go-ethereum/core/blockchain_snapshot_test.go

// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Tests that abnormal program termination (i.e.crash) and restart can recovery
// the snapshot properly if the snapshot is enabled.

package core

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"math/big"
	"os"
	"strings"
	"testing"
	"time"

	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/consensus/ethash"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/params"
)

// snapshotTestBasic wraps the common testing fields in the snapshot tests.
type snapshotTestBasic struct {
	chainBlocks   int    // Number of blocks to generate for the canonical chain
	snapshotBlock uint64 // Block number of the relevant snapshot disk layer
	commitBlock   uint64 // Block number for which to commit the state to disk

	expCanonicalBlocks int    // Number of canonical blocks expected to remain in the database (excl. genesis)
	expHeadHeader      uint64 // Block number of the expected head header
	expHeadFastBlock   uint64 // Block number of the expected head fast sync block
	expHeadBlock       uint64 // Block number of the expected head full block
	expSnapshotBottom  uint64 // The block height corresponding to the snapshot disk layer

	// share fields, set in runtime
	datadir string
	db      ethdb.Database
	gendb   ethdb.Database
	engine  consensus.Engine
}

func (basic *snapshotTestBasic) prepare(t *testing.T) (*BlockChain, []*types.Block) {
	// Create a temporary persistent database
	datadir, err := ioutil.TempDir("", "")
	if err != nil {
		t.Fatalf("Failed to create temporary datadir: %v", err)
	}
	os.RemoveAll(datadir)

	db, err := rawdb.NewLevelDBDatabaseWithFreezer(datadir, 0, 0, datadir, "", false)
	if err != nil {
		t.Fatalf("Failed to create persistent database: %v", err)
	}
	// Initialize a fresh chain
	var (
		genesis = (&Genesis{BaseFee: big.NewInt(params.InitialBaseFee)}).MustCommit(db)
		engine  = ethash.NewFullFaker()
		gendb   = rawdb.NewMemoryDatabase()

		// Snapshot is enabled, the first snapshot is created from the Genesis.
		// The snapshot memory allowance is 256MB, it means no snapshot flush
		// will happen during the block insertion.
		cacheConfig = defaultCacheConfig
	)
	chain, err := NewBlockChain(db, cacheConfig, params.AllEthashProtocolChanges, engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to create chain: %v", err)
	}
	blocks, _ := GenerateChain(params.TestChainConfig, genesis, engine, gendb, basic.chainBlocks, func(i int, b *BlockGen) {})

	// Insert the blocks with configured settings.
	var breakpoints []uint64
	if basic.commitBlock > basic.snapshotBlock {
		breakpoints = append(breakpoints, basic.snapshotBlock, basic.commitBlock)
	} else {
		breakpoints = append(breakpoints, basic.commitBlock, basic.snapshotBlock)
	}
	var startPoint uint64
	for _, point := range breakpoints {
		if _, err := chain.InsertChain(blocks[startPoint:point]); err != nil {
			t.Fatalf("Failed to import canonical chain start: %v", err)
		}
		startPoint = point

		if basic.commitBlock > 0 && basic.commitBlock == point {
			chain.stateCache.TrieDB().Commit(blocks[point-1].Root(), true, nil)
		}
		if basic.snapshotBlock > 0 && basic.snapshotBlock == point {
			// Flushing the entire snap tree into the disk, the
			// relavant (a) snapshot root and (b) snapshot generator
			// will be persisted atomically.
			chain.snaps.Cap(blocks[point-1].Root(), 0)
			diskRoot, blockRoot := chain.snaps.DiskRoot(), blocks[point-1].Root()
			if !bytes.Equal(diskRoot.Bytes(), blockRoot.Bytes()) {
				t.Fatalf("Failed to flush disk layer change, want %x, got %x", blockRoot, diskRoot)
			}
		}
	}
	if _, err := chain.InsertChain(blocks[startPoint:]); err != nil {
		t.Fatalf("Failed to import canonical chain tail: %v", err)
	}

	// Set runtime fields
	basic.datadir = datadir
	basic.db = db
	basic.gendb = gendb
	basic.engine = engine
	return chain, blocks
}

func (basic *snapshotTestBasic) verify(t *testing.T, chain *BlockChain, blocks []*types.Block) {
	// Iterate over all the remaining blocks and ensure there are no gaps
	verifyNoGaps(t, chain, true, blocks)
	verifyCutoff(t, chain, true, blocks, basic.expCanonicalBlocks)

	if head := chain.CurrentHeader(); head.Number.Uint64() != basic.expHeadHeader {
		t.Errorf("Head header mismatch: have %d, want %d", head.Number, basic.expHeadHeader)
	}
	if head := chain.CurrentFastBlock(); head.NumberU64() != basic.expHeadFastBlock {
		t.Errorf("Head fast block mismatch: have %d, want %d", head.NumberU64(), basic.expHeadFastBlock)
	}
	if head := chain.CurrentBlock(); head.NumberU64() != basic.expHeadBlock {
		t.Errorf("Head block mismatch: have %d, want %d", head.NumberU64(), basic.expHeadBlock)
	}

	// Check the disk layer, ensure they are matched
	block := chain.GetBlockByNumber(basic.expSnapshotBottom)
	if block == nil {
		t.Errorf("The correspnding block[%d] of snapshot disk layer is missing", basic.expSnapshotBottom)
	} else if !bytes.Equal(chain.snaps.DiskRoot().Bytes(), block.Root().Bytes()) {
		t.Errorf("The snapshot disk layer root is incorrect, want %x, get %x", block.Root(), chain.snaps.DiskRoot())
	}

	// Check the snapshot, ensure it's integrated
	if err := chain.snaps.Verify(block.Root()); err != nil {
		t.Errorf("The disk layer is not integrated %v", err)
	}
}

func (basic *snapshotTestBasic) dump() string {
	buffer := new(strings.Builder)

	fmt.Fprint(buffer, "Chain:\n  G")
	for i := 0; i < basic.chainBlocks; i++ {
		fmt.Fprintf(buffer, "->C%d", i+1)
	}
	fmt.Fprint(buffer, " (HEAD)\n\n")

	fmt.Fprintf(buffer, "Commit:   G")
	if basic.commitBlock > 0 {
		fmt.Fprintf(buffer, ", C%d", basic.commitBlock)
	}
	fmt.Fprint(buffer, "\n")

	fmt.Fprintf(buffer, "Snapshot: G")
	if basic.snapshotBlock > 0 {
		fmt.Fprintf(buffer, ", C%d", basic.snapshotBlock)
	}
	fmt.Fprint(buffer, "\n")

	//if crash {
	//	fmt.Fprintf(buffer, "\nCRASH\n\n")
	//} else {
	//	fmt.Fprintf(buffer, "\nSetHead(%d)\n\n", basic.setHead)
	//}
	fmt.Fprintf(buffer, "------------------------------\n\n")

	fmt.Fprint(buffer, "Expected in leveldb:\n  G")
	for i := 0; i < basic.expCanonicalBlocks; i++ {
		fmt.Fprintf(buffer, "->C%d", i+1)
	}
	fmt.Fprintf(buffer, "\n\n")
	fmt.Fprintf(buffer, "Expected head header    : C%d\n", basic.expHeadHeader)
	fmt.Fprintf(buffer, "Expected head fast block: C%d\n", basic.expHeadFastBlock)
	if basic.expHeadBlock == 0 {
		fmt.Fprintf(buffer, "Expected head block     : G\n")
	} else {
		fmt.Fprintf(buffer, "Expected head block     : C%d\n", basic.expHeadBlock)
	}
	if basic.expSnapshotBottom == 0 {
		fmt.Fprintf(buffer, "Expected snapshot disk  : G\n")
	} else {
		fmt.Fprintf(buffer, "Expected snapshot disk  : C%d\n", basic.expSnapshotBottom)
	}
	return buffer.String()
}

func (basic *snapshotTestBasic) teardown() {
	basic.db.Close()
	basic.gendb.Close()
	os.RemoveAll(basic.datadir)
}

// snapshotTest is a test case type for normal snapshot recovery.
// It can be used for testing that restart Geth normally.
type snapshotTest struct {
	snapshotTestBasic
}

func (snaptest *snapshotTest) test(t *testing.T) {
	// It's hard to follow the test case, visualize the input
	// log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
	// fmt.Println(tt.dump())
	chain, blocks := snaptest.prepare(t)

	// Restart the chain normally
	chain.Stop()
	newchain, err := NewBlockChain(snaptest.db, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	defer newchain.Stop()

	snaptest.verify(t, newchain, blocks)
}

// crashSnapshotTest is a test case type for innormal snapshot recovery.
// It can be used for testing that restart Geth after the crash.
type crashSnapshotTest struct {
	snapshotTestBasic
}

func (snaptest *crashSnapshotTest) test(t *testing.T) {
	// It's hard to follow the test case, visualize the input
	// log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
	// fmt.Println(tt.dump())
	chain, blocks := snaptest.prepare(t)

	// Pull the plug on the database, simulating a hard crash
	db := chain.db
	db.Close()

	// Start a new blockchain back up and see where the repair leads us
	newdb, err := rawdb.NewLevelDBDatabaseWithFreezer(snaptest.datadir, 0, 0, snaptest.datadir, "", false)
	if err != nil {
		t.Fatalf("Failed to reopen persistent database: %v", err)
	}
	defer newdb.Close()

	// The interesting thing is: instead of starting the blockchain after
	// the crash, we do restart twice here: one after the crash and one
	// after the normal stop. It's used to ensure the broken snapshot
	// can be detected all the time.
	newchain, err := NewBlockChain(newdb, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	newchain.Stop()

	newchain, err = NewBlockChain(newdb, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	defer newchain.Stop()

	snaptest.verify(t, newchain, blocks)
}

// gappedSnapshotTest is a test type used to test this scenario:
// - have a complete snapshot
// - restart without enabling the snapshot
// - insert a few blocks
// - restart with enabling the snapshot again
type gappedSnapshotTest struct {
	snapshotTestBasic
	gapped int // Number of blocks to insert without enabling snapshot
}

func (snaptest *gappedSnapshotTest) test(t *testing.T) {
	// It's hard to follow the test case, visualize the input
	// log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
	// fmt.Println(tt.dump())
	chain, blocks := snaptest.prepare(t)

	// Insert blocks without enabling snapshot if gapping is required.
	chain.Stop()
	gappedBlocks, _ := GenerateChain(params.TestChainConfig, blocks[len(blocks)-1], snaptest.engine, snaptest.gendb, snaptest.gapped, func(i int, b *BlockGen) {})

	// Insert a few more blocks without enabling snapshot
	var cacheConfig = &CacheConfig{
		TrieCleanLimit: 256,
		TrieDirtyLimit: 256,
		TrieTimeLimit:  5 * time.Minute,
		SnapshotLimit:  0,
	}
	newchain, err := NewBlockChain(snaptest.db, cacheConfig, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	newchain.InsertChain(gappedBlocks)
	newchain.Stop()

	// Restart the chain with enabling the snapshot
	newchain, err = NewBlockChain(snaptest.db, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	defer newchain.Stop()

	snaptest.verify(t, newchain, blocks)
}

// setHeadSnapshotTest is the test type used to test this scenario:
// - have a complete snapshot
// - set the head to a lower point
// - restart
type setHeadSnapshotTest struct {
	snapshotTestBasic
	setHead uint64 // Block number to set head back to
}

func (snaptest *setHeadSnapshotTest) test(t *testing.T) {
	// It's hard to follow the test case, visualize the input
	// log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
	// fmt.Println(tt.dump())
	chain, blocks := snaptest.prepare(t)

	// Rewind the chain if setHead operation is required.
	chain.SetHead(snaptest.setHead)
	chain.Stop()

	newchain, err := NewBlockChain(snaptest.db, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	defer newchain.Stop()

	snaptest.verify(t, newchain, blocks)
}

// restartCrashSnapshotTest is the test type used to test this scenario:
// - have a complete snapshot
// - restart chain
// - insert more blocks with enabling the snapshot
// - commit the snapshot
// - crash
// - restart again
type restartCrashSnapshotTest struct {
	snapshotTestBasic
	newBlocks int
}

func (snaptest *restartCrashSnapshotTest) test(t *testing.T) {
	// It's hard to follow the test case, visualize the input
	// log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
	// fmt.Println(tt.dump())
	chain, blocks := snaptest.prepare(t)

	// Firstly, stop the chain properly, with all snapshot journal
	// and state committed.
	chain.Stop()

	newchain, err := NewBlockChain(snaptest.db, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	newBlocks, _ := GenerateChain(params.TestChainConfig, blocks[len(blocks)-1], snaptest.engine, snaptest.gendb, snaptest.newBlocks, func(i int, b *BlockGen) {})
	newchain.InsertChain(newBlocks)

	// Commit the entire snapshot into the disk if requested. Note only
	// (a) snapshot root and (b) snapshot generator will be committed,
	// the diff journal is not.
	newchain.Snapshots().Cap(newBlocks[len(newBlocks)-1].Root(), 0)

	// Simulate the blockchain crash
	// Don't call chain.Stop here, so that no snapshot
	// journal and latest state will be committed

	// Restart the chain after the crash
	newchain, err = NewBlockChain(snaptest.db, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	defer newchain.Stop()

	snaptest.verify(t, newchain, blocks)
}

// wipeCrashSnapshotTest is the test type used to test this scenario:
// - have a complete snapshot
// - restart, insert more blocks without enabling the snapshot
// - restart again with enabling the snapshot
// - crash
type wipeCrashSnapshotTest struct {
	snapshotTestBasic
	newBlocks int
}

func (snaptest *wipeCrashSnapshotTest) test(t *testing.T) {
	// It's hard to follow the test case, visualize the input
	// log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
	// fmt.Println(tt.dump())
	chain, blocks := snaptest.prepare(t)

	// Firstly, stop the chain properly, with all snapshot journal
	// and state committed.
	chain.Stop()

	config := &CacheConfig{
		TrieCleanLimit: 256,
		TrieDirtyLimit: 256,
		TrieTimeLimit:  5 * time.Minute,
		SnapshotLimit:  0,
	}
	newchain, err := NewBlockChain(snaptest.db, config, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	newBlocks, _ := GenerateChain(params.TestChainConfig, blocks[len(blocks)-1], snaptest.engine, snaptest.gendb, snaptest.newBlocks, func(i int, b *BlockGen) {})
	newchain.InsertChain(newBlocks)
	newchain.Stop()

	// Restart the chain, the wiper should starts working
	config = &CacheConfig{
		TrieCleanLimit: 256,
		TrieDirtyLimit: 256,
		TrieTimeLimit:  5 * time.Minute,
		SnapshotLimit:  256,
		SnapshotWait:   false, // Don't wait rebuild
	}
	newchain, err = NewBlockChain(snaptest.db, config, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	// Simulate the blockchain crash.

	newchain, err = NewBlockChain(snaptest.db, nil, params.AllEthashProtocolChanges, snaptest.engine, vm.Config{}, nil, nil)
	if err != nil {
		t.Fatalf("Failed to recreate chain: %v", err)
	}
	snaptest.verify(t, newchain, blocks)
}

// Tests a Geth restart with valid snapshot. Before the shutdown, all snapshot
// journal will be persisted correctly. In this case no snapshot recovery is
// required.
func TestRestartWithNewSnapshot(t *testing.T) {
	// Chain:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8 (HEAD)
	//
	// Commit:   G
	// Snapshot: G
	//
	// SetHead(0)
	//
	// ------------------------------
	//
	// Expected in leveldb:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8
	//
	// Expected head header    : C8
	// Expected head fast block: C8
	// Expected head block     : C8
	// Expected snapshot disk  : G
	test := &snapshotTest{
		snapshotTestBasic{
			chainBlocks:        8,
			snapshotBlock:      0,
			commitBlock:        0,
			expCanonicalBlocks: 8,
			expHeadHeader:      8,
			expHeadFastBlock:   8,
			expHeadBlock:       8,
			expSnapshotBottom:  0, // Initial disk layer built from genesis
		},
	}
	test.test(t)
	test.teardown()
}

// Tests a Geth was crashed and restarts with a broken snapshot. In this case the
// chain head should be rewound to the point with available state. And also the
// new head should must be lower than disk layer. But there is no committed point
// so the chain should be rewound to genesis and the disk layer should be left
// for recovery.
func TestNoCommitCrashWithNewSnapshot(t *testing.T) {
	// Chain:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8 (HEAD)
	//
	// Commit:   G
	// Snapshot: G, C4
	//
	// CRASH
	//
	// ------------------------------
	//
	// Expected in leveldb:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8
	//
	// Expected head header    : C8
	// Expected head fast block: C8
	// Expected head block     : G
	// Expected snapshot disk  : C4
	test := &crashSnapshotTest{
		snapshotTestBasic{
			chainBlocks:        8,
			snapshotBlock:      4,
			commitBlock:        0,
			expCanonicalBlocks: 8,
			expHeadHeader:      8,
			expHeadFastBlock:   8,
			expHeadBlock:       0,
			expSnapshotBottom:  4, // Last committed disk layer, wait recovery
		},
	}
	test.test(t)
	test.teardown()
}

// Tests a Geth was crashed and restarts with a broken snapshot. In this case the
// chain head should be rewound to the point with available state. And also the
// new head should must be lower than disk layer. But there is only a low committed
// point so the chain should be rewound to committed point and the disk layer
// should be left for recovery.
func TestLowCommitCrashWithNewSnapshot(t *testing.T) {
	// Chain:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8 (HEAD)
	//
	// Commit:   G, C2
	// Snapshot: G, C4
	//
	// CRASH
	//
	// ------------------------------
	//
	// Expected in leveldb:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8
	//
	// Expected head header    : C8
	// Expected head fast block: C8
	// Expected head block     : C2
	// Expected snapshot disk  : C4
	test := &crashSnapshotTest{
		snapshotTestBasic{
			chainBlocks:        8,
			snapshotBlock:      4,
			commitBlock:        2,
			expCanonicalBlocks: 8,
			expHeadHeader:      8,
			expHeadFastBlock:   8,
			expHeadBlock:       2,
			expSnapshotBottom:  4, // Last committed disk layer, wait recovery
		},
	}
	test.test(t)
	test.teardown()
}

// Tests a Geth was crashed and restarts with a broken snapshot. In this case
// the chain head should be rewound to the point with available state. And also
// the new head should must be lower than disk layer. But there is only a high
// committed point so the chain should be rewound to genesis and the disk layer
// should be left for recovery.
func TestHighCommitCrashWithNewSnapshot(t *testing.T) {
	// Chain:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8 (HEAD)
	//
	// Commit:   G, C6
	// Snapshot: G, C4
	//
	// CRASH
	//
	// ------------------------------
	//
	// Expected in leveldb:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8
	//
	// Expected head header    : C8
	// Expected head fast block: C8
	// Expected head block     : G
	// Expected snapshot disk  : C4
	test := &crashSnapshotTest{
		snapshotTestBasic{
			chainBlocks:        8,
			snapshotBlock:      4,
			commitBlock:        6,
			expCanonicalBlocks: 8,
			expHeadHeader:      8,
			expHeadFastBlock:   8,
			expHeadBlock:       0,
			expSnapshotBottom:  4, // Last committed disk layer, wait recovery
		},
	}
	test.test(t)
	test.teardown()
}

// Tests a Geth was running with snapshot enabled. Then restarts without
// enabling snapshot and after that re-enable the snapshot again. In this
// case the snapshot should be rebuilt with latest chain head.
func TestGappedNewSnapshot(t *testing.T) {
	// Chain:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8 (HEAD)
	//
	// Commit:   G
	// Snapshot: G
	//
	// SetHead(0)
	//
	// ------------------------------
	//
	// Expected in leveldb:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8->C9->C10
	//
	// Expected head header    : C10
	// Expected head fast block: C10
	// Expected head block     : C10
	// Expected snapshot disk  : C10
	test := &gappedSnapshotTest{
		snapshotTestBasic: snapshotTestBasic{
			chainBlocks:        8,
			snapshotBlock:      0,
			commitBlock:        0,
			expCanonicalBlocks: 10,
			expHeadHeader:      10,
			expHeadFastBlock:   10,
			expHeadBlock:       10,
			expSnapshotBottom:  10, // Rebuilt snapshot from the latest HEAD
		},
		gapped: 2,
	}
	test.test(t)
	test.teardown()
}

// Tests the Geth was running with snapshot enabled and resetHead is applied.
// In this case the head is rewound to the target(with state available). After
// that the chain is restarted and the original disk layer is kept.
func TestSetHeadWithNewSnapshot(t *testing.T) {
	// Chain:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8 (HEAD)
	//
	// Commit:   G
	// Snapshot: G
	//
	// SetHead(4)
	//
	// ------------------------------
	//
	// Expected in leveldb:
	//   G->C1->C2->C3->C4
	//
	// Expected head header    : C4
	// Expected head fast block: C4
	// Expected head block     : C4
	// Expected snapshot disk  : G
	test := &setHeadSnapshotTest{
		snapshotTestBasic: snapshotTestBasic{
			chainBlocks:        8,
			snapshotBlock:      0,
			commitBlock:        0,
			expCanonicalBlocks: 4,
			expHeadHeader:      4,
			expHeadFastBlock:   4,
			expHeadBlock:       4,
			expSnapshotBottom:  0, // The initial disk layer is built from the genesis
		},
		setHead: 4,
	}
	test.test(t)
	test.teardown()
}

// Tests the Geth was running with a complete snapshot and then imports a few
// more new blocks on top without enabling the snapshot. After the restart,
// crash happens. Check everything is ok after the restart.
func TestRecoverSnapshotFromWipingCrash(t *testing.T) {
	// Chain:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8 (HEAD)
	//
	// Commit:   G
	// Snapshot: G
	//
	// SetHead(0)
	//
	// ------------------------------
	//
	// Expected in leveldb:
	//   G->C1->C2->C3->C4->C5->C6->C7->C8->C9->C10
	//
	// Expected head header    : C10
	// Expected head fast block: C10
	// Expected head block     : C8
	// Expected snapshot disk  : C10
	test := &wipeCrashSnapshotTest{
		snapshotTestBasic: snapshotTestBasic{
			chainBlocks:        8,
			snapshotBlock:      4,
			commitBlock:        0,
			expCanonicalBlocks: 10,
			expHeadHeader:      10,
			expHeadFastBlock:   10,
			expHeadBlock:       10,
			expSnapshotBottom:  10,
		},
		newBlocks: 2,
	}
	test.test(t)
	test.teardown()
}