Move Raft node construction onto NodeState

src/raft/node/follower.rs

@@ -1,9 +1,10 @@
-use super::super::{Address, Event, Instruction, Message, RequestID, Response};
+use super::super::{Address, Event, Instruction, Log, Message, RequestID, Response};
 use super::{rand_election_timeout, Candidate, Node, NodeID, NodeState, Role, Term, Ticks};
 use crate::error::{Error, Result};
 
 use ::log::{debug, error, info, warn};
 use std::collections::HashSet;
+use tokio::sync::mpsc;
 
 // A follower replicates state from a leader.
 #[derive(Clone, Debug, PartialEq)]
@@ -37,6 +38,19 @@ impl Follower {
 impl Role for Follower {}
 
 impl NodeState<Follower> {
+    /// Creates a new node as a leaderless follower.
+    pub fn new(
+        id: NodeID,
+        peers: HashSet<NodeID>,
+        mut log: Log,
+        node_tx: mpsc::UnboundedSender<Message>,
+        state_tx: mpsc::UnboundedSender<Instruction>,
+    ) -> Result<Self> {
+        let (term, voted_for) = log.get_term()?;
+        let role = Follower::new(None, voted_for);
+        Ok(NodeState { id, peers, term, log, node_tx, state_tx, role })
+    }
+
     /// Asserts internal invariants.
     fn assert(&mut self) -> Result<()> {
         self.assert_node()?;

src/raft/node/mod.rs

@@ -56,7 +56,8 @@ pub enum Node {
 }
 
 impl Node {
-    /// Creates a new Raft node, starting as a leaderless follower.
+    /// Creates a new Raft node, starting as a leaderless follower, or leader if
+    /// there are no peers.
     pub async fn new(
         id: NodeID,
         peers: HashSet<NodeID>,
@@ -69,16 +70,7 @@ impl Node {
         driver.apply_log(&mut *state, &mut log)?;
         tokio::spawn(driver.drive(state));
 
-        let (term, voted_for) = log.get_term()?;
-        let node = NodeState {
-            id,
-            peers,
-            term,
-            log,
-            node_tx,
-            state_tx,
-            role: Follower::new(None, voted_for),
-        };
+        let node = NodeState::new(id, peers, log, node_tx, state_tx)?;
         if node.peers.is_empty() {
             // If there are no peers, become leader immediately.
             return Ok(node.become_candidate()?.become_leader()?.into());
@@ -137,7 +129,7 @@ impl From<NodeState<Leader>> for Node {
 pub trait Role: Clone + std::fmt::Debug + PartialEq {}
 
 // A Raft node with role R
-pub struct NodeState<R: Role> {
+pub struct NodeState<R: Role = Follower> {
     id: NodeID,
     peers: HashSet<NodeID>,
     term: Term,