core/types: improve comments in new EIP-2718 code (#22402)

Responding to these comments:

    https://github.com/ethereum/go-ethereum/pull/21502/files#r579010962
    https://github.com/ethereum/go-ethereum/pull/21502/files#r579021565
    https://github.com/ethereum/go-ethereum/pull/21502/files#r579023510
    https://github.com/ethereum/go-ethereum/pull/21502/files#r578983734

core/types/hashing.go

@@ -36,6 +36,7 @@ var encodeBufferPool = sync.Pool{
 	New: func() interface{} { return new(bytes.Buffer) },
 }
 
+// rlpHash encodes x and hashes the encoded bytes.
 func rlpHash(x interface{}) (h common.Hash) {
 	sha := hasherPool.Get().(crypto.KeccakState)
 	defer hasherPool.Put(sha)
@@ -45,8 +46,8 @@ func rlpHash(x interface{}) (h common.Hash) {
 	return h
 }
 
-// prefixedRlpHash writes the prefix into the hasher before rlp-encoding the
-// given interface. It's used for typed transactions.
+// prefixedRlpHash writes the prefix into the hasher before rlp-encoding x.
+// It's used for typed transactions.
 func prefixedRlpHash(prefix byte, x interface{}) (h common.Hash) {
 	sha := hasherPool.Get().(crypto.KeccakState)
 	defer hasherPool.Put(sha)

core/types/hashing_test.go

@@ -1,3 +1,19 @@
+// Copyright 2021 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
 package types_test
 
 import (

core/types/receipt.go

@@ -38,6 +38,7 @@ var (
 	receiptStatusSuccessfulRLP = []byte{0x01}
 )
 
+// This error is returned when a typed receipt is decoded, but the string is empty.
 var errEmptyTypedReceipt = errors.New("empty typed receipt bytes")
 
 const (

core/types/transaction_signing.go

@@ -207,11 +207,7 @@ func (s eip2930Signer) Sender(tx *Transaction) (common.Address, error) {
 func (s eip2930Signer) SignatureValues(tx *Transaction, sig []byte) (R, S, V *big.Int, err error) {
 	switch txdata := tx.inner.(type) {
 	case *LegacyTx:
-		R, S, V = decodeSignature(sig)
-		if s.chainId.Sign() != 0 {
-			V = big.NewInt(int64(sig[64] + 35))
-			V.Add(V, s.chainIdMul)
-		}
+		return s.EIP155Signer.SignatureValues(tx, sig)
 	case *AccessListTx:
 		// Check that chain ID of tx matches the signer. We also accept ID zero here,
 		// because it indicates that the chain ID was not specified in the tx.