accounts/abi/bind/backends: add simulated reorgs (ethereum#22624)

* accounts/abi/bind/backends: add blockByHashNoLock

Signed-off-by: Oliver Tale-Yazdi <oliver@perun.network>

* accounts/abi/bind/backends: add 'parent' arg to rollback

Signed-off-by: Oliver Tale-Yazdi <oliver@perun.network>

* accounts/abi/bind/backends: add simulated forks

Signed-off-by: Oliver Tale-Yazdi <oliver@perun.network>

* accounts/abi/bind/backends: minor nitpicks

* accounts/abi/bind/backends: don't add defensive panics

Co-authored-by: Péter Szilágyi <peterke@gmail.com>

accounts/abi/bind/backends/simulated.go

@@ -86,7 +86,7 @@ func NewSimulatedBackendWithDatabase(database ethdb.Database, alloc core.Genesis
 		config:     genesis.Config,
 		events:     filters.NewEventSystem(&filterBackend{database, blockchain}, false),
 	}
-	backend.rollback()
+	backend.rollback(blockchain.CurrentBlock())
 	return backend
 }
 
@@ -112,30 +112,59 @@ func (b *SimulatedBackend) Commit() {
 	if _, err := b.blockchain.InsertChain([]*types.Block{b.pendingBlock}); err != nil {
 		panic(err) // This cannot happen unless the simulator is wrong, fail in that case
 	}
-	b.rollback()
+	// Using the last inserted block here makes it possible to build on a side
+	// chain after a fork.
+	b.rollback(b.pendingBlock)
 }
 
 // Rollback aborts all pending transactions, reverting to the last committed state.
 func (b *SimulatedBackend) Rollback() {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
-	b.rollback()
+	b.rollback(b.blockchain.CurrentBlock())
 }
 
-func (b *SimulatedBackend) rollback() {
-	blocks, _ := core.GenerateChain(b.config, b.blockchain.CurrentBlock(), ethash.NewFaker(), b.database, 1, func(int, *core.BlockGen) {})
+func (b *SimulatedBackend) rollback(parent *types.Block) {
+	blocks, _ := core.GenerateChain(b.config, parent, ethash.NewFaker(), b.database, 1, func(int, *core.BlockGen) {})
 
 	b.pendingBlock = blocks[0]
 	b.pendingState, _ = state.New(b.pendingBlock.Root(), b.blockchain.StateCache(), nil)
 }
 
+// Fork creates a side-chain that can be used to simulate reorgs.
+//
+// This function should be called with the ancestor block where the new side
+// chain should be started. Transactions (old and new) can then be applied on
+// top and Commit-ed.
+//
+// Note, the side-chain will only become canonical (and trigger the events) when
+// it becomes longer. Until then CallContract will still operate on the current
+// canonical chain.
+//
+// There is a % chance that the side chain becomes canonical at the same length
+// to simulate live network behavior.
+func (b *SimulatedBackend) Fork(ctx context.Context, parent common.Hash) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	if len(b.pendingBlock.Transactions()) != 0 {
+		return errors.New("pending block dirty")
+	}
+	block, err := b.blockByHash(ctx, parent)
+	if err != nil {
+		return err
+	}
+	b.rollback(block)
+	return nil
+}
+
 // stateByBlockNumber retrieves a state by a given blocknumber.
 func (b *SimulatedBackend) stateByBlockNumber(ctx context.Context, blockNumber *big.Int) (*state.StateDB, error) {
 	if blockNumber == nil || blockNumber.Cmp(b.blockchain.CurrentBlock().Number()) == 0 {
 		return b.blockchain.State()
 	}
-	block, err := b.blockByNumberNoLock(ctx, blockNumber)
+	block, err := b.blockByNumber(ctx, blockNumber)
 	if err != nil {
 		return nil, err
 	}
@@ -228,6 +257,11 @@ func (b *SimulatedBackend) BlockByHash(ctx context.Context, hash common.Hash) (*
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
+	return b.blockByHash(ctx, hash)
+}
+
+// blockByHash retrieves a block based on the block hash without Locking.
+func (b *SimulatedBackend) blockByHash(ctx context.Context, hash common.Hash) (*types.Block, error) {
 	if hash == b.pendingBlock.Hash() {
 		return b.pendingBlock, nil
 	}
@@ -246,12 +280,12 @@ func (b *SimulatedBackend) BlockByNumber(ctx context.Context, number *big.Int) (
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
-	return b.blockByNumberNoLock(ctx, number)
+	return b.blockByNumber(ctx, number)
 }
 
-// blockByNumberNoLock retrieves a block from the database by number, caching it
+// blockByNumber retrieves a block from the database by number, caching it
 // (associated with its hash) if found without Lock.
-func (b *SimulatedBackend) blockByNumberNoLock(ctx context.Context, number *big.Int) (*types.Block, error) {
+func (b *SimulatedBackend) blockByNumber(ctx context.Context, number *big.Int) (*types.Block, error) {
 	if number == nil || number.Cmp(b.pendingBlock.Number()) == 0 {
 		return b.blockchain.CurrentBlock(), nil
 	}
@@ -559,8 +593,12 @@ func (b *SimulatedBackend) SendTransaction(ctx context.Context, tx *types.Transa
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
-	// Check transaction validity.
-	block := b.blockchain.CurrentBlock()
+	// Get the last block
+	block, err := b.blockByHash(ctx, b.pendingBlock.ParentHash())
+	if err != nil {
+		panic("could not fetch parent")
+	}
+	// Check transaction validity
 	signer := types.MakeSigner(b.blockchain.Config(), block.Number())
 	sender, err := types.Sender(signer, tx)
 	if err != nil {
@@ -570,8 +608,7 @@ func (b *SimulatedBackend) SendTransaction(ctx context.Context, tx *types.Transa
 	if tx.Nonce() != nonce {
 		panic(fmt.Errorf("invalid transaction nonce: got %d, want %d", tx.Nonce(), nonce))
 	}
-
-	// Include tx in chain.
+	// Include tx in chain
 	blocks, _ := core.GenerateChain(b.config, block, ethash.NewFaker(), b.database, 1, func(number int, block *core.BlockGen) {
 		for _, tx := range b.pendingBlock.Transactions() {
 			block.AddTxWithChain(b.blockchain, tx)