api/bind: Add CallOpts.BlockHash to allow calling contracts at a specific block hash

accounts/abi/bind/backend.go

@@ -36,6 +36,10 @@ var (
 	// on a backend that doesn't implement PendingContractCaller.
 	ErrNoPendingState = errors.New("backend does not support pending state")
 
+	// ErrNoBlockHashState is raised when attempting to perform a block hash action
+	// on a backend that doesn't implement BlockHashContractCaller.
+	ErrNoBlockHashState = errors.New("backend does not support block hash state")
+
 	// ErrNoCodeAfterDeploy is returned by WaitDeployed if contract creation leaves
 	// an empty contract behind.
 	ErrNoCodeAfterDeploy = errors.New("no contract code after deployment")
@@ -64,6 +68,17 @@ type PendingContractCaller interface {
 	PendingCallContract(ctx context.Context, call ethereum.CallMsg) ([]byte, error)
 }
 
+// BlockHashContractCaller defines methods to perform contract calls on a specific block hash.
+// Call will try to discover this interface when access to a block by hash is requested.
+// If the backend does not support the block hash state, Call returns ErrNoBlockHashState.
+type BlockHashContractCaller interface {
+	// CodeAtHash returns the code of the given account in the state at the specified block hash.
+	CodeAtHash(ctx context.Context, contract common.Address, blockHash common.Hash) ([]byte, error)
+
+	// CallContractAtHash executes an Ethereum contract all against the state at the specified block hash.
+	CallContractAtHash(ctx context.Context, call ethereum.CallMsg, blockHash common.Hash) ([]byte, error)
+}
+
 // ContractTransactor defines the methods needed to allow operating with a contract
 // on a write only basis. Besides the transacting method, the remainder are helpers
 // used when the user does not provide some needed values, but rather leaves it up

accounts/abi/bind/backends/simulated.go

@@ -50,6 +50,7 @@ var _ bind.ContractBackend = (*SimulatedBackend)(nil)
 
 var (
 	errBlockNumberUnsupported  = errors.New("simulatedBackend cannot access blocks other than the latest block")
+	errBlockHashUnsupported    = errors.New("simulatedBackend cannot access blocks by hash other than the latest block")
 	errBlockDoesNotExist       = errors.New("block does not exist in blockchain")
 	errTransactionDoesNotExist = errors.New("transaction does not exist")
 )
@@ -105,16 +106,20 @@ func (b *SimulatedBackend) Close() error {
 
 // Commit imports all the pending transactions as a single block and starts a
 // fresh new state.
-func (b *SimulatedBackend) Commit() {
+func (b *SimulatedBackend) Commit() common.Hash {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
 	if _, err := b.blockchain.InsertChain([]*types.Block{b.pendingBlock}, nil); err != nil {
 		panic(err) // This cannot happen unless the simulator is wrong, fail in that case
 	}
+	blockHash := b.pendingBlock.Hash()
+
 	// Using the last inserted block here makes it possible to build on a side
 	// chain after a fork.
 	b.rollback(b.pendingBlock)
+
+	return blockHash
 }
 
 // Rollback aborts all pending transactions, reverting to the last committed state.
@@ -184,6 +189,24 @@ func (b *SimulatedBackend) CodeAt(ctx context.Context, contract common.Address,
 	return stateDB.GetCode(contract), nil
 }
 
+// CodeAtHash returns the code associated with a certain account in the blockchain.
+func (b *SimulatedBackend) CodeAtHash(ctx context.Context, contract common.Address, blockHash common.Hash) ([]byte, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	header, err := b.headerByHash(blockHash)
+	if err != nil {
+		return nil, err
+	}
+
+	stateDB, err := b.blockchain.StateAt(header.Root)
+	if err != nil {
+		return nil, err
+	}
+
+	return stateDB.GetCode(contract), nil
+}
+
 // BalanceAt returns the wei balance of a certain account in the blockchain.
 func (b *SimulatedBackend) BalanceAt(ctx context.Context, contract common.Address, blockNumber *big.Int) (*big.Int, error) {
 	b.mu.Lock()
@@ -302,7 +325,11 @@ func (b *SimulatedBackend) blockByNumber(ctx context.Context, number *big.Int) (
 func (b *SimulatedBackend) HeaderByHash(ctx context.Context, hash common.Hash) (*types.Header, error) {
 	b.mu.Lock()
 	defer b.mu.Unlock()
+	return b.headerByHash(hash)
+}
 
+// headerByHash retrieves a header from the database by hash without Lock.
+func (b *SimulatedBackend) headerByHash(hash common.Hash) (*types.Header, error) {
 	if hash == b.pendingBlock.Hash() {
 		return b.pendingBlock.Header(), nil
 	}
@@ -418,6 +445,22 @@ func (b *SimulatedBackend) CallContract(ctx context.Context, call ethereum.CallM
 	if blockNumber != nil && blockNumber.Cmp(b.blockchain.CurrentBlock().Number()) != 0 {
 		return nil, errBlockNumberUnsupported
 	}
+	return b.callContractAtHead(ctx, call)
+}
+
+// CallContractAtHash executes a contract call on a specific block hash.
+func (b *SimulatedBackend) CallContractAtHash(ctx context.Context, call ethereum.CallMsg, blockHash common.Hash) ([]byte, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	if blockHash != b.blockchain.CurrentBlock().Hash() {
+		return nil, errBlockHashUnsupported
+	}
+	return b.callContractAtHead(ctx, call)
+}
+
+// callContractAtHead executes a contract call against the latest block state.
+func (b *SimulatedBackend) callContractAtHead(ctx context.Context, call ethereum.CallMsg) ([]byte, error) {
 	stateDB, err := b.blockchain.State()
 	if err != nil {
 		return nil, err

accounts/abi/bind/backends/simulated_test.go

@@ -994,6 +994,43 @@ func TestCodeAt(t *testing.T) {
 	}
 }
 
+func TestCodeAtHash(t *testing.T) {
+	testAddr := crypto.PubkeyToAddress(testKey.PublicKey)
+	sim := simTestBackend(testAddr)
+	defer sim.Close()
+	bgCtx := context.Background()
+	code, err := sim.CodeAtHash(bgCtx, testAddr, sim.Blockchain().CurrentHeader().Hash())
+	if err != nil {
+		t.Errorf("could not get code at test addr: %v", err)
+	}
+	if len(code) != 0 {
+		t.Errorf("got code for account that does not have contract code")
+	}
+
+	parsed, err := abi.JSON(strings.NewReader(abiJSON))
+	if err != nil {
+		t.Errorf("could not get code at test addr: %v", err)
+	}
+	auth, _ := bind.NewKeyedTransactorWithChainID(testKey, big.NewInt(1337))
+	contractAddr, tx, contract, err := bind.DeployContract(auth, parsed, common.FromHex(abiBin), sim)
+	if err != nil {
+		t.Errorf("could not deploy contract: %v tx: %v contract: %v", err, tx, contract)
+	}
+
+	blockHash := sim.Commit()
+	code, err = sim.CodeAtHash(bgCtx, contractAddr, blockHash)
+	if err != nil {
+		t.Errorf("could not get code at test addr: %v", err)
+	}
+	if len(code) == 0 {
+		t.Errorf("did not get code for account that has contract code")
+	}
+	// ensure code received equals code deployed
+	if !bytes.Equal(code, common.FromHex(deployedCode)) {
+		t.Errorf("code received did not match expected deployed code:\n expected %v\n actual %v", common.FromHex(deployedCode), code)
+	}
+}
+
 // When receive("X") is called with sender 0x00... and value 1, it produces this tx receipt:
 //   receipt{status=1 cgas=23949 bloom=00000000004000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000800000000000000000000000000000000000040200000000000000000000000000000000001000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000080000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 logs=[log: b6818c8064f645cd82d99b59a1a267d6d61117ef [75fd880d39c1daf53b6547ab6cb59451fc6452d27caa90e5b6649dd8293b9eed] 000000000000000000000000376c47978271565f56deb45495afa69e59c16ab200000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000060000000000000000000000000000000000000000000000000000000000000000158 9ae378b6d4409eada347a5dc0c180f186cb62dc68fcc0f043425eb917335aa28 0 95d429d309bb9d753954195fe2d69bd140b4ae731b9b5b605c34323de162cf00 0]}
 func TestPendingAndCallContract(t *testing.T) {
@@ -1035,7 +1072,7 @@ func TestPendingAndCallContract(t *testing.T) {
 		t.Errorf("response from calling contract was expected to be 'hello world' instead received %v", string(res))
 	}
 
-	sim.Commit()
+	blockHash := sim.Commit()
 
 	// make sure you can call the contract
 	res, err = sim.CallContract(bgCtx, ethereum.CallMsg{
@@ -1053,6 +1090,23 @@ func TestPendingAndCallContract(t *testing.T) {
 	if !bytes.Equal(res, expectedReturn) || !strings.Contains(string(res), "hello world") {
 		t.Errorf("response from calling contract was expected to be 'hello world' instead received %v", string(res))
 	}
+
+	// make sure you can call the contract by hash
+	res, err = sim.CallContractAtHash(bgCtx, ethereum.CallMsg{
+		From: testAddr,
+		To:   &addr,
+		Data: input,
+	}, blockHash)
+	if err != nil {
+		t.Errorf("could not call receive method on contract: %v", err)
+	}
+	if len(res) == 0 {
+		t.Errorf("result of contract call was empty: %v", res)
+	}
+
+	if !bytes.Equal(res, expectedReturn) || !strings.Contains(string(res), "hello world") {
+		t.Errorf("response from calling contract was expected to be 'hello world' instead received %v", string(res))
+	}
 }
 
 // This test is based on the following contract:
@@ -1336,3 +1390,42 @@ func TestForkResendTx(t *testing.T) {
 		t.Errorf("TX included in wrong block: %d", h)
 	}
 }
+
+func TestCommitReturnValue(t *testing.T) {
+	testAddr := crypto.PubkeyToAddress(testKey.PublicKey)
+	sim := simTestBackend(testAddr)
+	defer sim.Close()
+
+	startBlockHeight := sim.blockchain.CurrentBlock().NumberU64()
+
+	// Test if Commit returns the correct block hash
+	h1 := sim.Commit()
+	if h1 != sim.blockchain.CurrentBlock().Hash() {
+		t.Error("Commit did not return the hash of the last block.")
+	}
+
+	// Create a block in the original chain (containing a transaction to force different block hashes)
+	head, _ := sim.HeaderByNumber(context.Background(), nil) // Should be child's, good enough
+	gasPrice := new(big.Int).Add(head.BaseFee, big.NewInt(1))
+	_tx := types.NewTransaction(0, testAddr, big.NewInt(1000), params.TxGas, gasPrice, nil)
+	tx, _ := types.SignTx(_tx, types.HomesteadSigner{}, testKey)
+	sim.SendTransaction(context.Background(), tx)
+	h2 := sim.Commit()
+
+	// Create another block in the original chain
+	sim.Commit()
+
+	// Fork at the first bock
+	if err := sim.Fork(context.Background(), h1); err != nil {
+		t.Errorf("forking: %v", err)
+	}
+
+	// Test if Commit returns the correct block hash after the reorg
+	h2fork := sim.Commit()
+	if h2 == h2fork {
+		t.Error("The block in the fork and the original block are the same block!")
+	}
+	if sim.blockchain.GetHeader(h2fork, startBlockHeight+2) == nil {
+		t.Error("Could not retrieve the just created block (side-chain)")
+	}
+}

accounts/abi/bind/base.go

@@ -41,6 +41,7 @@ type CallOpts struct {
 	Pending     bool            // Whether to operate on the pending state or the last known one
 	From        common.Address  // Optional the sender address, otherwise the first account is used
 	BlockNumber *big.Int        // Optional the block number on which the call should be performed
+	BlockHash   common.Hash     // Optional the block hash on which the call should be performed
 	Context     context.Context // Network context to support cancellation and timeouts (nil = no timeout)
 }
 
@@ -171,14 +172,34 @@ func (c *BoundContract) Call(opts *CallOpts, results *[]interface{}, method stri
 			return ErrNoPendingState
 		}
 		output, err = pb.PendingCallContract(ctx, msg)
-		if err == nil && len(output) == 0 {
+		if err != nil {
+			return err
+		}
+		if len(output) == 0 {
 			// Make sure we have a contract to operate on, and bail out otherwise.
 			if code, err = pb.PendingCodeAt(ctx, c.address); err != nil {
 				return err
 			} else if len(code) == 0 {
 				return ErrNoCode
 			}
 		}
+	} else if opts.BlockHash != (common.Hash{}) {
+		bh, ok := c.caller.(BlockHashContractCaller)
+		if !ok {
+			return ErrNoBlockHashState
+		}
+		output, err = bh.CallContractAtHash(ctx, msg, opts.BlockHash)
+		if err != nil {
+			return err
+		}
+		if len(output) == 0 {
+			// Make sure we have a contract to operate on, and bail out otherwise.
+			if code, err = bh.CodeAtHash(ctx, c.address, opts.BlockHash); err != nil {
+				return err
+			} else if len(code) == 0 {
+				return ErrNoCode
+			}
+		}
 	} else {
 		output, err = c.caller.CallContract(ctx, msg, opts.BlockNumber)
 		if err != nil {