO, FM>(self, f_out: FO, f_msg: FM) -> Step<D2>
+    where
+        D2: DistAlgorithm<NodeUid = D::NodeUid>,
+        FO: Fn(D::Output) -> D2::Output,
+        FM: Fn(D::Message) -> D2::Message,
+    {
+        Step {
+            output: self.output.into_iter().map(f_out).collect(),
+            fault_log: self.fault_log,
+            messages: self.messages.into_iter().map(|tm| tm.map(&f_msg)).collect(),
+        }
+    }
+
+    /// Extends `self` with `other`s messages and fault logs, and returns `other.output`.
+    pub fn extend_with<D2, FM>(&mut self, other: Step<D2>, f_msg: FM) -> VecDeque<D2::Output>
+    where
+        D2: DistAlgorithm<NodeUid = D::NodeUid>,
+        FM: Fn(D2::Message) -> D::Message,
+    {
+        self.fault_log.extend(other.fault_log);
+        let msgs = other.messages.into_iter().map(|tm| tm.map(&f_msg));
+        self.messages.extend(msgs);
+        other.output
+    }
+
+    /// Adds the outputs, fault logs and messages of `other` to `self`.
+    pub fn extend(&mut self, other: Self) {
+        self.output.extend(other.output);
+        self.fault_log.extend(other.fault_log);
+        self.messages.extend(other.messages);
+    }
+
+    /// Converts this step into an equivalent step for a different `DistAlgorithm`.
+    // This cannot be a `From` impl, because it would conflict with `impl From<T> for T`.
+    pub fn convert<D2>(self) -> Step<D2>
+    where
+        D2: DistAlgorithm<NodeUid = D::NodeUid, Output = D::Output, Message = D::Message>,
+    {
+        Step {
+            output: self.output,
+            fault_log: self.fault_log,
+            messages: self.messages,
+        }
+    }
+
+    /// Returns `true` if there are now messages, faults or outputs.
+    pub fn is_empty(&self) -> bool {
+        self.output.is_empty() && self.fault_log.is_empty() && self.messages.is_empty()
+    }
+}
+
+impl<D: DistAlgorithm> From<FaultLog<D::NodeUid>> for Step<D> {
+    fn from(fault_log: FaultLog<D::NodeUid>) -> Self {
+        Step {
+            fault_log,
+            ..Step::default()
+        }
+    }
+}
+
+impl<D: DistAlgorithm> From<TargetedMessage<D::Message, D::NodeUid>> for Step<D> {
+    fn from(msg: TargetedMessage<D::Message, D::NodeUid>) -> Self {
+        Step {
+            messages: once(msg).collect(),
+            ..Step::default()
+        }
     }
 }
 
@@ -96,47 +180,24 @@ pub trait DistAlgorithm {
     type Error: Debug;
 
     /// Handles an input provided by the user, and returns
-    fn input(
+    fn input(&mut self, input: Self::Input) -> Result<Step<Self>, Self::Error>
-        &mut self,
+    where
-        input: Self::Input,
+        Self: Sized;
-    ) -> Result<Step<Self::NodeUid, Self::Output>, Self::Error>;
 
     /// Handles a message received from node `sender_id`.
     fn handle_message(
         &mut self,
         sender_id: &Self::NodeUid,
         message: Self::Message,
-    ) -> Result<Step<Self::NodeUid, Self::Output>, Self::Error>;
+    ) -> Result<Step<Self>, Self::Error>
-
+    where
-    /// Returns a message that needs to be sent to another node.
+        Self: Sized;
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, Self::NodeUid>>;
 
     /// Returns `true` if execution has completed and this instance can be dropped.
     fn terminated(&self) -> bool;
 
     /// Returns this node's own ID.
     fn our_id(&self) -> &Self::NodeUid;
-
-    /// Returns an iterator over the outgoing messages.
-    fn message_iter(&mut self) -> MessageIter<Self>
-    where
-        Self: Sized,
-    {
-        MessageIter { algorithm: self }
-    }
-}
-
-/// An iterator over a distributed algorithm's outgoing messages.
-pub struct MessageIter<'a, D: DistAlgorithm + 'a> {
-    algorithm: &'a mut D,
-}
-
-impl<'a, D: DistAlgorithm + 'a> Iterator for MessageIter<'a, D> {
-    type Item = TargetedMessage<D::Message, D::NodeUid>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.algorithm.next_message()
-    }
 }
 
 /// Common data shared between algorithms: the nodes' IDs and key shares.

src/queueing_honey_badger.rs

@@ -21,7 +21,6 @@
 //! the same transaction multiple times.
 
 use std::cmp;
-use std::collections::VecDeque;
 use std::fmt::Debug;
 use std::hash::Hash;
 use std::marker::PhantomData;
@@ -30,8 +29,7 @@ use rand::Rand;
 use serde::{Deserialize, Serialize};
 
 use dynamic_honey_badger::{self, Batch as DhbBatch, DynamicHoneyBadger, Message};
-use fault_log::FaultLog;
+use messaging::{self, DistAlgorithm};
-use messaging::{DistAlgorithm, Step, TargetedMessage};
 use transaction_queue::TransactionQueue;
 
 pub use dynamic_honey_badger::{Change, ChangeState, Input};
@@ -59,6 +57,8 @@ where
 {
     /// Returns a new `QueueingHoneyBadgerBuilder` configured to use the node IDs and cryptographic
     /// keys specified by `netinfo`.
+    // TODO: Make it easier to build a `QueueingHoneyBadger` with a `JoinPlan`. Handle `Step`
+    // conversion internally.
     pub fn new(dyn_hb: DynamicHoneyBadger<Vec<Tx>, NodeUid>) -> Self {
         // TODO: Use the defaults from `HoneyBadgerBuilder`.
         QueueingHoneyBadgerBuilder {
@@ -75,7 +75,7 @@ where
     }
 
     /// Creates a new Queueing Honey Badger instance with an empty buffer.
-    pub fn build(self) -> QueueingHoneyBadger<Tx, NodeUid>
+    pub fn build(self) -> (QueueingHoneyBadger<Tx, NodeUid>, Step<Tx, NodeUid>)
     where
         Tx: Serialize + for<'r> Deserialize<'r> + Debug + Hash + Eq,
     {
@@ -85,7 +85,10 @@ where
 
     /// Returns a new Queueing Honey Badger instance that starts with the given transactions in its
     /// buffer.
-    pub fn build_with_transactions<TI>(self, txs: TI) -> Result<QueueingHoneyBadger<Tx, NodeUid>>
+    pub fn build_with_transactions<TI>(
+        self,
+        txs: TI,
+    ) -> Result<(QueueingHoneyBadger<Tx, NodeUid>, Step<Tx, NodeUid>)>
     where
         TI: IntoIterator<Item = Tx>,
         Tx: Serialize + for<'r> Deserialize<'r> + Debug + Hash + Eq,
@@ -95,10 +98,9 @@ where
             dyn_hb: self.dyn_hb,
             queue,
             batch_size: self.batch_size,
-            output: VecDeque::new(),
         };
-        let _ = qhb.propose()?; // Fault log is empty: no contact with other nodes yet.
+        let step = qhb.propose()?;
-        Ok(qhb)
+        Ok((qhb, step))
     }
 }
 
@@ -115,11 +117,9 @@ where
     dyn_hb: DynamicHoneyBadger<Vec<Tx>, NodeUid>,
     /// The queue of pending transactions that haven't been output in a batch yet.
     queue: TransactionQueue<Tx>,
-    /// The outputs from completed epochs.
-    output: VecDeque<Batch<Tx, NodeUid>>,
 }
 
-pub type QueueingHoneyBadgerStep<Tx, NodeUid> = Step<NodeUid, Batch<Tx, NodeUid>>;
+pub type Step<Tx, NodeUid> = messaging::Step<QueueingHoneyBadger<Tx, NodeUid>>;
 
 impl<Tx, NodeUid> DistAlgorithm for QueueingHoneyBadger<Tx, NodeUid>
 where
@@ -132,42 +132,32 @@ where
     type Message = Message<NodeUid>;
     type Error = Error;
 
-    fn input(&mut self, input: Self::Input) -> Result<QueueingHoneyBadgerStep<Tx, NodeUid>> {
+    fn input(&mut self, input: Self::Input) -> Result<Step<Tx, NodeUid>> {
         // User transactions are forwarded to `HoneyBadger` right away. Internal messages are
         // in addition signed and broadcast.
-        let fault_log = match input {
+        match input {
             Input::User(tx) => {
                 self.queue.0.push_back(tx);
-                FaultLog::new()
+                Ok(Step::default())
             }
-            Input::Change(change) => {
+            Input::Change(change) => Ok(self.dyn_hb.input(Input::Change(change))?.convert()),
-                let step = self.dyn_hb.input(Input::Change(change))?;
+        }
-                // FIXME: Use the output since `dyn_hb` can output immediately on input.
-                step.fault_log
-            }
-        };
-        self.step(fault_log)
     }
 
     fn handle_message(
         &mut self,
         sender_id: &NodeUid,
         message: Self::Message,
-    ) -> Result<QueueingHoneyBadgerStep<Tx, NodeUid>> {
+    ) -> Result<Step<Tx, NodeUid>> {
-        let Step {
+        let mut step = self
-            output,
+            .dyn_hb
-            mut fault_log,
+            .handle_message(sender_id, message)?
-        } = self.dyn_hb.handle_message(sender_id, message)?;
+            .convert::<Self>();
-        for batch in output {
+        for batch in &step.output {
             self.queue.remove_all(batch.iter());
-            self.output.push_back(batch);
         }
-        fault_log.extend(self.propose()?);
+        step.extend(self.propose()?);
-        self.step(fault_log)
+        Ok(step)
-    }
-
-    fn next_message(&mut self) -> Option<TargetedMessage<Self::Message, NodeUid>> {
-        self.dyn_hb.next_message()
     }
 
     fn terminated(&self) -> bool {
@@ -192,33 +182,22 @@ where
         QueueingHoneyBadgerBuilder::new(dyn_hb)
     }
 
-    fn step(
-        &mut self,
-        fault_log: FaultLog<NodeUid>,
-    ) -> Result<QueueingHoneyBadgerStep<Tx, NodeUid>> {
-        Ok(Step::new(self.output.drain(..).collect(), fault_log))
-    }
-
     /// Returns a reference to the internal `DynamicHoneyBadger` instance.
     pub fn dyn_hb(&self) -> &DynamicHoneyBadger<Vec<Tx>, NodeUid> {
         &self.dyn_hb
     }
 
     /// Initiates the next epoch by proposing a batch from the queue.
-    fn propose(&mut self) -> Result<FaultLog<NodeUid>> {
+    fn propose(&mut self) -> Result<Step<Tx, NodeUid>> {
         let amount = cmp::max(1, self.batch_size / self.dyn_hb.netinfo().num_nodes());
-        // TODO: This will loop forever if we are the only validator.
+        // TODO: This will output immediately if we are the only validator.
-        let mut fault_log = FaultLog::new();
+        if self.dyn_hb.has_input() {
-        while !self.dyn_hb.has_input() {
+            Ok(Step::default()) // Error?
+        } else {
             let proposal = self.queue.choose(amount, self.batch_size);
             let step = self.dyn_hb.input(Input::User(proposal))?;
-            fault_log.extend(step.fault_log);
+            Ok(Step::new(step.output, step.fault_log, step.messages))
-            for batch in step.output {
-                self.queue.remove_all(batch.iter());
-                self.output.push_back(batch);
-            }
         }
-        Ok(fault_log)
     }
 }
 

tests/broadcast.rs

@@ -80,8 +80,9 @@ impl Adversary<Broadcast<NodeUid>> for ProposeAdversary {
         let netinfo = Arc::new(NetworkInfo::generate_map(node_ids).remove(&id).unwrap());
         let mut bc = Broadcast::new(netinfo, id).expect("broadcast instance");
         // FIXME: Use the output.
-        let _ = bc.input(b"Fake news".to_vec()).expect("propose");
+        let step = bc.input(b"Fake news".to_vec()).expect("propose");
-        bc.message_iter()
+        step.messages
+            .into_iter()
             .map(|msg| MessageWithSender::new(id, msg))
             .collect()
     }

tests/dynamic_honey_badger.rs

@@ -127,9 +127,7 @@ where
 // Allow passing `netinfo` by value. `TestNetwork` expects this function signature.
 #[cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]
 fn new_dynamic_hb(netinfo: Arc<NetworkInfo<NodeUid>>) -> UsizeDhb {
-    DynamicHoneyBadger::builder((*netinfo).clone())
+    DynamicHoneyBadger::builder().build((*netinfo).clone())
-        .build()
-        .expect("instantiate DHB")
 }
 
 fn test_dynamic_honey_badger_different_sizes<A, F>(new_adversary: F, num_txs: usize)

tests/network/mod.rs

@@ -6,7 +6,7 @@ use std::sync::Arc;
 use rand::{self, Rng};
 
 use hbbft::crypto::SecretKeyShare;
-use hbbft::messaging::{DistAlgorithm, NetworkInfo, Target, TargetedMessage};
+use hbbft::messaging::{DistAlgorithm, NetworkInfo, Step, Target, TargetedMessage};
 
 /// A node identifier. In the tests, nodes are simply numbered.
 #[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Clone, Copy, Serialize, Deserialize, Rand)]
@@ -22,6 +22,8 @@ pub struct TestNode<D: DistAlgorithm> {
     pub queue: VecDeque<(D::NodeUid, D::Message)>,
     /// The values this node has output so far.
     outputs: Vec<D::Output>,
+    /// Outgoing messages to be sent to other nodes.
+    messages: VecDeque<TargetedMessage<D::Message, D::NodeUid>>,
 }
 
 impl<D: DistAlgorithm> TestNode<D> {
@@ -40,6 +42,7 @@ impl<D: DistAlgorithm> TestNode<D> {
     pub fn input(&mut self, input: D::Input) {
         let step = self.algo.input(input).expect("input");
         self.outputs.extend(step.output);
+        self.messages.extend(step.messages);
     }
 
     /// Returns the internal algorithm's instance.
@@ -49,12 +52,13 @@ impl<D: DistAlgorithm> TestNode<D> {
     }
 
     /// Creates a new test node with the given broadcast instance.
-    fn new(algo: D) -> TestNode<D> {
+    fn new((algo, step): (D, Step<D>)) -> TestNode<D> {
         TestNode {
             id: algo.our_id().clone(),
             algo,
             queue: VecDeque::new(),
-            outputs: Vec::new(),
+            outputs: step.output.into_iter().collect(),
+            messages: step.messages,
         }
     }
 
@@ -67,6 +71,7 @@ impl<D: DistAlgorithm> TestNode<D> {
             .handle_message(&from_id, msg)
             .expect("handling message");
         self.outputs.extend(step.output);
+        self.messages.extend(step.messages);
     }
 
     /// Checks whether the node has messages to process
@@ -364,6 +369,7 @@ where
 {
     /// Creates a new network with `good_num` good nodes, and the given `adversary` controlling
     /// `adv_num` nodes.
+    #[allow(unused)] // Not used in all tests.
     pub fn new<F, G>(
         good_num: usize,
         adv_num: usize,
@@ -373,6 +379,23 @@ where
     where
         F: Fn(Arc<NetworkInfo<NodeUid>>) -> D,
         G: Fn(BTreeMap<D::NodeUid, Arc<NetworkInfo<D::NodeUid>>>) -> A,
+    {
+        Self::new_with_step(good_num, adv_num, adversary, |netinfo| {
+            (new_algo(netinfo), Step::default())
+        })
+    }
+
+    /// Creates a new network with `good_num` good nodes, and the given `adversary` controlling
+    /// `adv_num` nodes.
+    pub fn new_with_step<F, G>(
+        good_num: usize,
+        adv_num: usize,
+        adversary: G,
+        new_algo: F,
+    ) -> TestNetwork<A, D>
+    where
+        F: Fn(Arc<NetworkInfo<NodeUid>>) -> (D, Step<D>),
+        G: Fn(BTreeMap<D::NodeUid, Arc<NetworkInfo<D::NodeUid>>>) -> A,
     {
         let mut rng = rand::thread_rng();
         let mut netinfos = NetworkInfo::generate_map((0..(good_num + adv_num)).map(NodeUid));
@@ -412,7 +435,7 @@ where
         }
         let mut initial_msgs: Vec<(D::NodeUid, Vec<_>)> = Vec::new();
         for (id, node) in &mut network.nodes {
-            initial_msgs.push((*id, node.algo.message_iter().collect()));
+            initial_msgs.push((*id, node.messages.drain(..).collect()));
         }
         for (id, msgs) in initial_msgs {
             network.dispatch_messages(id, msgs);
@@ -476,7 +499,7 @@ where
 
         // The node handles the incoming message and creates new outgoing ones to be dispatched.
         let msgs: Vec<_> = {
-            let node = self.nodes.get_mut(&id).unwrap();
+            let mut node = self.nodes.get_mut(&id).unwrap();
 
             // Ensure the adversary is playing fair by selecting a node that will result in actual
             // progress being made, otherwise `TestNode::handle_message()` will panic on `expect()`
@@ -487,7 +510,7 @@ where
             );
 
             node.handle_message();
-            node.algo.message_iter().collect()
+            node.messages.drain(..).collect()
         };
         self.dispatch_messages(id, msgs);
 
@@ -497,9 +520,9 @@ where
     /// Inputs a value in node `id`.
     pub fn input(&mut self, id: NodeUid, value: D::Input) {
         let msgs: Vec<_> = {
-            let node = self.nodes.get_mut(&id).expect("input instance");
+            let mut node = self.nodes.get_mut(&id).expect("input instance");
             node.input(value);
-            node.algo.message_iter().collect()
+            node.messages.drain(..).collect()
         };
         self.dispatch_messages(id, msgs);
     }

tests/queueing_honey_badger.rs

@@ -21,7 +21,7 @@ use std::sync::Arc;
 
 use hbbft::dynamic_honey_badger::DynamicHoneyBadger;
 use hbbft::messaging::NetworkInfo;
-use hbbft::queueing_honey_badger::{Batch, Change, ChangeState, Input, QueueingHoneyBadger};
+use hbbft::queueing_honey_badger::{Batch, Change, ChangeState, Input, QueueingHoneyBadger, Step};
 use itertools::Itertools;
 use rand::Rng;
 
@@ -107,10 +107,10 @@ where
 
 // Allow passing `netinfo` by value. `TestNetwork` expects this function signature.
 #[cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]
-fn new_queueing_hb(netinfo: Arc<NetworkInfo<NodeUid>>) -> QueueingHoneyBadger<usize, NodeUid> {
+fn new_queueing_hb(
-    let dyn_hb = DynamicHoneyBadger::builder((*netinfo).clone())
+    netinfo: Arc<NetworkInfo<NodeUid>>,
-        .build()
+) -> (QueueingHoneyBadger<usize, NodeUid>, Step<usize, NodeUid>) {
-        .expect("instantiate DHB");
+    let dyn_hb = DynamicHoneyBadger::builder().build((*netinfo).clone());
     QueueingHoneyBadger::builder(dyn_hb).batch_size(3).build()
 }
 
@@ -133,7 +133,8 @@ where
             num_good_nodes, num_adv_nodes
         );
         let adversary = |adv_nodes| new_adversary(num_good_nodes, num_adv_nodes, adv_nodes);
-        let network = TestNetwork::new(num_good_nodes, num_adv_nodes, adversary, new_queueing_hb);
+        let network =
+            TestNetwork::new_with_step(num_good_nodes, num_adv_nodes, adversary, new_queueing_hb);
         test_queueing_honey_badger(network, num_txs);
     }
 }