eth/tracers: add support for block overrides in debug_traceCall (ethereum#24871)

This PR adds support for block overrides when doing debug_traceCall.

- Previously, debug_traceCall against pending erroneously used a common.Hash{} stateroot when looking up the state, meaning that a totally empty state was used -- so it always failed,
- With this change, we reject executing debug_traceCall against pending.
- And we add ability to override all evm-visible header fields.

Author: holiman

core/evm.go

@@ -89,6 +89,11 @@ func GetHashFn(ref *types.Header, chain ChainContext) func(n uint64) common.Hash
 	var cache []common.Hash
 
 	return func(n uint64) common.Hash {
+		if ref.Number.Uint64() <= n {
+			// This situation can happen if we're doing tracing and using
+			// block overrides.
+			return common.Hash{}
+		}
 		// If there's no hash cache yet, make one
 		if len(cache) == 0 {
 			cache = append(cache, ref.ParentHash)

eth/tracers/api.go

@@ -196,6 +196,7 @@ type TraceCallConfig struct {
 	Timeout        *string
 	Reexec         *uint64
 	StateOverrides *ethapi.StateOverride
+	BlockOverrides *ethapi.BlockOverrides
 }
 
 // StdTraceConfig holds extra parameters to standard-json trace functions.
@@ -823,7 +824,6 @@ func (api *API) TraceTransaction(ctx context.Context, hash common.Hash, config *
 // TraceCall lets you trace a given eth_call. It collects the structured logs
 // created during the execution of EVM if the given transaction was added on
 // top of the provided block and returns them as a JSON object.
-// You can provide -2 as a block number to trace on top of the pending block.
 func (api *API) TraceCall(ctx context.Context, args ethapi.TransactionArgs, blockNrOrHash rpc.BlockNumberOrHash, config *TraceCallConfig) (interface{}, error) {
 	// Try to retrieve the specified block
 	var (
@@ -833,6 +833,14 @@ func (api *API) TraceCall(ctx context.Context, args ethapi.TransactionArgs, bloc
 	if hash, ok := blockNrOrHash.Hash(); ok {
 		block, err = api.blockByHash(ctx, hash)
 	} else if number, ok := blockNrOrHash.Number(); ok {
+		if number == rpc.PendingBlockNumber {
+			// We don't have access to the miner here. For tracing 'future' transactions,
+			// it can be done with block- and state-overrides instead, which offers
+			// more flexibility and stability than trying to trace on 'pending', since
+			// the contents of 'pending' is unstable and probably not a true representation
+			// of what the next actual block is likely to contain.
+			return nil, errors.New("tracing on top of pending is not supported")
+		}
 		block, err = api.blockByNumber(ctx, number)
 	} else {
 		return nil, errors.New("invalid arguments; neither block nor hash specified")
@@ -849,18 +857,19 @@ func (api *API) TraceCall(ctx context.Context, args ethapi.TransactionArgs, bloc
 	if err != nil {
 		return nil, err
 	}
-	// Apply the customized state rules if required.
+	vmctx := core.NewEVMBlockContext(block.Header(), api.chainContext(ctx), nil)
+	// Apply the customization rules if required.
 	if config != nil {
 		if err := config.StateOverrides.Apply(statedb); err != nil {
 			return nil, err
 		}
+		config.BlockOverrides.Apply(&vmctx)
 	}
 	// Execute the trace
 	msg, err := args.ToMessage(api.backend.RPCGasCap(), block.BaseFee())
 	if err != nil {
 		return nil, err
 	}
-	vmctx := core.NewEVMBlockContext(block.Header(), api.chainContext(ctx), nil)
 
 	var traceConfig *TraceConfig
 	if config != nil {

eth/tracers/api_test.go

@@ -202,13 +202,12 @@ func TestTraceCall(t *testing.T) {
 		tx, _ := types.SignTx(types.NewTransaction(uint64(i), accounts[1].addr, big.NewInt(1000), params.TxGas, b.BaseFee(), nil), signer, accounts[0].key)
 		b.AddTx(tx)
 	}))
-
 	var testSuite = []struct {
 		blockNumber rpc.BlockNumber
 		call        ethapi.TransactionArgs
 		config      *TraceCallConfig
 		expectErr   error
-		expect      interface{}
+		expect      string
 	}{
 		// Standard JSON trace upon the genesis, plain transfer.
 		{
@@ -220,12 +219,7 @@ func TestTraceCall(t *testing.T) {
 			},
 			config:    nil,
 			expectErr: nil,
-			expect: &logger.ExecutionResult{
-				Gas:         params.TxGas,
-				Failed:      false,
-				ReturnValue: "",
-				StructLogs:  []logger.StructLogRes{},
-			},
+			expect:    `{"gas":21000,"failed":false,"returnValue":"","structLogs":[]}`,
 		},
 		// Standard JSON trace upon the head, plain transfer.
 		{
@@ -237,12 +231,7 @@ func TestTraceCall(t *testing.T) {
 			},
 			config:    nil,
 			expectErr: nil,
-			expect: &logger.ExecutionResult{
-				Gas:         params.TxGas,
-				Failed:      false,
-				ReturnValue: "",
-				StructLogs:  []logger.StructLogRes{},
-			},
+			expect:    `{"gas":21000,"failed":false,"returnValue":"","structLogs":[]}`,
 		},
 		// Standard JSON trace upon the non-existent block, error expects
 		{
@@ -254,7 +243,7 @@ func TestTraceCall(t *testing.T) {
 			},
 			config:    nil,
 			expectErr: fmt.Errorf("block #%d not found", genBlocks+1),
-			expect:    nil,
+			//expect:    nil,
 		},
 		// Standard JSON trace upon the latest block
 		{
@@ -266,14 +255,9 @@ func TestTraceCall(t *testing.T) {
 			},
 			config:    nil,
 			expectErr: nil,
-			expect: &logger.ExecutionResult{
-				Gas:         params.TxGas,
-				Failed:      false,
-				ReturnValue: "",
-				StructLogs:  []logger.StructLogRes{},
-			},
+			expect:    `{"gas":21000,"failed":false,"returnValue":"","structLogs":[]}`,
 		},
-		// Standard JSON trace upon the pending block
+		// Tracing on 'pending' should fail:
 		{
 			blockNumber: rpc.PendingBlockNumber,
 			call: ethapi.TransactionArgs{
@@ -282,36 +266,48 @@ func TestTraceCall(t *testing.T) {
 				Value: (*hexutil.Big)(big.NewInt(1000)),
 			},
 			config:    nil,
-			expectErr: nil,
-			expect: &logger.ExecutionResult{
-				Gas:         params.TxGas,
-				Failed:      false,
-				ReturnValue: "",
-				StructLogs:  []logger.StructLogRes{},
+			expectErr: errors.New("tracing on top of pending is not supported"),
+		},
+		{
+			blockNumber: rpc.LatestBlockNumber,
+			call: ethapi.TransactionArgs{
+				From:  &accounts[0].addr,
+				Input: &hexutil.Bytes{0x43}, // blocknumber
+			},
+			config: &TraceCallConfig{
+				BlockOverrides: &ethapi.BlockOverrides{Number: (*hexutil.Big)(big.NewInt(0x1337))},
 			},
+			expectErr: nil,
+			expect: ` {"gas":53018,"failed":false,"returnValue":"","structLogs":[
+		{"pc":0,"op":"NUMBER","gas":24946984,"gasCost":2,"depth":1,"stack":[]},
+		{"pc":1,"op":"STOP","gas":24946982,"gasCost":0,"depth":1,"stack":["0x1337"]}]}`,
 		},
 	}
-	for _, testspec := range testSuite {
+	for i, testspec := range testSuite {
 		result, err := api.TraceCall(context.Background(), testspec.call, rpc.BlockNumberOrHash{BlockNumber: &testspec.blockNumber}, testspec.config)
 		if testspec.expectErr != nil {
 			if err == nil {
-				t.Errorf("Expect error %v, get nothing", testspec.expectErr)
+				t.Errorf("test %d: expect error %v, got nothing", i, testspec.expectErr)
 				continue
 			}
 			if !reflect.DeepEqual(err, testspec.expectErr) {
-				t.Errorf("Error mismatch, want %v, get %v", testspec.expectErr, err)
+				t.Errorf("test %d: error mismatch, want %v, git %v", i, testspec.expectErr, err)
 			}
 		} else {
 			if err != nil {
-				t.Errorf("Expect no error, get %v", err)
+				t.Errorf("test %d: expect no error, got %v", i, err)
 				continue
 			}
 			var have *logger.ExecutionResult
 			if err := json.Unmarshal(result.(json.RawMessage), &have); err != nil {
-				t.Errorf("failed to unmarshal result %v", err)
+				t.Errorf("test %d: failed to unmarshal result %v", i, err)
+			}
+			var want *logger.ExecutionResult
+			if err := json.Unmarshal([]byte(testspec.expect), &want); err != nil {
+				t.Errorf("test %d: failed to unmarshal result %v", i, err)
 			}
-			if !reflect.DeepEqual(have, testspec.expect) {
-				t.Errorf("Result mismatch, want %v, get %v", testspec.expect, have)
+			if !reflect.DeepEqual(have, want) {
+				t.Errorf("test %d: result mismatch, want %v, got %v", i, testspec.expect, string(result.(json.RawMessage)))
 			}
 		}
 	}
@@ -452,7 +448,7 @@ func TestTracingWithOverrides(t *testing.T) {
 	type res struct {
 		Gas         int
 		Failed      bool
-		returnValue string
+		ReturnValue string
 	}
 	var testSuite = []struct {
 		blockNumber rpc.BlockNumber
@@ -463,7 +459,7 @@ func TestTracingWithOverrides(t *testing.T) {
 	}{
 		// Call which can only succeed if state is state overridden
 		{
-			blockNumber: rpc.PendingBlockNumber,
+			blockNumber: rpc.LatestBlockNumber,
 			call: ethapi.TransactionArgs{
 				From:  &randomAccounts[0].addr,
 				To:    &randomAccounts[1].addr,
@@ -478,7 +474,7 @@ func TestTracingWithOverrides(t *testing.T) {
 		},
 		// Invalid call without state overriding
 		{
-			blockNumber: rpc.PendingBlockNumber,
+			blockNumber: rpc.LatestBlockNumber,
 			call: ethapi.TransactionArgs{
 				From:  &randomAccounts[0].addr,
 				To:    &randomAccounts[1].addr,
@@ -504,7 +500,7 @@ func TestTracingWithOverrides(t *testing.T) {
 		//      }
 		//  }
 		{
-			blockNumber: rpc.PendingBlockNumber,
+			blockNumber: rpc.LatestBlockNumber,
 			call: ethapi.TransactionArgs{
 				From: &randomAccounts[0].addr,
 				To:   &randomAccounts[2].addr,
@@ -521,6 +517,39 @@ func TestTracingWithOverrides(t *testing.T) {
 			},
 			want: `{"gas":23347,"failed":false,"returnValue":"000000000000000000000000000000000000000000000000000000000000007b"}`,
 		},
+		{ // Override blocknumber
+			blockNumber: rpc.LatestBlockNumber,
+			call: ethapi.TransactionArgs{
+				From: &accounts[0].addr,
+				// BLOCKNUMBER PUSH1 MSTORE
+				Input: newRPCBytes(common.Hex2Bytes("4360005260206000f3")),
+				//&hexutil.Bytes{0x43}, // blocknumber
+			},
+			config: &TraceCallConfig{
+				BlockOverrides: &ethapi.BlockOverrides{Number: (*hexutil.Big)(big.NewInt(0x1337))},
+			},
+			want: `{"gas":59537,"failed":false,"returnValue":"0000000000000000000000000000000000000000000000000000000000001337"}`,
+		},
+		{ // Override blocknumber, and query a blockhash
+			blockNumber: rpc.LatestBlockNumber,
+			call: ethapi.TransactionArgs{
+				From: &accounts[0].addr,
+				Input: &hexutil.Bytes{
+					0x60, 0x00, 0x40, // BLOCKHASH(0)
+					0x60, 0x00, 0x52, // STORE memory offset 0
+					0x61, 0x13, 0x36, 0x40, // BLOCKHASH(0x1336)
+					0x60, 0x20, 0x52, // STORE memory offset 32
+					0x61, 0x13, 0x37, 0x40, // BLOCKHASH(0x1337)
+					0x60, 0x40, 0x52, // STORE memory offset 64
+					0x60, 0x60, 0x60, 0x00, 0xf3, // RETURN (0-96)
+
+				}, // blocknumber
+			},
+			config: &TraceCallConfig{
+				BlockOverrides: &ethapi.BlockOverrides{Number: (*hexutil.Big)(big.NewInt(0x1337))},
+			},
+			want: `{"gas":72666,"failed":false,"returnValue":"000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"}`,
+		},
 	}
 	for i, tc := range testSuite {
 		result, err := api.TraceCall(context.Background(), tc.call, rpc.BlockNumberOrHash{BlockNumber: &tc.blockNumber}, tc.config)

internal/ethapi/api.go

@@ -888,6 +888,41 @@ func (diff *StateOverride) Apply(state *state.StateDB) error {
 	return nil
 }
 
+// BlockOverrides is a set of header fields to override.
+type BlockOverrides struct {
+	Number     *hexutil.Big
+	Difficulty *hexutil.Big
+	Time       *hexutil.Big
+	GasLimit   *hexutil.Uint64
+	Coinbase   *common.Address
+	Random     *common.Hash
+}
+
+// Apply overrides the given header fields into the given block context.
+func (diff *BlockOverrides) Apply(blockCtx *vm.BlockContext) {
+	if diff == nil {
+		return
+	}
+	if diff.Number != nil {
+		blockCtx.BlockNumber = diff.Number.ToInt()
+	}
+	if diff.Difficulty != nil {
+		blockCtx.Difficulty = diff.Difficulty.ToInt()
+	}
+	if diff.Time != nil {
+		blockCtx.Time = diff.Time.ToInt()
+	}
+	if diff.GasLimit != nil {
+		blockCtx.GasLimit = uint64(*diff.GasLimit)
+	}
+	if diff.Coinbase != nil {
+		blockCtx.Coinbase = *diff.Coinbase
+	}
+	if diff.Random != nil {
+		blockCtx.Random = diff.Random
+	}
+}
+
 func DoCall(ctx context.Context, b Backend, args TransactionArgs, blockNrOrHash rpc.BlockNumberOrHash, overrides *StateOverride, timeout time.Duration, globalGasCap uint64) (*core.ExecutionResult, error) {
 	defer func(start time.Time) { log.Debug("Executing EVM call finished", "runtime", time.Since(start)) }(time.Now())