path: root/dex/fetcher/fetcher_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 fetcher

import (
    "errors"
    "math/big"
    "sync"
    "sync/atomic"
    "testing"
    "time"

    "github.com/dexon-foundation/dexon/common"
    "github.com/dexon-foundation/dexon/consensus/ethash"
    "github.com/dexon-foundation/dexon/core"
    "github.com/dexon-foundation/dexon/core/types"
    "github.com/dexon-foundation/dexon/crypto"
    "github.com/dexon-foundation/dexon/ethdb"
    "github.com/dexon-foundation/dexon/params"
)

var (
    testdb       = ethdb.NewMemDatabase()
    testKey, _   = crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
    testAddress  = crypto.PubkeyToAddress(testKey.PublicKey)
    genesis      = core.GenesisBlockForTesting(testdb, testAddress, big.NewInt(1000000000))
    unknownBlock = types.NewBlock(&types.Header{GasLimit: params.GenesisGasLimit}, nil, nil, nil)
)

// makeChain creates a chain of n blocks starting at and including parent.
// the returned hash chain is ordered head->parent. In addition, every 3rd block
// contains a transaction and every 5th an uncle to allow testing correct block
// reassembly.
func makeChain(n int, seed byte, parent *types.Block) ([]common.Hash, map[common.Hash]*types.Block) {
    blocks, _ := core.GenerateChain(params.TestChainConfig, parent, ethash.NewFaker(), testdb, n, func(i int, block *core.BlockGen) {
        block.SetCoinbase(common.Address{seed})

        // If the block number is multiple of 3, send a bonus transaction to the miner
        if parent == genesis && i%3 == 0 {
            signer := types.MakeSigner(params.TestChainConfig, block.Number())
            tx, err := types.SignTx(types.NewTransaction(block.TxNonce(testAddress), common.Address{seed}, big.NewInt(1000), params.TxGas, nil, nil), signer, testKey)
            if err != nil {
                panic(err)
            }
            block.AddTx(tx)
        }
        // If the block number is a multiple of 5, add a bonus uncle to the block
        if i%5 == 0 {
            block.AddUncle(&types.Header{ParentHash: block.PrevBlock(i - 1).Hash(), Number: big.NewInt(int64(i - 1))})
        }
    })
    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
}

// fetcherTester is a test simulator for mocking out local block chain.
type fetcherTester struct {
    fetcher *Fetcher

    hashes []common.Hash                // Hash chain belonging to the tester
    blocks map[common.Hash]*types.Block // Blocks belonging to the tester
    drops  map[string]bool              // Map of peers dropped by the fetcher

    lock sync.RWMutex
}

// newTester creates a new fetcher test mocker.
func newTester() *fetcherTester {
    tester := &fetcherTester{
        hashes: []common.Hash{genesis.Hash()},
        blocks: map[common.Hash]*types.Block{genesis.Hash(): genesis},
        drops:  make(map[string]bool),
    }
    tester.fetcher = New(tester.getBlock, tester.verifyHeader, tester.broadcastBlock, tester.chainHeight, tester.insertChain, tester.dropPeer)
    tester.fetcher.Start()

    return tester
}

// getBlock retrieves a block from the tester's block chain.
func (f *fetcherTester) getBlock(hash common.Hash) *types.Block {
    f.lock.RLock()
    defer f.lock.RUnlock()

    return f.blocks[hash]
}

// verifyHeader is a nop placeholder for the block header verification.
func (f *fetcherTester) verifyHeader(header *types.Header) error {
    return nil
}

// broadcastBlock is a nop placeholder for the block broadcasting.
func (f *fetcherTester) broadcastBlock(block *types.Block, propagate bool) {
}

// chainHeight retrieves the current height (block number) of the chain.
func (f *fetcherTester) chainHeight() uint64 {
    f.lock.RLock()
    defer f.lock.RUnlock()

    return f.blocks[f.hashes[len(f.hashes)-1]].NumberU64()
}

// insertChain injects a new blocks into the simulated chain.
func (f *fetcherTester) insertChain(blocks types.Blocks) (int, error) {
    f.lock.Lock()
    defer f.lock.Unlock()

    for i, block := range blocks {
        // Make sure the parent in known
        if _, ok := f.blocks[block.ParentHash()]; !ok {
            return i, errors.New("unknown parent")
        }
        // Discard any new blocks if the same height already exists
        if block.NumberU64() <= f.blocks[f.hashes[len(f.hashes)-1]].NumberU64() {
            return i, nil
        }
        // Otherwise build our current chain
        f.hashes = append(f.hashes, block.Hash())
        f.blocks[block.Hash()] = block
    }
    return 0, nil
}

// dropPeer is an emulator for the peer removal, simply accumulating the various
// peers dropped by the fetcher.
func (f *fetcherTester) dropPeer(peer string) {
    f.lock.Lock()
    defer f.lock.Unlock()

    f.drops[peer] = true
}

// makeHeaderFetcher retrieves a block header fetcher associated with a simulated peer.
func (f *fetcherTester) makeHeaderFetcher(peer string, blocks map[common.Hash]*types.Block, drift time.Duration) headerRequesterFn {
    closure := make(map[common.Hash]*types.Block)
    for hash, block := range blocks {
        closure[hash] = block
    }
    // Create a function that return a header from the closure
    return func(hash common.Hash) error {
        // Gather the blocks to return
        headers := make([]*types.Header, 0, 1)
        if block, ok := closure[hash]; ok {
            headers = append(headers, block.Header())
        }
        // Return on a new thread
        go f.fetcher.FilterHeaders(peer, headers, time.Now().Add(drift))

        return nil
    }
}

// makeBodyFetcher retrieves a block body fetcher associated with a simulated peer.
func (f *fetcherTester) makeBodyFetcher(peer string, blocks map[common.Hash]*types.Block, drift time.Duration) bodyRequesterFn {
    closure := make(map[common.Hash]*types.Block)
    for hash, block := range blocks {
        closure[hash] = block
    }
    // Create a function that returns blocks from the closure
    return func(hashes []common.Hash) error {
        // Gather the block bodies to return
        transactions := make([][]*types.Transaction, 0, len(hashes))
        uncles := make([][]*types.Header, 0, len(hashes))

        for _, hash := range hashes {
            if block, ok := closure[hash]; ok {
                transactions = append(transactions, block.Transactions())
                uncles = append(uncles, block.Uncles())
            }
        }
        // Return on a new thread
        go f.fetcher.FilterBodies(peer, transactions, uncles, time.Now().Add(drift))

        return nil
    }
}

// verifyFetchingEvent verifies that one single event arrive on a fetching channel.
func verifyFetchingEvent(t *testing.T, fetching chan []common.Hash, arrive bool) {
    if arrive {
        select {
        case <-fetching:
        case <-time.After(time.Second):
            t.Fatalf("fetching timeout")
        }
    } else {
        select {
        case <-fetching:
            t.Fatalf("fetching invoked")
        case <-time.After(10 * time.Millisecond):
        }
    }
}

// verifyCompletingEvent verifies that one single event arrive on an completing channel.
func verifyCompletingEvent(t *testing.T, completing chan []common.Hash, arrive bool) {
    if arrive {
        select {
        case <-completing:
        case <-time.After(time.Second):
            t.Fatalf("completing timeout")
        }
    } else {
        select {
        case <-completing:
            t.Fatalf("completing invoked")
        case <-time.After(10 * time.Millisecond):
        }
    }
}

// verifyImportEvent verifies that one single event arrive on an import channel.
func verifyImportEvent(t *testing.T, imported chan *types.Block, arrive bool) {
    if arrive {
        select {
        case <-imported:
        case <-time.After(time.Second):
            t.Fatalf("import timeout")
        }
    } else {
        select {
        case <-imported:
            t.Fatalf("import invoked")
        case <-time.After(10 * time.Millisecond):
        }
    }
}

// verifyImportCount verifies that exactly count number of events arrive on an
// import hook channel.
func verifyImportCount(t *testing.T, imported chan *types.Block, count int) {
    for i := 0; i < count; i++ {
        select {
        case <-imported:
        case <-time.After(time.Second):
            t.Fatalf("block %d: import timeout", i+1)
        }
    }
    verifyImportDone(t, imported)
}

// verifyImportDone verifies that no more events are arriving on an import channel.
func verifyImportDone(t *testing.T, imported chan *types.Block) {
    select {
    case <-imported:
        t.Fatalf("extra block imported")
    case <-time.After(50 * time.Millisecond):
    }
}

// Tests that a fetcher accepts block announcements and initiates retrievals for
// them, successfully importing into the local chain.
func TestSequentialAnnouncements62(t *testing.T) { testSequentialAnnouncements(t, 62) }
func TestSequentialAnnouncements63(t *testing.T) { testSequentialAnnouncements(t, 63) }
func TestSequentialAnnouncements64(t *testing.T) { testSequentialAnnouncements(t, 64) }

func testSequentialAnnouncements(t *testing.T, protocol int) {
    // Create a chain of blocks to import
    targetBlocks := 4 * hashLimit
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    tester := newTester()
    headerFetcher := tester.makeHeaderFetcher("valid", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("valid", blocks, 0)

    // Iteratively announce blocks until all are imported
    imported := make(chan *types.Block)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    for i := len(hashes) - 2; i >= 0; i-- {
        tester.fetcher.Notify("valid", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
        verifyImportEvent(t, imported, true)
    }
    verifyImportDone(t, imported)
}

// Tests that if blocks are announced by multiple peers (or even the same buggy
// peer), they will only get downloaded at most once.
func TestConcurrentAnnouncements62(t *testing.T) { testConcurrentAnnouncements(t, 62) }
func TestConcurrentAnnouncements63(t *testing.T) { testConcurrentAnnouncements(t, 63) }
func TestConcurrentAnnouncements64(t *testing.T) { testConcurrentAnnouncements(t, 64) }

func testConcurrentAnnouncements(t *testing.T, protocol int) {
    // Create a chain of blocks to import
    targetBlocks := 4 * hashLimit
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    // Assemble a tester with a built in counter for the requests
    tester := newTester()
    firstHeaderFetcher := tester.makeHeaderFetcher("first", blocks, -gatherSlack)
    firstBodyFetcher := tester.makeBodyFetcher("first", blocks, 0)
    secondHeaderFetcher := tester.makeHeaderFetcher("second", blocks, -gatherSlack)
    secondBodyFetcher := tester.makeBodyFetcher("second", blocks, 0)

    counter := uint32(0)
    firstHeaderWrapper := func(hash common.Hash) error {
        atomic.AddUint32(&counter, 1)
        return firstHeaderFetcher(hash)
    }
    secondHeaderWrapper := func(hash common.Hash) error {
        atomic.AddUint32(&counter, 1)
        return secondHeaderFetcher(hash)
    }
    // Iteratively announce blocks until all are imported
    imported := make(chan *types.Block)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    for i := len(hashes) - 2; i >= 0; i-- {
        tester.fetcher.Notify("first", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout), firstHeaderWrapper, firstBodyFetcher)
        tester.fetcher.Notify("second", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout+time.Millisecond), secondHeaderWrapper, secondBodyFetcher)
        tester.fetcher.Notify("second", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout-time.Millisecond), secondHeaderWrapper, secondBodyFetcher)
        verifyImportEvent(t, imported, true)
    }
    verifyImportDone(t, imported)

    // Make sure no blocks were retrieved twice
    if int(counter) != targetBlocks {
        t.Fatalf("retrieval count mismatch: have %v, want %v", counter, targetBlocks)
    }
}

// Tests that announcements arriving while a previous is being fetched still
// results in a valid import.
func TestOverlappingAnnouncements62(t *testing.T) { testOverlappingAnnouncements(t, 62) }
func TestOverlappingAnnouncements63(t *testing.T) { testOverlappingAnnouncements(t, 63) }
func TestOverlappingAnnouncements64(t *testing.T) { testOverlappingAnnouncements(t, 64) }

func testOverlappingAnnouncements(t *testing.T, protocol int) {
    // Create a chain of blocks to import
    targetBlocks := 4 * hashLimit
    hashes, blocks := makeChain(targetBlocks, 0, genesis)

    tester := newTester()
    headerFetcher := tester.makeHeaderFetcher("valid", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("valid", blocks, 0)

    // Iteratively announce blocks, but overlap them continuously
    overlap := 16
    imported := make(chan *types.Block, len(hashes)-1)
    for i := 0; i < overlap; i++ {
        imported <- nil
    }
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    for i := len(hashes) - 2; i >= 0; i-- {
        tester.fetcher.Notify("valid", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
        select {
        case <-imported:
        case <-time.After(time.Second):
            t.Fatalf("block %d: import timeout", len(hashes)-i)
        }
    }
    // Wait for all the imports to complete and check count
    verifyImportCount(t, imported, overlap)
}

// Tests that announces already being retrieved will not be duplicated.
func TestPendingDeduplication62(t *testing.T) { testPendingDeduplication(t, 62) }
func TestPendingDeduplication63(t *testing.T) { testPendingDeduplication(t, 63) }
func TestPendingDeduplication64(t *testing.T) { testPendingDeduplication(t, 64) }

func testPendingDeduplication(t *testing.T, protocol int) {
    // Create a hash and corresponding block
    hashes, blocks := makeChain(1, 0, genesis)

    // Assemble a tester with a built in counter and delayed fetcher
    tester := newTester()
    headerFetcher := tester.makeHeaderFetcher("repeater", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("repeater", blocks, 0)

    delay := 50 * time.Millisecond
    counter := uint32(0)
    headerWrapper := func(hash common.Hash) error {
        atomic.AddUint32(&counter, 1)

        // Simulate a long running fetch
        go func() {
            time.Sleep(delay)
            headerFetcher(hash)
        }()
        return nil
    }
    // Announce the same block many times until it's fetched (wait for any pending ops)
    for tester.getBlock(hashes[0]) == nil {
        tester.fetcher.Notify("repeater", hashes[0], 1, time.Now().Add(-arriveTimeout), headerWrapper, bodyFetcher)
        time.Sleep(time.Millisecond)
    }
    time.Sleep(delay)

    // Check that all blocks were imported and none fetched twice
    if imported := len(tester.blocks); imported != 2 {
        t.Fatalf("synchronised block mismatch: have %v, want %v", imported, 2)
    }
    if int(counter) != 1 {
        t.Fatalf("retrieval count mismatch: have %v, want %v", counter, 1)
    }
}

// Tests that announcements retrieved in a random order are cached and eventually
// imported when all the gaps are filled in.
func TestRandomArrivalImport62(t *testing.T) { testRandomArrivalImport(t, 62) }
func TestRandomArrivalImport63(t *testing.T) { testRandomArrivalImport(t, 63) }
func TestRandomArrivalImport64(t *testing.T) { testRandomArrivalImport(t, 64) }

func testRandomArrivalImport(t *testing.T, protocol int) {
    // Create a chain of blocks to import, and choose one to delay
    targetBlocks := maxQueueDist
    hashes, blocks := makeChain(targetBlocks, 0, genesis)
    skip := targetBlocks / 2

    tester := newTester()
    headerFetcher := tester.makeHeaderFetcher("valid", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("valid", blocks, 0)

    // Iteratively announce blocks, skipping one entry
    imported := make(chan *types.Block, len(hashes)-1)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    for i := len(hashes) - 1; i >= 0; i-- {
        if i != skip {
            tester.fetcher.Notify("valid", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
            time.Sleep(time.Millisecond)
        }
    }
    // Finally announce the skipped entry and check full import
    tester.fetcher.Notify("valid", hashes[skip], uint64(len(hashes)-skip-1), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
    verifyImportCount(t, imported, len(hashes)-1)
}

// Tests that direct block enqueues (due to block propagation vs. hash announce)
// are correctly schedule, filling and import queue gaps.
func TestQueueGapFill62(t *testing.T) { testQueueGapFill(t, 62) }
func TestQueueGapFill63(t *testing.T) { testQueueGapFill(t, 63) }
func TestQueueGapFill64(t *testing.T) { testQueueGapFill(t, 64) }

func testQueueGapFill(t *testing.T, protocol int) {
    // Create a chain of blocks to import, and choose one to not announce at all
    targetBlocks := maxQueueDist
    hashes, blocks := makeChain(targetBlocks, 0, genesis)
    skip := targetBlocks / 2

    tester := newTester()
    headerFetcher := tester.makeHeaderFetcher("valid", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("valid", blocks, 0)

    // Iteratively announce blocks, skipping one entry
    imported := make(chan *types.Block, len(hashes)-1)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    for i := len(hashes) - 1; i >= 0; i-- {
        if i != skip {
            tester.fetcher.Notify("valid", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
            time.Sleep(time.Millisecond)
        }
    }
    // Fill the missing block directly as if propagated
    tester.fetcher.Enqueue("valid", blocks[hashes[skip]])
    verifyImportCount(t, imported, len(hashes)-1)
}

// Tests that blocks arriving from various sources (multiple propagations, hash
// announces, etc) do not get scheduled for import multiple times.
func TestImportDeduplication62(t *testing.T) { testImportDeduplication(t, 62) }
func TestImportDeduplication63(t *testing.T) { testImportDeduplication(t, 63) }
func TestImportDeduplication64(t *testing.T) { testImportDeduplication(t, 64) }

func testImportDeduplication(t *testing.T, protocol int) {
    // Create two blocks to import (one for duplication, the other for stalling)
    hashes, blocks := makeChain(2, 0, genesis)

    // Create the tester and wrap the importer with a counter
    tester := newTester()
    headerFetcher := tester.makeHeaderFetcher("valid", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("valid", blocks, 0)

    counter := uint32(0)
    tester.fetcher.insertChain = func(blocks types.Blocks) (int, error) {
        atomic.AddUint32(&counter, uint32(len(blocks)))
        return tester.insertChain(blocks)
    }
    // Instrument the fetching and imported events
    fetching := make(chan []common.Hash)
    imported := make(chan *types.Block, len(hashes)-1)
    tester.fetcher.fetchingHook = func(hashes []common.Hash) { fetching <- hashes }
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    // Announce the duplicating block, wait for retrieval, and also propagate directly
    tester.fetcher.Notify("valid", hashes[0], 1, time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
    <-fetching

    tester.fetcher.Enqueue("valid", blocks[hashes[0]])
    tester.fetcher.Enqueue("valid", blocks[hashes[0]])
    tester.fetcher.Enqueue("valid", blocks[hashes[0]])

    // Fill the missing block directly as if propagated, and check import uniqueness
    tester.fetcher.Enqueue("valid", blocks[hashes[1]])
    verifyImportCount(t, imported, 2)

    if counter != 2 {
        t.Fatalf("import invocation count mismatch: have %v, want %v", counter, 2)
    }
}

// Tests that blocks with numbers much lower or higher than out current head get
// discarded to prevent wasting resources on useless blocks from faulty peers.
func TestDistantPropagationDiscarding(t *testing.T) {
    // Create a long chain to import and define the discard boundaries
    hashes, blocks := makeChain(3*maxQueueDist, 0, genesis)
    head := hashes[len(hashes)/2]

    low, high := len(hashes)/2+maxUncleDist+1, len(hashes)/2-maxQueueDist-1

    // Create a tester and simulate a head block being the middle of the above chain
    tester := newTester()

    tester.lock.Lock()
    tester.hashes = []common.Hash{head}
    tester.blocks = map[common.Hash]*types.Block{head: blocks[head]}
    tester.lock.Unlock()

    // Ensure that a block with a lower number than the threshold is discarded
    tester.fetcher.Enqueue("lower", blocks[hashes[low]])
    time.Sleep(10 * time.Millisecond)
    if !tester.fetcher.queue.Empty() {
        t.Fatalf("fetcher queued stale block")
    }
    // Ensure that a block with a higher number than the threshold is discarded
    tester.fetcher.Enqueue("higher", blocks[hashes[high]])
    time.Sleep(10 * time.Millisecond)
    if !tester.fetcher.queue.Empty() {
        t.Fatalf("fetcher queued future block")
    }
}

// Tests that announcements with numbers much lower or higher than out current
// head get discarded to prevent wasting resources on useless blocks from faulty
// peers.
func TestDistantAnnouncementDiscarding62(t *testing.T) { testDistantAnnouncementDiscarding(t, 62) }
func TestDistantAnnouncementDiscarding63(t *testing.T) { testDistantAnnouncementDiscarding(t, 63) }
func TestDistantAnnouncementDiscarding64(t *testing.T) { testDistantAnnouncementDiscarding(t, 64) }

func testDistantAnnouncementDiscarding(t *testing.T, protocol int) {
    // Create a long chain to import and define the discard boundaries
    hashes, blocks := makeChain(3*maxQueueDist, 0, genesis)
    head := hashes[len(hashes)/2]

    low, high := len(hashes)/2+maxUncleDist+1, len(hashes)/2-maxQueueDist-1

    // Create a tester and simulate a head block being the middle of the above chain
    tester := newTester()

    tester.lock.Lock()
    tester.hashes = []common.Hash{head}
    tester.blocks = map[common.Hash]*types.Block{head: blocks[head]}
    tester.lock.Unlock()

    headerFetcher := tester.makeHeaderFetcher("lower", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("lower", blocks, 0)

    fetching := make(chan struct{}, 2)
    tester.fetcher.fetchingHook = func(hashes []common.Hash) { fetching <- struct{}{} }

    // Ensure that a block with a lower number than the threshold is discarded
    tester.fetcher.Notify("lower", hashes[low], blocks[hashes[low]].NumberU64(), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
    select {
    case <-time.After(50 * time.Millisecond):
    case <-fetching:
        t.Fatalf("fetcher requested stale header")
    }
    // Ensure that a block with a higher number than the threshold is discarded
    tester.fetcher.Notify("higher", hashes[high], blocks[hashes[high]].NumberU64(), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)
    select {
    case <-time.After(50 * time.Millisecond):
    case <-fetching:
        t.Fatalf("fetcher requested future header")
    }
}

// Tests that peers announcing blocks with invalid numbers (i.e. not matching
// the headers provided afterwards) get dropped as malicious.
func TestInvalidNumberAnnouncement62(t *testing.T) { testInvalidNumberAnnouncement(t, 62) }
func TestInvalidNumberAnnouncement63(t *testing.T) { testInvalidNumberAnnouncement(t, 63) }
func TestInvalidNumberAnnouncement64(t *testing.T) { testInvalidNumberAnnouncement(t, 64) }

func testInvalidNumberAnnouncement(t *testing.T, protocol int) {
    // Create a single block to import and check numbers against
    hashes, blocks := makeChain(1, 0, genesis)

    tester := newTester()
    badHeaderFetcher := tester.makeHeaderFetcher("bad", blocks, -gatherSlack)
    badBodyFetcher := tester.makeBodyFetcher("bad", blocks, 0)

    imported := make(chan *types.Block)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    // Announce a block with a bad number, check for immediate drop
    tester.fetcher.Notify("bad", hashes[0], 2, time.Now().Add(-arriveTimeout), badHeaderFetcher, badBodyFetcher)
    verifyImportEvent(t, imported, false)

    tester.lock.RLock()
    dropped := tester.drops["bad"]
    tester.lock.RUnlock()

    if !dropped {
        t.Fatalf("peer with invalid numbered announcement not dropped")
    }

    goodHeaderFetcher := tester.makeHeaderFetcher("good", blocks, -gatherSlack)
    goodBodyFetcher := tester.makeBodyFetcher("good", blocks, 0)
    // Make sure a good announcement passes without a drop
    tester.fetcher.Notify("good", hashes[0], 1, time.Now().Add(-arriveTimeout), goodHeaderFetcher, goodBodyFetcher)
    verifyImportEvent(t, imported, true)

    tester.lock.RLock()
    dropped = tester.drops["good"]
    tester.lock.RUnlock()

    if dropped {
        t.Fatalf("peer with valid numbered announcement dropped")
    }
    verifyImportDone(t, imported)
}

// Tests that if a block is empty (i.e. header only), no body request should be
// made, and instead the header should be assembled into a whole block in itself.
func TestEmptyBlockShortCircuit62(t *testing.T) { testEmptyBlockShortCircuit(t, 62) }
func TestEmptyBlockShortCircuit63(t *testing.T) { testEmptyBlockShortCircuit(t, 63) }
func TestEmptyBlockShortCircuit64(t *testing.T) { testEmptyBlockShortCircuit(t, 64) }

func testEmptyBlockShortCircuit(t *testing.T, protocol int) {
    // Create a chain of blocks to import
    hashes, blocks := makeChain(32, 0, genesis)

    tester := newTester()
    headerFetcher := tester.makeHeaderFetcher("valid", blocks, -gatherSlack)
    bodyFetcher := tester.makeBodyFetcher("valid", blocks, 0)

    // Add a monitoring hook for all internal events
    fetching := make(chan []common.Hash)
    tester.fetcher.fetchingHook = func(hashes []common.Hash) { fetching <- hashes }

    completing := make(chan []common.Hash)
    tester.fetcher.completingHook = func(hashes []common.Hash) { completing <- hashes }

    imported := make(chan *types.Block)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }

    // Iteratively announce blocks until all are imported
    for i := len(hashes) - 2; i >= 0; i-- {
        tester.fetcher.Notify("valid", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout), headerFetcher, bodyFetcher)

        // All announces should fetch the header
        verifyFetchingEvent(t, fetching, true)

        // Only blocks with data contents should request bodies
        verifyCompletingEvent(t, completing, len(blocks[hashes[i]].Transactions()) > 0 || len(blocks[hashes[i]].Uncles()) > 0)

        // Irrelevant of the construct, import should succeed
        verifyImportEvent(t, imported, true)
    }
    verifyImportDone(t, imported)
}

// Tests that a peer is unable to use unbounded memory with sending infinite
// block announcements to a node, but that even in the face of such an attack,
// the fetcher remains operational.
func TestHashMemoryExhaustionAttack62(t *testing.T) { testHashMemoryExhaustionAttack(t, 62) }
func TestHashMemoryExhaustionAttack63(t *testing.T) { testHashMemoryExhaustionAttack(t, 63) }
func TestHashMemoryExhaustionAttack64(t *testing.T) { testHashMemoryExhaustionAttack(t, 64) }

func testHashMemoryExhaustionAttack(t *testing.T, protocol int) {
    // Create a tester with instrumented import hooks
    tester := newTester()

    imported, announces := make(chan *types.Block), int32(0)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }
    tester.fetcher.announceChangeHook = func(hash common.Hash, added bool) {
        if added {
            atomic.AddInt32(&announces, 1)
        } else {
            atomic.AddInt32(&announces, -1)
        }
    }
    // Create a valid chain and an infinite junk chain
    targetBlocks := hashLimit + 2*maxQueueDist
    hashes, blocks := makeChain(targetBlocks, 0, genesis)
    validHeaderFetcher := tester.makeHeaderFetcher("valid", blocks, -gatherSlack)
    validBodyFetcher := tester.makeBodyFetcher("valid", blocks, 0)

    attack, _ := makeChain(targetBlocks, 0, unknownBlock)
    attackerHeaderFetcher := tester.makeHeaderFetcher("attacker", nil, -gatherSlack)
    attackerBodyFetcher := tester.makeBodyFetcher("attacker", nil, 0)

    // Feed the tester a huge hashset from the attacker, and a limited from the valid peer
    for i := 0; i < len(attack); i++ {
        if i < maxQueueDist {
            tester.fetcher.Notify("valid", hashes[len(hashes)-2-i], uint64(i+1), time.Now(), validHeaderFetcher, validBodyFetcher)
        }
        tester.fetcher.Notify("attacker", attack[i], 1 /* don't distance drop */, time.Now(), attackerHeaderFetcher, attackerBodyFetcher)
    }
    if count := atomic.LoadInt32(&announces); count != hashLimit+maxQueueDist {
        t.Fatalf("queued announce count mismatch: have %d, want %d", count, hashLimit+maxQueueDist)
    }
    // Wait for fetches to complete
    verifyImportCount(t, imported, maxQueueDist)

    // Feed the remaining valid hashes to ensure DOS protection state remains clean
    for i := len(hashes) - maxQueueDist - 2; i >= 0; i-- {
        tester.fetcher.Notify("valid", hashes[i], uint64(len(hashes)-i-1), time.Now().Add(-arriveTimeout), validHeaderFetcher, validBodyFetcher)
        verifyImportEvent(t, imported, true)
    }
    verifyImportDone(t, imported)
}

// Tests that blocks sent to the fetcher (either through propagation or via hash
// announces and retrievals) don't pile up indefinitely, exhausting available
// system memory.
func TestBlockMemoryExhaustionAttack(t *testing.T) {
    // Create a tester with instrumented import hooks
    tester := newTester()

    imported, enqueued := make(chan *types.Block), int32(0)
    tester.fetcher.importedHook = func(block *types.Block) { imported <- block }
    tester.fetcher.queueChangeHook = func(hash common.Hash, added bool) {
        if added {
            atomic.AddInt32(&enqueued, 1)
        } else {
            atomic.AddInt32(&enqueued, -1)
        }
    }
    // Create a valid chain and a batch of dangling (but in range) blocks
    targetBlocks := hashLimit + 2*maxQueueDist
    hashes, blocks := makeChain(targetBlocks, 0, genesis)
    attack := make(map[common.Hash]*types.Block)
    for i := byte(0); len(attack) < blockLimit+2*maxQueueDist; i++ {
        hashes, blocks := makeChain(maxQueueDist-1, i, unknownBlock)
        for _, hash := range hashes[:maxQueueDist-2] {
            attack[hash] = blocks[hash]
        }
    }
    // Try to feed all the attacker blocks make sure only a limited batch is accepted
    for _, block := range attack {
        tester.fetcher.Enqueue("attacker", block)
    }
    time.Sleep(200 * time.Millisecond)
    if queued := atomic.LoadInt32(&enqueued); queued != blockLimit {
        t.Fatalf("queued block count mismatch: have %d, want %d", queued, blockLimit)
    }
    // Queue up a batch of valid blocks, and check that a new peer is allowed to do so
    for i := 0; i < maxQueueDist-1; i++ {
        tester.fetcher.Enqueue("valid", blocks[hashes[len(hashes)-3-i]])
    }
    time.Sleep(100 * time.Millisecond)
    if queued := atomic.LoadInt32(&enqueued); queued != blockLimit+maxQueueDist-1 {
        t.Fatalf("queued block count mismatch: have %d, want %d", queued, blockLimit+maxQueueDist-1)
    }
    // Insert the missing piece (and sanity check the import)
    tester.fetcher.Enqueue("valid", blocks[hashes[len(hashes)-2]])
    verifyImportCount(t, imported, maxQueueDist)

    // Insert the remaining blocks in chunks to ensure clean DOS protection
    for i := maxQueueDist; i < len(hashes)-1; i++ {
        tester.fetcher.Enqueue("valid", blocks[hashes[len(hashes)-2-i]])
        verifyImportEvent(t, imported, true)
    }
    verifyImportDone(t, imported)
}