Add an impl of ProtocolError for ()

entropyxyz · Nov 3, 2024 · 7738979 · 7738979
1 parent d0be605
commit 7738979
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Showing 4 changed files with 29 additions and 60 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Re-export `digest` from the `session` module. ([#56])
 - Added `Message::destination()`. ([#56])
 - `PartyId` trait alias for the combination of bounds needed for a party identifier. ([#59])
+- An impl of `ProtocolError` for `()` for protocols that don't use errors. ([#60])
 
 
 [#32]: https://github.com/entropyxyz/manul/pull/32

diff --git a/manul/benches/empty_rounds.rs b/manul/benches/empty_rounds.rs
@@ -1,17 +1,14 @@
 extern crate alloc;
 
-use alloc::{
-    collections::{BTreeMap, BTreeSet},
-    string::String,
-};
+use alloc::collections::{BTreeMap, BTreeSet};
 use core::fmt::Debug;
 
 use criterion::{criterion_group, criterion_main, Criterion};
 use manul::{
     protocol::{
         Artifact, BoxedRound, Deserializer, DirectMessage, EchoBroadcast, EntryPoint, FinalizeError, FinalizeOutcome,
-        LocalError, NormalBroadcast, PartyId, Payload, Protocol, ProtocolError, ProtocolMessagePart,
-        ProtocolValidationError, ReceiveError, Round, RoundId, Serializer,
+        LocalError, NormalBroadcast, PartyId, Payload, Protocol, ProtocolMessagePart, ReceiveError, Round, RoundId,
+        Serializer,
     },
     session::{signature::Keypair, SessionOutcome},
     testing::{run_sync, BinaryFormat, TestSessionParams, TestSigner, TestVerifier},
@@ -22,31 +19,9 @@ use serde::{Deserialize, Serialize};
 #[derive(Debug)]
 pub struct EmptyProtocol;
 
-#[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct EmptyProtocolError;
-
-impl ProtocolError for EmptyProtocolError {
-    fn description(&self) -> String {
-        unimplemented!()
-    }
-    fn verify_messages_constitute_error(
-        &self,
-        _deserializer: &Deserializer,
-        _echo_broadcast: &EchoBroadcast,
-        _normal_broadcast: &NormalBroadcast,
-        _direct_message: &DirectMessage,
-        _echo_broadcasts: &BTreeMap<RoundId, EchoBroadcast>,
-        _normal_broadcasts: &BTreeMap<RoundId, NormalBroadcast>,
-        _direct_messages: &BTreeMap<RoundId, DirectMessage>,
-        _combined_echos: &BTreeMap<RoundId, Vec<EchoBroadcast>>,
-    ) -> Result<(), ProtocolValidationError> {
-        unimplemented!()
-    }
-}
-
 impl Protocol for EmptyProtocol {
     type Result = ();
-    type ProtocolError = EmptyProtocolError;
+    type ProtocolError = ();
     type CorrectnessProof = ();
 }
 

diff --git a/manul/src/protocol/round.rs b/manul/src/protocol/round.rs
@@ -201,6 +201,28 @@ pub trait ProtocolError: Debug + Clone + Send {
     ) -> Result<(), ProtocolValidationError>;
 }
 
+// A convenience implementation for protocols that don't define any errors.
+// Have to do it for `()`, since `!` is unstable.
+impl ProtocolError for () {
+    fn description(&self) -> String {
+        panic!("Attempt to use an empty error type in an evidence. This is a bug in the protocol implementation.")
+    }
+
+    fn verify_messages_constitute_error(
+        &self,
+        _deserializer: &Deserializer,
+        _echo_broadcast: &EchoBroadcast,
+        _normal_broadcast: &NormalBroadcast,
+        _direct_message: &DirectMessage,
+        _echo_broadcasts: &BTreeMap<RoundId, EchoBroadcast>,
+        _normal_broadcasts: &BTreeMap<RoundId, NormalBroadcast>,
+        _direct_messages: &BTreeMap<RoundId, DirectMessage>,
+        _combined_echos: &BTreeMap<RoundId, Vec<EchoBroadcast>>,
+    ) -> Result<(), ProtocolValidationError> {
+        panic!("Attempt to use an empty error type in an evidence. This is a bug in the protocol implementation.")
+    }
+}
+
 /// Message payload created in [`Round::receive_message`].
 #[derive(Debug)]
 pub struct Payload(pub Box<dyn Any + Send + Sync>);

diff --git a/manul/src/session/session.rs b/manul/src/session/session.rs
@@ -816,17 +816,11 @@ fn filter_messages<Verifier>(
 
 #[cfg(test)]
 mod tests {
-    use alloc::{collections::BTreeMap, string::String, vec::Vec};
-
     use impls::impls;
-    use serde::{Deserialize, Serialize};
 
     use super::{Message, ProcessedArtifact, ProcessedMessage, Session, VerifiedMessage};
     use crate::{
-        protocol::{
-            Deserializer, DirectMessage, EchoBroadcast, NormalBroadcast, Protocol, ProtocolError,
-            ProtocolValidationError, RoundId,
-        },
+        protocol::Protocol,
         testing::{BinaryFormat, TestSessionParams, TestVerifier},
     };
 
@@ -842,32 +836,9 @@ mod tests {
 
         struct DummyProtocol;
 
-        #[derive(Debug, Clone, Serialize, Deserialize)]
-        struct DummyProtocolError;
-
-        impl ProtocolError for DummyProtocolError {
-            fn description(&self) -> String {
-                unimplemented!()
-            }
-
-            fn verify_messages_constitute_error(
-                &self,
-                _deserializer: &Deserializer,
-                _echo_broadcast: &EchoBroadcast,
-                _normal_broadcast: &NormalBroadcast,
-                _direct_message: &DirectMessage,
-                _echo_broadcasts: &BTreeMap<RoundId, EchoBroadcast>,
-                _normal_broadcasts: &BTreeMap<RoundId, NormalBroadcast>,
-                _direct_messages: &BTreeMap<RoundId, DirectMessage>,
-                _combined_echos: &BTreeMap<RoundId, Vec<EchoBroadcast>>,
-            ) -> Result<(), ProtocolValidationError> {
-                unimplemented!()
-            }
-        }
-
         impl Protocol for DummyProtocol {
             type Result = ();
-            type ProtocolError = DummyProtocolError;
+            type ProtocolError = ();
             type CorrectnessProof = ();
         }