core, core/vm: implemented a generic environment (#3348)

Environment is now a struct (not an interface). This
reduces a lot of tech-debt throughout the codebase where a virtual
machine environment had to be implemented in order to test or run it.

The new environment is suitable to be used en the json tests, core
consensus and light client.

1 files changed, 73 insertions, 0 deletions

diff --git a/core/evm.go b/core/evm.go
new file mode 100644
index 000000000..6a5713075
--- /dev/null
+++ b/core/evm.go
@@ -0,0 +1,73 @@
+// Copyright 2014 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 core
+
+import (
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/core/vm"
+)
+
+// BlockFetcher retrieves headers by their hash
+type HeaderFetcher interface {
+	// GetHeader returns the hash corresponding to their hash
+	GetHeader(common.Hash, uint64) *types.Header
+}
+
+// NewEVMContext creates a new context for use in the EVM.
+func NewEVMContext(msg Message, header *types.Header, chain HeaderFetcher) vm.Context {
+	return vm.Context{
+		CanTransfer: CanTransfer,
+		Transfer:    Transfer,
+		GetHash:     GetHashFn(header, chain),
+
+		Origin:      msg.From(),
+		Coinbase:    header.Coinbase,
+		BlockNumber: new(big.Int).Set(header.Number),
+		Time:        new(big.Int).Set(header.Time),
+		Difficulty:  new(big.Int).Set(header.Difficulty),
+		GasLimit:    new(big.Int).Set(header.GasLimit),
+		GasPrice:    new(big.Int).Set(msg.GasPrice()),
+	}
+}
+
+// GetHashFn returns a GetHashFunc which retrieves header hashes by number
+func GetHashFn(ref *types.Header, chain HeaderFetcher) func(n uint64) common.Hash {
+	return func(n uint64) common.Hash {
+		for header := chain.GetHeader(ref.ParentHash, ref.Number.Uint64()-1); header != nil; header = chain.GetHeader(header.ParentHash, header.Number.Uint64()-1) {
+			if header.Number.Uint64() == n {
+				return header.Hash()
+			}
+		}
+
+		return common.Hash{}
+	}
+}
+
+// CanTransfer checks wether there are enough funds in the address' account to make a transfer.
+// This does not take the necessary gas in to account to make the transfer valid.
+func CanTransfer(db vm.StateDB, addr common.Address, amount *big.Int) bool {
+	return db.GetBalance(addr).Cmp(amount) >= 0
+}
+
+// Transfer subtracts amount from sender and adds amount to recipient using the given Db
+func Transfer(db vm.StateDB, sender, recipient common.Address, amount *big.Int) {
+	db.SubBalance(sender, amount)
+	db.AddBalance(recipient, amount)
+}