cmd/evm: add difficulty calculation to t8n tool (ethereum#23353)

This PR adds functionality to the evm t8n to calculate ethash difficulty. If the caller does not provide a currentDifficulty, but instead provides the parentTimestamp (well, semi-optional, will default to 0 if not given), and parentDifficulty, we can calculate it for him.

The caller can also provide a parentUncleHash. In most, but not all cases, the parent uncle hash also affects the formula. If no such hash is provided (or, if the empty all-zero hash is provided), it's assumed that there were no uncles.

cmd/evm/internal/t8ntool/execution.go

@@ -23,6 +23,7 @@ import (
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/math"
+	"github.com/ethereum/go-ethereum/consensus/ethash"
 	"github.com/ethereum/go-ethereum/consensus/misc"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/rawdb"
@@ -46,13 +47,14 @@ type Prestate struct {
 // ExecutionResult contains the execution status after running a state test, any
 // error that might have occurred and a dump of the final state if requested.
 type ExecutionResult struct {
-	StateRoot   common.Hash    `json:"stateRoot"`
-	TxRoot      common.Hash    `json:"txRoot"`
-	ReceiptRoot common.Hash    `json:"receiptRoot"`
-	LogsHash    common.Hash    `json:"logsHash"`
-	Bloom       types.Bloom    `json:"logsBloom"        gencodec:"required"`
-	Receipts    types.Receipts `json:"receipts"`
-	Rejected    []*rejectedTx  `json:"rejected,omitempty"`
+	StateRoot   common.Hash           `json:"stateRoot"`
+	TxRoot      common.Hash           `json:"txRoot"`
+	ReceiptRoot common.Hash           `json:"receiptRoot"`
+	LogsHash    common.Hash           `json:"logsHash"`
+	Bloom       types.Bloom           `json:"logsBloom"        gencodec:"required"`
+	Receipts    types.Receipts        `json:"receipts"`
+	Rejected    []*rejectedTx         `json:"rejected,omitempty"`
+	Difficulty  *math.HexOrDecimal256 `json:"currentDifficulty" gencodec:"required"`
 }
 
 type ommer struct {
@@ -62,23 +64,28 @@ type ommer struct {
 
 //go:generate gencodec -type stEnv -field-override stEnvMarshaling -out gen_stenv.go
 type stEnv struct {
-	Coinbase    common.Address                      `json:"currentCoinbase"   gencodec:"required"`
-	Difficulty  *big.Int                            `json:"currentDifficulty" gencodec:"required"`
-	GasLimit    uint64                              `json:"currentGasLimit"   gencodec:"required"`
-	Number      uint64                              `json:"currentNumber"     gencodec:"required"`
-	Timestamp   uint64                              `json:"currentTimestamp"  gencodec:"required"`
-	BlockHashes map[math.HexOrDecimal64]common.Hash `json:"blockHashes,omitempty"`
-	Ommers      []ommer                             `json:"ommers,omitempty"`
-	BaseFee     *big.Int                            `json:"currentBaseFee,omitempty"`
+	Coinbase         common.Address                      `json:"currentCoinbase"   gencodec:"required"`
+	Difficulty       *big.Int                            `json:"currentDifficulty"`
+	ParentDifficulty *big.Int                            `json:"parentDifficulty"`
+	GasLimit         uint64                              `json:"currentGasLimit"   gencodec:"required"`
+	Number           uint64                              `json:"currentNumber"     gencodec:"required"`
+	Timestamp        uint64                              `json:"currentTimestamp"  gencodec:"required"`
+	ParentTimestamp  uint64                              `json:"parentTimestamp,omitempty"`
+	BlockHashes      map[math.HexOrDecimal64]common.Hash `json:"blockHashes,omitempty"`
+	Ommers           []ommer                             `json:"ommers,omitempty"`
+	BaseFee          *big.Int                            `json:"currentBaseFee,omitempty"`
+	ParentUncleHash  common.Hash                         `json:"parentUncleHash"`
 }
 
 type stEnvMarshaling struct {
-	Coinbase   common.UnprefixedAddress
-	Difficulty *math.HexOrDecimal256
-	GasLimit   math.HexOrDecimal64
-	Number     math.HexOrDecimal64
-	Timestamp  math.HexOrDecimal64
-	BaseFee    *math.HexOrDecimal256
+	Coinbase         common.UnprefixedAddress
+	Difficulty       *math.HexOrDecimal256
+	ParentDifficulty *math.HexOrDecimal256
+	GasLimit         math.HexOrDecimal64
+	Number           math.HexOrDecimal64
+	Timestamp        math.HexOrDecimal64
+	ParentTimestamp  math.HexOrDecimal64
+	BaseFee          *math.HexOrDecimal256
 }
 
 type rejectedTx struct {
@@ -247,6 +254,7 @@ func (pre *Prestate) Apply(vmConfig vm.Config, chainConfig *params.ChainConfig,
 		LogsHash:    rlpHash(statedb.Logs()),
 		Receipts:    receipts,
 		Rejected:    rejectedTxs,
+		Difficulty:  (*math.HexOrDecimal256)(vmContext.Difficulty),
 	}
 	return statedb, execRs, nil
 }
@@ -274,3 +282,23 @@ func rlpHash(x interface{}) (h common.Hash) {
 	hw.Sum(h[:0])
 	return h
 }
+
+// calcDifficulty is based on ethash.CalcDifficulty. This method is used in case
+// the caller does not provide an explicit difficulty, but instead provides only
+// parent timestamp + difficulty.
+// Note: this method only works for ethash engine.
+func calcDifficulty(config *params.ChainConfig, number, currentTime, parentTime uint64,
+	parentDifficulty *big.Int, parentUncleHash common.Hash) *big.Int {
+	uncleHash := parentUncleHash
+	if uncleHash == (common.Hash{}) {
+		uncleHash = types.EmptyUncleHash
+	}
+	parent := &types.Header{
+		ParentHash: common.Hash{},
+		UncleHash:  uncleHash,
+		Difficulty: parentDifficulty,
+		Number:     new(big.Int).SetUint64(number - 1),
+		Time:       parentTime,
+	}
+	return ethash.CalcDifficulty(config, currentTime, parent)
+}

cmd/evm/internal/t8ntool/transition.go

@@ -252,6 +252,20 @@ func Main(ctx *cli.Context) error {
 			return NewError(ErrorVMConfig, errors.New("EIP-1559 config but missing 'currentBaseFee' in env section"))
 		}
 	}
+	if env := prestate.Env; env.Difficulty == nil {
+		// If difficulty was not provided by caller, we need to calculate it.
+		switch {
+		case env.ParentDifficulty == nil:
+			return NewError(ErrorVMConfig, errors.New("currentDifficulty was not provided, and cannot be calculated due to missing parentDifficulty"))
+		case env.Number == 0:
+			return NewError(ErrorVMConfig, errors.New("currentDifficulty needs to be provided for block number 0"))
+		case env.Timestamp <= env.ParentTimestamp:
+			return NewError(ErrorVMConfig, fmt.Errorf("currentDifficulty cannot be calculated -- currentTime (%d) needs to be after parent time (%d)",
+				env.Timestamp, env.ParentTimestamp))
+		}
+		prestate.Env.Difficulty = calcDifficulty(chainConfig, env.Number, env.Timestamp,
+			env.ParentTimestamp, env.ParentDifficulty, env.ParentUncleHash)
+	}
 	// Run the test and aggregate the result
 	s, result, err := prestate.Apply(vmConfig, chainConfig, txs, ctx.Int64(RewardFlag.Name), getTracer)
 	if err != nil {

cmd/evm/testdata/14/alloc.json

@@ -0,0 +1,12 @@
+{
+  "a94f5374fce5edbc8e2a8697c15331677e6ebf0b": {
+    "balance": "0x5ffd4878be161d74",
+    "code": "0x",
+    "nonce": "0xac",
+    "storage": {}
+  },
+  "0x8a8eafb1cf62bfbeb1741769dae1a9dd47996192":{
+    "balance": "0xfeedbead",
+    "nonce" : "0x00"
+  }
+}

cmd/evm/testdata/14/env.json

@@ -0,0 +1,9 @@
+{
+  "currentCoinbase": "0xc94f5374fce5edbc8e2a8697c15331677e6ebf0b",
+  "currentGasLimit": "0x750a163df65e8a",
+  "currentBaseFee": "0x500",
+  "currentNumber": "12800000",
+  "currentTimestamp": "10015",
+  "parentTimestamp" : "99999",
+  "parentDifficulty" : "0x2000000000000"
+}

cmd/evm/testdata/14/env.uncles.json

@@ -0,0 +1,10 @@
+{
+  "currentCoinbase": "0xc94f5374fce5edbc8e2a8697c15331677e6ebf0b",
+  "currentGasLimit": "0x750a163df65e8a",
+  "currentBaseFee": "0x500",
+  "currentNumber": "12800000",
+  "currentTimestamp": "10035",
+  "parentTimestamp" : "99999",
+  "parentDifficulty" : "0x2000000000000",
+  "parentUncleHash" : "0x000000000000000000000000000000000000000000000000000000000000beef"
+}

cmd/evm/testdata/14/readme.md

@@ -0,0 +1,41 @@
+## Difficulty calculation
+
+This test shows how the `evm t8n` can be used to calculate the (ethash) difficulty, if none is provided by the caller. 
+
+Calculating it (with an empty set of txs) using `London` rules (and no provided unclehash for the parent block):
+```
+[user@work evm]$ ./evm t8n --input.alloc=./testdata/14/alloc.json --input.txs=./testdata/14/txs.json --input.env=./testdata/14/env.json --output.result=stdout --state.fork=London
+INFO [08-08|17:35:46.876] Trie dumping started                     root=6f0588..7f4bdc
+INFO [08-08|17:35:46.876] Trie dumping complete                    accounts=2 elapsed="89.313µs"
+INFO [08-08|17:35:46.877] Wrote file                               file=alloc.json
+{
+ "result": {
+  "stateRoot": "0x6f058887ca01549716789c380ede95aecc510e6d1fdc4dbf67d053c7c07f4bdc",
+  "txRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
+  "receiptRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
+  "logsHash": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
+  "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+  "receipts": [],
+  "currentDifficulty": 3311729559732224
+ }
+}
+```
+Same thing, but this time providing a non-empty (and non-`emptyKeccak`) unclehash, which leads to a slightly different result:
+```
+[user@work evm]$ ./evm t8n --input.alloc=./testdata/14/alloc.json --input.txs=./testdata/14/txs.json --input.env=./testdata/14/env.uncles.json --output.result=stdout --state.fork=London
+INFO [08-08|17:35:49.232] Trie dumping started                     root=6f0588..7f4bdc
+INFO [08-08|17:35:49.232] Trie dumping complete                    accounts=2 elapsed="83.069µs"
+INFO [08-08|17:35:49.233] Wrote file                               file=alloc.json
+{
+ "result": {
+  "stateRoot": "0x6f058887ca01549716789c380ede95aecc510e6d1fdc4dbf67d053c7c07f4bdc",
+  "txRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
+  "receiptRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
+  "logsHash": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
+  "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+  "receipts": [],
+  "currentDifficulty": 3311179803918336
+ }
+}
+```
+

cmd/evm/testdata/14/txs.json

@@ -0,0 +1 @@
+[]