path: root/eth/handler.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 eth

import (
    "encoding/json"
    "errors"
    "fmt"
    "math"
    "math/big"
    "sync"
    "sync/atomic"
    "time"

    "github.com/dexon-foundation/dexon/common"
    "github.com/dexon-foundation/dexon/consensus"
    "github.com/dexon-foundation/dexon/core"
    "github.com/dexon-foundation/dexon/core/types"
    "github.com/dexon-foundation/dexon/eth/downloader"
    "github.com/dexon-foundation/dexon/eth/fetcher"
    "github.com/dexon-foundation/dexon/ethdb"
    "github.com/dexon-foundation/dexon/event"
    "github.com/dexon-foundation/dexon/log"
    "github.com/dexon-foundation/dexon/p2p"
    "github.com/dexon-foundation/dexon/p2p/enode"
    "github.com/dexon-foundation/dexon/params"
    "github.com/dexon-foundation/dexon/rlp"
)

const (
    softResponseLimit = 2 * 1024 * 1024 // Target maximum size of returned blocks, headers or node data.
    estHeaderRlpSize  = 500             // Approximate size of an RLP encoded block header

    // txChanSize is the size of channel listening to NewTxsEvent.
    // The number is referenced from the size of tx pool.
    txChanSize = 4096

    // minimim number of peers to broadcast new blocks to
    minBroadcastPeers = 4
)

var (
    syncChallengeTimeout = 15 * time.Second // Time allowance for a node to reply to the sync progress challenge
)

// errIncompatibleConfig is returned if the requested protocols and configs are
// not compatible (low protocol version restrictions and high requirements).
var errIncompatibleConfig = errors.New("incompatible configuration")

func errResp(code errCode, format string, v ...interface{}) error {
    return fmt.Errorf("%v - %v", code, fmt.Sprintf(format, v...))
}

type ProtocolManager struct {
    networkID uint64

    fastSync  uint32 // Flag whether fast sync is enabled (gets disabled if we already have blocks)
    acceptTxs uint32 // Flag whether we're considered synchronised (enables transaction processing)

    checkpointNumber uint64      // Block number for the sync progress validator to cross reference
    checkpointHash   common.Hash // Block hash for the sync progress validator to cross reference

    txpool      txPool
    blockchain  *core.BlockChain
    chainconfig *params.ChainConfig
    maxPeers    int

    downloader *downloader.Downloader
    fetcher    *fetcher.Fetcher
    peers      *peerSet

    SubProtocols []p2p.Protocol

    eventMux      *event.TypeMux
    txsCh         chan core.NewTxsEvent
    txsSub        event.Subscription
    minedBlockSub *event.TypeMuxSubscription

    whitelist map[uint64]common.Hash

    // channels for fetcher, syncer, txsyncLoop
    newPeerCh   chan *peer
    txsyncCh    chan *txsync
    quitSync    chan struct{}
    noMorePeers chan struct{}

    // wait group is used for graceful shutdowns during downloading
    // and processing
    wg sync.WaitGroup
}

// NewProtocolManager returns a new Ethereum sub protocol manager. The Ethereum sub protocol manages peers capable
// with the Ethereum network.
func NewProtocolManager(config *params.ChainConfig, mode downloader.SyncMode, networkID uint64, mux *event.TypeMux, txpool txPool, engine consensus.Engine, blockchain *core.BlockChain, chaindb ethdb.Database, whitelist map[uint64]common.Hash) (*ProtocolManager, error) {
    // Create the protocol manager with the base fields
    manager := &ProtocolManager{
        networkID:   networkID,
        eventMux:    mux,
        txpool:      txpool,
        blockchain:  blockchain,
        chainconfig: config,
        peers:       newPeerSet(),
        whitelist:   whitelist,
        newPeerCh:   make(chan *peer),
        noMorePeers: make(chan struct{}),
        txsyncCh:    make(chan *txsync),
        quitSync:    make(chan struct{}),
    }
    // Figure out whether to allow fast sync or not
    if mode == downloader.FastSync && blockchain.CurrentBlock().NumberU64() > 0 {
        log.Warn("Blockchain not empty, fast sync disabled")
        mode = downloader.FullSync
    }
    if mode == downloader.FastSync {
        manager.fastSync = uint32(1)
    }
    // If we have trusted checkpoints, enforce them on the chain
    if checkpoint, ok := params.TrustedCheckpoints[blockchain.Genesis().Hash()]; ok {
        manager.checkpointNumber = (checkpoint.SectionIndex+1)*params.CHTFrequencyClient - 1
        manager.checkpointHash = checkpoint.SectionHead
    }
    // Initiate a sub-protocol for every implemented version we can handle
    manager.SubProtocols = make([]p2p.Protocol, 0, len(ProtocolVersions))
    for i, version := range ProtocolVersions {
        // Skip protocol version if incompatible with the mode of operation
        if mode == downloader.FastSync && version < eth63 {
            continue
        }
        // Compatible; initialise the sub-protocol
        version := version // Closure for the run
        manager.SubProtocols = append(manager.SubProtocols, p2p.Protocol{
            Name:    ProtocolName,
            Version: version,
            Length:  ProtocolLengths[i],
            Run: func(p *p2p.Peer, rw p2p.MsgReadWriter) error {
                peer := manager.newPeer(int(version), p, rw)
                select {
                case manager.newPeerCh <- peer:
                    manager.wg.Add(1)
                    defer manager.wg.Done()
                    return manager.handle(peer)
                case <-manager.quitSync:
                    return p2p.DiscQuitting
                }
            },
            NodeInfo: func() interface{} {
                return manager.NodeInfo()
            },
            PeerInfo: func(id enode.ID) interface{} {
                if p := manager.peers.Peer(fmt.Sprintf("%x", id[:8])); p != nil {
                    return p.Info()
                }
                return nil
            },
        })
    }
    if len(manager.SubProtocols) == 0 {
        return nil, errIncompatibleConfig
    }
    // Construct the different synchronisation mechanisms
    manager.downloader = downloader.New(mode, manager.checkpointNumber, chaindb, manager.eventMux, blockchain, nil, manager.removePeer)

    validator := func(header *types.Header) error {
        return engine.VerifyHeader(blockchain, header, true)
    }
    heighter := func() uint64 {
        return blockchain.CurrentBlock().NumberU64()
    }
    inserter := func(blocks types.Blocks) (int, error) {
        // If fast sync is running, deny importing weird blocks
        if atomic.LoadUint32(&manager.fastSync) == 1 {
            log.Warn("Discarded bad propagated block", "number", blocks[0].Number(), "hash", blocks[0].Hash())
            return 0, nil
        }
        atomic.StoreUint32(&manager.acceptTxs, 1) // Mark initial sync done on any fetcher import
        return manager.blockchain.InsertChain(blocks)
    }
    manager.fetcher = fetcher.New(blockchain.GetBlockByHash, validator, manager.BroadcastBlock, heighter, inserter, manager.removePeer)

    return manager, nil
}

func (pm *ProtocolManager) removePeer(id string) {
    // Short circuit if the peer was already removed
    peer := pm.peers.Peer(id)
    if peer == nil {
        return
    }
    log.Debug("Removing Ethereum peer", "peer", id)

    // Unregister the peer from the downloader and Ethereum peer set
    pm.downloader.UnregisterPeer(id)
    if err := pm.peers.Unregister(id); err != nil {
        log.Error("Peer removal failed", "peer", id, "err", err)
    }
    // Hard disconnect at the networking layer
    if peer != nil {
        peer.Peer.Disconnect(p2p.DiscUselessPeer)
    }
}

func (pm *ProtocolManager) Start(maxPeers int) {
    pm.maxPeers = maxPeers

    // broadcast transactions
    pm.txsCh = make(chan core.NewTxsEvent, txChanSize)
    pm.txsSub = pm.txpool.SubscribeNewTxsEvent(pm.txsCh)
    go pm.txBroadcastLoop()

    // broadcast mined blocks
    pm.minedBlockSub = pm.eventMux.Subscribe(core.NewMinedBlockEvent{})
    go pm.minedBroadcastLoop()

    // start sync handlers
    go pm.syncer()
    go pm.txsyncLoop()
}

func (pm *ProtocolManager) Stop() {
    log.Info("Stopping Ethereum protocol")

    pm.txsSub.Unsubscribe()        // quits txBroadcastLoop
    pm.minedBlockSub.Unsubscribe() // quits blockBroadcastLoop

    // Quit the sync loop.
    // After this send has completed, no new peers will be accepted.
    pm.noMorePeers <- struct{}{}

    // Quit fetcher, txsyncLoop.
    close(pm.quitSync)

    // Disconnect existing sessions.
    // This also closes the gate for any new registrations on the peer set.
    // sessions which are already established but not added to pm.peers yet
    // will exit when they try to register.
    pm.peers.Close()

    // Wait for all peer handler goroutines and the loops to come down.
    pm.wg.Wait()

    log.Info("Ethereum protocol stopped")
}

func (pm *ProtocolManager) newPeer(pv int, p *p2p.Peer, rw p2p.MsgReadWriter) *peer {
    return newPeer(pv, p, newMeteredMsgWriter(rw))
}

// handle is the callback invoked to manage the life cycle of an eth peer. When
// this function terminates, the peer is disconnected.
func (pm *ProtocolManager) handle(p *peer) error {
    // Ignore maxPeers if this is a trusted peer
    if pm.peers.Len() >= pm.maxPeers && !p.Peer.Info().Network.Trusted {
        return p2p.DiscTooManyPeers
    }
    p.Log().Debug("Ethereum peer connected", "name", p.Name())

    // Execute the Ethereum handshake
    var (
        genesis = pm.blockchain.Genesis()
        head    = pm.blockchain.CurrentHeader()
        hash    = head.Hash()
        number  = head.Number.Uint64()
        td      = pm.blockchain.GetTd(hash, number)
    )
    if err := p.Handshake(pm.networkID, td, hash, genesis.Hash()); err != nil {
        p.Log().Debug("Ethereum handshake failed", "err", err)
        return err
    }
    if rw, ok := p.rw.(*meteredMsgReadWriter); ok {
        rw.Init(p.version)
    }
    // Register the peer locally
    if err := pm.peers.Register(p); err != nil {
        p.Log().Error("Ethereum peer registration failed", "err", err)
        return err
    }
    defer pm.removePeer(p.id)

    // Register the peer in the downloader. If the downloader considers it banned, we disconnect
    if err := pm.downloader.RegisterPeer(p.id, p.version, p); err != nil {
        return err
    }
    // Propagate existing transactions. new transactions appearing
    // after this will be sent via broadcasts.
    pm.syncTransactions(p)

    // If we have a trusted CHT, reject all peers below that (avoid fast sync eclipse)
    if pm.checkpointHash != (common.Hash{}) {
        // Request the peer's checkpoint header for chain height/weight validation
        if err := p.RequestHeadersByNumber(pm.checkpointNumber, 1, 0, false); err != nil {
            return err
        }
        // Start a timer to disconnect if the peer doesn't reply in time
        p.syncDrop = time.AfterFunc(syncChallengeTimeout, func() {
            p.Log().Warn("Checkpoint challenge timed out, dropping", "addr", p.RemoteAddr(), "type", p.Name())
            pm.removePeer(p.id)
        })
        // Make sure it's cleaned up if the peer dies off
        defer func() {
            if p.syncDrop != nil {
                p.syncDrop.Stop()
                p.syncDrop = nil
            }
        }()
    }
    // If we have any explicit whitelist block hashes, request them
    for number := range pm.whitelist {
        if err := p.RequestHeadersByNumber(number, 1, 0, false); err != nil {
            return err
        }
    }
    // Handle incoming messages until the connection is torn down
    for {
        if err := pm.handleMsg(p); err != nil {
            p.Log().Debug("Ethereum message handling failed", "err", err)
            return err
        }
    }
}

// handleMsg is invoked whenever an inbound message is received from a remote
// peer. The remote connection is torn down upon returning any error.
func (pm *ProtocolManager) handleMsg(p *peer) error {
    // Read the next message from the remote peer, and ensure it's fully consumed
    msg, err := p.rw.ReadMsg()
    if err != nil {
        return err
    }
    if msg.Size > ProtocolMaxMsgSize {
        return errResp(ErrMsgTooLarge, "%v > %v", msg.Size, ProtocolMaxMsgSize)
    }
    defer msg.Discard()

    // Handle the message depending on its contents
    switch {
    case msg.Code == StatusMsg:
        // Status messages should never arrive after the handshake
        return errResp(ErrExtraStatusMsg, "uncontrolled status message")

    // Block header query, collect the requested headers and reply
    case msg.Code == GetBlockHeadersMsg:
        // Decode the complex header query
        var query getBlockHeadersData
        if err := msg.Decode(&query); err != nil {
            return errResp(ErrDecode, "%v: %v", msg, err)
        }
        hashMode := query.Origin.Hash != (common.Hash{})
        first := true
        maxNonCanonical := uint64(100)

        // Gather headers until the fetch or network limits is reached
        var (
            bytes   common.StorageSize
            headers []*types.Header
            unknown bool
        )
        for !unknown && len(headers) < int(query.Amount) && bytes < softResponseLimit && len(headers) < downloader.MaxHeaderFetch {
            // Retrieve the next header satisfying the query
            var origin *types.Header
            if hashMode {
                if first {
                    first = false
                    origin = pm.blockchain.GetHeaderByHash(query.Origin.Hash)
                    if origin != nil {
                        query.Origin.Number = origin.Number.Uint64()
                    }
                } else {
                    origin = pm.blockchain.GetHeader(query.Origin.Hash, query.Origin.Number)
                }
            } else {
                origin = pm.blockchain.GetHeaderByNumber(query.Origin.Number)
            }
            if origin == nil {
                break
            }
            headers = append(headers, origin)
            bytes += estHeaderRlpSize

            // Advance to the next header of the query
            switch {
            case hashMode && query.Reverse:
                // Hash based traversal towards the genesis block
                ancestor := query.Skip + 1
                if ancestor == 0 {
                    unknown = true
                } else {
                    query.Origin.Hash, query.Origin.Number = pm.blockchain.GetAncestor(query.Origin.Hash, query.Origin.Number, ancestor, &maxNonCanonical)
                    unknown = (query.Origin.Hash == common.Hash{})
                }
            case hashMode && !query.Reverse:
                // Hash based traversal towards the leaf block
                var (
                    current = origin.Number.Uint64()
                    next    = current + query.Skip + 1
                )
                if next <= current {
                    infos, _ := json.MarshalIndent(p.Peer.Info(), "", "  ")
                    p.Log().Warn("GetBlockHeaders skip overflow attack", "current", current, "skip", query.Skip, "next", next, "attacker", infos)
                    unknown = true
                } else {
                    if header := pm.blockchain.GetHeaderByNumber(next); header != nil {
                        nextHash := header.Hash()
                        expOldHash, _ := pm.blockchain.GetAncestor(nextHash, next, query.Skip+1, &maxNonCanonical)
                        if expOldHash == query.Origin.Hash {
                            query.Origin.Hash, query.Origin.Number = nextHash, next
                        } else {
                            unknown = true
                        }
                    } else {
                        unknown = true
                    }
                }
            case query.Reverse:
                // Number based traversal towards the genesis block
                if query.Origin.Number >= query.Skip+1 {
                    query.Origin.Number -= query.Skip + 1
                } else {
                    unknown = true
                }

            case !query.Reverse:
                // Number based traversal towards the leaf block
                query.Origin.Number += query.Skip + 1
            }
        }
        return p.SendBlockHeaders(headers)

    case msg.Code == BlockHeadersMsg:
        // A batch of headers arrived to one of our previous requests
        var headers []*types.Header
        if err := msg.Decode(&headers); err != nil {
            return errResp(ErrDecode, "msg %v: %v", msg, err)
        }
        // If no headers were received, but we're expencting a checkpoint header, consider it that
        if len(headers) == 0 && p.syncDrop != nil {
            // Stop the timer either way, decide later to drop or not
            p.syncDrop.Stop()
            p.syncDrop = nil

            // If we're doing a fast sync, we must enforce the checkpoint block to avoid
            // eclipse attacks. Unsynced nodes are welcome to connect after we're done
            // joining the network
            if atomic.LoadUint32(&pm.fastSync) == 1 {
                p.Log().Warn("Dropping unsynced node during fast sync", "addr", p.RemoteAddr(), "type", p.Name())
                return errors.New("unsynced node cannot serve fast sync")
            }
        }
        // Filter out any explicitly requested headers, deliver the rest to the downloader
        filter := len(headers) == 1
        if filter {
            // If it's a potential sync progress check, validate the content and advertised chain weight
            if p.syncDrop != nil && headers[0].Number.Uint64() == pm.checkpointNumber {
                // Disable the sync drop timer
                p.syncDrop.Stop()
                p.syncDrop = nil

                // Validate the header and either drop the peer or continue
                if headers[0].Hash() != pm.checkpointHash {
                    return errors.New("checkpoint hash mismatch")
                }
                return nil
            }
            // Otherwise if it's a whitelisted block, validate against the set
            if want, ok := pm.whitelist[headers[0].Number.Uint64()]; ok {
                if hash := headers[0].Hash(); want != hash {
                    p.Log().Info("Whitelist mismatch, dropping peer", "number", headers[0].Number.Uint64(), "hash", hash, "want", want)
                    return errors.New("whitelist block mismatch")
                }
                p.Log().Debug("Whitelist block verified", "number", headers[0].Number.Uint64(), "hash", want)
            }
            // Irrelevant of the fork checks, send the header to the fetcher just in case
            headers = pm.fetcher.FilterHeaders(p.id, headers, time.Now())
        }
        if len(headers) > 0 || !filter {
            err := pm.downloader.DeliverHeaders(p.id, headers)
            if err != nil {
                log.Debug("Failed to deliver headers", "err", err)
            }
        }

    case msg.Code == GetBlockBodiesMsg:
        // Decode the retrieval message
        msgStream := rlp.NewStream(msg.Payload, uint64(msg.Size))
        if _, err := msgStream.List(); err != nil {
            return err
        }
        // Gather blocks until the fetch or network limits is reached
        var (
            hash   common.Hash
            bytes  int
            bodies []rlp.RawValue
        )
        for bytes < softResponseLimit && len(bodies) < downloader.MaxBlockFetch {
            // Retrieve the hash of the next block
            if err := msgStream.Decode(&hash); err == rlp.EOL {
                break
            } else if err != nil {
                return errResp(ErrDecode, "msg %v: %v", msg, err)
            }
            // Retrieve the requested block body, stopping if enough was found
            if data := pm.blockchain.GetBodyRLP(hash); len(data) != 0 {
                bodies = append(bodies, data)
                bytes += len(data)
            }
        }
        return p.SendBlockBodiesRLP(bodies)

    case msg.Code == BlockBodiesMsg:
        // A batch of block bodies arrived to one of our previous requests
        var request blockBodiesData
        if err := msg.Decode(&request); err != nil {
            return errResp(ErrDecode, "msg %v: %v", msg, err)
        }
        // Deliver them all to the downloader for queuing
        transactions := make([][]*types.Transaction, len(request))
        uncles := make([][]*types.Header, len(request))

        for i, body := range request {
            transactions[i] = body.Transactions
            uncles[i] = body.Uncles
        }
        // Filter out any explicitly requested bodies, deliver the rest to the downloader
        filter := len(transactions) > 0 || len(uncles) > 0
        if filter {
            transactions, uncles = pm.fetcher.FilterBodies(p.id, transactions, uncles, time.Now())
        }
        if len(transactions) > 0 || len(uncles) > 0 || !filter {
            err := pm.downloader.DeliverBodies(p.id, transactions, uncles)
            if err != nil {
                log.Debug("Failed to deliver bodies", "err", err)
            }
        }

    case p.version >= eth63 && msg.Code == GetNodeDataMsg:
        // Decode the retrieval message
        msgStream := rlp.NewStream(msg.Payload, uint64(msg.Size))
        if _, err := msgStream.List(); err != nil {
            return err
        }
        // Gather state data until the fetch or network limits is reached
        var (
            hash  common.Hash
            bytes int
            data  [][]byte
        )
        for bytes < softResponseLimit && len(data) < downloader.MaxStateFetch {
            // Retrieve the hash of the next state entry
            if err := msgStream.Decode(&hash); err == rlp.EOL {
                break
            } else if err != nil {
                return errResp(ErrDecode, "msg %v: %v", msg, err)
            }
            // Retrieve the requested state entry, stopping if enough was found
            if entry, err := pm.blockchain.TrieNode(hash); err == nil {
                data = append(data, entry)
                bytes += len(entry)
            }
        }
        return p.SendNodeData(data)

    case p.version >= eth63 && msg.Code == NodeDataMsg:
        // A batch of node state data arrived to one of our previous requests
        var data [][]byte
        if err := msg.Decode(&data); err != nil {
            return errResp(ErrDecode, "msg %v: %v", msg, err)
        }
        // Deliver all to the downloader
        if err := pm.downloader.DeliverNodeData(p.id, data); err != nil {
            log.Debug("Failed to deliver node state data", "err", err)
        }

    case p.version >= eth63 && msg.Code == GetReceiptsMsg:
        // Decode the retrieval message
        msgStream := rlp.NewStream(msg.Payload, uint64(msg.Size))
        if _, err := msgStream.List(); err != nil {
            return err
        }
        // Gather state data until the fetch or network limits is reached
        var (
            hash     common.Hash
            bytes    int
            receipts []rlp.RawValue
        )
        for bytes < softResponseLimit && len(receipts) < downloader.MaxReceiptFetch {
            // Retrieve the hash of the next block
            if err := msgStream.Decode(&hash); err == rlp.EOL {
                break
            } else if err != nil {
                return errResp(ErrDecode, "msg %v: %v", msg, err)
            }
            // Retrieve the requested block's receipts, skipping if unknown to us
            results := pm.blockchain.GetReceiptsByHash(hash)
            if results == nil {
                if header := pm.blockchain.GetHeaderByHash(hash); header == nil || header.ReceiptHash != types.EmptyRootHash {
                    continue
                }
            }
            // If known, encode and queue for response packet
            if encoded, err := rlp.EncodeToBytes(results); err != nil {
                log.Error("Failed to encode receipt", "err", err)
            } else {
                receipts = append(receipts, encoded)
                bytes += len(encoded)
            }
        }
        return p.SendReceiptsRLP(receipts)

    case p.version >= eth63 && msg.Code == ReceiptsMsg:
        // A batch of receipts arrived to one of our previous requests
        var receipts [][]*types.Receipt
        if err := msg.Decode(&receipts); err != nil {
            return errResp(ErrDecode, "msg %v: %v", msg, err)
        }
        // Deliver all to the downloader
        if err := pm.downloader.DeliverReceipts(p.id, receipts); err != nil {
            log.Debug("Failed to deliver receipts", "err", err)
        }

    case msg.Code == NewBlockHashesMsg:
        var announces newBlockHashesData
        if err := msg.Decode(&announces); err != nil {
            return errResp(ErrDecode, "%v: %v", msg, err)
        }
        // Mark the hashes as present at the remote node
        for _, block := range announces {
            p.MarkBlock(block.Hash)
        }
        // Schedule all the unknown hashes for retrieval
        unknown := make(newBlockHashesData, 0, len(announces))
        for _, block := range announces {
            if !pm.blockchain.HasBlock(block.Hash, block.Number) {
                unknown = append(unknown, block)
            }
        }
        for _, block := range unknown {
            pm.fetcher.Notify(p.id, block.Hash, block.Number, time.Now(), p.RequestOneHeader, p.RequestBodies)
        }

    case msg.Code == NewBlockMsg:
        // Retrieve and decode the propagated block
        var request newBlockData
        if err := msg.Decode(&request); err != nil {
            return errResp(ErrDecode, "%v: %v", msg, err)
        }
        request.Block.ReceivedAt = msg.ReceivedAt
        request.Block.ReceivedFrom = p

        // Mark the peer as owning the block and schedule it for import
        p.MarkBlock(request.Block.Hash())
        pm.fetcher.Enqueue(p.id, request.Block)

        // Assuming the block is importable by the peer, but possibly not yet done so,
        // calculate the head hash and TD that the peer truly must have.
        var (
            trueHead = request.Block.ParentHash()
            trueTD   = new(big.Int).Sub(request.TD, request.Block.Difficulty())
        )
        // Update the peer's total difficulty if better than the previous
        if _, td := p.Head(); trueTD.Cmp(td) > 0 {
            p.SetHead(trueHead, trueTD)

            // Schedule a sync if above ours. Note, this will not fire a sync for a gap of
            // a single block (as the true TD is below the propagated block), however this
            // scenario should easily be covered by the fetcher.
            currentBlock := pm.blockchain.CurrentBlock()
            if trueTD.Cmp(pm.blockchain.GetTd(currentBlock.Hash(), currentBlock.NumberU64())) > 0 {
                go pm.synchronise(p)
            }
        }

    case msg.Code == TxMsg:
        // Transactions arrived, make sure we have a valid and fresh chain to handle them
        if atomic.LoadUint32(&pm.acceptTxs) == 0 {
            break
        }
        // Transactions can be processed, parse all of them and deliver to the pool
        var txs []*types.Transaction
        if err := msg.Decode(&txs); err != nil {
            return errResp(ErrDecode, "msg %v: %v", msg, err)
        }
        for i, tx := range txs {
            // Validate and mark the remote transaction
            if tx == nil {
                return errResp(ErrDecode, "transaction %d is nil", i)
            }
            p.MarkTransaction(tx.Hash())
        }
        pm.txpool.AddRemotes(txs)

    default:
        return errResp(ErrInvalidMsgCode, "%v", msg.Code)
    }
    return nil
}

// BroadcastBlock will either propagate a block to a subset of it's peers, or
// will only announce it's availability (depending what's requested).
func (pm *ProtocolManager) BroadcastBlock(block *types.Block, propagate bool) {
    hash := block.Hash()
    peers := pm.peers.PeersWithoutBlock(hash)

    // If propagation is requested, send to a subset of the peer
    if propagate {
        // Calculate the TD of the block (it's not imported yet, so block.Td is not valid)
        var td *big.Int
        if parent := pm.blockchain.GetBlock(block.ParentHash(), block.NumberU64()-1); parent != nil {
            td = new(big.Int).Add(block.Difficulty(), pm.blockchain.GetTd(block.ParentHash(), block.NumberU64()-1))
        } else {
            log.Error("Propagating dangling block", "number", block.Number(), "hash", hash)
            return
        }
        // Send the block to a subset of our peers
        transferLen := int(math.Sqrt(float64(len(peers))))
        if transferLen < minBroadcastPeers {
            transferLen = minBroadcastPeers
        }
        if transferLen > len(peers) {
            transferLen = len(peers)
        }
        transfer := peers[:transferLen]
        for _, peer := range transfer {
            peer.AsyncSendNewBlock(block, td)
        }
        log.Trace("Propagated block", "hash", hash, "recipients", len(transfer), "duration", common.PrettyDuration(time.Since(block.ReceivedAt)))
        return
    }
    // Otherwise if the block is indeed in out own chain, announce it
    if pm.blockchain.HasBlock(hash, block.NumberU64()) {
        for _, peer := range peers {
            peer.AsyncSendNewBlockHash(block)
        }
        log.Trace("Announced block", "hash", hash, "recipients", len(peers), "duration", common.PrettyDuration(time.Since(block.ReceivedAt)))
    }
}

// BroadcastTxs will propagate a batch of transactions to all peers which are not known to
// already have the given transaction.
func (pm *ProtocolManager) BroadcastTxs(txs types.Transactions) {
    var txset = make(map[*peer]types.Transactions)

    // Broadcast transactions to a batch of peers not knowing about it
    for _, tx := range txs {
        peers := pm.peers.PeersWithoutTx(tx.Hash())
        for _, peer := range peers {
            txset[peer] = append(txset[peer], tx)
        }
        log.Trace("Broadcast transaction", "hash", tx.Hash(), "recipients", len(peers))
    }
    // FIXME include this again: peers = peers[:int(math.Sqrt(float64(len(peers))))]
    for peer, txs := range txset {
        peer.AsyncSendTransactions(txs)
    }
}

// Mined broadcast loop
func (pm *ProtocolManager) minedBroadcastLoop() {
    // automatically stops if unsubscribe
    for obj := range pm.minedBlockSub.Chan() {
        if ev, ok := obj.Data.(core.NewMinedBlockEvent); ok {
            pm.BroadcastBlock(ev.Block, true)  // First propagate block to peers
            pm.BroadcastBlock(ev.Block, false) // Only then announce to the rest
        }
    }
}

func (pm *ProtocolManager) txBroadcastLoop() {
    for {
        select {
        case event := <-pm.txsCh:
            pm.BroadcastTxs(event.Txs)

        // Err() channel will be closed when unsubscribing.
        case <-pm.txsSub.Err():
            return
        }
    }
}

// NodeInfo represents a short summary of the Ethereum sub-protocol metadata
// known about the host peer.
type NodeInfo struct {
    Network    uint64              `json:"network"`    // Ethereum network ID (1=Frontier, 2=Morden, Ropsten=3, Rinkeby=4)
    Difficulty *big.Int            `json:"difficulty"` // Total difficulty of the host's blockchain
    Genesis    common.Hash         `json:"genesis"`    // SHA3 hash of the host's genesis block
    Config     *params.ChainConfig `json:"config"`     // Chain configuration for the fork rules
    Head       common.Hash         `json:"head"`       // SHA3 hash of the host's best owned block
}

// NodeInfo retrieves some protocol metadata about the running host node.
func (pm *ProtocolManager) NodeInfo() *NodeInfo {
    currentBlock := pm.blockchain.CurrentBlock()
    return &NodeInfo{
        Network:    pm.networkID,
        Difficulty: pm.blockchain.GetTd(currentBlock.Hash(), currentBlock.NumberU64()),
        Genesis:    pm.blockchain.Genesis().Hash(),
        Config:     pm.blockchain.Config(),
        Head:       currentBlock.Hash(),
    }
}