extend `BlockHeader` for EIP-4844 (#570)

Extends `BlockHeader` with `excessDataGas` according to EIP-4844
(used by Nimbus-CL in empty block prod fallback).

eth/common/eth_types.nim

@@ -121,6 +121,7 @@ type
     # `baseFee` is the get/set of `fee`
     fee*:             Option[UInt256]   # EIP-1559
     withdrawalsRoot*: Option[Hash256]   # EIP-4895
+    excessDataGas*:   Option[GasInt]    # EIP-4844
 
   BlockBody* = object
     transactions*:  seq[Transaction]

eth/common/eth_types_rlp.nim

@@ -318,25 +318,28 @@ proc append*(w: var RlpWriter, h: BlockHeader) =
   var len = 15
   if h.fee.isSome: inc len
   if h.withdrawalsRoot.isSome: inc len
+  if h.excessDataGas.isSome: inc len
   w.startList(len)
   for k, v in fieldPairs(h):
-    when k notin ["fee", "withdrawalsRoot"]:
+    when v isnot Option:
       w.append(v)
   if h.fee.isSome:
     w.append(h.fee.get())
   if h.withdrawalsRoot.isSome:
     w.append(h.withdrawalsRoot.get())
+  if h.excessDataGas.isSome:
+    w.append(h.excessDataGas.get())
 
 proc read*(rlp: var Rlp, T: type BlockHeader): T =
   let len = rlp.listLen
 
-  if len notin {15, 16, 17}:
+  if len notin {15, 16, 17, 18}:
     raise newException(UnsupportedRlpError,
-      "BlockHeader elems should be 15, 16, or 17 got " & $len)
+      "BlockHeader elems should be 15, 16, 17, or 18 got " & $len)
 
   rlp.tryEnterList()
   for k, v in fieldPairs(result):
-    when k notin ["fee", "withdrawalsRoot"]:
+    when v isnot Option:
       v = rlp.read(type v)
 
   if len >= 16:
@@ -345,6 +348,9 @@ proc read*(rlp: var Rlp, T: type BlockHeader): T =
   if len >= 17:
     # EIP-4895
     result.withdrawalsRoot = some rlp.read(Hash256)
+  if len >= 18:
+    # EIP-4844
+    result.excessDataGas = some rlp.read(GasInt)
 
 proc rlpHash*[T](v: T): Hash256 =
   keccakHash(rlp.encode(v))

tests/rlp/test_common.nim

@@ -97,11 +97,27 @@ proc suite2() =
     for i in 0..<10:
       loadFile(i)
 
-    test "rlp roundtrip EIP1559":
+    test "rlp roundtrip EIP1559 / EIP4895 / EIP4844":
+      proc doTest(h: BlockHeader) =
+        let xy = rlp.encode(h)
+        let hh = rlp.decode(xy, BlockHeader)
+        check h == hh
+
       var h: BlockHeader
-      let xy = rlp.encode(h)
-      let hh = rlp.decode(xy, BlockHeader)
-      check h == hh
+      doTest h
+
+      # EIP-1559
+      h.fee = some 1234.u256
+      doTest h
+
+      # EIP-4895
+      h.withdrawalsRoot = some Hash256.fromHex(
+        "0x7a64245f7f95164f6176d90bd4903dbdd3e5433d555dd1385e81787f9672c588")
+      doTest h
+
+      # EIP-4844
+      h.excessDataGas = some GasInt(1337)
+      doTest h
 
 suite1()
 suite2()