Official Go implementation of the Ethereum protocol
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go-ethereum/p2p/dnsdisc/client.go

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// Copyright 2019 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 dnsdisc
import (
"bytes"
"context"
"fmt"
"math/rand"
"net"
"strings"
"sync"
"time"
"github.com/ethereum/go-ethereum/common/mclock"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/log"
"github.com/ethereum/go-ethereum/p2p/enode"
"github.com/ethereum/go-ethereum/p2p/enr"
lru "github.com/hashicorp/golang-lru"
"golang.org/x/sync/singleflight"
"golang.org/x/time/rate"
)
// Client discovers nodes by querying DNS servers.
type Client struct {
cfg Config
clock mclock.Clock
entries *lru.Cache
ratelimit *rate.Limiter
singleflight singleflight.Group
}
// Config holds configuration options for the client.
type Config struct {
Timeout time.Duration // timeout used for DNS lookups (default 5s)
RecheckInterval time.Duration // time between tree root update checks (default 30min)
CacheLimit int // maximum number of cached records (default 1000)
RateLimit float64 // maximum DNS requests / second (default 3)
ValidSchemes enr.IdentityScheme // acceptable ENR identity schemes (default enode.ValidSchemes)
Resolver Resolver // the DNS resolver to use (defaults to system DNS)
Logger log.Logger // destination of client log messages (defaults to root logger)
}
// Resolver is a DNS resolver that can query TXT records.
type Resolver interface {
LookupTXT(ctx context.Context, domain string) ([]string, error)
}
func (cfg Config) withDefaults() Config {
const (
defaultTimeout = 5 * time.Second
defaultRecheck = 30 * time.Minute
defaultRateLimit = 3
defaultCache = 1000
)
if cfg.Timeout == 0 {
cfg.Timeout = defaultTimeout
}
if cfg.RecheckInterval == 0 {
cfg.RecheckInterval = defaultRecheck
}
if cfg.CacheLimit == 0 {
cfg.CacheLimit = defaultCache
}
if cfg.RateLimit == 0 {
cfg.RateLimit = defaultRateLimit
}
if cfg.ValidSchemes == nil {
cfg.ValidSchemes = enode.ValidSchemes
}
if cfg.Resolver == nil {
cfg.Resolver = new(net.Resolver)
}
if cfg.Logger == nil {
cfg.Logger = log.Root()
}
return cfg
}
// NewClient creates a client.
func NewClient(cfg Config) *Client {
cfg = cfg.withDefaults()
cache, err := lru.New(cfg.CacheLimit)
if err != nil {
panic(err)
}
rlimit := rate.NewLimiter(rate.Limit(cfg.RateLimit), 10)
return &Client{
cfg: cfg,
entries: cache,
clock: mclock.System{},
ratelimit: rlimit,
}
}
// SyncTree downloads the entire node tree at the given URL.
func (c *Client) SyncTree(url string) (*Tree, error) {
le, err := parseLink(url)
if err != nil {
return nil, fmt.Errorf("invalid enrtree URL: %v", err)
}
ct := newClientTree(c, new(linkCache), le)
t := &Tree{entries: make(map[string]entry)}
if err := ct.syncAll(t.entries); err != nil {
return nil, err
}
t.root = ct.root
return t, nil
}
// NewIterator creates an iterator that visits all nodes at the
// given tree URLs.
func (c *Client) NewIterator(urls ...string) (enode.Iterator, error) {
it := c.newRandomIterator()
for _, url := range urls {
if err := it.addTree(url); err != nil {
return nil, err
}
}
return it, nil
}
// resolveRoot retrieves a root entry via DNS.
func (c *Client) resolveRoot(ctx context.Context, loc *linkEntry) (rootEntry, error) {
e, err, _ := c.singleflight.Do(loc.str, func() (interface{}, error) {
txts, err := c.cfg.Resolver.LookupTXT(ctx, loc.domain)
c.cfg.Logger.Trace("Updating DNS discovery root", "tree", loc.domain, "err", err)
if err != nil {
return rootEntry{}, err
}
for _, txt := range txts {
if strings.HasPrefix(txt, rootPrefix) {
return parseAndVerifyRoot(txt, loc)
}
}
return rootEntry{}, nameError{loc.domain, errNoRoot}
})
return e.(rootEntry), err
}
func parseAndVerifyRoot(txt string, loc *linkEntry) (rootEntry, error) {
e, err := parseRoot(txt)
if err != nil {
return e, err
}
if !e.verifySignature(loc.pubkey) {
return e, entryError{typ: "root", err: errInvalidSig}
}
return e, nil
}
// resolveEntry retrieves an entry from the cache or fetches it from the network
// if it isn't cached.
func (c *Client) resolveEntry(ctx context.Context, domain, hash string) (entry, error) {
// The rate limit always applies, even when the result might be cached. This is
// important because it avoids hot-spinning in consumers of node iterators created on
// this client.
if err := c.ratelimit.Wait(ctx); err != nil {
return nil, err
}
cacheKey := truncateHash(hash)
if e, ok := c.entries.Get(cacheKey); ok {
return e.(entry), nil
}
ei, err, _ := c.singleflight.Do(cacheKey, func() (interface{}, error) {
e, err := c.doResolveEntry(ctx, domain, hash)
if err != nil {
return nil, err
}
c.entries.Add(cacheKey, e)
return e, nil
})
e, _ := ei.(entry)
return e, err
}
// doResolveEntry fetches an entry via DNS.
func (c *Client) doResolveEntry(ctx context.Context, domain, hash string) (entry, error) {
wantHash, err := b32format.DecodeString(hash)
if err != nil {
return nil, fmt.Errorf("invalid base32 hash")
}
name := hash + "." + domain
txts, err := c.cfg.Resolver.LookupTXT(ctx, hash+"."+domain)
c.cfg.Logger.Trace("DNS discovery lookup", "name", name, "err", err)
if err != nil {
return nil, err
}
for _, txt := range txts {
e, err := parseEntry(txt, c.cfg.ValidSchemes)
if err == errUnknownEntry {
continue
}
if !bytes.HasPrefix(crypto.Keccak256([]byte(txt)), wantHash) {
err = nameError{name, errHashMismatch}
} else if err != nil {
err = nameError{name, err}
}
return e, err
}
return nil, nameError{name, errNoEntry}
}
// randomIterator traverses a set of trees and returns nodes found in them.
type randomIterator struct {
cur *enode.Node
ctx context.Context
cancelFn context.CancelFunc
c *Client
mu sync.Mutex
lc linkCache // tracks tree dependencies
trees map[string]*clientTree // all trees
// buffers for syncableTrees
syncableList []*clientTree
disabledList []*clientTree
}
func (c *Client) newRandomIterator() *randomIterator {
ctx, cancel := context.WithCancel(context.Background())
return &randomIterator{
c: c,
ctx: ctx,
cancelFn: cancel,
trees: make(map[string]*clientTree),
}
}
// Node returns the current node.
func (it *randomIterator) Node() *enode.Node {
return it.cur
}
// Close closes the iterator.
func (it *randomIterator) Close() {
it.cancelFn()
it.mu.Lock()
defer it.mu.Unlock()
it.trees = nil
}
// Next moves the iterator to the next node.
func (it *randomIterator) Next() bool {
it.cur = it.nextNode()
return it.cur != nil
}
// addTree adds an enrtree:// URL to the iterator.
func (it *randomIterator) addTree(url string) error {
le, err := parseLink(url)
if err != nil {
return fmt.Errorf("invalid enrtree URL: %v", err)
}
it.lc.addLink("", le.str)
return nil
}
// nextNode syncs random tree entries until it finds a node.
func (it *randomIterator) nextNode() *enode.Node {
for {
ct := it.pickTree()
if ct == nil {
return nil
}
n, err := ct.syncRandom(it.ctx)
if err != nil {
if err == it.ctx.Err() {
return nil // context canceled.
}
it.c.cfg.Logger.Debug("Error in DNS random node sync", "tree", ct.loc.domain, "err", err)
continue
}
if n != nil {
return n
}
}
}
// pickTree returns a random tree to sync from.
func (it *randomIterator) pickTree() *clientTree {
it.mu.Lock()
defer it.mu.Unlock()
// First check if iterator was closed.
// Need to do this here to avoid nil map access in rebuildTrees.
if it.trees == nil {
return nil
}
// Rebuild the trees map if any links have changed.
if it.lc.changed {
it.rebuildTrees()
it.lc.changed = false
}
for {
canSync, trees := it.syncableTrees()
switch {
case canSync:
// Pick a random tree.
return trees[rand.Intn(len(trees))]
case len(trees) > 0:
// No sync action can be performed on any tree right now. The only meaningful
// thing to do is waiting for any root record to get updated.
if !it.waitForRootUpdates(trees) {
// Iterator was closed while waiting.
return nil
}
default:
// There are no trees left, the iterator was closed.
return nil
}
}
}
// syncableTrees finds trees on which any meaningful sync action can be performed.
func (it *randomIterator) syncableTrees() (canSync bool, trees []*clientTree) {
// Resize tree lists.
it.syncableList = it.syncableList[:0]
it.disabledList = it.disabledList[:0]
// Partition them into the two lists.
for _, ct := range it.trees {
if ct.canSyncRandom() {
it.syncableList = append(it.syncableList, ct)
} else {
it.disabledList = append(it.disabledList, ct)
}
}
if len(it.syncableList) > 0 {
return true, it.syncableList
}
return false, it.disabledList
}
// waitForRootUpdates waits for the closest scheduled root check time on the given trees.
func (it *randomIterator) waitForRootUpdates(trees []*clientTree) bool {
var minTree *clientTree
var nextCheck mclock.AbsTime
for _, ct := range trees {
check := ct.nextScheduledRootCheck()
if minTree == nil || check < nextCheck {
minTree = ct
nextCheck = check
}
}
sleep := nextCheck.Sub(it.c.clock.Now())
it.c.cfg.Logger.Debug("DNS iterator waiting for root updates", "sleep", sleep, "tree", minTree.loc.domain)
timeout := it.c.clock.NewTimer(sleep)
defer timeout.Stop()
select {
case <-timeout.C():
return true
case <-it.ctx.Done():
return false // Iterator was closed.
}
}
// rebuildTrees rebuilds the 'trees' map.
func (it *randomIterator) rebuildTrees() {
// Delete removed trees.
for loc := range it.trees {
if !it.lc.isReferenced(loc) {
delete(it.trees, loc)
}
}
// Add new trees.
for loc := range it.lc.backrefs {
if it.trees[loc] == nil {
link, _ := parseLink(linkPrefix + loc)
it.trees[loc] = newClientTree(it.c, &it.lc, link)
}
}
}