feat(miniprotocols): Allow step-by-step agents (#85)

pallas-miniprotocols/src/machines.rs

@@ -1,6 +1,7 @@
 pub use crate::payloads::*;
 use pallas_codec::{minicbor, Fragment};
 use pallas_multiplexer::{Channel, Payload};
+use std::cell::Cell;
 use std::fmt::{Debug, Display};
 use std::sync::mpsc::Sender;
 
@@ -86,36 +87,90 @@ pub trait Agent: Sized {
     fn apply_inbound(self, msg: Self::Message) -> Transition<Self>;
 }
 
-pub fn run_agent<T>(agent: T, channel: &mut Channel) -> Result<T, Box<dyn std::error::Error>>
+pub struct Runner<A>
 where
-    T: Agent + Debug,
+    A: Agent,
+{
+    agent: Cell<Option<A>>,
+    buffer: Vec<u8>,
+}
+
+impl<'a, A> Runner<A>
+where
+    A: Agent,
+    A::Message: Fragment + Debug,
+{
+    pub fn new(agent: A) -> Self {
+        Self {
+            agent: Cell::new(Some(agent)),
+            buffer: Vec::new(),
+        }
+    }
+
+    pub fn start(&mut self) -> Result<(), Error> {
+        let prev = self.agent.take().unwrap();
+        let next = prev.apply_start()?;
+        self.agent.set(Some(next));
+        Ok(())
+    }
+
+    pub fn run_step(&mut self, channel: &mut Channel) -> Result<bool, Error> {
+        let prev = self.agent.take().unwrap();
+        let next = run_agent_step(prev, channel, &mut self.buffer)?;
+        let is_done = next.is_done();
+
+        self.agent.set(Some(next));
+
+        Ok(is_done)
+    }
+
+    pub fn fulfill(mut self, channel: &mut Channel) -> Result<(), Error> {
+        self.start()?;
+
+        while self.run_step(channel)? {}
+
+        Ok(())
+    }
+}
+
+pub fn run_agent_step<T>(agent: T, channel: &mut Channel, buffer: &mut Vec<u8>) -> Transition<T>
+where
+    T: Agent,
     T::Message: Fragment + Debug,
 {
     let Channel(tx, rx) = channel;
 
+    match agent.has_agency() {
+        true => {
+            let msg = agent.build_next();
+            log::trace!("processing outbound msg: {:?}", msg);
+
+            let mut payload = Vec::new();
+            minicbor::encode(&msg, &mut payload)?;
+            tx.send(payload)?;
+
+            agent.apply_outbound(msg)
+        }
+        false => {
+            let msg = read_until_full_msg::<T::Message>(buffer, rx).unwrap();
+            log::trace!("procesing inbound msg: {:?}", msg);
+
+            agent.apply_inbound(msg)
+        }
+    }
+}
+
+pub fn run_agent<T>(agent: T, channel: &mut Channel) -> Result<T, Box<dyn std::error::Error>>
+where
+    T: Agent,
+    T::Message: Fragment + Debug,
+{
     let mut buffer = Vec::new();
 
     let mut agent = agent.apply_start()?;
 
     while !agent.is_done() {
-        log::debug!("evaluating agent {:?}", agent);
-
-        match agent.has_agency() {
-            true => {
-                let msg = agent.build_next();
-
-                let mut payload = Vec::new();
-                minicbor::encode(&msg, &mut payload)?;
-                tx.send(payload)?;
-
-                agent = agent.apply_outbound(msg)?;
-            }
-            false => {
-                let msg = read_until_full_msg::<T::Message>(&mut buffer, rx).unwrap();
-                log::trace!("procesing inbound msg: {:?}", msg);
-                agent = agent.apply_inbound(msg)?;
-            }
-        }
+        agent = run_agent_step(agent, channel, &mut buffer)?;
     }
 
     Ok(agent)