path: root/dex/downloader/downloader_test.go

// Copyright 2015 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/>.

package downloader

import (
    "errors"
    "fmt"
    "sync"
    "sync/atomic"
    "testing"
    "time"

    ethereum "github.com/dexon-foundation/dexon"
    dexCore "github.com/dexon-foundation/dexon-consensus/core"
    "github.com/dexon-foundation/dexon/common"
    "github.com/dexon-foundation/dexon/core/state"
    "github.com/dexon-foundation/dexon/core/types"
    vm "github.com/dexon-foundation/dexon/core/vm/evm"
    "github.com/dexon-foundation/dexon/ethdb"
    "github.com/dexon-foundation/dexon/event"
    "github.com/dexon-foundation/dexon/trie"
)

// Reduce some of the parameters to make the tester faster.
func init() {
    MaxForkAncestry = uint64(10000)
    blockCacheItems = 1024
    fsHeaderContCheck = 500 * time.Millisecond
}

// downloadTester is a test simulator for mocking out local block chain.
type downloadTester struct {
    downloader *Downloader

    genesis *types.Block   // Genesis blocks used by the tester and peers
    stateDb ethdb.Database // Database used by the tester for syncing from peers
    peerDb  ethdb.Database // Database of the peers containing all data
    peers   map[string]*downloadTesterPeer

    ownHashes   []common.Hash                  // Hash chain belonging to the tester
    ownHeaders  map[common.Hash]*types.Header  // Headers belonging to the tester
    ownBlocks   map[common.Hash]*types.Block   // Blocks belonging to the tester
    ownReceipts map[common.Hash]types.Receipts // Receipts belonging to the tester

    lock sync.RWMutex
}

// newTester creates a new downloader test mocker.
func newTester() *downloadTester {
    tester := &downloadTester{
        genesis:     testGenesis,
        peerDb:      testDB,
        peers:       make(map[string]*downloadTesterPeer),
        ownHashes:   []common.Hash{testGenesis.Hash()},
        ownHeaders:  map[common.Hash]*types.Header{testGenesis.Hash(): testGenesis.Header()},
        ownBlocks:   map[common.Hash]*types.Block{testGenesis.Hash(): testGenesis},
        ownReceipts: map[common.Hash]types.Receipts{testGenesis.Hash(): nil},
    }
    tester.stateDb = ethdb.NewMemDatabase()
    tester.stateDb.Put(testGenesis.Root().Bytes(), []byte{0x00})
    tester.downloader = New(FullSync, tester.stateDb, new(event.TypeMux), tester, nil, tester.dropPeer)
    return tester
}

// terminate aborts any operations on the embedded downloader and releases all
// held resources.
func (dl *downloadTester) terminate() {
    dl.downloader.Terminate()
}

// sync starts synchronizing with a remote peer, blocking until it completes.
func (dl *downloadTester) sync(id string, number uint64, mode SyncMode) error {
    dl.lock.RLock()
    hash := dl.peers[id].chain.headBlock().Hash()
    // If no particular number was requested, load from the peer's blockchain
    if number == 0 {
        number, _ = dl.peers[id].chain.hashToNumber(hash)
    }
    dl.lock.RUnlock()

    // Synchronise with the chosen peer and ensure proper cleanup afterwards
    err := dl.downloader.synchronise(id, hash, number, mode)
    select {
    case <-dl.downloader.cancelCh:
        // Ok, downloader fully cancelled after sync cycle
    default:
        // Downloader is still accepting packets, can block a peer up
        panic("downloader active post sync cycle") // panic will be caught by tester
    }
    return err
}

// HasHeader checks if a header is present in the testers canonical chain.
func (dl *downloadTester) HasHeader(hash common.Hash, number uint64) bool {
    return dl.GetHeaderByHash(hash) != nil
}

// HasBlock checks if a block is present in the testers canonical chain.
func (dl *downloadTester) HasBlock(hash common.Hash, number uint64) bool {
    return dl.GetBlockByHash(hash) != nil
}

// GetHeader retrieves a header from the testers canonical chain.
func (dl *downloadTester) GetHeaderByHash(hash common.Hash) *types.Header {
    dl.lock.RLock()
    defer dl.lock.RUnlock()

    return dl.ownHeaders[hash]
}

func (dl *downloadTester) GetHeaderByNumber(number uint64) *types.Header {
    dl.lock.RLock()
    defer dl.lock.RUnlock()
    return dl.ownHeaders[dl.ownHashes[number]]
}

// GetBlock retrieves a block from the testers canonical chain.
func (dl *downloadTester) GetBlockByHash(hash common.Hash) *types.Block {
    dl.lock.RLock()
    defer dl.lock.RUnlock()

    return dl.ownBlocks[hash]
}

func (dl *downloadTester) GetGovStateByNumber(number uint64) (*types.GovState, error) {
    header, ok := dl.ownHeaders[dl.ownHashes[number]]
    if !ok {
        return nil, fmt.Errorf("header with number %d not exists", number)
    }
    statedb, err := state.New(header.Root, state.NewDatabase(dl.peerDb))
    if err != nil {
        return nil, err
    }
    return state.GetGovState(statedb, header, vm.GovernanceContractAddress)
}

// CurrentHeader retrieves the current head header from the canonical chain.
func (dl *downloadTester) CurrentHeader() *types.Header {
    dl.lock.RLock()
    defer dl.lock.RUnlock()

    for i := len(dl.ownHashes) - 1; i >= 0; i-- {
        if header := dl.ownHeaders[dl.ownHashes[i]]; header != nil {
            return header
        }
    }
    return dl.genesis.Header()
}

// CurrentBlock retrieves the current head block from the canonical chain.
func (dl *downloadTester) CurrentBlock() *types.Block {
    dl.lock.RLock()
    defer dl.lock.RUnlock()

    for i := len(dl.ownHashes) - 1; i >= 0; i-- {
        if block := dl.ownBlocks[dl.ownHashes[i]]; block != nil {
            if _, err := dl.stateDb.Get(block.Root().Bytes()); err == nil {
                return block
            }
        }
    }
    return dl.genesis
}

// CurrentFastBlock retrieves the current head fast-sync block from the canonical chain.
func (dl *downloadTester) CurrentFastBlock() *types.Block {
    dl.lock.RLock()
    defer dl.lock.RUnlock()

    for i := len(dl.ownHashes) - 1; i >= 0; i-- {
        if block := dl.ownBlocks[dl.ownHashes[i]]; block != nil {
            return block
        }
    }
    return dl.genesis
}

// FastSyncCommitHead manually sets the head block to a given hash.
func (dl *downloadTester) FastSyncCommitHead(hash common.Hash) error {
    // For now only check that the state trie is correct
    if block := dl.GetBlockByHash(hash); block != nil {
        _, err := trie.NewSecure(block.Root(), trie.NewDatabase(dl.stateDb), 0)
        return err
    }
    return fmt.Errorf("non existent block: %x", hash[:4])
}

// InsertDexonHeaderChain injects a new batch of headers into the simulated chain.
func (dl *downloadTester) InsertDexonHeaderChain(headers []*types.HeaderWithGovState, verifierCache *dexCore.TSigVerifierCache) (i int, err error) {
    dl.lock.Lock()
    defer dl.lock.Unlock()

    // Do a quick check, as the blockchain.InsertDexonHeaderChain doesn't insert anything in case of errors
    if _, ok := dl.ownHeaders[headers[0].ParentHash]; !ok {
        return 0, errors.New("unknown parent")
    }
    for i := 1; i < len(headers); i++ {
        if headers[i].ParentHash != headers[i-1].Hash() {
            return i, errors.New("unknown parent")
        }
    }
    // Do a full insert if pre-checks passed
    for i, header := range headers {
        if _, ok := dl.ownHeaders[header.Hash()]; ok {
            continue
        }
        if _, ok := dl.ownHeaders[header.ParentHash]; !ok {
            return i, errors.New("unknown parent")
        }
        dl.ownHashes = append(dl.ownHashes, header.Hash())
        dl.ownHeaders[header.Hash()] = header.Header
    }
    return len(headers), nil
}

// InsertDexonChain injects a new batch of blocks into the simulated chain.
func (dl *downloadTester) InsertDexonChain(blocks types.Blocks) (i int, err error) {
    dl.lock.Lock()
    defer dl.lock.Unlock()

    for i, block := range blocks {
        if parent, ok := dl.ownBlocks[block.ParentHash()]; !ok {
            return i, errors.New("unknown parent")
        } else if _, err := dl.stateDb.Get(parent.Root().Bytes()); err != nil {
            return i, fmt.Errorf("unknown parent state %x: %v", parent.Root(), err)
        }
        if _, ok := dl.ownHeaders[block.Hash()]; !ok {
            dl.ownHashes = append(dl.ownHashes, block.Hash())
            dl.ownHeaders[block.Hash()] = block.Header()
        }
        dl.ownBlocks[block.Hash()] = block
        dl.stateDb.Put(block.Root().Bytes(), []byte{0x00})
    }
    return len(blocks), nil
}

// InsertReceiptChain injects a new batch of receipts into the simulated chain.
func (dl *downloadTester) InsertReceiptChain(blocks types.Blocks, receipts []types.Receipts) (i int, err error) {
    dl.lock.Lock()
    defer dl.lock.Unlock()

    for i := 0; i < len(blocks) && i < len(receipts); i++ {
        if _, ok := dl.ownHeaders[blocks[i].Hash()]; !ok {
            return i, errors.New("unknown owner")
        }
        if _, ok := dl.ownBlocks[blocks[i].ParentHash()]; !ok {
            return i, errors.New("unknown parent")
        }
        dl.ownBlocks[blocks[i].Hash()] = blocks[i]
        dl.ownReceipts[blocks[i].Hash()] = receipts[i]
    }
    return len(blocks), nil
}

// Rollback removes some recently added elements from the chain.
func (dl *downloadTester) Rollback(hashes []common.Hash) {
    dl.lock.Lock()
    defer dl.lock.Unlock()

    for i := len(hashes) - 1; i >= 0; i-- {
        if dl.ownHashes[len(dl.ownHashes)-1] == hashes[i] {
            dl.ownHashes = dl.ownHashes[:len(dl.ownHashes)-1]
        }
        delete(dl.ownHeaders, hashes[i])
        delete(dl.ownReceipts, hashes[i])
        delete(dl.ownBlocks, hashes[i])
    }
}

// newPeer registers a new block download source into the downloader.
func (dl *downloadTester) newPeer(id string, version int, chain *testChain) error {
    dl.lock.Lock()
    defer dl.lock.Unlock()

    peer := &downloadTesterPeer{dl: dl, id: id, chain: chain}
    dl.peers[id] = peer
    return dl.downloader.RegisterPeer(id, version, peer)
}

// dropPeer simulates a hard peer removal from the connection pool.
func (dl *downloadTester) dropPeer(id string) {
    dl.lock.Lock()
    defer dl.lock.Unlock()

    delete(dl.peers, id)
    dl.downloader.UnregisterPeer(id)
}

type downloadTesterPeer struct {
    dl            *downloadTester
    id            string
    lock          sync.RWMutex
    chain         *testChain
    missingStates map[common.Hash]bool // State entries that fast sync should not return
}

// Head constructs a function to retrieve a peer's current head hash
// and total difficulty.
func (dlp *downloadTesterPeer) Head() (common.Hash, uint64) {
    b := dlp.chain.headBlock()
    number, _ := dlp.chain.hashToNumber(b.Hash())
    return b.Hash(), number
}

// RequestHeadersByHash constructs a GetBlockHeaders function based on a hashed
// origin; associated with a particular peer in the download tester. The returned
// function can be used to retrieve batches of headers from the particular peer.
func (dlp *downloadTesterPeer) RequestHeadersByHash(origin common.Hash, amount int, skip int, reverse, withGov bool) error {
    if reverse {
        panic("reverse header requests not supported")
    }

    result := dlp.chain.headersByHash(origin, amount, skip)
    go dlp.dl.downloader.DeliverHeaders(dlp.id, result)
    return nil
}

// RequestHeadersByNumber constructs a GetBlockHeaders function based on a numbered
// origin; associated with a particular peer in the download tester. The returned
// function can be used to retrieve batches of headers from the particular peer.
func (dlp *downloadTesterPeer) RequestHeadersByNumber(origin uint64, amount int, skip int, reverse, withGov bool) error {
    if reverse {
        panic("reverse header requests not supported")
    }

    result := dlp.chain.headersByNumber(origin, amount, skip)
    go dlp.dl.downloader.DeliverHeaders(dlp.id, result)
    return nil
}

func (dlp *downloadTesterPeer) RequestGovStateByHash(hash common.Hash) error {
    result := dlp.chain.govStateByHash(hash)
    go dlp.dl.downloader.DeliverGovState(dlp.id, result)
    return nil
}

// RequestBodies constructs a getBlockBodies method associated with a particular
// peer in the download tester. The returned function can be used to retrieve
// batches of block bodies from the particularly requested peer.
func (dlp *downloadTesterPeer) RequestBodies(hashes []common.Hash) error {
    txs, uncles := dlp.chain.bodies(hashes)
    go dlp.dl.downloader.DeliverBodies(dlp.id, txs, uncles)
    return nil
}

// RequestReceipts constructs a getReceipts method associated with a particular
// peer in the download tester. The returned function can be used to retrieve
// batches of block receipts from the particularly requested peer.
func (dlp *downloadTesterPeer) RequestReceipts(hashes []common.Hash) error {
    receipts := dlp.chain.receipts(hashes)
    go dlp.dl.downloader.DeliverReceipts(dlp.id, receipts)
    return nil
}

// RequestNodeData constructs a getNodeData method associated with a particular
// peer in the download tester. The returned function can be used to retrieve
// batches of node state data from the particularly requested peer.
func (dlp *downloadTesterPeer) RequestNodeData(hashes []common.Hash) error {
    dlp.dl.lock.RLock()
    defer dlp.dl.lock.RUnlock()

    results := make([][]byte, 0, len(hashes))
    for _, hash := range hashes {
        if data, err := dlp.dl.peerDb.Get(hash.Bytes()); err == nil {
            if !dlp.missingStates[hash] {
                results = append(results, data)
            }
        }
    }
    go dlp.dl.downloader.DeliverNodeData(dlp.id, results)
    return nil
}

// assertOwnChain checks if the local chain contains the correct number of items
// of the various chain components.
func assertOwnChain(t *testing.T, tester *downloadTester, length int) {
    assertOwnForkedChain(t, tester, 1, []int{length})
}

// assertOwnForkedChain checks if the local forked chain contains the correct
// number of items of the various chain components.
func assertOwnForkedChain(t *testing.T, tester *downloadTester, common int, lengths []int) {
    // Initialize the counters for the first fork
    headers, blocks, receipts := lengths[0], lengths[0], lengths[0]-fsMinFullBlocks

    if receipts < 0 {
        receipts = 1
    }
    // Update the counters for each subsequent fork
    for _, length := range lengths[1:] {
        headers += length - common
        blocks += length - common
        receipts += length - common - fsMinFullBlocks
    }
    switch tester.downloader.mode {
    case FullSync:
        receipts = 1
    case LightSync:
        blocks, receipts = 1, 1
    }
    if hs := len(tester.ownHeaders); hs != headers {
        t.Fatalf("synchronised headers mismatch: have %v, want %v", hs, headers)
    }
    if bs := len(tester.ownBlocks); bs != blocks {
        t.Fatalf("synchronised blocks mismatch: have %v, want %v", bs, blocks)
    }
    if rs := len(tester.ownReceipts); rs != receipts {
        t.Fatalf("synchronised receipts mismatch: have %v, want %v", rs, receipts)
    }
}

// Tests that simple synchronization against a canonical chain works correctly.
// In this test common ancestor lookup should be short circuited and not require
// binary searching.
func TestCanonicalSynchronisation62(t *testing.T)      { testCanonicalSynchronisation(t, 62, FullSync) }
func TestCanonicalSynchronisation63Full(t *testing.T)  { testCanonicalSynchronisation(t, 63, FullSync) }
func TestCanonicalSynchronisation63Fast(t *testing.T)  { testCanonicalSynchronisation(t, 63, FastSync) }
func TestCanonicalSynchronisation64Full(t *testing.T)  { testCanonicalSynchronisation(t, 64, FullSync) }
func TestCanonicalSynchronisation64Fast(t *testing.T)  { testCanonicalSynchronisation(t, 64, FastSync) }
func TestCanonicalSynchronisation64Light(t *testing.T) { testCanonicalSynchronisation(t, 64, LightSync) }

func testCanonicalSynchronisation(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    // Create a small enough block chain to download
    chain := testChainBase.shorten(blockCacheItems - 15)
    tester.newPeer("peer", protocol, chain)

    // Synchronise with the peer and make sure all relevant data was retrieved
    if err := tester.sync("peer", 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    assertOwnChain(t, tester, chain.len())
}

// Tests that if a large batch of blocks are being downloaded, it is throttled
// until the cached blocks are retrieved.
func TestThrottling62(t *testing.T)     { testThrottling(t, 62, FullSync) }
func TestThrottling63Full(t *testing.T) { testThrottling(t, 63, FullSync) }
func TestThrottling63Fast(t *testing.T) { testThrottling(t, 63, FastSync) }
func TestThrottling64Full(t *testing.T) { testThrottling(t, 64, FullSync) }
func TestThrottling64Fast(t *testing.T) { testThrottling(t, 64, FastSync) }

func testThrottling(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()
    tester := newTester()
    defer tester.terminate()

    // Create a long block chain to download and the tester
    targetBlocks := testChainBase.len() - 1
    tester.newPeer("peer", protocol, testChainBase)

    // Wrap the importer to allow stepping
    blocked, proceed := uint32(0), make(chan struct{})
    tester.downloader.chainInsertHook = func(results []*fetchResult) {
        atomic.StoreUint32(&blocked, uint32(len(results)))
        <-proceed
    }
    // Start a synchronisation concurrently
    errc := make(chan error)
    go func() {
        errc <- tester.sync("peer", 0, mode)
    }()
    // Iteratively take some blocks, always checking the retrieval count
    for {
        // Check the retrieval count synchronously (! reason for this ugly block)
        tester.lock.RLock()
        retrieved := len(tester.ownBlocks)
        tester.lock.RUnlock()
        if retrieved >= targetBlocks+1 {
            break
        }
        // Wait a bit for sync to throttle itself
        var cached, frozen int
        for start := time.Now(); time.Since(start) < 3*time.Second; {
            time.Sleep(25 * time.Millisecond)

            tester.lock.Lock()
            tester.downloader.queue.lock.Lock()
            cached = len(tester.downloader.queue.blockDonePool)
            if mode == FastSync {
                if receipts := len(tester.downloader.queue.receiptDonePool); receipts < cached {
                    cached = receipts
                }
            }
            frozen = int(atomic.LoadUint32(&blocked))
            retrieved = len(tester.ownBlocks)
            tester.downloader.queue.lock.Unlock()
            tester.lock.Unlock()

            if cached == blockCacheItems || cached == blockCacheItems-reorgProtHeaderDelay || retrieved+cached+frozen == targetBlocks+1 || retrieved+cached+frozen == targetBlocks+1-reorgProtHeaderDelay {
                break
            }
        }
        // Make sure we filled up the cache, then exhaust it
        time.Sleep(25 * time.Millisecond) // give it a chance to screw up

        tester.lock.RLock()
        retrieved = len(tester.ownBlocks)
        tester.lock.RUnlock()
        if cached != blockCacheItems && cached != blockCacheItems-reorgProtHeaderDelay && retrieved+cached+frozen != targetBlocks+1 && retrieved+cached+frozen != targetBlocks+1-reorgProtHeaderDelay {
            t.Fatalf("block count mismatch: have %v, want %v (owned %v, blocked %v, target %v)", cached, blockCacheItems, retrieved, frozen, targetBlocks+1)
        }
        // Permit the blocked blocks to import
        if atomic.LoadUint32(&blocked) > 0 {
            atomic.StoreUint32(&blocked, uint32(0))
            proceed <- struct{}{}
        }
    }
    // Check that we haven't pulled more blocks than available
    assertOwnChain(t, tester, targetBlocks+1)
    if err := <-errc; err != nil {
        t.Fatalf("block synchronization failed: %v", err)
    }
}

// Tests that an inactive downloader will not accept incoming block headers and
// bodies.
func TestInactiveDownloader62(t *testing.T) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    // Check that neither block headers nor bodies are accepted
    if err := tester.downloader.DeliverHeaders("bad peer", []*types.HeaderWithGovState{}); err != errNoSyncActive {
        t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
    }
    if err := tester.downloader.DeliverBodies("bad peer", [][]*types.Transaction{}, [][]*types.Header{}); err != errNoSyncActive {
        t.Errorf("error mismatch: have %v, want  %v", err, errNoSyncActive)
    }
}

// Tests that an inactive downloader will not accept incoming block headers,
// bodies and receipts.
func TestInactiveDownloader63(t *testing.T) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    // Check that neither block headers nor bodies are accepted
    if err := tester.downloader.DeliverHeaders("bad peer", []*types.HeaderWithGovState{}); err != errNoSyncActive {
        t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
    }
    if err := tester.downloader.DeliverBodies("bad peer", [][]*types.Transaction{}, [][]*types.Header{}); err != errNoSyncActive {
        t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
    }
    if err := tester.downloader.DeliverReceipts("bad peer", [][]*types.Receipt{}); err != errNoSyncActive {
        t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
    }
}

// Tests that a canceled download wipes all previously accumulated state.
func TestCancel62(t *testing.T)      { testCancel(t, 62, FullSync) }
func TestCancel63Full(t *testing.T)  { testCancel(t, 63, FullSync) }
func TestCancel63Fast(t *testing.T)  { testCancel(t, 63, FastSync) }
func TestCancel64Full(t *testing.T)  { testCancel(t, 64, FullSync) }
func TestCancel64Fast(t *testing.T)  { testCancel(t, 64, FastSync) }
func TestCancel64Light(t *testing.T) { testCancel(t, 64, LightSync) }

func testCancel(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    chain := testChainBase.shorten(MaxHeaderFetch)
    tester.newPeer("peer", protocol, chain)

    // Make sure canceling works with a pristine downloader
    tester.downloader.Cancel()
    if !tester.downloader.queue.Idle() {
        t.Errorf("download queue not idle")
    }
    // Synchronise with the peer, but cancel afterwards
    if err := tester.sync("peer", 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    tester.downloader.Cancel()
    if !tester.downloader.queue.Idle() {
        t.Errorf("download queue not idle")
    }
}

// Tests that synchronisation from multiple peers works as intended (multi thread sanity test).
func TestMultiSynchronisation62(t *testing.T)      { testMultiSynchronisation(t, 62, FullSync) }
func TestMultiSynchronisation63Full(t *testing.T)  { testMultiSynchronisation(t, 63, FullSync) }
func TestMultiSynchronisation63Fast(t *testing.T)  { testMultiSynchronisation(t, 63, FastSync) }
func TestMultiSynchronisation64Full(t *testing.T)  { testMultiSynchronisation(t, 64, FullSync) }
func TestMultiSynchronisation64Fast(t *testing.T)  { testMultiSynchronisation(t, 64, FastSync) }
func TestMultiSynchronisation64Light(t *testing.T) { testMultiSynchronisation(t, 64, LightSync) }

func testMultiSynchronisation(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    // Create various peers with various parts of the chain
    targetPeers := 8
    chain := testChainBase.shorten(targetPeers * 100)

    for i := 0; i < targetPeers; i++ {
        id := fmt.Sprintf("peer #%d", i)
        tester.newPeer(id, protocol, chain.shorten(chain.len()/(i+1)))
    }
    if err := tester.sync("peer #0", 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    assertOwnChain(t, tester, chain.len())
}

// Tests that synchronisations behave well in multi-version protocol environments
// and not wreak havoc on other nodes in the network.
func TestMultiProtoSynchronisation62(t *testing.T)      { testMultiProtoSync(t, 62, FullSync) }
func TestMultiProtoSynchronisation63Full(t *testing.T)  { testMultiProtoSync(t, 63, FullSync) }
func TestMultiProtoSynchronisation63Fast(t *testing.T)  { testMultiProtoSync(t, 63, FastSync) }
func TestMultiProtoSynchronisation64Full(t *testing.T)  { testMultiProtoSync(t, 64, FullSync) }
func TestMultiProtoSynchronisation64Fast(t *testing.T)  { testMultiProtoSync(t, 64, FastSync) }
func TestMultiProtoSynchronisation64Light(t *testing.T) { testMultiProtoSync(t, 64, LightSync) }

func testMultiProtoSync(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    // Create a small enough block chain to download
    chain := testChainBase.shorten(blockCacheItems - 15)

    // Create peers of every type
    tester.newPeer("peer 62", 62, chain)
    tester.newPeer("peer 63", 63, chain)
    tester.newPeer("peer 64", 64, chain)

    // Synchronise with the requested peer and make sure all blocks were retrieved
    if err := tester.sync(fmt.Sprintf("peer %d", protocol), 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    assertOwnChain(t, tester, chain.len())

    // Check that no peers have been dropped off
    for _, version := range []int{62, 63, 64} {
        peer := fmt.Sprintf("peer %d", version)
        if _, ok := tester.peers[peer]; !ok {
            t.Errorf("%s dropped", peer)
        }
    }
}

// Tests that if a block is empty (e.g. header only), no body request should be
// made, and instead the header should be assembled into a whole block in itself.
func TestEmptyShortCircuit62(t *testing.T)      { testEmptyShortCircuit(t, 62, FullSync) }
func TestEmptyShortCircuit63Full(t *testing.T)  { testEmptyShortCircuit(t, 63, FullSync) }
func TestEmptyShortCircuit63Fast(t *testing.T)  { testEmptyShortCircuit(t, 63, FastSync) }
func TestEmptyShortCircuit64Full(t *testing.T)  { testEmptyShortCircuit(t, 64, FullSync) }
func TestEmptyShortCircuit64Fast(t *testing.T)  { testEmptyShortCircuit(t, 64, FastSync) }
func TestEmptyShortCircuit64Light(t *testing.T) { testEmptyShortCircuit(t, 64, LightSync) }

func testEmptyShortCircuit(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    // Create a block chain to download
    chain := testChainBase
    tester.newPeer("peer", protocol, chain)

    // Instrument the downloader to signal body requests
    bodiesHave, receiptsHave := int32(0), int32(0)
    tester.downloader.bodyFetchHook = func(headers []*types.Header) {
        atomic.AddInt32(&bodiesHave, int32(len(headers)))
    }
    tester.downloader.receiptFetchHook = func(headers []*types.Header) {
        atomic.AddInt32(&receiptsHave, int32(len(headers)))
    }
    // Synchronise with the peer and make sure all blocks were retrieved
    if err := tester.sync("peer", 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    assertOwnChain(t, tester, chain.len())

    // Validate the number of block bodies that should have been requested
    bodiesNeeded, receiptsNeeded := 0, 0
    for _, block := range chain.blockm {
        if mode != LightSync && block != tester.genesis && (len(block.Transactions()) > 0 || len(block.Uncles()) > 0) {
            bodiesNeeded++
        }
    }
    for _, receipt := range chain.receiptm {
        if mode == FastSync && len(receipt) > 0 {
            receiptsNeeded++
        }
    }
    if int(bodiesHave) != bodiesNeeded {
        t.Errorf("body retrieval count mismatch: have %v, want %v", bodiesHave, bodiesNeeded)
    }
    if int(receiptsHave) != receiptsNeeded {
        t.Errorf("receipt retrieval count mismatch: have %v, want %v", receiptsHave, receiptsNeeded)
    }
}

// Tests that headers are enqueued continuously, preventing malicious nodes from
// stalling the downloader by feeding gapped header chains.
func TestMissingHeaderAttack62(t *testing.T)      { testMissingHeaderAttack(t, 62, FullSync) }
func TestMissingHeaderAttack63Full(t *testing.T)  { testMissingHeaderAttack(t, 63, FullSync) }
func TestMissingHeaderAttack63Fast(t *testing.T)  { testMissingHeaderAttack(t, 63, FastSync) }
func TestMissingHeaderAttack64Full(t *testing.T)  { testMissingHeaderAttack(t, 64, FullSync) }
func TestMissingHeaderAttack64Fast(t *testing.T)  { testMissingHeaderAttack(t, 64, FastSync) }
func TestMissingHeaderAttack64Light(t *testing.T) { testMissingHeaderAttack(t, 64, LightSync) }

func testMissingHeaderAttack(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    chain := testChainBase.shorten(blockCacheItems - 15)
    brokenChain := chain.shorten(chain.len())
    delete(brokenChain.headerm, brokenChain.chain[brokenChain.len()/2])
    tester.newPeer("attack", protocol, brokenChain)

    if err := tester.sync("attack", 0, mode); err == nil {
        t.Fatalf("succeeded attacker synchronisation")
    }
    // Synchronise with the valid peer and make sure sync succeeds
    tester.newPeer("valid", protocol, chain)
    if err := tester.sync("valid", 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    assertOwnChain(t, tester, chain.len())
}

// Tests that if requested headers are shifted (i.e. first is missing), the queue
// detects the invalid numbering.
func TestShiftedHeaderAttack62(t *testing.T)      { testShiftedHeaderAttack(t, 62, FullSync) }
func TestShiftedHeaderAttack63Full(t *testing.T)  { testShiftedHeaderAttack(t, 63, FullSync) }
func TestShiftedHeaderAttack63Fast(t *testing.T)  { testShiftedHeaderAttack(t, 63, FastSync) }
func TestShiftedHeaderAttack64Full(t *testing.T)  { testShiftedHeaderAttack(t, 64, FullSync) }
func TestShiftedHeaderAttack64Fast(t *testing.T)  { testShiftedHeaderAttack(t, 64, FastSync) }
func TestShiftedHeaderAttack64Light(t *testing.T) { testShiftedHeaderAttack(t, 64, LightSync) }

func testShiftedHeaderAttack(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    chain := testChainBase.shorten(blockCacheItems - 15)

    // Attempt a full sync with an attacker feeding shifted headers
    brokenChain := chain.shorten(chain.len())
    delete(brokenChain.headerm, brokenChain.chain[1])
    delete(brokenChain.blockm, brokenChain.chain[1])
    delete(brokenChain.receiptm, brokenChain.chain[1])
    tester.newPeer("attack", protocol, brokenChain)
    if err := tester.sync("attack", 0, mode); err == nil {
        t.Fatalf("succeeded attacker synchronisation")
    }

    // Synchronise with the valid peer and make sure sync succeeds
    tester.newPeer("valid", protocol, chain)
    if err := tester.sync("valid", 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    assertOwnChain(t, tester, chain.len())
}

// Tests that upon detecting an invalid header, the recent ones are rolled back
// for various failure scenarios. Afterwards a full sync is attempted to make
// sure no state was corrupted.
func TestInvalidHeaderRollback63Fast(t *testing.T)  { testInvalidHeaderRollback(t, 63, FastSync) }
func TestInvalidHeaderRollback64Fast(t *testing.T)  { testInvalidHeaderRollback(t, 64, FastSync) }
func TestInvalidHeaderRollback64Light(t *testing.T) { testInvalidHeaderRollback(t, 64, LightSync) }

func testInvalidHeaderRollback(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    // Create a small enough block chain to download
    targetBlocks := 3*fsHeaderSafetyNet + 256 + fsMinFullBlocks
    chain := testChainBase.shorten(targetBlocks)

    // Attempt to sync with an attacker that feeds junk during the fast sync phase.
    // This should result in the last fsHeaderSafetyNet headers being rolled back.
    missing := fsHeaderSafetyNet + MaxHeaderFetch + 1
    fastAttackChain := chain.shorten(chain.len())
    delete(fastAttackChain.headerm, fastAttackChain.chain[missing])
    tester.newPeer("fast-attack", protocol, fastAttackChain)

    if err := tester.sync("fast-attack", 0, mode); err == nil {
        t.Fatalf("succeeded fast attacker synchronisation")
    }
    if head := tester.CurrentHeader().Number.Int64(); int(head) > MaxHeaderFetch {
        t.Errorf("rollback head mismatch: have %v, want at most %v", head, MaxHeaderFetch)
    }

    // Attempt to sync with an attacker that feeds junk during the block import phase.
    // This should result in both the last fsHeaderSafetyNet number of headers being
    // rolled back, and also the pivot point being reverted to a non-block status.
    missing = 3*fsHeaderSafetyNet + MaxHeaderFetch + 1
    blockAttackChain := chain.shorten(chain.len())
    delete(fastAttackChain.headerm, fastAttackChain.chain[missing]) // Make sure the fast-attacker doesn't fill in
    delete(blockAttackChain.headerm, blockAttackChain.chain[missing])
    tester.newPeer("block-attack", protocol, blockAttackChain)

    if err := tester.sync("block-attack", 0, mode); err == nil {
        t.Fatalf("succeeded block attacker synchronisation")
    }
    if head := tester.CurrentHeader().Number.Int64(); int(head) > 2*fsHeaderSafetyNet+MaxHeaderFetch {
        t.Errorf("rollback head mismatch: have %v, want at most %v", head, 2*fsHeaderSafetyNet+MaxHeaderFetch)
    }
    if mode == FastSync {
        if head := tester.CurrentBlock().NumberU64(); head != 0 {
            t.Errorf("fast sync pivot block #%d not rolled back", head)
        }
    }

    // Attempt to sync with an attacker that withholds promised blocks after the
    // fast sync pivot point. This could be a trial to leave the node with a bad
    // but already imported pivot block.
    withholdAttackChain := chain.shorten(chain.len())
    tester.newPeer("withhold-attack", protocol, withholdAttackChain)
    tester.downloader.syncInitHook = func(uint64, uint64) {
        for i := missing; i < withholdAttackChain.len(); i++ {
            delete(withholdAttackChain.headerm, withholdAttackChain.chain[i])
        }
        tester.downloader.syncInitHook = nil
    }
    if err := tester.sync("withhold-attack", 0, mode); err == nil {
        t.Fatalf("succeeded withholding attacker synchronisation")
    }
    if head := tester.CurrentHeader().Number.Int64(); int(head) > 2*fsHeaderSafetyNet+MaxHeaderFetch {
        t.Errorf("rollback head mismatch: have %v, want at most %v", head, 2*fsHeaderSafetyNet+MaxHeaderFetch)
    }
    if mode == FastSync {
        if head := tester.CurrentBlock().NumberU64(); head != 0 {
            t.Errorf("fast sync pivot block #%d not rolled back", head)
        }
    }

    // synchronise with the valid peer and make sure sync succeeds. Since the last rollback
    // should also disable fast syncing for this process, verify that we did a fresh full
    // sync. Note, we can't assert anything about the receipts since we won't purge the
    // database of them, hence we can't use assertOwnChain.
    tester.newPeer("valid", protocol, chain)
    if err := tester.sync("valid", 0, mode); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    if hs := len(tester.ownHeaders); hs != chain.len() {
        t.Fatalf("synchronised headers mismatch: have %v, want %v", hs, chain.len())
    }
    if mode != LightSync {
        if bs := len(tester.ownBlocks); bs != chain.len() {
            t.Fatalf("synchronised blocks mismatch: have %v, want %v", bs, chain.len())
        }
    }
}

// Tests that a peer advertising an high number doesn't get to stall the downloader
// afterwards by not sending any useful hashes.
func TestHighNumberStarvationAttack62(t *testing.T) { testHighNumberStarvationAttack(t, 62, FullSync) }
func TestHighNumberStarvationAttack63Full(t *testing.T) {
    testHighNumberStarvationAttack(t, 63, FullSync)
}
func TestHighNumberStarvationAttack63Fast(t *testing.T) {
    testHighNumberStarvationAttack(t, 63, FastSync)
}
func TestHighNumberStarvationAttack64Full(t *testing.T) {
    testHighNumberStarvationAttack(t, 64, FullSync)
}
func TestHighNumberStarvationAttack64Fast(t *testing.T) {
    testHighNumberStarvationAttack(t, 64, FastSync)
}
func TestHighNumberStarvationAttack64Light(t *testing.T) {
    testHighNumberStarvationAttack(t, 64, LightSync)
}

func testHighNumberStarvationAttack(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()

    chain := testChainBase.shorten(1)
    tester.newPeer("attack", protocol, chain)
    if err := tester.sync("attack", 1000000, mode); err != errStallingPeer {
        t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errStallingPeer)
    }
}

// Tests that misbehaving peers are disconnected, whilst behaving ones are not.
func TestBlockHeaderAttackerDropping62(t *testing.T) { testBlockHeaderAttackerDropping(t, 62) }
func TestBlockHeaderAttackerDropping63(t *testing.T) { testBlockHeaderAttackerDropping(t, 63) }
func TestBlockHeaderAttackerDropping64(t *testing.T) { testBlockHeaderAttackerDropping(t, 64) }

func testBlockHeaderAttackerDropping(t *testing.T, protocol int) {
    t.Parallel()

    // Define the disconnection requirement for individual hash fetch errors
    tests := []struct {
        result error
        drop   bool
    }{
        {nil, false},                        // Sync succeeded, all is well
        {errBusy, false},                    // Sync is already in progress, no problem
        {errUnknownPeer, false},             // Peer is unknown, was already dropped, don't double drop
        {errBadPeer, true},                  // Peer was deemed bad for some reason, drop it
        {errStallingPeer, true},             // Peer was detected to be stalling, drop it
        {errNoPeers, false},                 // No peers to download from, soft race, no issue
        {errTimeout, true},                  // No hashes received in due time, drop the peer
        {errEmptyHeaderSet, true},           // No headers were returned as a response, drop as it's a dead end
        {errPeersUnavailable, true},         // Nobody had the advertised blocks, drop the advertiser
        {errInvalidAncestor, true},          // Agreed upon ancestor is not acceptable, drop the chain rewriter
        {errInvalidChain, true},             // Hash chain was detected as invalid, definitely drop
        {errInvalidBlock, false},            // A bad peer was detected, but not the sync origin
        {errInvalidBody, false},             // A bad peer was detected, but not the sync origin
        {errInvalidReceipt, false},          // A bad peer was detected, but not the sync origin
        {errCancelBlockFetch, false},        // Synchronisation was canceled, origin may be innocent, don't drop
        {errCancelHeaderFetch, false},       // Synchronisation was canceled, origin may be innocent, don't drop
        {errCancelBodyFetch, false},         // Synchronisation was canceled, origin may be innocent, don't drop
        {errCancelReceiptFetch, false},      // Synchronisation was canceled, origin may be innocent, don't drop
        {errCancelHeaderProcessing, false},  // Synchronisation was canceled, origin may be innocent, don't drop
        {errCancelContentProcessing, false}, // Synchronisation was canceled, origin may be innocent, don't drop
    }
    // Run the tests and check disconnection status
    tester := newTester()
    defer tester.terminate()
    chain := testChainBase.shorten(1)

    for i, tt := range tests {
        // Register a new peer and ensure it's presence
        id := fmt.Sprintf("test %d", i)
        if err := tester.newPeer(id, protocol, chain); err != nil {
            t.Fatalf("test %d: failed to register new peer: %v", i, err)
        }
        if _, ok := tester.peers[id]; !ok {
            t.Fatalf("test %d: registered peer not found", i)
        }
        // Simulate a synchronisation and check the required result
        tester.downloader.synchroniseMock = func(string, common.Hash) error { return tt.result }

        tester.downloader.Synchronise(id, tester.genesis.Hash(), 1000, FullSync)
        if _, ok := tester.peers[id]; !ok != tt.drop {
            t.Errorf("test %d: peer drop mismatch for %v: have %v, want %v", i, tt.result, !ok, tt.drop)
        }
    }
}

// Tests that synchronisation progress (origin block number, current block number
// and highest block number) is tracked and updated correctly.
func TestSyncProgress62(t *testing.T)      { testSyncProgress(t, 62, FullSync) }
func TestSyncProgress63Full(t *testing.T)  { testSyncProgress(t, 63, FullSync) }
func TestSyncProgress63Fast(t *testing.T)  { testSyncProgress(t, 63, FastSync) }
func TestSyncProgress64Full(t *testing.T)  { testSyncProgress(t, 64, FullSync) }
func TestSyncProgress64Fast(t *testing.T)  { testSyncProgress(t, 64, FastSync) }
func TestSyncProgress64Light(t *testing.T) { testSyncProgress(t, 64, LightSync) }

func testSyncProgress(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()
    chain := testChainBase.shorten(blockCacheItems - 15)

    // Set a sync init hook to catch progress changes
    starting := make(chan struct{})
    progress := make(chan struct{})

    tester.downloader.syncInitHook = func(origin, latest uint64) {
        starting <- struct{}{}
        <-progress
    }
    checkProgress(t, tester.downloader, "pristine", ethereum.SyncProgress{})

    // Synchronise half the blocks and check initial progress
    tester.newPeer("peer-half", protocol, chain.shorten(chain.len()/2))
    pending := new(sync.WaitGroup)
    pending.Add(1)

    go func() {
        defer pending.Done()
        if err := tester.sync("peer-half", 0, mode); err != nil {
            panic(fmt.Sprintf("failed to synchronise blocks: %v", err))
        }
    }()
    <-starting
    checkProgress(t, tester.downloader, "initial", ethereum.SyncProgress{
        HighestBlock: uint64(chain.len()/2 - 1),
    })
    progress <- struct{}{}
    pending.Wait()

    // Synchronise all the blocks and check continuation progress
    tester.newPeer("peer-full", protocol, chain)
    pending.Add(1)
    go func() {
        defer pending.Done()
        if err := tester.sync("peer-full", 0, mode); err != nil {
            panic(fmt.Sprintf("failed to synchronise blocks: %v", err))
        }
    }()
    <-starting
    checkProgress(t, tester.downloader, "completing", ethereum.SyncProgress{
        StartingBlock: uint64(chain.len()/2 - 1),
        CurrentBlock:  uint64(chain.len()/2 - 1),
        HighestBlock:  uint64(chain.len() - 1),
    })

    // Check final progress after successful sync
    progress <- struct{}{}
    pending.Wait()
    checkProgress(t, tester.downloader, "final", ethereum.SyncProgress{
        StartingBlock: uint64(chain.len()/2 - 1),
        CurrentBlock:  uint64(chain.len() - 1),
        HighestBlock:  uint64(chain.len() - 1),
    })
}

func checkProgress(t *testing.T, d *Downloader, stage string, want ethereum.SyncProgress) {
    t.Helper()
    p := d.Progress()
    p.KnownStates, p.PulledStates = 0, 0
    want.KnownStates, want.PulledStates = 0, 0
    if p != want {
        t.Fatalf("%s progress mismatch:\nhave %+v\nwant %+v", stage, p, want)
    }
}

// Tests that if synchronisation is aborted due to some failure, then the progress
// origin is not updated in the next sync cycle, as it should be considered the
// continuation of the previous sync and not a new instance.
func TestFailedSyncProgress62(t *testing.T)      { testFailedSyncProgress(t, 62, FullSync) }
func TestFailedSyncProgress63Full(t *testing.T)  { testFailedSyncProgress(t, 63, FullSync) }
func TestFailedSyncProgress63Fast(t *testing.T)  { testFailedSyncProgress(t, 63, FastSync) }
func TestFailedSyncProgress64Full(t *testing.T)  { testFailedSyncProgress(t, 64, FullSync) }
func TestFailedSyncProgress64Fast(t *testing.T)  { testFailedSyncProgress(t, 64, FastSync) }
func TestFailedSyncProgress64Light(t *testing.T) { testFailedSyncProgress(t, 64, LightSync) }

func testFailedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()
    chain := testChainBase.shorten(blockCacheItems - 15)

    // Set a sync init hook to catch progress changes
    starting := make(chan struct{})
    progress := make(chan struct{})

    tester.downloader.syncInitHook = func(origin, latest uint64) {
        starting <- struct{}{}
        <-progress
    }
    checkProgress(t, tester.downloader, "pristine", ethereum.SyncProgress{})

    // Attempt a full sync with a faulty peer
    brokenChain := chain.shorten(chain.len())
    missing := brokenChain.len() / 2
    delete(brokenChain.headerm, brokenChain.chain[missing])
    delete(brokenChain.blockm, brokenChain.chain[missing])
    delete(brokenChain.receiptm, brokenChain.chain[missing])
    tester.newPeer("faulty", protocol, brokenChain)

    pending := new(sync.WaitGroup)
    pending.Add(1)
    go func() {
        defer pending.Done()
        if err := tester.sync("faulty", 0, mode); err == nil {
            panic("succeeded faulty synchronisation")
        }
    }()
    <-starting
    checkProgress(t, tester.downloader, "initial", ethereum.SyncProgress{
        HighestBlock: uint64(brokenChain.len() - 1),
    })
    progress <- struct{}{}
    pending.Wait()
    afterFailedSync := tester.downloader.Progress()

    // Synchronise with a good peer and check that the progress origin remind the same
    // after a failure
    tester.newPeer("valid", protocol, chain)
    pending.Add(1)
    go func() {
        defer pending.Done()
        if err := tester.sync("valid", 0, mode); err != nil {
            panic(fmt.Sprintf("failed to synchronise blocks: %v", err))
        }
    }()
    <-starting
    checkProgress(t, tester.downloader, "completing", afterFailedSync)

    // Check final progress after successful sync
    progress <- struct{}{}
    pending.Wait()
    checkProgress(t, tester.downloader, "final", ethereum.SyncProgress{
        CurrentBlock: uint64(chain.len() - 1),
        HighestBlock: uint64(chain.len() - 1),
    })
}

// Tests that if an attacker fakes a chain height, after the attack is detected,
// the progress height is successfully reduced at the next sync invocation.
func TestFakedSyncProgress62(t *testing.T)      { testFakedSyncProgress(t, 62, FullSync) }
func TestFakedSyncProgress63Full(t *testing.T)  { testFakedSyncProgress(t, 63, FullSync) }
func TestFakedSyncProgress63Fast(t *testing.T)  { testFakedSyncProgress(t, 63, FastSync) }
func TestFakedSyncProgress64Full(t *testing.T)  { testFakedSyncProgress(t, 64, FullSync) }
func TestFakedSyncProgress64Fast(t *testing.T)  { testFakedSyncProgress(t, 64, FastSync) }
func TestFakedSyncProgress64Light(t *testing.T) { testFakedSyncProgress(t, 64, LightSync) }

func testFakedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
    t.Parallel()

    tester := newTester()
    defer tester.terminate()
    chain := testChainBase.shorten(blockCacheItems - 15)

    // Set a sync init hook to catch progress changes
    starting := make(chan struct{})
    progress := make(chan struct{})
    tester.downloader.syncInitHook = func(origin, latest uint64) {
        starting <- struct{}{}
        <-progress
    }
    checkProgress(t, tester.downloader, "pristine", ethereum.SyncProgress{})

    // Create and sync with an attacker that promises a higher chain than available.
    brokenChain := chain.shorten(chain.len())
    numMissing := 5
    for i := brokenChain.len() - 2; i > brokenChain.len()-numMissing; i-- {
        delete(brokenChain.headerm, brokenChain.chain[i])
    }
    tester.newPeer("attack", protocol, brokenChain)

    pending := new(sync.WaitGroup)
    pending.Add(1)
    go func() {
        defer pending.Done()
        if err := tester.sync("attack", 0, mode); err == nil {
            panic("succeeded attacker synchronisation")
        }
    }()
    <-starting
    checkProgress(t, tester.downloader, "initial", ethereum.SyncProgress{
        HighestBlock: uint64(brokenChain.len() - 1),
    })
    progress <- struct{}{}
    pending.Wait()
    afterFailedSync := tester.downloader.Progress()

    // Synchronise with a good peer and check that the progress height has been reduced to
    // the true value.
    validChain := chain.shorten(chain.len() - numMissing)
    tester.newPeer("valid", protocol, validChain)
    pending.Add(1)

    go func() {
        defer pending.Done()
        if err := tester.sync("valid", 0, mode); err != nil {
            panic(fmt.Sprintf("failed to synchronise blocks: %v", err))
        }
    }()
    <-starting
    checkProgress(t, tester.downloader, "completing", ethereum.SyncProgress{
        CurrentBlock: afterFailedSync.CurrentBlock,
        HighestBlock: uint64(validChain.len() - 1),
    })

    // Check final progress after successful sync.
    progress <- struct{}{}
    pending.Wait()
    checkProgress(t, tester.downloader, "final", ethereum.SyncProgress{
        CurrentBlock: uint64(validChain.len() - 1),
        HighestBlock: uint64(validChain.len() - 1),
    })
}

// This test reproduces an issue where unexpected deliveries would
// block indefinitely if they arrived at the right time.
func TestDeliverHeadersHang(t *testing.T) {
    t.Parallel()

    testCases := []struct {
        protocol int
        syncMode SyncMode
    }{
        {62, FullSync},
        {63, FullSync},
        {63, FastSync},
        {64, FullSync},
        {64, FastSync},
        {64, LightSync},
    }
    for _, tc := range testCases {
        t.Run(fmt.Sprintf("protocol %d mode %v", tc.protocol, tc.syncMode), func(t *testing.T) {
            t.Parallel()
            testDeliverHeadersHang(t, tc.protocol, tc.syncMode)
        })
    }
}

func testDeliverHeadersHang(t *testing.T, protocol int, mode SyncMode) {
    master := newTester()
    defer master.terminate()
    chain := testChainBase.shorten(15)

    for i := 0; i < 200; i++ {
        tester := newTester()
        tester.peerDb = master.peerDb
        tester.newPeer("peer", protocol, chain)

        // Whenever the downloader requests headers, flood it with
        // a lot of unrequested header deliveries.
        tester.downloader.peers.peers["peer"].peer = &floodingTestPeer{
            peer:   tester.downloader.peers.peers["peer"].peer,
            tester: tester,
        }
        if err := tester.sync("peer", 0, mode); err != nil {
            t.Errorf("test %d: sync failed: %v", i, err)
        }
        tester.terminate()
    }
}

type floodingTestPeer struct {
    peer   Peer
    tester *downloadTester
}

func (ftp *floodingTestPeer) Head() (common.Hash, uint64) { return ftp.peer.Head() }
func (ftp *floodingTestPeer) RequestHeadersByHash(hash common.Hash, count int, skip int, reverse, withGov bool) error {
    return ftp.peer.RequestHeadersByHash(hash, count, skip, reverse, withGov)
}
func (ftp *floodingTestPeer) RequestGovStateByHash(hash common.Hash) error {
    return ftp.peer.RequestGovStateByHash(hash)
}
func (ftp *floodingTestPeer) RequestBodies(hashes []common.Hash) error {
    return ftp.peer.RequestBodies(hashes)
}
func (ftp *floodingTestPeer) RequestReceipts(hashes []common.Hash) error {
    return ftp.peer.RequestReceipts(hashes)
}
func (ftp *floodingTestPeer) RequestNodeData(hashes []common.Hash) error {
    return ftp.peer.RequestNodeData(hashes)
}

func (ftp *floodingTestPeer) RequestHeadersByNumber(from uint64, count, skip int, reverse, withGov bool) error {
    deliveriesDone := make(chan struct{}, 500)
    for i := 0; i < cap(deliveriesDone)-1; i++ {
        peer := fmt.Sprintf("fake-peer%d", i)
        go func() {
            ftp.tester.downloader.DeliverHeaders(peer, []*types.HeaderWithGovState{{}, {}, {}, {}})
            deliveriesDone <- struct{}{}
        }()
    }

    // None of the extra deliveries should block.
    timeout := time.After(60 * time.Second)
    launched := false
    for i := 0; i < cap(deliveriesDone); i++ {
        select {
        case <-deliveriesDone:
            if !launched {
                // Start delivering the requested headers
                // after one of the flooding responses has arrived.
                go func() {
                    ftp.peer.RequestHeadersByNumber(from, count, skip, reverse, withGov)
                    deliveriesDone <- struct{}{}
                }()
                launched = true
            }
        case <-timeout:
            panic("blocked")
        }
    }
    return nil
}