Unify error enums in substrate and ethereum clients with thiserror (#1094)

* Unify error enums in substrate and ethereum clients with `thiserror`

Related to https://github.com/paritytech/parity-bridges-common/issues/857

* Add license pre-amble

* rustfmt

* Fix spelling

bridges/relays/client-ethereum/Cargo.toml

@@ -17,3 +17,4 @@ log = "0.4.11"
 relay-utils = { path = "../utils" }
 tokio = "1.8"
 web3 = { git = "https://github.com/svyatonik/rust-web3.git", branch = "bump-deps" }
+thiserror = "1.0.26"

bridges/relays/client-ethereum/src/error.rs

@@ -20,49 +20,47 @@ use crate::types::U256;
 
 use jsonrpsee_ws_client::types::Error as RpcError;
 use relay_utils::MaybeConnectionError;
+use thiserror::Error;
 
 /// Result type used by Ethereum client.
 pub type Result<T> = std::result::Result<T, Error>;
 
 /// Errors that can occur only when interacting with
 /// an Ethereum node through RPC.
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum Error {
 	/// IO error.
-	Io(std::io::Error),
+	#[error("IO error: {0}")]
+	Io(#[from] std::io::Error),
 	/// An error that can occur when making an HTTP request to
 	/// an JSON-RPC client.
-	RpcError(RpcError),
+	#[error("RPC error: {0}")]
+	RpcError(#[from] RpcError),
 	/// Failed to parse response.
+	#[error("Response parse failed: {0}")]
 	ResponseParseFailed(String),
 	/// We have received a header with missing fields.
+	#[error("Incomplete Ethereum Header Received (missing some of required fields - hash, number, logs_bloom).")]
 	IncompleteHeader,
 	/// We have received a transaction missing a `raw` field.
+	#[error("Incomplete Ethereum Transaction (missing required field - raw).")]
 	IncompleteTransaction,
 	/// An invalid Substrate block number was received from
 	/// an Ethereum node.
+	#[error("Received an invalid Substrate block from Ethereum Node.")]
 	InvalidSubstrateBlockNumber,
 	/// An invalid index has been received from an Ethereum node.
+	#[error("Received an invalid incomplete index from Ethereum Node.")]
 	InvalidIncompleteIndex,
 	/// The client we're connected to is not synced, so we can't rely on its state. Contains
 	/// number of unsynced headers.
+	#[error("Ethereum client is not synced: syncing {0} headers.")]
 	ClientNotSynced(U256),
 	/// Custom logic error.
+	#[error("{0}")]
 	Custom(String),
 }
 
-impl From<RpcError> for Error {
-	fn from(error: RpcError) -> Self {
-		Error::RpcError(error)
-	}
-}
-
-impl From<std::io::Error> for Error {
-	fn from(error: std::io::Error) -> Self {
-		Error::Io(error)
-	}
-}
-
 impl From<tokio::task::JoinError> for Error {
 	fn from(error: tokio::task::JoinError) -> Self {
 		Error::Custom(format!("Failed to wait tokio task: {}", error))
@@ -82,24 +80,3 @@ impl MaybeConnectionError for Error {
 		)
 	}
 }
-
-impl ToString for Error {
-	fn to_string(&self) -> String {
-		match self {
-			Self::Io(e) => e.to_string(),
-			Self::RpcError(e) => e.to_string(),
-			Self::ResponseParseFailed(e) => e.to_string(),
-			Self::IncompleteHeader => {
-				"Incomplete Ethereum Header Received (missing some of required fields - hash, number, logs_bloom)"
-					.to_string()
-			}
-			Self::IncompleteTransaction => "Incomplete Ethereum Transaction (missing required field - raw)".to_string(),
-			Self::InvalidSubstrateBlockNumber => "Received an invalid Substrate block from Ethereum Node".to_string(),
-			Self::InvalidIncompleteIndex => "Received an invalid incomplete index from Ethereum Node".to_string(),
-			Self::ClientNotSynced(missing_headers) => {
-				format!("Ethereum client is not synced: syncing {} headers", missing_headers)
-			}
-			Self::Custom(ref e) => e.clone(),
-		}
-	}
-}