Fix block body encoding (#598)

why:
  List wrapper was missing in `append()` mixin.

eth/common/eth_types_rlp.nim

@@ -358,10 +358,11 @@ proc rlpHash*[T](v: T): Hash256 =
 func blockHash*(h: BlockHeader): KeccakHash {.inline.} = rlpHash(h)
 
 proc append*(w: var RlpWriter, b: BlockBody) =
+  w.startList 2 + b.withdrawals.isSome.ord
   w.append(b.transactions)
   w.append(b.uncles)
   if b.withdrawals.isSome:
-    w.append(b.withdrawals.get)
+    w.append(b.withdrawals.unsafeGet)
 
 # Is there a better way of doing this? We have tests that call
 # rlp.readRecordType(BlockBody, false), so I overrode

tests/rlp/test_api_usage.nim

@@ -4,12 +4,38 @@ import
   std/[math, strutils],
   unittest2,
   stew/byteutils,
-  ../../eth/rlp
+  ../../eth/[common, rlp]
 
 proc q(s: string): string = "\"" & s & "\""
 proc i(s: string): string = s.replace(" ").replace("\n")
 proc inspectMatch(r: Rlp, s: string): bool = r.inspect.i == s.i
 
+proc `==`(a,b: ChainId): bool {.borrow.}
+  ## helper for ` test_calcBlockBodyTranscode()`
+
+proc test_blockBodyTranscode() =
+  ## RLP encode/decode a list of `BlockBody` objects. Note that tere is/was a
+  ## problem in `eth/common/eth_types_rlp.append()` for `BlockBody` encoding.
+  let blkSeq = @[
+    BlockBody(
+      transactions: @[
+        Transaction(nonce: 1)]),
+    BlockBody(
+      uncles: @[
+        BlockHeader(nonce: [0x20u8,0,0,0,0,0,0,0])]),
+    BlockBody(),
+    BlockBody(
+      transactions: @[
+        Transaction(nonce: 3),
+        Transaction(nonce: 4)])]
+
+  let trBlkSeq = blkSeq.encode.decode(typeof blkSeq)
+
+  check trBlkSeq.len == blkSeq.len
+  for n in 0 ..< min(trBlkSeq.len, trBlkSeq.len):
+    check (n, trBlkSeq[n]) == (n, blkSeq[n])
+
+
 when (NimMajor, NimMinor, NimPatch) < (1, 4, 0):
   type AssertionDefect = AssertionError
 
@@ -120,6 +146,9 @@ suite "test api usage":
     check(not list.hasData)
     expect AssertionDefect: list.skipElem
 
+  test "encode and decode block body":
+    test_blockBodyTranscode()
+
   test "toBytes":
     let rlp = rlpFromHex("f2cb847f000001827666827666a040ef02798f211da2e8173d37f255be908871ae65060dbb2f77fb29c0421447f4845ab90b50")
     let tok = rlp.listElem(1).toBytes()