path: root/eth/downloader/downloader_test.go

package downloader

import (
    "crypto/rand"
    "errors"
    "fmt"
    "math/big"
    "sync/atomic"
    "testing"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/ethdb"
    "github.com/ethereum/go-ethereum/event"
)

const (
    eth60 = 60
    eth61 = 61
)

var (
    testdb, _ = ethdb.NewMemDatabase()
    genesis   = core.GenesisBlockForTesting(testdb, common.Address{}, big.NewInt(0))
)

// makeChain creates a chain of n blocks starting at and including
// parent. the returned hash chain is ordered head->parent.
func makeChain(n int, seed byte, parent *types.Block) ([]common.Hash, map[common.Hash]*types.Block) {
    blocks := core.GenerateChain(parent, testdb, n, func(i int, gen *core.BlockGen) {
        gen.SetCoinbase(common.Address{seed})
    })
    hashes := make([]common.Hash, n+1)
    hashes[len(hashes)-1] = parent.Hash()
    blockm := make(map[common.Hash]*types.Block, n+1)
    blockm[parent.Hash()] = parent
    for i, b := range blocks {
        hashes[len(hashes)-i-2] = b.Hash()
        blockm[b.Hash()] = b
    }
    return hashes, blockm
}

// makeChainFork creates two chains of length n, such that h1[:f] and
// h2[:f] are different but have a common suffix of length n-f.
func makeChainFork(n, f int, parent *types.Block) (h1, h2 []common.Hash, b1, b2 map[common.Hash]*types.Block) {
    // Create the common suffix.
    h, b := makeChain(n-f-1, 0, parent)
    // Create the forks.
    h1, b1 = makeChain(f, 1, b[h[0]])
    h1 = append(h1, h[1:]...)
    h2, b2 = makeChain(f, 2, b[h[0]])
    h2 = append(h2, h[1:]...)
    for hash, block := range b {
        b1[hash] = block
        b2[hash] = block
    }
    return h1, h2, b1, b2
}

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

    ownHashes  []common.Hash                           // Hash chain belonging to the tester
    ownBlocks  map[common.Hash]*types.Block            // Blocks belonging to the tester
    peerHashes map[string][]common.Hash                // Hash chain belonging to different test peers
    peerBlocks map[string]map[common.Hash]*types.Block // Blocks belonging to different test peers

    maxHashFetch int // Overrides the maximum number of retrieved hashes
}

// newTester creates a new downloader test mocker.
func newTester() *downloadTester {
    tester := &downloadTester{
        ownHashes:  []common.Hash{genesis.Hash()},
        ownBlocks:  map[common.Hash]*types.Block{genesis.Hash(): genesis},
        peerHashes: make(map[string][]common.Hash),
        peerBlocks: make(map[string]map[common.Hash]*types.Block),
    }
    tester.downloader = New(new(event.TypeMux), tester.hasBlock, tester.getBlock, tester.insertChain, tester.dropPeer)

    return tester
}

// sync starts synchronizing with a remote peer, blocking until it completes.
func (dl *downloadTester) sync(id string) error {
    err := dl.downloader.synchronise(id, dl.peerHashes[id][0])
    for atomic.LoadInt32(&dl.downloader.processing) == 1 {
        time.Sleep(time.Millisecond)
    }
    return err
}

// hasBlock checks if a block is pres   ent in the testers canonical chain.
func (dl *downloadTester) hasBlock(hash common.Hash) bool {
    return dl.getBlock(hash) != nil
}

// getBlock retrieves a block from the testers canonical chain.
func (dl *downloadTester) getBlock(hash common.Hash) *types.Block {
    return dl.ownBlocks[hash]
}

// insertChain injects a new batch of blocks into the simulated chain.
func (dl *downloadTester) insertChain(blocks types.Blocks) (int, error) {
    for i, block := range blocks {
        if _, ok := dl.ownBlocks[block.ParentHash()]; !ok {
            return i, errors.New("unknown parent")
        }
        dl.ownHashes = append(dl.ownHashes, block.Hash())
        dl.ownBlocks[block.Hash()] = block
    }
    return len(blocks), nil
}

// newPeer registers a new block download source into the downloader.
func (dl *downloadTester) newPeer(id string, version int, hashes []common.Hash, blocks map[common.Hash]*types.Block) error {
    return dl.newSlowPeer(id, version, hashes, blocks, 0)
}

// newSlowPeer registers a new block download source into the downloader, with a
// specific delay time on processing the network packets sent to it, simulating
// potentially slow network IO.
func (dl *downloadTester) newSlowPeer(id string, version int, hashes []common.Hash, blocks map[common.Hash]*types.Block, delay time.Duration) error {
    err := dl.downloader.RegisterPeer(id, version, hashes[0], dl.peerGetHashesFn(id, delay), dl.peerGetBlocksFn(id, delay))
    if err == nil {
        // Assign the owned hashes and blocks to the peer (deep copy)
        dl.peerHashes[id] = make([]common.Hash, len(hashes))
        copy(dl.peerHashes[id], hashes)
        dl.peerBlocks[id] = make(map[common.Hash]*types.Block)
        for hash, block := range blocks {
            dl.peerBlocks[id][hash] = block
        }
    }
    return err
}

// dropPeer simulates a hard peer removal from the connection pool.
func (dl *downloadTester) dropPeer(id string) {
    delete(dl.peerHashes, id)
    delete(dl.peerBlocks, id)

    dl.downloader.UnregisterPeer(id)
}

// peerGetBlocksFn constructs a getHashes function associated with a particular
// peer in the download tester. The returned function can be used to retrieve
// batches of hashes from the particularly requested peer.
func (dl *downloadTester) peerGetHashesFn(id string, delay time.Duration) func(head common.Hash) error {
    return func(head common.Hash) error {
        time.Sleep(delay)

        limit := MaxHashFetch
        if dl.maxHashFetch > 0 {
            limit = dl.maxHashFetch
        }
        // Gather the next batch of hashes
        hashes := dl.peerHashes[id]
        result := make([]common.Hash, 0, limit)
        for i, hash := range hashes {
            if hash == head {
                i++
                for len(result) < cap(result) && i < len(hashes) {
                    result = append(result, hashes[i])
                    i++
                }
                break
            }
        }
        // Delay delivery a bit to allow attacks to unfold
        go func() {
            time.Sleep(time.Millisecond)
            dl.downloader.DeliverHashes(id, result)
        }()
        return nil
    }
}

// peerGetBlocksFn constructs a getBlocks function associated with a particular
// peer in the download tester. The returned function can be used to retrieve
// batches of blocks from the particularly requested peer.
func (dl *downloadTester) peerGetBlocksFn(id string, delay time.Duration) func([]common.Hash) error {
    return func(hashes []common.Hash) error {
        time.Sleep(delay)

        blocks := dl.peerBlocks[id]
        result := make([]*types.Block, 0, len(hashes))
        for _, hash := range hashes {
            if block, ok := blocks[hash]; ok {
                result = append(result, block)
            }
        }
        go dl.downloader.DeliverBlocks(id, result)

        return nil
    }
}

// Tests that simple synchronization, without throttling from a good peer works.
func TestSynchronisation(t *testing.T) {
    // Create a small enough block chain to download and the tester
    targetBlocks := blockCacheLimit - 15
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    tester := newTester()
    tester.newPeer("peer", eth60, hashes, blocks)

    // Synchronise with the peer and make sure all blocks were retrieved
    if err := tester.sync("peer"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    if imported := len(tester.ownBlocks); imported != targetBlocks+1 {
        t.Fatalf("synchronised block mismatch: have %v, want %v", imported, targetBlocks+1)
    }
}

// Tests that an inactive downloader will not accept incoming hashes and blocks.
func TestInactiveDownloader(t *testing.T) {
    tester := newTester()

    // Check that neither hashes nor blocks are accepted
    if err := tester.downloader.DeliverHashes("bad peer", []common.Hash{}); err != errNoSyncActive {
        t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
    }
    if err := tester.downloader.DeliverBlocks("bad peer", []*types.Block{}); err != errNoSyncActive {
        t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
    }
}

// Tests that a canceled download wipes all previously accumulated state.
func TestCancel(t *testing.T) {
    // Create a small enough block chain to download and the tester
    targetBlocks := blockCacheLimit - 15
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    tester := newTester()
    tester.newPeer("peer", eth60, hashes, blocks)

    // Make sure canceling works with a pristine downloader
    tester.downloader.cancel()
    hashCount, blockCount := tester.downloader.queue.Size()
    if hashCount > 0 || blockCount > 0 {
        t.Errorf("block or hash count mismatch: %d hashes, %d blocks, want 0", hashCount, blockCount)
    }
    // Synchronise with the peer, but cancel afterwards
    if err := tester.sync("peer"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    tester.downloader.cancel()
    hashCount, blockCount = tester.downloader.queue.Size()
    if hashCount > 0 || blockCount > 0 {
        t.Errorf("block or hash count mismatch: %d hashes, %d blocks, want 0", hashCount, blockCount)
    }
}

// Tests that if a large batch of blocks are being downloaded, it is throttled
// until the cached blocks are retrieved.
func TestThrottling(t *testing.T) {
    // Create a long block chain to download and the tester
    targetBlocks := 8 * blockCacheLimit
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    tester := newTester()
    tester.newPeer("peer", eth60, hashes, blocks)

    // Wrap the importer to allow stepping
    done := make(chan int)
    tester.downloader.insertChain = func(blocks types.Blocks) (int, error) {
        n, err := tester.insertChain(blocks)
        done <- n
        return n, err
    }
    // Start a synchronisation concurrently
    errc := make(chan error)
    go func() {
        errc <- tester.sync("peer")
    }()
    // Iteratively take some blocks, always checking the retrieval count
    for len(tester.ownBlocks) < targetBlocks+1 {
        // Wait a bit for sync to throttle itself
        var cached int
        for start := time.Now(); time.Since(start) < 3*time.Second; {
            time.Sleep(25 * time.Millisecond)

            cached = len(tester.downloader.queue.blockPool)
            if cached == blockCacheLimit || len(tester.ownBlocks)+cached == targetBlocks+1 {
                break
            }
        }
        // Make sure we filled up the cache, then exhaust it
        time.Sleep(25 * time.Millisecond) // give it a chance to screw up
        if cached != blockCacheLimit && len(tester.ownBlocks)+cached < targetBlocks+1 {
            t.Fatalf("block count mismatch: have %v, want %v", cached, blockCacheLimit)
        }
        <-done // finish previous blocking import
        for cached > maxBlockProcess {
            cached -= <-done
        }
        time.Sleep(25 * time.Millisecond) // yield to the insertion
    }
    <-done // finish the last blocking import

    // Check that we haven't pulled more blocks than available
    if len(tester.ownBlocks) > targetBlocks+1 {
        t.Fatalf("target block count mismatch: have %v, want %v", len(tester.ownBlocks), targetBlocks+1)
    }
    if err := <-errc; err != nil {
        t.Fatalf("block synchronization failed: %v", err)
    }
}

// Tests that synchronisation from multiple peers works as intended (multi thread sanity test).
func TestMultiSynchronisation(t *testing.T) {
    // Create various peers with various parts of the chain
    targetPeers := 16
    targetBlocks := targetPeers*blockCacheLimit - 15
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    tester := newTester()
    for i := 0; i < targetPeers; i++ {
        id := fmt.Sprintf("peer #%d", i)
        tester.newPeer(id, eth60, hashes[i*blockCacheLimit:], blocks)
    }
    // Synchronise with the middle peer and make sure half of the blocks were retrieved
    id := fmt.Sprintf("peer #%d", targetPeers/2)
    if err := tester.sync(id); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    if imported := len(tester.ownBlocks); imported != len(tester.peerHashes[id]) {
        t.Fatalf("synchronised block mismatch: have %v, want %v", imported, len(tester.peerHashes[id]))
    }
    // Synchronise with the best peer and make sure everything is retrieved
    if err := tester.sync("peer #0"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    if imported := len(tester.ownBlocks); imported != targetBlocks+1 {
        t.Fatalf("synchronised block mismatch: have %v, want %v", imported, targetBlocks+1)
    }
}

// Tests that synchronising with a peer who's very slow at network IO does not
// stall the other peers in the system.
func TestSlowSynchronisation(t *testing.T) {
    tester := newTester()

    // Create a batch of blocks, with a slow and a full speed peer
    targetCycles := 2
    targetBlocks := targetCycles*blockCacheLimit - 15
    targetIODelay := time.Second
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    tester.newSlowPeer("fast", eth60, hashes, blocks, 0)
    tester.newSlowPeer("slow", eth60, hashes, blocks, targetIODelay)

    // Try to sync with the peers (pull hashes from fast)
    start := time.Now()
    if err := tester.sync("fast"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    if imported := len(tester.ownBlocks); imported != targetBlocks+1 {
        t.Fatalf("synchronised block mismatch: have %v, want %v", imported, targetBlocks+1)
    }
    // Check that the slow peer got hit at most once per block-cache-size import
    limit := time.Duration(targetCycles+1) * targetIODelay
    if delay := time.Since(start); delay >= limit {
        t.Fatalf("synchronisation exceeded delay limit: have %v, want %v", delay, limit)
    }
}

// Tests that if a peer returns an invalid chain with a block pointing to a non-
// existing parent, it is correctly detected and handled.
func TestNonExistingParentAttack(t *testing.T) {
    tester := newTester()

    // Forge a single-link chain with a forged header
    hashes, blocks := makeChain(1, 0, genesis)
    tester.newPeer("valid", eth60, hashes, blocks)

    wrongblock := types.NewBlock(&types.Header{}, nil, nil, nil)
    wrongblock.Td = blocks[hashes[0]].Td
    hashes, blocks = makeChain(1, 0, wrongblock)
    tester.newPeer("attack", eth60, hashes, blocks)

    // Try and sync with the malicious node and check that it fails
    if err := tester.sync("attack"); err == nil {
        t.Fatalf("block synchronization succeeded")
    }
    if tester.hasBlock(hashes[0]) {
        t.Fatalf("tester accepted unknown-parent block: %v", blocks[hashes[0]])
    }
    // Try to synchronize with the valid chain and make sure it succeeds
    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    if !tester.hasBlock(tester.peerHashes["valid"][0]) {
        t.Fatalf("tester didn't accept known-parent block: %v", tester.peerBlocks["valid"][hashes[0]])
    }
}

// Tests that if a malicious peers keeps sending us repeating hashes, we don't
// loop indefinitely.
func TestRepeatingHashAttack(t *testing.T) { // TODO: Is this thing valid??
    tester := newTester()

    // Create a valid chain, but drop the last link
    hashes, blocks := makeChain(blockCacheLimit, 0, genesis)
    tester.newPeer("valid", eth60, hashes, blocks)
    tester.newPeer("attack", eth60, hashes[:len(hashes)-1], blocks)

    // Try and sync with the malicious node
    errc := make(chan error)
    go func() {
        errc <- tester.sync("attack")
    }()
    // Make sure that syncing returns and does so with a failure
    select {
    case <-time.After(time.Second):
        t.Fatalf("synchronisation blocked")
    case err := <-errc:
        if err == nil {
            t.Fatalf("synchronisation succeeded")
        }
    }
    // Ensure that a valid chain can still pass sync
    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
}

// Tests that if a malicious peers returns a non-existent block hash, it should
// eventually time out and the sync reattempted.
func TestNonExistingBlockAttack(t *testing.T) {
    tester := newTester()

    // Create a valid chain, but forge the last link
    hashes, blocks := makeChain(blockCacheLimit, 0, genesis)
    tester.newPeer("valid", eth60, hashes, blocks)

    hashes[len(hashes)/2] = common.Hash{}
    tester.newPeer("attack", eth60, hashes, blocks)

    // Try and sync with the malicious node and check that it fails
    if err := tester.sync("attack"); err != errPeersUnavailable {
        t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errPeersUnavailable)
    }
    // Ensure that a valid chain can still pass sync
    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
}

// Tests that if a malicious peer is returning hashes in a weird order, that the
// sync throttler doesn't choke on them waiting for the valid blocks.
func TestInvalidHashOrderAttack(t *testing.T) {
    tester := newTester()

    // Create a valid long chain, but reverse some hashes within
    hashes, blocks := makeChain(4*blockCacheLimit, 0, genesis)
    tester.newPeer("valid", eth60, hashes, blocks)

    chunk1 := make([]common.Hash, blockCacheLimit)
    chunk2 := make([]common.Hash, blockCacheLimit)
    copy(chunk1, hashes[blockCacheLimit:2*blockCacheLimit])
    copy(chunk2, hashes[2*blockCacheLimit:3*blockCacheLimit])

    copy(hashes[2*blockCacheLimit:], chunk1)
    copy(hashes[blockCacheLimit:], chunk2)
    tester.newPeer("attack", eth60, hashes, blocks)

    // Try and sync with the malicious node and check that it fails
    if err := tester.sync("attack"); err != errInvalidChain {
        t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errInvalidChain)
    }
    // Ensure that a valid chain can still pass sync
    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
}

// Tests that if a malicious peer makes up a random hash chain and tries to push
// indefinitely, it actually gets caught with it.
func TestMadeupHashChainAttack(t *testing.T) {
    tester := newTester()
    blockSoftTTL = 100 * time.Millisecond
    crossCheckCycle = 25 * time.Millisecond

    // Create a long chain of hashes without backing blocks
    hashes, blocks := makeChain(4*blockCacheLimit, 0, genesis)

    randomHashes := make([]common.Hash, 1024*blockCacheLimit)
    for i := range randomHashes {
        rand.Read(randomHashes[i][:])
    }

    tester.newPeer("valid", eth60, hashes, blocks)
    tester.newPeer("attack", eth60, randomHashes, nil)

    // Try and sync with the malicious node and check that it fails
    if err := tester.sync("attack"); err != errCrossCheckFailed {
        t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errCrossCheckFailed)
    }
    // Ensure that a valid chain can still pass sync
    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
}

// Tests that if a malicious peer makes up a random hash chain, and tries to push
// indefinitely, one hash at a time, it actually gets caught with it. The reason
// this is separate from the classical made up chain attack is that sending hashes
// one by one prevents reliable block/parent verification.
func TestMadeupHashChainDrippingAttack(t *testing.T) {
    // Create a random chain of hashes to drip
    randomHashes := make([]common.Hash, 16*blockCacheLimit)
    for i := range randomHashes {
        rand.Read(randomHashes[i][:])
    }
    randomHashes[len(randomHashes)-1] = genesis.Hash()
    tester := newTester()

    // Try and sync with the attacker, one hash at a time
    tester.maxHashFetch = 1
    tester.newPeer("attack", eth60, randomHashes, nil)
    if err := tester.sync("attack"); err != errStallingPeer {
        t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errStallingPeer)
    }
}

// Tests that if a malicious peer makes up a random block chain, and tried to
// push indefinitely, it actually gets caught with it.
func TestMadeupBlockChainAttack(t *testing.T) {
    defaultBlockTTL := blockSoftTTL
    defaultCrossCheckCycle := crossCheckCycle

    blockSoftTTL = 100 * time.Millisecond
    crossCheckCycle = 25 * time.Millisecond

    // Create a long chain of blocks and simulate an invalid chain by dropping every second
    hashes, blocks := makeChain(16*blockCacheLimit, 0, genesis)
    gapped := make([]common.Hash, len(hashes)/2)
    for i := 0; i < len(gapped); i++ {
        gapped[i] = hashes[2*i]
    }
    // Try and sync with the malicious node and check that it fails
    tester := newTester()
    tester.newPeer("attack", eth60, gapped, blocks)
    if err := tester.sync("attack"); err != errCrossCheckFailed {
        t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errCrossCheckFailed)
    }
    // Ensure that a valid chain can still pass sync
    blockSoftTTL = defaultBlockTTL
    crossCheckCycle = defaultCrossCheckCycle

    tester.newPeer("valid", eth60, hashes, blocks)
    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
}

// Tests that if one/multiple malicious peers try to feed a banned blockchain to
// the downloader, it will not keep refetching the same chain indefinitely, but
// gradually block pieces of it, until its head is also blocked.
func TestBannedChainStarvationAttack(t *testing.T) {
    n := 8 * blockCacheLimit
    fork := n/2 - 23
    hashes, forkHashes, blocks, forkBlocks := makeChainFork(n, fork, genesis)

    // Create the tester and ban the selected hash.
    tester := newTester()
    tester.downloader.banned.Add(forkHashes[fork-1])
    tester.newPeer("valid", eth60, hashes, blocks)
    tester.newPeer("attack", eth60, forkHashes, forkBlocks)

    // Iteratively try to sync, and verify that the banned hash list grows until
    // the head of the invalid chain is blocked too.
    for banned := tester.downloader.banned.Size(); ; {
        // Try to sync with the attacker, check hash chain failure
        if err := tester.sync("attack"); err != errInvalidChain {
            if tester.downloader.banned.Has(forkHashes[0]) && err == errBannedHead {
                break
            }
            t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errInvalidChain)
        }
        // Check that the ban list grew with at least 1 new item, or all banned
        bans := tester.downloader.banned.Size()
        if bans < banned+1 {
            t.Fatalf("ban count mismatch: have %v, want %v+", bans, banned+1)
        }
        banned = bans
    }
    // Check that after banning an entire chain, bad peers get dropped
    if err := tester.newPeer("new attacker", eth60, forkHashes, forkBlocks); err != errBannedHead {
        t.Fatalf("peer registration mismatch: have %v, want %v", err, errBannedHead)
    }
    if peer := tester.downloader.peers.Peer("new attacker"); peer != nil {
        t.Fatalf("banned attacker registered: %v", peer)
    }
    // Ensure that a valid chain can still pass sync
    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
}

// Tests that if a peer sends excessively many/large invalid chains that are
// gradually banned, it will have an upper limit on the consumed memory and also
// the origin bad hashes will not be evacuated.
func TestBannedChainMemoryExhaustionAttack(t *testing.T) {
    // Construct a banned chain with more chunks than the ban limit
    n := 8 * blockCacheLimit
    fork := n/2 - 23
    hashes, forkHashes, blocks, forkBlocks := makeChainFork(n, fork, genesis)

    // Create the tester and ban the root hash of the fork.
    tester := newTester()
    tester.downloader.banned.Add(forkHashes[fork-1])

    // Reduce the test size a bit
    defaultMaxBlockFetch := MaxBlockFetch
    defaultMaxBannedHashes := maxBannedHashes

    MaxBlockFetch = 4
    maxBannedHashes = 256

    tester.newPeer("valid", eth60, hashes, blocks)
    tester.newPeer("attack", eth60, forkHashes, forkBlocks)

    // Iteratively try to sync, and verify that the banned hash list grows until
    // the head of the invalid chain is blocked too.
    for {
        // Try to sync with the attacker, check hash chain failure
        if err := tester.sync("attack"); err != errInvalidChain {
            t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errInvalidChain)
        }
        // Short circuit if the entire chain was banned.
        if tester.downloader.banned.Has(forkHashes[0]) {
            break
        }
        // Otherwise ensure we never exceed the memory allowance and the hard coded bans are untouched
        if bans := tester.downloader.banned.Size(); bans > maxBannedHashes {
            t.Fatalf("ban cap exceeded: have %v, want max %v", bans, maxBannedHashes)
        }
        for hash, _ := range core.BadHashes {
            if !tester.downloader.banned.Has(hash) {
                t.Fatalf("hard coded ban evacuated: %x", hash)
            }
        }
    }
    // Ensure that a valid chain can still pass sync
    MaxBlockFetch = defaultMaxBlockFetch
    maxBannedHashes = defaultMaxBannedHashes

    if err := tester.sync("valid"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
}

// Tests a corner case (potential attack) where a peer delivers both good as well
// as unrequested blocks to a hash request. This may trigger a different code
// path than the fully correct or fully invalid delivery, potentially causing
// internal state problems
//
// No, don't delete this test, it actually did happen!
func TestOverlappingDeliveryAttack(t *testing.T) {
    // Create an arbitrary batch of blocks ( < cache-size not to block)
    targetBlocks := blockCacheLimit - 23
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    // Register an attacker that always returns non-requested blocks too
    tester := newTester()
    tester.newPeer("attack", eth60, hashes, blocks)

    rawGetBlocks := tester.downloader.peers.Peer("attack").getBlocks
    tester.downloader.peers.Peer("attack").getBlocks = func(request []common.Hash) error {
        // Add a non requested hash the screw the delivery (genesis should be fine)
        return rawGetBlocks(append(request, hashes[0]))
    }
    // Test that synchronisation can complete, check for import success
    if err := tester.sync("attack"); err != nil {
        t.Fatalf("failed to synchronise blocks: %v", err)
    }
    start := time.Now()
    for len(tester.ownHashes) != len(hashes) && time.Since(start) < time.Second {
        time.Sleep(50 * time.Millisecond)
    }
    if len(tester.ownHashes) != len(hashes) {
        t.Fatalf("chain length mismatch: have %v, want %v", len(tester.ownHashes), len(hashes))
    }
}

// Tests that misbehaving peers are disconnected, whilst behaving ones are not.
func TestHashAttackerDropping(t *testing.T) {
    // 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
        {errBannedHead, true},        // Peer's head hash is a known bad hash, drop it
        {errNoPeers, false},          // No peers to download from, soft race, no issue
        {errPendingQueue, false},     // There are blocks still cached, wait to exhaust, no issue
        {errTimeout, true},           // No hashes received in due time, drop the peer
        {errEmptyHashSet, true},      // No hashes were returned as a response, drop as it's a dead end
        {errPeersUnavailable, true},  // Nobody had the advertised blocks, drop the advertiser
        {errInvalidChain, true},      // Hash chain was detected as invalid, definitely drop
        {errCrossCheckFailed, true},  // Hash-origin failed to pass a block cross check, drop
        {errCancelHashFetch, false},  // Synchronisation was canceled, origin may be innocent, don't drop
        {errCancelBlockFetch, false}, // Synchronisation was canceled, origin may be innocent, don't drop
    }
    // Run the tests and check disconnection status
    tester := newTester()
    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, eth60, []common.Hash{genesis.Hash()}, nil); err != nil {
            t.Fatalf("test %d: failed to register new peer: %v", i, err)
        }
        if _, ok := tester.peerHashes[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, genesis.Hash())
        if _, ok := tester.peerHashes[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 feeding bad blocks will result in a peer drop.
func TestBlockAttackerDropping(t *testing.T) {
    // Define the disconnection requirement for individual block import errors
    tests := []struct {
        failure bool
        drop    bool
    }{
        {true, true},
        {false, false},
    }

    // Run the tests and check disconnection status
    tester := newTester()
    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, eth60, []common.Hash{common.Hash{}}, nil); err != nil {
            t.Fatalf("test %d: failed to register new peer: %v", i, err)
        }
        if _, ok := tester.peerHashes[id]; !ok {
            t.Fatalf("test %d: registered peer not found", i)
        }
        // Assemble a good or bad block, depending of the test
        raw := core.GenerateChain(genesis, testdb, 1, nil)[0]
        if tt.failure {
            parent := types.NewBlock(&types.Header{}, nil, nil, nil)
            raw = core.GenerateChain(parent, testdb, 1, nil)[0]
        }
        block := &Block{OriginPeer: id, RawBlock: raw}

        // Simulate block processing and check the result
        tester.downloader.queue.blockCache[0] = block
        tester.downloader.process()
        if _, ok := tester.peerHashes[id]; !ok != tt.drop {
            t.Errorf("test %d: peer drop mismatch for %v: have %v, want %v", i, tt.failure, !ok, tt.drop)
        }
    }
}