package blockpool import ( "fmt" "math/big" "sync" "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/errs" "github.com/ethereum/go-ethereum/event" ethlogger "github.com/ethereum/go-ethereum/logger" "github.com/ethereum/go-ethereum/logger/glog" "github.com/ethereum/go-ethereum/pow" ) var plog = ethlogger.NewLogger("Blockpool") var ( // max number of block hashes sent in one request blockHashesBatchSize = 256 // max number of blocks sent in one request blockBatchSize = 64 // interval between two consecutive block checks (and requests) blocksRequestInterval = 3 * time.Second // level of redundancy in block requests sent blocksRequestRepetition = 1 // interval between two consecutive block hash checks (and requests) blockHashesRequestInterval = 3 * time.Second // max number of idle iterations, ie., check through a section without new blocks coming in blocksRequestMaxIdleRounds = 20 // timeout interval: max time allowed for peer without sending a block hash blockHashesTimeout = 60 * time.Second // timeout interval: max time allowed for peer without sending a block blocksTimeout = 60 * time.Second // timeout interval: max time allowed for best peer to remain idle (not send new block after sync complete) idleBestPeerTimeout = 120 * time.Second // duration of suspension after peer fatal error during which peer is not allowed to reconnect peerSuspensionInterval = 300 * time.Second // status is logged every statusUpdateInterval statusUpdateInterval = 3 * time.Second ) // blockpool config, values default to constants type Config struct { BlockHashesBatchSize int BlockBatchSize int BlocksRequestRepetition int BlocksRequestMaxIdleRounds int BlockHashesRequestInterval time.Duration BlocksRequestInterval time.Duration BlockHashesTimeout time.Duration BlocksTimeout time.Duration IdleBestPeerTimeout time.Duration PeerSuspensionInterval time.Duration StatusUpdateInterval time.Duration } // blockpool errors const ( ErrInvalidBlock = iota ErrInvalidPoW ErrInsufficientChainInfo ErrIdleTooLong ErrIncorrectTD ErrUnrequestedBlock ) // error descriptions var errorToString = map[int]string{ ErrInvalidBlock: "Invalid block", // fatal ErrInvalidPoW: "Invalid PoW", // fatal ErrInsufficientChainInfo: "Insufficient chain info", // fatal ErrIdleTooLong: "Idle too long", // fatal ErrIncorrectTD: "Incorrect Total Difficulty", // fatal ErrUnrequestedBlock: "Unrequested block", } // error severity func severity(code int) ethlogger.LogLevel { switch code { case ErrUnrequestedBlock: return ethlogger.WarnLevel default: return ethlogger.ErrorLevel } } // init initialises the Config, zero values fall back to constants func (self *Config) init() { if self.BlockHashesBatchSize == 0 { self.BlockHashesBatchSize = blockHashesBatchSize } if self.BlockBatchSize == 0 { self.BlockBatchSize = blockBatchSize } if self.BlocksRequestRepetition == 0 { self.BlocksRequestRepetition = blocksRequestRepetition } if self.BlocksRequestMaxIdleRounds == 0 { self.BlocksRequestMaxIdleRounds = blocksRequestMaxIdleRounds } if self.BlockHashesRequestInterval == 0 { self.BlockHashesRequestInterval = blockHashesRequestInterval } if self.BlocksRequestInterval == 0 { self.BlocksRequestInterval = blocksRequestInterval } if self.BlockHashesTimeout == 0 { self.BlockHashesTimeout = blockHashesTimeout } if self.BlocksTimeout == 0 { self.BlocksTimeout = blocksTimeout } if self.IdleBestPeerTimeout == 0 { self.IdleBestPeerTimeout = idleBestPeerTimeout } if self.PeerSuspensionInterval == 0 { self.PeerSuspensionInterval = peerSuspensionInterval } if self.StatusUpdateInterval == 0 { self.StatusUpdateInterval = statusUpdateInterval } } // node is the basic unit of the internal model of block chain/tree in the blockpool type node struct { lock sync.RWMutex hash common.Hash block *types.Block hashBy string blockBy string td *big.Int } type index struct { int } // entry is the struct kept and indexed in the pool type entry struct { node *node section *section index *index } type BlockPool struct { Config *Config // the minimal interface with blockchain manager hasBlock func(hash common.Hash) bool // query if block is known insertChain func(types.Blocks) error // add section to blockchain verifyPoW func(pow.Block) bool // soft PoW verification chainEvents *event.TypeMux // ethereum eventer for chainEvents tdSub event.Subscription // subscription to core.ChainHeadEvent td *big.Int // our own total difficulty pool map[common.Hash]*entry // the actual blockpool peers *peers // peers manager in peers.go status *status // info about blockpool (UI interface) in status.go lock sync.RWMutex chainLock sync.RWMutex // alloc-easy pool of hash slices hashSlicePool chan []common.Hash // waitgroup is used in tests to wait for result-critical routines // as well as in determining idle / syncing status wg sync.WaitGroup // quit chan bool // chan used for quitting parallel routines running bool // } // public constructor // after blockpool returned, config can be set // BlockPool.Start will call Config.init to set missing values func New( hasBlock func(hash common.Hash) bool, insertChain func(types.Blocks) error, verifyPoW func(pow.Block) bool, chainEvents *event.TypeMux, td *big.Int, ) *BlockPool { return &BlockPool{ Config: &Config{}, hasBlock: hasBlock, insertChain: insertChain, verifyPoW: verifyPoW, chainEvents: chainEvents, td: td, } } // allows restart func (self *BlockPool) Start() { self.lock.Lock() defer self.lock.Unlock() if self.running { return } // set missing values self.Config.init() self.hashSlicePool = make(chan []common.Hash, 150) self.status = newStatus() self.quit = make(chan bool) self.pool = make(map[common.Hash]*entry) self.running = true self.peers = &peers{ errors: &errs.Errors{ Package: "Blockpool", Errors: errorToString, Level: severity, }, peers: make(map[string]*peer), blacklist: make(map[string]time.Time), status: self.status, bp: self, } // subscribe and listen to core.ChainHeadEvent{} for uptodate TD self.tdSub = self.chainEvents.Subscribe(core.ChainHeadEvent{}) // status update interval timer := time.NewTicker(self.Config.StatusUpdateInterval) go func() { for { select { case <-self.quit: return case event := <-self.tdSub.Chan(): if ev, ok := event.(core.ChainHeadEvent); ok { td := ev.Block.Td var height *big.Int if (ev.Block.HeaderHash == common.Hash{}) { height = ev.Block.Header().Number } plog.DebugDetailf("ChainHeadEvent: height: %v, td: %v, hash: %s", height, td, hex(ev.Block.Hash())) self.setTD(td) self.peers.lock.Lock() if best := self.peers.best; best != nil { // only switch if we strictly go above otherwise we may stall if only if td.Cmp(best.td) > 0 { self.peers.best = nil self.switchPeer(best, nil) } } self.peers.lock.Unlock() } case <-timer.C: plog.DebugDetailf("status:\n%v", self.Status()) } } }() glog.V(ethlogger.Info).Infoln("Blockpool started") } func (self *BlockPool) Stop() { self.lock.Lock() if !self.running { self.lock.Unlock() return } self.running = false self.lock.Unlock() plog.Infoln("Stopping...") self.tdSub.Unsubscribe() close(self.quit) self.lock.Lock() self.peers = nil self.pool = nil self.lock.Unlock() plog.Infoln("Stopped") } // Wait blocks until active processes finish func (self *BlockPool) Wait(t time.Duration) { self.lock.Lock() if !self.running { self.lock.Unlock() return } self.lock.Unlock() plog.Infoln("Waiting for processes to complete...") w := make(chan bool) go func() { self.wg.Wait() close(w) }() select { case <-w: plog.Infoln("Processes complete") case <-time.After(t): plog.Warnf("Timeout") } } /* AddPeer is called by the eth protocol instance running on the peer after the status message has been received with total difficulty and current block hash Called a second time with the same peer id, it is used to update chain info for a peer. This is used when a new (mined) block message is received. RemovePeer needs to be called when the peer disconnects. Peer info is currently not persisted across disconnects (or sessions) except for suspension */ func (self *BlockPool) AddPeer( td *big.Int, currentBlockHash common.Hash, peerId string, requestBlockHashes func(common.Hash) error, requestBlocks func([]common.Hash) error, peerError func(*errs.Error), ) (best bool, suspended bool) { return self.peers.addPeer(td, currentBlockHash, peerId, requestBlockHashes, requestBlocks, peerError) } // RemovePeer needs to be called when the peer disconnects func (self *BlockPool) RemovePeer(peerId string) { self.peers.removePeer(peerId) } /* AddBlockHashes Entry point for eth protocol to add block hashes received via BlockHashesMsg Only hashes from the best peer are handled Initiates further hash requests until a known parent is reached (unless cancelled by a peerSwitch event, i.e., when a better peer becomes best peer) Launches all block request processes on each chain section The first argument is an iterator function. Using this block hashes are decoded from the rlp message payload on demand. As a result, AddBlockHashes needs to run synchronously for one peer since the message is discarded if the caller thread returns. */ func (self *BlockPool) AddBlockHashes(next func() (common.Hash, bool), peerId string) { bestpeer, best := self.peers.getPeer(peerId) if !best { return } // bestpeer is still the best peer self.wg.Add(1) defer func() { self.wg.Done() }() self.status.lock.Lock() self.status.activePeers[bestpeer.id]++ self.status.lock.Unlock() var n int var hash common.Hash var ok, headSection, peerswitch bool var sec, child, parent *section var entry *entry var nodes []*node hash, ok = next() bestpeer.lock.Lock() plog.Debugf("AddBlockHashes: peer <%s> starting from [%s] (peer head: %s)", peerId, hex(bestpeer.parentHash), hex(bestpeer.currentBlockHash)) // first check if we are building the head section of a peer's chain if bestpeer.parentHash == hash { if self.hasBlock(bestpeer.currentBlockHash) { return } /* When peer is promoted in switchPeer, a new header section process is launched. Once the head section skeleton is actually created here, it is signaled to the process so that it can quit. In the special case that the node for parent of the head block is found in the blockpool (with or without fetched block), a singleton section containing only the head block node is created. */ headSection = true if entry := self.get(bestpeer.currentBlockHash); entry == nil { plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) head section starting from [%s] ", peerId, hex(bestpeer.currentBlockHash), hex(bestpeer.parentHash)) // if head block is not yet in the pool, create entry and start node list for section node := &node{ hash: bestpeer.currentBlockHash, block: bestpeer.currentBlock, hashBy: peerId, blockBy: peerId, td: bestpeer.td, } // nodes is a list of nodes in one section ordered top-bottom (old to young) nodes = append(nodes, node) n++ } else { // otherwise set child section iff found node is the root of a section // this is a possible scenario when a singleton head section was created // on an earlier occasion when this peer or another with the same block was best peer if entry.node == entry.section.bottom { child = entry.section plog.DebugDetailf("AddBlockHashes: peer <%s>: connects to child section root %s", peerId, hex(bestpeer.currentBlockHash)) } } } else { // otherwise : we are not building the head section of the peer plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) section starting from [%s] ", peerId, hex(bestpeer.currentBlockHash), hex(hash)) } // the switch channel signals peerswitch event switchC := bestpeer.switchC bestpeer.lock.Unlock() // iterate over hashes coming from peer (first round we have hash set above) LOOP: for ; ok; hash, ok = next() { select { case <-self.quit: // global quit for blockpool return case <-switchC: // if the peer is demoted, no more hashes read plog.DebugDetailf("AddBlockHashes: demoted peer <%s> (head: %s)", peerId, hex(bestpeer.currentBlockHash), hex(hash)) peerswitch = true break LOOP default: } // if we reach the blockchain we stop reading further blockhashes if self.hasBlock(hash) { // check if known block connecting the downloaded chain to our blockchain plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) found block %s in the blockchain", peerId, hex(bestpeer.currentBlockHash), hex(hash)) if len(nodes) == 1 { plog.DebugDetailf("AddBlockHashes: singleton section pushed to blockchain peer <%s> (head: %s) found block %s in the blockchain", peerId, hex(bestpeer.currentBlockHash), hex(hash)) // create new section if needed and push it to the blockchain sec = self.newSection(nodes) sec.addSectionToBlockChain(bestpeer) } else { /* not added hash yet but according to peer child section built earlier chain connects with blockchain this maybe a potential vulnarability the root block arrives (or already there but its parenthash was not pointing to known block in the blockchain) we start inserting -> error -> remove the entire chain instead of punishing this peer solution: when switching peers always make sure best peers own head block and td together with blockBy are recorded on the node */ if len(nodes) == 0 && child != nil { plog.DebugDetailf("AddBlockHashes: child section [%s] pushed to blockchain peer <%s> (head: %s) found block %s in the blockchain", sectionhex(child), peerId, hex(bestpeer.currentBlockHash), hex(hash)) child.addSectionToBlockChain(bestpeer) } } break LOOP } // look up node in the pool entry = self.get(hash) if entry != nil { // reached a known chain in the pool if entry.node == entry.section.bottom && n == 1 { /* The first block hash received is an orphan node in the pool This also supports clients that (despite the spec) include hash in their response to hashes request. Note that by providing we can link sections without having to wait for the root block of the child section to arrive, so it allows for superior performance. */ plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) found head block [%s] as root of connecting child section [%s] skipping", peerId, hex(bestpeer.currentBlockHash), hex(hash), sectionhex(entry.section)) // record the entry's chain section as child section child = entry.section continue LOOP } // otherwise record entry's chain section as parent connecting it to the pool plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) found block [%s] in section [%s]. Connected to pool.", peerId, hex(bestpeer.currentBlockHash), hex(hash), sectionhex(entry.section)) parent = entry.section break LOOP } // finally if node for block hash does not exist, create it and append node to section nodes node := &node{ hash: hash, hashBy: peerId, } nodes = append(nodes, node) } //for /* we got here if - run out of hashes (parent = nil) sent by our best peer - our peer is demoted (peerswitch = true) - reached blockchain or blockpool - quitting */ self.chainLock.Lock() plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s): %v nodes in new section", peerId, hex(bestpeer.currentBlockHash), len(nodes)) /* Handle forks where connecting node is mid-section by splitting section at fork. No splitting needed if connecting node is head of a section. */ if parent != nil && entry != nil && entry.node != parent.top && len(nodes) > 0 { plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s): fork after %s", peerId, hex(bestpeer.currentBlockHash), hex(hash)) self.splitSection(parent, entry) self.status.lock.Lock() self.status.values.Forks++ self.status.lock.Unlock() } // If new section is created, link it to parent/child sections. sec = self.linkSections(nodes, parent, child) if sec != nil { self.status.lock.Lock() self.status.values.BlockHashes += len(nodes) self.status.lock.Unlock() plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s): section [%s] created", peerId, hex(bestpeer.currentBlockHash), sectionhex(sec)) } self.chainLock.Unlock() /* If a blockpool node is reached (parent section is not nil), activate section (unless our peer is demoted by now). This can be the bottom half of a newly split section in case of a fork. bestPeer is nil if we got here after our peer got demoted while processing. In this case no activation should happen */ if parent != nil && !peerswitch { self.activateChain(parent, bestpeer, nil) plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s): parent section [%s]", peerId, hex(bestpeer.currentBlockHash), sectionhex(parent)) } /* If a new section was created, register section iff head section or no child known Activate it with this peer. */ if sec != nil { // switch on section process (it is paused by switchC) if !peerswitch { if headSection || child == nil { bestpeer.lock.Lock() bestpeer.sections = append(bestpeer.sections, sec.top.hash) bestpeer.lock.Unlock() } /* Request another batch of older block hashes for parent section here. But only once, repeating only when the section's root block arrives. Otherwise no way to check if it arrived. */ bestpeer.requestBlockHashes(sec.bottom.hash) plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s): start requesting blocks for section [%s]", peerId, hex(bestpeer.currentBlockHash), sectionhex(sec)) sec.activate(bestpeer) } else { plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) no longer best: delay requesting blocks for section [%s]", peerId, hex(bestpeer.currentBlockHash), sectionhex(sec)) sec.deactivate() } } // If we are processing peer's head section, signal it to headSection process that it is created. if headSection { plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) head section registered on head section process", peerId, hex(bestpeer.currentBlockHash)) var headSec *section switch { case sec != nil: headSec = sec case child != nil: headSec = child default: headSec = parent } if !peerswitch { plog.DebugDetailf("AddBlockHashes: peer <%s> (head: %s) head section [%s] created signalled to head section process", peerId, hex(bestpeer.currentBlockHash), sectionhex(headSec)) bestpeer.headSectionC <- headSec } } } /* AddBlock is the entry point for the eth protocol to call when blockMsg is received. It has a strict interpretation of the protocol in that if the block received has not been requested, it results in an error. At the same time it is opportunistic in that if a requested block may be provided by any peer. The received block is checked for PoW. Only the first PoW-valid block for a hash is considered legit. If the block received is the head block of the current best peer, signal it to the head section process */ func (self *BlockPool) AddBlock(block *types.Block, peerId string) { hash := block.Hash() sender, _ := self.peers.getPeer(peerId) if sender == nil { return } self.status.lock.Lock() self.status.activePeers[peerId]++ self.status.lock.Unlock() entry := self.get(hash) // a peer's current head block is appearing the first time sender.lock.Lock() if hash == sender.currentBlockHash { if sender.currentBlock == nil { plog.Debugf("AddBlock: add head block %s for peer <%s> (head: %s)", hex(hash), peerId, hex(sender.currentBlockHash)) sender.setChainInfoFromBlock(block) self.status.lock.Lock() self.status.values.BlockHashes++ self.status.values.Blocks++ self.status.values.BlocksInPool++ self.status.lock.Unlock() select { case sender.currentBlockC <- block: case <-sender.switchC: } } else { plog.DebugDetailf("AddBlock: head block %s for peer <%s> (head: %s) already known", hex(hash), peerId, hex(sender.currentBlockHash)) // signal to head section process } // self.wg.Add(1) // go func() { // timeout := time.After(1 * time.Second) // select { // case sender.currentBlockC <- block: // case <-timeout: // } // self.wg.Done() // }() } else { plog.DebugDetailf("AddBlock: block %s received from peer <%s> (head: %s)", hex(hash), peerId, hex(sender.currentBlockHash)) // update peer chain info if more recent than what we registered if block.Td != nil && block.Td.Cmp(sender.td) > 0 { sender.td = block.Td sender.currentBlockHash = block.Hash() sender.parentHash = block.ParentHash() sender.currentBlock = block sender.headSection = nil } /* @zelig !!! requested 5 hashes from both A & B. A responds sooner then B, process blocks. Close section. delayed B sends you block ... UNREQUESTED. Blocked if entry == nil { plog.DebugDetailf("AddBlock: unrequested block %s received from peer <%s> (head: %s)", hex(hash), peerId, hex(sender.currentBlockHash)) sender.addError(ErrUnrequestedBlock, "%x", hash) self.status.lock.Lock() self.status.badPeers[peerId]++ self.status.lock.Unlock() return } */ } sender.lock.Unlock() if entry == nil { return } node := entry.node node.lock.Lock() defer node.lock.Unlock() // check if block already received if node.block != nil { plog.DebugDetailf("AddBlock: block %s from peer <%s> (head: %s) already sent by <%s> ", hex(hash), peerId, hex(sender.currentBlockHash), node.blockBy) return } // check if block is already inserted in the blockchain if self.hasBlock(hash) { plog.DebugDetailf("AddBlock: block %s from peer <%s> (head: %s) already in the blockchain", hex(hash), peerId, hex(sender.currentBlockHash)) return } /* @zelig needs discussing // validate block for PoW if !self.verifyPoW(block) { plog.Warnf("AddBlock: invalid PoW on block %s from peer <%s> (head: %s)", hex(hash), peerId, hex(sender.currentBlockHash)) sender.addError(ErrInvalidPoW, "%x", hash) self.status.lock.Lock() self.status.badPeers[peerId]++ self.status.lock.Unlock() return } */ node.block = block node.blockBy = peerId node.td = block.Td // optional field self.status.lock.Lock() self.status.values.Blocks++ self.status.values.BlocksInPool++ self.status.lock.Unlock() } /* activateChain iterates down a chain section by section. It activates the section process on incomplete sections with peer. It relinks orphaned sections with their parent if root block (and its parent hash) is known. */ func (self *BlockPool) activateChain(sec *section, p *peer, connected map[common.Hash]*section) { p.lock.RLock() switchC := p.switchC p.lock.RUnlock() var i int LOOP: for sec != nil { parent := self.getParent(sec) plog.DebugDetailf("activateChain: section [%s] activated by peer <%s>", sectionhex(sec), p.id) sec.activate(p) if i > 0 && connected != nil { connected[sec.top.hash] = sec } /* Need to relink both complete and incomplete sections An incomplete section could have been blockHashesRequestsComplete before being delinked from its parent. */ if parent == nil { if sec.bottom.block != nil { if entry := self.get(sec.bottom.block.ParentHash()); entry != nil { parent = entry.section plog.DebugDetailf("activateChain: [%s]-[%s] link", sectionhex(parent), sectionhex(sec)) link(parent, sec) } } else { plog.DebugDetailf("activateChain: section [%s] activated by peer <%s> has missing root block", sectionhex(sec), p.id) } } sec = parent // stop if peer got demoted or global quit select { case <-switchC: break LOOP case <-self.quit: break LOOP default: } } } // check if block's actual TD (calculated after successful insertChain) is identical to TD advertised for peer's head block. func (self *BlockPool) checkTD(nodes ...*node) { for _, n := range nodes { if n.td != nil { plog.DebugDetailf("peer td %v =?= block td %v", n.td, n.block.Td) if n.td.Cmp(n.block.Td) != 0 { //self.peers.peerError(n.blockBy, ErrIncorrectTD, "on block %x", n.hash) //self.status.lock.Lock() //self.status.badPeers[n.blockBy]++ //self.status.lock.Unlock() } } } } // requestBlocks must run in separate go routine, otherwise // switchpeer -> activateChain -> activate deadlocks on section process select and peers.lock func (self *BlockPool) requestBlocks(attempts int, hashes []common.Hash) { self.wg.Add(1) go func() { self.peers.requestBlocks(attempts, hashes) self.wg.Done() }() } // convenience methods to access adjacent sections func (self *BlockPool) getParent(sec *section) *section { self.chainLock.RLock() defer self.chainLock.RUnlock() return sec.parent } func (self *BlockPool) getChild(sec *section) *section { self.chainLock.RLock() defer self.chainLock.RUnlock() return sec.child } // accessor and setter for entries in the pool func (self *BlockPool) get(hash common.Hash) *entry { self.lock.RLock() defer self.lock.RUnlock() return self.pool[hash] } func (self *BlockPool) set(hash common.Hash, e *entry) { self.lock.Lock() defer self.lock.Unlock() self.pool[hash] = e } // accessor and setter for total difficulty func (self *BlockPool) getTD() *big.Int { self.lock.RLock() defer self.lock.RUnlock() return self.td } func (self *BlockPool) setTD(td *big.Int) { self.lock.Lock() defer self.lock.Unlock() self.td = td } func (self *BlockPool) remove(sec *section) { // delete node entries from pool index under pool lock self.lock.Lock() defer self.lock.Unlock() for _, node := range sec.nodes { delete(self.pool, node.hash) } if sec.initialised && sec.poolRootIndex != 0 { self.status.lock.Lock() self.status.values.BlocksInPool -= len(sec.nodes) - sec.missing self.status.lock.Unlock() } } // get/put for optimised allocation similar to sync.Pool func (self *BlockPool) getHashSlice() (s []common.Hash) { select { case s = <-self.hashSlicePool: default: s = make([]common.Hash, self.Config.BlockBatchSize) } return } func (self *BlockPool) putHashSlice(s []common.Hash) { if len(s) == self.Config.BlockBatchSize { select { case self.hashSlicePool <- s: default: } } } // pretty prints hash (byte array) with first 4 bytes in hex func hex(hash common.Hash) (name string) { if (hash == common.Hash{}) { name = "" } else { name = fmt.Sprintf("%x", hash[:4]) } return } // pretty prints a section using first 4 bytes in hex of bottom and top blockhash of the section func sectionhex(section *section) (name string) { if section == nil { name = "" } else { name = fmt.Sprintf("%x-%x", section.bottom.hash[:4], section.top.hash[:4]) } return }