internal/ethapi: fix tx.from in eth_simulateV1 (#31480)

Issue statement: when user requests eth_simulateV1 to return full
transaction objects, these objects always had an empty `from` field. The
reason is we lose the sender when translation the message into a
types.Transaction which is then later on serialized.

I did think of an alternative but opted to keep with this approach as it
keeps complexity at the edge. The alternative would be to pass down a
signer object to RPCMarshal* methods and define a custom signer which
keeps the senders in its state and doesn't attempt the signature
recovery.

internal/ethapi/api_test.go

@@ -2488,6 +2488,77 @@ func TestSimulateV1ChainLinkage(t *testing.T) {
 	require.Equal(t, block2.Hash().Bytes(), []byte(results[2].Calls[1].ReturnValue), "returned blockhash for block2 does not match")
 }
 
+func TestSimulateV1TxSender(t *testing.T) {
+	var (
+		sender    = common.Address{0xaa, 0xaa}
+		sender2   = common.Address{0xaa, 0xab}
+		sender3   = common.Address{0xaa, 0xac}
+		recipient = common.Address{0xbb, 0xbb}
+		gspec     = &core.Genesis{
+			Config: params.MergedTestChainConfig,
+			Alloc: types.GenesisAlloc{
+				sender:  {Balance: big.NewInt(params.Ether)},
+				sender2: {Balance: big.NewInt(params.Ether)},
+				sender3: {Balance: big.NewInt(params.Ether)},
+			},
+		}
+		ctx = context.Background()
+	)
+	backend := newTestBackend(t, 0, gspec, beacon.New(ethash.NewFaker()), func(i int, b *core.BlockGen) {})
+	stateDB, baseHeader, err := backend.StateAndHeaderByNumberOrHash(ctx, rpc.BlockNumberOrHashWithNumber(rpc.LatestBlockNumber))
+	if err != nil {
+		t.Fatalf("failed to get state and header: %v", err)
+	}
+
+	sim := &simulator{
+		b:              backend,
+		state:          stateDB,
+		base:           baseHeader,
+		chainConfig:    backend.ChainConfig(),
+		gp:             new(core.GasPool).AddGas(math.MaxUint64),
+		traceTransfers: false,
+		validate:       false,
+		fullTx:         true,
+	}
+
+	results, err := sim.execute(ctx, []simBlock{
+		{Calls: []TransactionArgs{
+			{From: &sender, To: &recipient, Value: (*hexutil.Big)(big.NewInt(1000))},
+			{From: &sender2, To: &recipient, Value: (*hexutil.Big)(big.NewInt(2000))},
+			{From: &sender3, To: &recipient, Value: (*hexutil.Big)(big.NewInt(3000))},
+		}},
+		{Calls: []TransactionArgs{
+			{From: &sender2, To: &recipient, Value: (*hexutil.Big)(big.NewInt(4000))},
+		}},
+	})
+	if err != nil {
+		t.Fatalf("simulation execution failed: %v", err)
+	}
+	require.Len(t, results, 2, "expected 2 simulated blocks")
+	require.Len(t, results[0].Block.Transactions(), 3, "expected 3 transaction in simulated block")
+	require.Len(t, results[1].Block.Transactions(), 1, "expected 1 transaction in 2nd simulated block")
+	enc, err := json.Marshal(results)
+	if err != nil {
+		t.Fatalf("failed to marshal results: %v", err)
+	}
+	type resultType struct {
+		Transactions []struct {
+			From common.Address `json:"from"`
+		}
+	}
+	var summary []resultType
+	if err := json.Unmarshal(enc, &summary); err != nil {
+		t.Fatalf("failed to unmarshal results: %v", err)
+	}
+	require.Len(t, summary, 2, "expected 2 simulated blocks")
+	require.Len(t, summary[0].Transactions, 3, "expected 3 transaction in simulated block")
+	require.Equal(t, sender, summary[0].Transactions[0].From, "sender address mismatch")
+	require.Equal(t, sender2, summary[0].Transactions[1].From, "sender address mismatch")
+	require.Equal(t, sender3, summary[0].Transactions[2].From, "sender address mismatch")
+	require.Len(t, summary[1].Transactions, 1, "expected 1 transaction in simulated block")
+	require.Equal(t, sender2, summary[1].Transactions[0].From, "sender address mismatch")
+}
+
 func TestSignTransaction(t *testing.T) {
 	t.Parallel()
 	// Initialize test accounts

internal/ethapi/simulate.go

@@ -78,11 +78,25 @@ type simBlockResult struct {
 	chainConfig *params.ChainConfig
 	Block       *types.Block
 	Calls       []simCallResult
+	// senders is a map of transaction hashes to their senders.
+	senders map[common.Hash]common.Address
 }
 
 func (r *simBlockResult) MarshalJSON() ([]byte, error) {
 	blockData := RPCMarshalBlock(r.Block, true, r.fullTx, r.chainConfig)
 	blockData["calls"] = r.Calls
+	// Set tx sender if user requested full tx objects.
+	if r.fullTx {
+		if raw, ok := blockData["transactions"].([]any); ok {
+			for _, tx := range raw {
+				if tx, ok := tx.(*RPCTransaction); ok {
+					tx.From = r.senders[tx.Hash]
+				} else {
+					return nil, errors.New("simulated transaction result has invalid type")
+				}
+			}
+		}
+	}
 	return json.Marshal(blockData)
 }
 
@@ -181,18 +195,18 @@ func (sim *simulator) execute(ctx context.Context, blocks []simBlock) ([]*simBlo
 		parent  = sim.base
 	)
 	for bi, block := range blocks {
-		result, callResults, err := sim.processBlock(ctx, &block, headers[bi], parent, headers[:bi], timeout)
+		result, callResults, senders, err := sim.processBlock(ctx, &block, headers[bi], parent, headers[:bi], timeout)
 		if err != nil {
 			return nil, err
 		}
 		headers[bi] = result.Header()
-		results[bi] = &simBlockResult{fullTx: sim.fullTx, chainConfig: sim.chainConfig, Block: result, Calls: callResults}
+		results[bi] = &simBlockResult{fullTx: sim.fullTx, chainConfig: sim.chainConfig, Block: result, Calls: callResults, senders: senders}
 		parent = result.Header()
 	}
 	return results, nil
 }
 
-func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header, parent *types.Header, headers []*types.Header, timeout time.Duration) (*types.Block, []simCallResult, error) {
+func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header, parent *types.Header, headers []*types.Header, timeout time.Duration) (*types.Block, []simCallResult, map[common.Hash]common.Address, error) {
 	// Set header fields that depend only on parent block.
 	// Parent hash is needed for evm.GetHashFn to work.
 	header.ParentHash = parent.Hash()
@@ -222,7 +236,7 @@ func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header,
 	precompiles := sim.activePrecompiles(sim.base)
 	// State overrides are applied prior to execution of a block
 	if err := block.StateOverrides.Apply(sim.state, precompiles); err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 	var (
 		gasUsed, blobGasUsed uint64
@@ -235,6 +249,10 @@ func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header,
 			NoBaseFee: !sim.validate,
 			Tracer:    tracer.Hooks(),
 		}
+		// senders is a map of transaction hashes to their senders.
+		// Transaction objects contain only the signature, and we lose track
+		// of the sender when translating the arguments into a transaction object.
+		senders = make(map[common.Hash]common.Address)
 	)
 	tracingStateDB := vm.StateDB(sim.state)
 	if hooks := tracer.Hooks(); hooks != nil {
@@ -255,16 +273,17 @@ func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header,
 	var allLogs []*types.Log
 	for i, call := range block.Calls {
 		if err := ctx.Err(); err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 		if err := sim.sanitizeCall(&call, sim.state, header, blockContext, &gasUsed); err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 		var (
 			tx     = call.ToTransaction(types.DynamicFeeTxType)
 			txHash = tx.Hash()
 		)
 		txes[i] = tx
+		senders[txHash] = call.from()
 		tracer.reset(txHash, uint(i))
 		sim.state.SetTxContext(txHash, i)
 		// EoA check is always skipped, even in validation mode.
@@ -272,7 +291,7 @@ func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header,
 		result, err := applyMessageWithEVM(ctx, evm, msg, timeout, sim.gp)
 		if err != nil {
 			txErr := txValidationError(err)
-			return nil, nil, txErr
+			return nil, nil, nil, txErr
 		}
 		// Update the state with pending changes.
 		var root []byte
@@ -311,15 +330,15 @@ func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header,
 		requests = [][]byte{}
 		// EIP-6110
 		if err := core.ParseDepositLogs(&requests, allLogs, sim.chainConfig); err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 		// EIP-7002
 		if err := core.ProcessWithdrawalQueue(&requests, evm); err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 		// EIP-7251
 		if err := core.ProcessConsolidationQueue(&requests, evm); err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 	}
 	if requests != nil {
@@ -330,10 +349,10 @@ func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header,
 	chainHeadReader := &simChainHeadReader{ctx, sim.b}
 	b, err := sim.b.Engine().FinalizeAndAssemble(chainHeadReader, header, sim.state, blockBody, receipts)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 	repairLogs(callResults, b.Hash())
-	return b, callResults, nil
+	return b, callResults, senders, nil
 }
 
 // repairLogs updates the block hash in the logs present in the result of