Decoding headers can fail (#8570)

* rlp::decode returns Result

* Fix journaldb to handle rlp::decode Result

* Fix ethcore to work with rlp::decode returning Result

* Light client handles rlp::decode returning Result

* Fix tests in rlp_derive

* Fix tests

* Cleanup

* cleanup

* Allow panic rather than breaking out of iterator

* Let decoding failures when reading from disk blow up

* syntax

* Fix the trivial grumbles

* Fix failing tests

* Make Account::from_rlp return Result

* Syntx, sigh

* Temp-fix for decoding failures

* Header::decode returns Result

Handle new return type throughout the code base.

* Do not continue reading from the DB when a value could not be read

* Fix tests

* Handle header decoding in light_sync

* Handling header decoding errors

* Let the DecodeError bubble up unchanged

* Remove redundant error conversion

ethcore/light/src/client/mod.rs

@@ -318,7 +318,7 @@ impl<T: ChainDataFetcher> Client<T> {
 
 			let epoch_proof =  self.engine.is_epoch_end(
 				&verified_header,
-				&|h| self.chain.block_header(BlockId::Hash(h)).map(|hdr| hdr.decode()),
+				&|h| self.chain.block_header(BlockId::Hash(h)).and_then(|hdr| hdr.decode().ok()),
 				&|h| self.chain.pending_transition(h),
 			);
 
@@ -426,7 +426,15 @@ impl<T: ChainDataFetcher> Client<T> {
 		};
 
 		// Verify Block Family
-		let verify_family_result = self.engine.verify_block_family(&verified_header, &parent_header.decode());
+
+		let verify_family_result = {
+			parent_header.decode()
+				.map_err(|dec_err| dec_err.into())
+				.and_then(|decoded| {
+					self.engine.verify_block_family(&verified_header, &decoded)
+				})
+
+		};
 		if let Err(e) = verify_family_result {
 			warn!(target: "client", "Stage 3 block verification failed for #{} ({})\nError: {:?}",
 				verified_header.number(), verified_header.hash(), e);