fix aura backcompat: revert to manual encoding/decoding of transition proofs (#6665)

ethcore/src/engines/epoch.rs

@@ -18,8 +18,10 @@
 
 use bigint::hash::H256;
 
+use rlp::{Encodable, Decodable, DecoderError, RlpStream, UntrustedRlp};
+
 /// A full epoch transition.
-#[derive(Debug, Clone, RlpEncodable, RlpDecodable)]
+#[derive(Debug, Clone)]
 pub struct Transition {
 	/// Block hash at which the transition occurred.
 	pub block_hash: H256,
@@ -29,14 +31,46 @@ pub struct Transition {
 	pub proof: Vec<u8>,
 }
 
+impl Encodable for Transition {
+	fn rlp_append(&self, s: &mut RlpStream) {
+		s.begin_list(3)
+			.append(&self.block_hash)
+			.append(&self.block_number)
+			.append(&self.proof);
+	}
+}
+
+impl Decodable for Transition {
+	fn decode(rlp: &UntrustedRlp) -> Result<Self, DecoderError> {
+		Ok(Transition {
+			block_hash: rlp.val_at(0)?,
+			block_number: rlp.val_at(1)?,
+			proof: rlp.val_at(2)?,
+		})
+	}
+}
+
 /// An epoch transition pending a finality proof.
 /// Not all transitions need one.
-#[derive(RlpEncodableWrapper, RlpDecodableWrapper)]
 pub struct PendingTransition {
 	/// "transition/epoch" proof from the engine.
 	pub proof: Vec<u8>,
 }
 
+impl Encodable for PendingTransition {
+	fn rlp_append(&self, s: &mut RlpStream) {
+		s.append(&self.proof);
+	}
+}
+
+impl Decodable for PendingTransition {
+	fn decode(rlp: &UntrustedRlp) -> Result<Self, DecoderError> {
+		Ok(PendingTransition {
+			proof: rlp.as_val()?,
+		})
+	}
+}
+
 /// Verifier for all blocks within an epoch with self-contained state.
 pub trait EpochVerifier<M: ::parity_machine::Machine>: Send + Sync {
 	/// Lightly verify the next block header.