Don't panic in import_block if invalid rlp (#8522)

* Don't panic in import_block if invalid rlp

* Remove redundant type annotation

* Replace RLP header view usage with safe decoding

Using the view will panic with invalid RLP. Here we use Rlp decoding directly which will return a `Result<_, DecoderError>`. While this path currently should not have any invalid RLP - it makes it safer if ever called with invalid RLP from other code paths.

ethcore/src/tests/client.rs

@@ -36,6 +36,7 @@ use views::BlockView;
 use ethkey::KeyPair;
 use transaction::{PendingTransaction, Transaction, Action, Condition};
 use miner::MinerService;
+use rlp::{RlpStream, EMPTY_LIST_RLP};
 use tempdir::TempDir;
 
 #[test]
@@ -111,6 +112,25 @@ fn imports_good_block() {
 	assert!(!block.into_inner().is_empty());
 }
 
+#[test]
+fn fails_to_import_block_with_invalid_rlp() {
+	use error::{BlockImportError, BlockImportErrorKind};
+
+	let client = generate_dummy_client(6);
+	let mut rlp = RlpStream::new_list(3);
+	rlp.append_raw(&EMPTY_LIST_RLP, 1); // empty header
+	rlp.append_raw(&EMPTY_LIST_RLP, 1);
+	rlp.append_raw(&EMPTY_LIST_RLP, 1);
+	let invalid_header_block = rlp.out();
+
+	match client.import_block(invalid_header_block) {
+		Err(BlockImportError(BlockImportErrorKind::Decoder(_), _)) => (), // all good
+		Err(_) => panic!("Should fail with a decoder error"),
+		Ok(_) => panic!("Should not import block with invalid header"),
+	}
+}
+
+
 #[test]
 fn query_none_block() {
 	let tempdir = TempDir::new("").unwrap();