Return proper error to CLI for all expected scenarios

When a CLI requests a spot price have some errors that are expected, where we can provide a proper error message for the CLI:
- Balance of ASB too low
- Buy amount sent by CLI exceeds maximum buy amount accepted by ASB
- ASB is running in maintenance mode and does not accept incoming swap requests

All of these errors returns a proper error to the CLI and prints a warning in the ASB logs.
Any other unexpected error will result in closing the channel with the CLI and printing an error in the ASB logs.

CHANGELOG.md

@@ -20,6 +20,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   If you want to access data created by a previous version you will have to rename the data folder or one of the following:
   1. For the CLI you can use `--data-dir` to point to the old directory.
   2. For the ASB you can change the data-dir in the config file of the ASB.
+- The CLI receives proper Error messages if setting up a swap with the ASB fails.
+  This is a breaking change because the spot-price protocol response changed.
+  Expected errors scenarios that are now reported back to the CLI:
+  1. Balance of ASB too low
+  2. Buy amount sent by CLI exceeds maximum buy amount accepted by ASB
+  3. ASB is running in resume-only mode and does not accept incoming swap requests
 
 ## [0.5.0] - 2021-04-17
 

swap/src/monero.rs

@@ -192,12 +192,6 @@ pub struct InsufficientFunds {
     pub actual: Amount,
 }
 
-#[derive(Debug, Clone, Copy, thiserror::Error)]
-#[error("The balance is too low, current balance: {balance}")]
-pub struct BalanceTooLow {
-    pub balance: Amount,
-}
-
 #[derive(thiserror::Error, Debug, Clone, PartialEq)]
 #[error("Overflow, cannot convert {0} to u64")]
 pub struct OverflowError(pub String);

swap/src/network/spot_price.rs

@@ -1,6 +1,6 @@
+use crate::monero;
 use crate::network::cbor_request_response::CborCodec;
 use crate::protocol::{alice, bob};
-use crate::{bitcoin, monero};
 use libp2p::core::ProtocolName;
 use libp2p::request_response::{
     ProtocolSupport, RequestResponse, RequestResponseConfig, RequestResponseEvent,
@@ -40,9 +40,9 @@ pub struct Request {
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone)]
-pub struct Response {
+pub enum Response {
-    pub xmr: Option<monero::Amount>,
+    Xmr(monero::Amount),
-    pub error: Option<Error>,
+    Error(Error),
 }
 
 #[derive(Clone, Debug, thiserror::Error, Serialize, Deserialize)]
@@ -51,6 +51,18 @@ pub enum Error {
         "This seller currently does not accept incoming swap requests, please try again later"
     )]
     MaintenanceMode,
+    #[error("Seller refused to buy {buy} because the maximum configured buy limit is {max}")]
+    MaxBuyAmountExceeded {
+        #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
+        max: bitcoin::Amount,
+        #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
+        buy: bitcoin::Amount,
+    },
+    #[error("This seller's XMR balance is currently too low to fulfill the swap request to buy {buy}, please try again later")]
+    BalanceTooLow {
+        #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
+        buy: bitcoin::Amount,
+    },
 }
 
 /// Constructs a new instance of the `spot-price` behaviour to be used by Alice.

swap/src/protocol/alice/event_loop.rs

@@ -1,12 +1,11 @@
 use crate::asb::Rate;
 use crate::database::Database;
 use crate::env::Config;
-use crate::monero::BalanceTooLow;
 use crate::network::quote::BidQuote;
 use crate::network::{spot_price, transfer_proof};
 use crate::protocol::alice::{AliceState, Behaviour, OutEvent, State0, State3, Swap};
 use crate::{bitcoin, kraken, monero};
-use anyhow::{bail, Context, Result};
+use anyhow::{Context, Result};
 use futures::future;
 use futures::future::{BoxFuture, FutureExt};
 use futures::stream::{FuturesUnordered, StreamExt};
@@ -148,30 +147,30 @@ where
                 swarm_event = self.swarm.next_event() => {
                     match swarm_event {
                         SwarmEvent::Behaviour(OutEvent::SpotPriceRequested { request, channel, peer }) => {
-                            if self.resume_only {
-                                tracing::warn!(%peer, "Ignoring spot price request from {} because ASB started in resume-only mode", peer);
-
-                                match self.swarm.behaviour_mut().spot_price.send_response(channel, spot_price::Response { xmr: None, error: Some(spot_price::Error::MaintenanceMode) }) {
-                                    Ok(_) => {},
-                                    Err(_) => {
-                                        tracing::debug!(%peer, "Failed to respond with error to spot price request");
-                                        continue;
-                                    }
-                                }
-
-                                continue;
-                            }
-
                             let btc = request.btc;
                             let xmr = match self.handle_spot_price_request(btc, self.monero_wallet.clone()).await {
-                                Ok(xmr) => xmr,
+                                Ok(xmr) => match xmr {
+                                    Ok(xmr) => xmr,
+                                    Err(e) => {
+                                        tracing::warn!(%peer, "Ignoring spot price request from {} because: {:#}", peer, e);
+                                        match self.swarm.behaviour_mut().spot_price.send_response(channel, spot_price::Response::Error(e)) {
+                                            Ok(_) => {
+                                                continue;
+                                            },
+                                            Err(_) => {
+                                                tracing::debug!(%peer, "Failed to respond with error to spot price request");
+                                                continue;
+                                            }
+                                        }
+                                    }
+                                },
                                 Err(e) => {
-                                    tracing::warn!(%peer, "Failed to produce spot price for {}: {:#}", btc, e);
+                                    tracing::error!(%peer, "Unrecoverable error while producing spot price for {}: {:#}", btc, e);
                                     continue;
                                 }
                             };
 
-                            match self.swarm.behaviour_mut().spot_price.send_response(channel, spot_price::Response { xmr: Some(xmr), error: None }) {
+                            match self.swarm.behaviour_mut().spot_price.send_response(channel, spot_price::Response::Xmr(xmr)) {
                                 Ok(_) => {},
                                 Err(_) => {
                                     // if we can't respond, the peer probably just disconnected so it is not a huge deal, only log this on debug
@@ -365,17 +364,21 @@ where
         &mut self,
         btc: bitcoin::Amount,
         monero_wallet: Arc<monero::Wallet>,
-    ) -> Result<monero::Amount> {
+    ) -> Result<Result<monero::Amount, spot_price::Error>> {
+        if self.resume_only {
+            return Ok(Err(spot_price::Error::MaintenanceMode));
+        }
+
         let rate = self
             .latest_rate
             .latest_rate()
             .context("Failed to get latest rate")?;
 
         if btc > self.max_buy {
-            bail!(MaximumBuyAmountExceeded {
+            return Ok(Err(spot_price::Error::MaxBuyAmountExceeded {
-                actual: btc,
+                buy: btc,
-                max: self.max_buy
+                max: self.max_buy,
-            })
+            }));
         }
 
         let xmr_balance = monero_wallet.get_balance().await?;
@@ -383,12 +386,10 @@ where
         let xmr = rate.sell_quote(btc)?;
 
         if xmr_balance < xmr + xmr_lock_fees {
-            bail!(BalanceTooLow {
+            return Ok(Err(spot_price::Error::BalanceTooLow { buy: btc }));
-                balance: xmr_balance
-            })
         }
 
-        Ok(xmr)
+        Ok(Ok(xmr))
     }
 
     async fn make_quote(&mut self, max_buy: bitcoin::Amount) -> Result<BidQuote> {
@@ -569,13 +570,6 @@ impl EventLoopHandle {
     }
 }
 
-#[derive(Debug, Clone, Copy, thiserror::Error)]
-#[error("Refusing to buy {actual} because the maximum configured limit is {max}")]
-pub struct MaximumBuyAmountExceeded {
-    pub max: bitcoin::Amount,
-    pub actual: bitcoin::Amount,
-}
-
 #[allow(missing_debug_implementations)]
 struct MpscChannels<T> {
     sender: mpsc::Sender<T>,

swap/src/protocol/bob/event_loop.rs

@@ -1,5 +1,6 @@
 use crate::bitcoin::EncryptedSignature;
 use crate::network::quote::BidQuote;
+use crate::network::spot_price::Response;
 use crate::network::{encrypted_signature, spot_price};
 use crate::protocol::bob::{Behaviour, OutEvent, State0, State2};
 use crate::{bitcoin, monero};
@@ -266,16 +267,11 @@ impl EventLoopHandle {
             .send_receive(spot_price::Request { btc })
             .await?;
 
-        match (response.xmr, response.error) {
+        match response {
-            (Some(xmr), None) => Ok(xmr),
+            Response::Xmr(xmr) => Ok(xmr),
-            (_, Some(error)) => {
+            Response::Error(error) => {
                 bail!(error);
             }
-            (None, None) => {
-                bail!(
-                    "Unexpected response for spot-price request, neither price nor error received"
-                );
-            }
         }
     }