Provide stronger isolation of kraken module

Instead of leaking the tokio::sync:⌚:Receiver type in our
return value, we create a newtype that implements the desired
interface. This allows us to get rid of the `RateService` structs
and instead implement `LatestRate` directly on top of this struct.

Given that `LatestRate` is only used within the event_loop module,
we move the definition of this type into there.

swap/src/asb.rs

@@ -1,13 +1,7 @@
-mod amounts;
 pub mod command;
 pub mod config;
-pub mod fixed_rate;
-pub mod kraken;
+mod fixed_rate;
+mod rate;
 
-pub use amounts::Rate;
-
-pub trait LatestRate {
-    type Error: std::error::Error + Send + Sync + 'static;
-
-    fn latest_rate(&mut self) -> Result<Rate, Self::Error>;
-}
+pub use self::fixed_rate::FixedRate;
+pub use self::rate::Rate;

swap/src/asb/fixed_rate.rs

@@ -1,23 +1,20 @@
-use crate::asb::{LatestRate, Rate};
-use std::convert::Infallible;
+use crate::asb::Rate;
 
-pub const RATE: f64 = 0.01;
+#[derive(Clone, Debug)]
+pub struct FixedRate(Rate);
 
-#[derive(Clone)]
-pub struct RateService(Rate);
+impl FixedRate {
+    pub const RATE: f64 = 0.01;
 
-impl LatestRate for RateService {
-    type Error = Infallible;
-
-    fn latest_rate(&mut self) -> Result<Rate, Infallible> {
-        Ok(self.0)
+    pub fn value(&self) -> Rate {
+        self.0
     }
 }
 
-impl Default for RateService {
+impl Default for FixedRate {
     fn default() -> Self {
         Self(Rate {
-            ask: bitcoin::Amount::from_btc(RATE).expect("Static value should never fail"),
+            ask: bitcoin::Amount::from_btc(Self::RATE).expect("Static value should never fail"),
         })
     }
 }

swap/src/asb/kraken.rs

@@ -1,25 +0,0 @@
-use crate::asb::{LatestRate, Rate};
-use crate::kraken;
-use anyhow::Result;
-use tokio::sync::watch::Receiver;
-
-#[derive(Clone)]
-pub struct RateService {
-    receiver: Receiver<Result<Rate, kraken::Error>>,
-}
-
-impl LatestRate for RateService {
-    type Error = kraken::Error;
-
-    fn latest_rate(&mut self) -> Result<Rate, Self::Error> {
-        (*self.receiver.borrow()).clone()
-    }
-}
-
-impl RateService {
-    pub async fn new() -> Result<Self> {
-        Ok(Self {
-            receiver: kraken::connect().await?,
-        })
-    }
-}

swap/src/bin/asb.rs

@@ -23,7 +23,6 @@ use swap::asb::command::{Arguments, Command};
 use swap::asb::config::{
     initial_setup, query_user_for_initial_testnet_config, read_config, Config, ConfigNotInitialized,
 };
-use swap::asb::kraken;
 use swap::database::Database;
 use swap::execution_params::GetExecutionParams;
 use swap::fs::default_config_path;
@@ -31,7 +30,7 @@ use swap::monero::Amount;
 use swap::protocol::alice::EventLoop;
 use swap::seed::Seed;
 use swap::trace::init_tracing;
-use swap::{bitcoin, execution_params, monero};
+use swap::{bitcoin, execution_params, kraken, monero};
 use tracing::{info, warn};
 use tracing_subscriber::filter::LevelFilter;
 
@@ -93,7 +92,7 @@ async fn main() -> Result<()> {
                 bitcoin_wallet.new_address().await?
             );
 
-            let rate_service = kraken::RateService::new().await?;
+            let kraken_rate_updates = kraken::connect().await?;
 
             let (event_loop, _) = EventLoop::new(
                 config.network.listen,
@@ -102,7 +101,7 @@ async fn main() -> Result<()> {
                 Arc::new(bitcoin_wallet),
                 Arc::new(monero_wallet),
                 Arc::new(db),
-                rate_service,
+                kraken_rate_updates,
                 max_buy,
             )
             .unwrap();

swap/src/bin/kraken_ticker.rs

@@ -11,9 +11,7 @@ async fn main() -> Result<()> {
         .context("Failed to connect to kraken")?;
 
     loop {
-        ticker.changed().await?;
-
-        match &*ticker.borrow() {
+        match ticker.wait_for_update().await? {
             Ok(rate) => println!("Rate update: {}", rate),
             Err(e) => println!("Error: {:#}", e),
         }

swap/src/kraken.rs

@@ -10,7 +10,7 @@ use tokio::sync::watch;
 use tokio_tungstenite::tungstenite;
 use tracing::{error, trace};
 
-pub async fn connect() -> Result<watch::Receiver<Result<Rate, Error>>> {
+pub async fn connect() -> Result<RateUpdateStream> {
     let (rate_update, rate_update_receiver) = watch::channel(Err(Error::NotYetRetrieved));
 
     let (rate_stream, _response) =
@@ -88,7 +88,26 @@ pub async fn connect() -> Result<watch::Receiver<Result<Rate, Error>>> {
         .send(SUBSCRIBE_XMR_BTC_TICKER_PAYLOAD.into())
         .await?;
 
-    Ok(rate_update_receiver)
+    Ok(RateUpdateStream {
+        inner: rate_update_receiver,
+    })
+}
+
+#[derive(Clone, Debug)]
+pub struct RateUpdateStream {
+    inner: watch::Receiver<Result<Rate, Error>>,
+}
+
+impl RateUpdateStream {
+    pub async fn wait_for_update(&mut self) -> Result<Result<Rate, Error>> {
+        self.inner.changed().await?;
+
+        Ok(self.inner.borrow().clone())
+    }
+
+    pub fn latest_update(&mut self) -> Result<Rate, Error> {
+        self.inner.borrow().clone()
+    }
 }
 
 const KRAKEN_WS_URL: &str = "wss://ws.kraken.com";

swap/src/protocol/alice/event_loop.rs

@@ -1,4 +1,4 @@
-use crate::asb::LatestRate;
+use crate::asb::{FixedRate, Rate};
 use crate::database::Database;
 use crate::execution_params::ExecutionParams;
 use crate::monero::BalanceTooLow;
@@ -8,13 +8,14 @@ use crate::protocol::alice;
 use crate::protocol::alice::{AliceState, Behaviour, OutEvent, State3, Swap, TransferProof};
 use crate::protocol::bob::EncryptedSignature;
 use crate::seed::Seed;
-use crate::{bitcoin, monero};
+use crate::{bitcoin, kraken, monero};
 use anyhow::{bail, Context, Result};
 use futures::future::RemoteHandle;
 use libp2p::core::Multiaddr;
 use libp2p::futures::FutureExt;
 use libp2p::{PeerId, Swarm};
 use rand::rngs::OsRng;
+use std::convert::Infallible;
 use std::sync::Arc;
 use tokio::sync::mpsc::error::SendError;
 use tokio::sync::{broadcast, mpsc};
@@ -80,7 +81,7 @@ pub struct EventLoop<RS> {
     bitcoin_wallet: Arc<bitcoin::Wallet>,
     monero_wallet: Arc<monero::Wallet>,
     db: Arc<Database>,
-    rate_service: RS,
+    latest_rate: RS,
     max_buy: bitcoin::Amount,
 
     recv_encrypted_signature: broadcast::Sender<EncryptedSignature>,
@@ -92,9 +93,31 @@ pub struct EventLoop<RS> {
     swap_handle_sender: mpsc::Sender<RemoteHandle<Result<AliceState>>>,
 }
 
-impl<RS> EventLoop<RS>
+pub trait LatestRate {
+    type Error: std::error::Error + Send + Sync + 'static;
+
+    fn latest_rate(&mut self) -> Result<Rate, Self::Error>;
+}
+
+impl LatestRate for FixedRate {
+    type Error = Infallible;
+
+    fn latest_rate(&mut self) -> Result<Rate, Self::Error> {
+        Ok(self.value())
+    }
+}
+
+impl LatestRate for kraken::RateUpdateStream {
+    type Error = kraken::Error;
+
+    fn latest_rate(&mut self) -> Result<Rate, Self::Error> {
+        self.latest_update()
+    }
+}
+
+impl<LR> EventLoop<LR>
 where
-    RS: LatestRate,
+    LR: LatestRate,
 {
     #[allow(clippy::too_many_arguments)]
     pub fn new(
@@ -104,7 +127,7 @@ where
         bitcoin_wallet: Arc<bitcoin::Wallet>,
         monero_wallet: Arc<monero::Wallet>,
         db: Arc<Database>,
-        rate_service: RS,
+        latest_rate: LR,
         max_buy: bitcoin::Amount,
     ) -> Result<(Self, mpsc::Receiver<RemoteHandle<Result<AliceState>>>)> {
         let identity = seed.derive_libp2p_identity();
@@ -132,7 +155,7 @@ where
             bitcoin_wallet,
             monero_wallet,
             db,
-            rate_service,
+            latest_rate,
             recv_encrypted_signature: recv_encrypted_signature.sender,
             send_transfer_proof: send_transfer_proof.receiver,
             send_transfer_proof_sender: send_transfer_proof.sender,
@@ -239,7 +262,7 @@ where
         monero_wallet: Arc<monero::Wallet>,
     ) -> Result<monero::Amount> {
         let rate = self
-            .rate_service
+            .latest_rate
             .latest_rate()
             .context("Failed to get latest rate")?;
 
@@ -265,7 +288,7 @@ where
 
     async fn make_quote(&mut self, max_buy: bitcoin::Amount) -> Result<BidQuote> {
         let rate = self
-            .rate_service
+            .latest_rate
             .latest_rate()
             .context("Failed to get latest rate")?;
 

swap/tests/testutils/mod.rs

@@ -14,8 +14,7 @@ use std::convert::Infallible;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 use std::time::Duration;
-use swap::asb::fixed_rate;
-use swap::asb::fixed_rate::RATE;
+use swap::asb::FixedRate;
 use swap::bitcoin::{CancelTimelock, PunishTimelock};
 use swap::database::Database;
 use swap::execution_params::{ExecutionParams, GetExecutionParams};
@@ -344,7 +343,7 @@ where
     let (monero, containers) = testutils::init_containers(&cli).await;
 
     let btc_amount = bitcoin::Amount::from_sat(1_000_000);
-    let xmr_amount = monero::Amount::from_monero(btc_amount.as_btc() / RATE).unwrap();
+    let xmr_amount = monero::Amount::from_monero(btc_amount.as_btc() / FixedRate::RATE).unwrap();
 
     let alice_starting_balances = StartingBalances {
         xmr: xmr_amount * 10,
@@ -410,7 +409,7 @@ where
         alice_bitcoin_wallet.clone(),
         alice_monero_wallet.clone(),
         alice_db,
-        fixed_rate::RateService::default(),
+        FixedRate::default(),
         bitcoin::Amount::ONE_BTC,
     )
     .unwrap();