b4374436f3
nodeDB.querySeeds was not safe for concurrent use but could be called concurrenty on multiple goroutines in the following case: - the table was empty - a timed refresh started - a lookup was started and initiated refresh These conditions are unlikely to coincide during normal use, but are much more likely to occur all at once when the user's machine just woke from sleep. The root cause of the issue is that querySeeds reused the same leveldb iterator until it was exhausted. This commit moves the refresh scheduling logic into its own goroutine (so only one refresh is ever active) and changes querySeeds to not use a persistent iterator. The seed node selection is now more random and ignores nodes that have not been contacted in the last 5 days.
632 lines
18 KiB
Go
632 lines
18 KiB
Go
// Copyright 2015 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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// Package discover implements the Node Discovery Protocol.
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//
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// The Node Discovery protocol provides a way to find RLPx nodes that
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// can be connected to. It uses a Kademlia-like protocol to maintain a
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// distributed database of the IDs and endpoints of all listening
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// nodes.
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package discover
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import (
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"crypto/rand"
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"encoding/binary"
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"net"
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"sort"
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"sync"
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"time"
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"github.com/ethereum/go-ethereum/common"
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"github.com/ethereum/go-ethereum/crypto"
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"github.com/ethereum/go-ethereum/logger"
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"github.com/ethereum/go-ethereum/logger/glog"
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)
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const (
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alpha = 3 // Kademlia concurrency factor
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bucketSize = 16 // Kademlia bucket size
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hashBits = len(common.Hash{}) * 8
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nBuckets = hashBits + 1 // Number of buckets
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maxBondingPingPongs = 16
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maxFindnodeFailures = 5
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autoRefreshInterval = 1 * time.Hour
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seedCount = 30
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seedMaxAge = 5 * 24 * time.Hour
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)
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type Table struct {
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mutex sync.Mutex // protects buckets, their content, and nursery
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buckets [nBuckets]*bucket // index of known nodes by distance
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nursery []*Node // bootstrap nodes
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db *nodeDB // database of known nodes
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refreshReq chan struct{}
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closeReq chan struct{}
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closed chan struct{}
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bondmu sync.Mutex
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bonding map[NodeID]*bondproc
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bondslots chan struct{} // limits total number of active bonding processes
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nodeAddedHook func(*Node) // for testing
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net transport
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self *Node // metadata of the local node
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}
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type bondproc struct {
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err error
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n *Node
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done chan struct{}
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}
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// transport is implemented by the UDP transport.
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// it is an interface so we can test without opening lots of UDP
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// sockets and without generating a private key.
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type transport interface {
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ping(NodeID, *net.UDPAddr) error
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waitping(NodeID) error
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findnode(toid NodeID, addr *net.UDPAddr, target NodeID) ([]*Node, error)
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close()
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}
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// bucket contains nodes, ordered by their last activity. the entry
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// that was most recently active is the first element in entries.
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type bucket struct {
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lastLookup time.Time
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entries []*Node
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}
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func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string) *Table {
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// If no node database was given, use an in-memory one
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db, err := newNodeDB(nodeDBPath, Version, ourID)
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if err != nil {
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glog.V(logger.Warn).Infoln("Failed to open node database:", err)
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db, _ = newNodeDB("", Version, ourID)
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}
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tab := &Table{
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net: t,
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db: db,
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self: newNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
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bonding: make(map[NodeID]*bondproc),
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bondslots: make(chan struct{}, maxBondingPingPongs),
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refreshReq: make(chan struct{}),
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closeReq: make(chan struct{}),
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closed: make(chan struct{}),
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}
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for i := 0; i < cap(tab.bondslots); i++ {
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tab.bondslots <- struct{}{}
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}
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for i := range tab.buckets {
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tab.buckets[i] = new(bucket)
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}
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go tab.refreshLoop()
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return tab
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}
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// Self returns the local node.
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// The returned node should not be modified by the caller.
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func (tab *Table) Self() *Node {
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return tab.self
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}
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// ReadRandomNodes fills the given slice with random nodes from the
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// table. It will not write the same node more than once. The nodes in
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// the slice are copies and can be modified by the caller.
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func (tab *Table) ReadRandomNodes(buf []*Node) (n int) {
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tab.mutex.Lock()
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defer tab.mutex.Unlock()
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// TODO: tree-based buckets would help here
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// Find all non-empty buckets and get a fresh slice of their entries.
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var buckets [][]*Node
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for _, b := range tab.buckets {
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if len(b.entries) > 0 {
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buckets = append(buckets, b.entries[:])
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}
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}
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if len(buckets) == 0 {
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return 0
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}
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// Shuffle the buckets.
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for i := uint32(len(buckets)) - 1; i > 0; i-- {
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j := randUint(i)
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buckets[i], buckets[j] = buckets[j], buckets[i]
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}
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// Move head of each bucket into buf, removing buckets that become empty.
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var i, j int
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for ; i < len(buf); i, j = i+1, (j+1)%len(buckets) {
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b := buckets[j]
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buf[i] = &(*b[0])
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buckets[j] = b[1:]
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if len(b) == 1 {
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buckets = append(buckets[:j], buckets[j+1:]...)
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}
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if len(buckets) == 0 {
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break
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}
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}
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return i + 1
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}
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func randUint(max uint32) uint32 {
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if max == 0 {
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return 0
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}
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var b [4]byte
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rand.Read(b[:])
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return binary.BigEndian.Uint32(b[:]) % max
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}
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// Close terminates the network listener and flushes the node database.
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func (tab *Table) Close() {
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select {
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case <-tab.closed:
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// already closed.
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case tab.closeReq <- struct{}{}:
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<-tab.closed // wait for refreshLoop to end.
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}
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}
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// Bootstrap sets the bootstrap nodes. These nodes are used to connect
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// to the network if the table is empty. Bootstrap will also attempt to
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// fill the table by performing random lookup operations on the
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// network.
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func (tab *Table) Bootstrap(nodes []*Node) {
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tab.mutex.Lock()
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// TODO: maybe filter nodes with bad fields (nil, etc.) to avoid strange crashes
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tab.nursery = make([]*Node, 0, len(nodes))
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for _, n := range nodes {
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cpy := *n
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cpy.sha = crypto.Sha3Hash(n.ID[:])
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tab.nursery = append(tab.nursery, &cpy)
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}
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tab.mutex.Unlock()
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tab.requestRefresh()
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}
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// Lookup performs a network search for nodes close
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// to the given target. It approaches the target by querying
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// nodes that are closer to it on each iteration.
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// The given target does not need to be an actual node
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// identifier.
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func (tab *Table) Lookup(targetID NodeID) []*Node {
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var (
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target = crypto.Sha3Hash(targetID[:])
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asked = make(map[NodeID]bool)
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seen = make(map[NodeID]bool)
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reply = make(chan []*Node, alpha)
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pendingQueries = 0
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)
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// don't query further if we hit ourself.
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// unlikely to happen often in practice.
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asked[tab.self.ID] = true
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tab.mutex.Lock()
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// update last lookup stamp (for refresh logic)
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tab.buckets[logdist(tab.self.sha, target)].lastLookup = time.Now()
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// generate initial result set
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result := tab.closest(target, bucketSize)
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tab.mutex.Unlock()
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// If the result set is empty, all nodes were dropped, refresh.
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if len(result.entries) == 0 {
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tab.requestRefresh()
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return nil
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}
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for {
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// ask the alpha closest nodes that we haven't asked yet
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for i := 0; i < len(result.entries) && pendingQueries < alpha; i++ {
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n := result.entries[i]
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if !asked[n.ID] {
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asked[n.ID] = true
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pendingQueries++
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go func() {
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// Find potential neighbors to bond with
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r, err := tab.net.findnode(n.ID, n.addr(), targetID)
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if err != nil {
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// Bump the failure counter to detect and evacuate non-bonded entries
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fails := tab.db.findFails(n.ID) + 1
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tab.db.updateFindFails(n.ID, fails)
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glog.V(logger.Detail).Infof("Bumping failures for %x: %d", n.ID[:8], fails)
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if fails >= maxFindnodeFailures {
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glog.V(logger.Detail).Infof("Evacuating node %x: %d findnode failures", n.ID[:8], fails)
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tab.delete(n)
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}
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}
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reply <- tab.bondall(r)
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}()
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}
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}
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if pendingQueries == 0 {
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// we have asked all closest nodes, stop the search
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break
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}
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// wait for the next reply
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for _, n := range <-reply {
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if n != nil && !seen[n.ID] {
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seen[n.ID] = true
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result.push(n, bucketSize)
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}
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}
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pendingQueries--
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}
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return result.entries
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}
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func (tab *Table) requestRefresh() {
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select {
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case tab.refreshReq <- struct{}{}:
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case <-tab.closed:
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}
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}
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func (tab *Table) refreshLoop() {
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defer func() {
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tab.db.close()
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if tab.net != nil {
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tab.net.close()
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}
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close(tab.closed)
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}()
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timer := time.NewTicker(autoRefreshInterval)
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var done chan struct{}
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for {
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select {
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case <-timer.C:
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if done == nil {
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done = make(chan struct{})
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go tab.doRefresh(done)
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}
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case <-tab.refreshReq:
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if done == nil {
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done = make(chan struct{})
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go tab.doRefresh(done)
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}
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case <-done:
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done = nil
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case <-tab.closeReq:
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if done != nil {
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<-done
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}
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return
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}
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}
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}
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// doRefresh performs a lookup for a random target to keep buckets
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// full. seed nodes are inserted if the table is empty (initial
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// bootstrap or discarded faulty peers).
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func (tab *Table) doRefresh(done chan struct{}) {
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defer close(done)
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// The Kademlia paper specifies that the bucket refresh should
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// perform a lookup in the least recently used bucket. We cannot
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// adhere to this because the findnode target is a 512bit value
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// (not hash-sized) and it is not easily possible to generate a
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// sha3 preimage that falls into a chosen bucket.
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// We perform a lookup with a random target instead.
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var target NodeID
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rand.Read(target[:])
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result := tab.Lookup(target)
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if len(result) > 0 {
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return
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}
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// The table is empty. Load nodes from the database and insert
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// them. This should yield a few previously seen nodes that are
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// (hopefully) still alive.
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seeds := tab.db.querySeeds(seedCount, seedMaxAge)
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seeds = tab.bondall(append(seeds, tab.nursery...))
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if glog.V(logger.Debug) {
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if len(seeds) == 0 {
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glog.Infof("no seed nodes found")
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}
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for _, n := range seeds {
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age := time.Since(tab.db.lastPong(n.ID))
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glog.Infof("seed node (age %v): %v", age, n)
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}
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}
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tab.mutex.Lock()
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tab.stuff(seeds)
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tab.mutex.Unlock()
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// Finally, do a self lookup to fill up the buckets.
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tab.Lookup(tab.self.ID)
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}
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// closest returns the n nodes in the table that are closest to the
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// given id. The caller must hold tab.mutex.
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func (tab *Table) closest(target common.Hash, nresults int) *nodesByDistance {
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// This is a very wasteful way to find the closest nodes but
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// obviously correct. I believe that tree-based buckets would make
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// this easier to implement efficiently.
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close := &nodesByDistance{target: target}
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for _, b := range tab.buckets {
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for _, n := range b.entries {
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close.push(n, nresults)
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}
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}
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return close
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}
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func (tab *Table) len() (n int) {
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for _, b := range tab.buckets {
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n += len(b.entries)
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}
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return n
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}
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// bondall bonds with all given nodes concurrently and returns
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// those nodes for which bonding has probably succeeded.
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func (tab *Table) bondall(nodes []*Node) (result []*Node) {
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rc := make(chan *Node, len(nodes))
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for i := range nodes {
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go func(n *Node) {
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nn, _ := tab.bond(false, n.ID, n.addr(), uint16(n.TCP))
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rc <- nn
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}(nodes[i])
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}
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for _ = range nodes {
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if n := <-rc; n != nil {
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result = append(result, n)
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}
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}
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return result
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}
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// bond ensures the local node has a bond with the given remote node.
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// It also attempts to insert the node into the table if bonding succeeds.
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// The caller must not hold tab.mutex.
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//
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// A bond is must be established before sending findnode requests.
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// Both sides must have completed a ping/pong exchange for a bond to
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// exist. The total number of active bonding processes is limited in
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// order to restrain network use.
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//
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// bond is meant to operate idempotently in that bonding with a remote
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// node which still remembers a previously established bond will work.
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// The remote node will simply not send a ping back, causing waitping
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// to time out.
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//
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// If pinged is true, the remote node has just pinged us and one half
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// of the process can be skipped.
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func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) (*Node, error) {
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// Retrieve a previously known node and any recent findnode failures
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node, fails := tab.db.node(id), 0
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if node != nil {
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fails = tab.db.findFails(id)
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}
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// If the node is unknown (non-bonded) or failed (remotely unknown), bond from scratch
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var result error
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age := time.Since(tab.db.lastPong(id))
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if node == nil || fails > 0 || age > nodeDBNodeExpiration {
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glog.V(logger.Detail).Infof("Bonding %x: known=%t, fails=%d age=%v", id[:8], node != nil, fails, age)
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tab.bondmu.Lock()
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w := tab.bonding[id]
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if w != nil {
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// Wait for an existing bonding process to complete.
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tab.bondmu.Unlock()
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<-w.done
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} else {
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// Register a new bonding process.
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w = &bondproc{done: make(chan struct{})}
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tab.bonding[id] = w
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tab.bondmu.Unlock()
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// Do the ping/pong. The result goes into w.
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tab.pingpong(w, pinged, id, addr, tcpPort)
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// Unregister the process after it's done.
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tab.bondmu.Lock()
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delete(tab.bonding, id)
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tab.bondmu.Unlock()
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}
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// Retrieve the bonding results
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result = w.err
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if result == nil {
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node = w.n
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}
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}
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if node != nil {
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// Add the node to the table even if the bonding ping/pong
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// fails. It will be relaced quickly if it continues to be
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// unresponsive.
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tab.add(node)
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tab.db.updateFindFails(id, 0)
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}
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return node, result
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}
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func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) {
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// Request a bonding slot to limit network usage
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<-tab.bondslots
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defer func() { tab.bondslots <- struct{}{} }()
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// Ping the remote side and wait for a pong.
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if w.err = tab.ping(id, addr); w.err != nil {
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close(w.done)
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return
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}
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if !pinged {
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// Give the remote node a chance to ping us before we start
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// sending findnode requests. If they still remember us,
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// waitping will simply time out.
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tab.net.waitping(id)
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}
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// Bonding succeeded, update the node database.
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w.n = newNode(id, addr.IP, uint16(addr.Port), tcpPort)
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tab.db.updateNode(w.n)
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close(w.done)
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}
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// ping a remote endpoint and wait for a reply, also updating the node
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// database accordingly.
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func (tab *Table) ping(id NodeID, addr *net.UDPAddr) error {
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tab.db.updateLastPing(id, time.Now())
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if err := tab.net.ping(id, addr); err != nil {
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return err
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}
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tab.db.updateLastPong(id, time.Now())
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// Start the background expiration goroutine after the first
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// successful communication. Subsequent calls have no effect if it
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// is already running. We do this here instead of somewhere else
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// so that the search for seed nodes also considers older nodes
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// that would otherwise be removed by the expiration.
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tab.db.ensureExpirer()
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return nil
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}
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// add attempts to add the given node its corresponding bucket. If the
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// bucket has space available, adding the node succeeds immediately.
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// Otherwise, the node is added if the least recently active node in
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// the bucket does not respond to a ping packet.
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//
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// The caller must not hold tab.mutex.
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func (tab *Table) add(new *Node) {
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b := tab.buckets[logdist(tab.self.sha, new.sha)]
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tab.mutex.Lock()
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defer tab.mutex.Unlock()
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if b.bump(new) {
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return
|
|
}
|
|
var oldest *Node
|
|
if len(b.entries) == bucketSize {
|
|
oldest = b.entries[bucketSize-1]
|
|
if oldest.contested {
|
|
// The node is already being replaced, don't attempt
|
|
// to replace it.
|
|
return
|
|
}
|
|
oldest.contested = true
|
|
// Let go of the mutex so other goroutines can access
|
|
// the table while we ping the least recently active node.
|
|
tab.mutex.Unlock()
|
|
err := tab.ping(oldest.ID, oldest.addr())
|
|
tab.mutex.Lock()
|
|
oldest.contested = false
|
|
if err == nil {
|
|
// The node responded, don't replace it.
|
|
return
|
|
}
|
|
}
|
|
added := b.replace(new, oldest)
|
|
if added && tab.nodeAddedHook != nil {
|
|
tab.nodeAddedHook(new)
|
|
}
|
|
}
|
|
|
|
// stuff adds nodes the table to the end of their corresponding bucket
|
|
// if the bucket is not full. The caller must hold tab.mutex.
|
|
func (tab *Table) stuff(nodes []*Node) {
|
|
outer:
|
|
for _, n := range nodes {
|
|
if n.ID == tab.self.ID {
|
|
continue // don't add self
|
|
}
|
|
bucket := tab.buckets[logdist(tab.self.sha, n.sha)]
|
|
for i := range bucket.entries {
|
|
if bucket.entries[i].ID == n.ID {
|
|
continue outer // already in bucket
|
|
}
|
|
}
|
|
if len(bucket.entries) < bucketSize {
|
|
bucket.entries = append(bucket.entries, n)
|
|
if tab.nodeAddedHook != nil {
|
|
tab.nodeAddedHook(n)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// delete removes an entry from the node table (used to evacuate
|
|
// failed/non-bonded discovery peers).
|
|
func (tab *Table) delete(node *Node) {
|
|
tab.mutex.Lock()
|
|
defer tab.mutex.Unlock()
|
|
bucket := tab.buckets[logdist(tab.self.sha, node.sha)]
|
|
for i := range bucket.entries {
|
|
if bucket.entries[i].ID == node.ID {
|
|
bucket.entries = append(bucket.entries[:i], bucket.entries[i+1:]...)
|
|
return
|
|
}
|
|
}
|
|
}
|
|
|
|
func (b *bucket) replace(n *Node, last *Node) bool {
|
|
// Don't add if b already contains n.
|
|
for i := range b.entries {
|
|
if b.entries[i].ID == n.ID {
|
|
return false
|
|
}
|
|
}
|
|
// Replace last if it is still the last entry or just add n if b
|
|
// isn't full. If is no longer the last entry, it has either been
|
|
// replaced with someone else or became active.
|
|
if len(b.entries) == bucketSize && (last == nil || b.entries[bucketSize-1].ID != last.ID) {
|
|
return false
|
|
}
|
|
if len(b.entries) < bucketSize {
|
|
b.entries = append(b.entries, nil)
|
|
}
|
|
copy(b.entries[1:], b.entries)
|
|
b.entries[0] = n
|
|
return true
|
|
}
|
|
|
|
func (b *bucket) bump(n *Node) bool {
|
|
for i := range b.entries {
|
|
if b.entries[i].ID == n.ID {
|
|
// move it to the front
|
|
copy(b.entries[1:], b.entries[:i])
|
|
b.entries[0] = n
|
|
return true
|
|
}
|
|
}
|
|
return false
|
|
}
|
|
|
|
// nodesByDistance is a list of nodes, ordered by
|
|
// distance to target.
|
|
type nodesByDistance struct {
|
|
entries []*Node
|
|
target common.Hash
|
|
}
|
|
|
|
// push adds the given node to the list, keeping the total size below maxElems.
|
|
func (h *nodesByDistance) push(n *Node, maxElems int) {
|
|
ix := sort.Search(len(h.entries), func(i int) bool {
|
|
return distcmp(h.target, h.entries[i].sha, n.sha) > 0
|
|
})
|
|
if len(h.entries) < maxElems {
|
|
h.entries = append(h.entries, n)
|
|
}
|
|
if ix == len(h.entries) {
|
|
// farther away than all nodes we already have.
|
|
// if there was room for it, the node is now the last element.
|
|
} else {
|
|
// slide existing entries down to make room
|
|
// this will overwrite the entry we just appended.
|
|
copy(h.entries[ix+1:], h.entries[ix:])
|
|
h.entries[ix] = n
|
|
}
|
|
}
|