mirror of
https://gitlab.com/pulsechaincom/erigon-pulse.git
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395 lines
10 KiB
Go
395 lines
10 KiB
Go
// Copyright 2019 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 dnsdisc
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import (
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"bytes"
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"context"
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"errors"
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"fmt"
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"math/rand"
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"net"
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"strings"
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"sync"
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"time"
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"github.com/hashicorp/golang-lru/v2"
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"github.com/ledgerwatch/erigon/common/mclock"
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"github.com/ledgerwatch/erigon/crypto"
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"github.com/ledgerwatch/erigon/p2p/enode"
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"github.com/ledgerwatch/erigon/p2p/enr"
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"github.com/ledgerwatch/log/v3"
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"golang.org/x/sync/singleflight"
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"golang.org/x/time/rate"
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)
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// Client discovers nodes by querying DNS servers.
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type Client struct {
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cfg Config
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clock mclock.Clock
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entries *lru.Cache[string, entry]
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ratelimit *rate.Limiter
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singleflight singleflight.Group
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}
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// Config holds configuration options for the client.
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type Config struct {
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Timeout time.Duration // timeout used for DNS lookups (default 5s)
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RecheckInterval time.Duration // time between tree root update checks (default 30min)
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CacheLimit int // maximum number of cached records (default 1000)
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RateLimit float64 // maximum DNS requests / second (default 3)
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ValidSchemes enr.IdentityScheme // acceptable ENR identity schemes (default enode.ValidSchemes)
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Resolver Resolver // the DNS resolver to use (defaults to system DNS)
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Logger log.Logger // destination of client log messages (defaults to root logger)
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}
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// Resolver is a DNS resolver that can query TXT records.
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type Resolver interface {
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LookupTXT(ctx context.Context, domain string) ([]string, error)
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}
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func (cfg Config) withDefaults() Config {
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const (
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defaultTimeout = 5 * time.Second
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defaultRecheck = 30 * time.Minute
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defaultRateLimit = 3
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defaultCache = 1000
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)
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if cfg.Timeout == 0 {
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cfg.Timeout = defaultTimeout
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}
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if cfg.RecheckInterval == 0 {
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cfg.RecheckInterval = defaultRecheck
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}
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if cfg.CacheLimit == 0 {
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cfg.CacheLimit = defaultCache
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}
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if cfg.RateLimit == 0 {
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cfg.RateLimit = defaultRateLimit
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}
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if cfg.ValidSchemes == nil {
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cfg.ValidSchemes = enode.ValidSchemes
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}
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if cfg.Resolver == nil {
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cfg.Resolver = new(net.Resolver)
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}
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if cfg.Logger == nil {
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cfg.Logger = log.Root()
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}
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return cfg
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}
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// NewClient creates a client.
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func NewClient(cfg Config) *Client {
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cfg = cfg.withDefaults()
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rlimit := rate.NewLimiter(rate.Limit(cfg.RateLimit), 10)
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entries, err := lru.New[string, entry](cfg.CacheLimit)
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if err != nil {
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log.Warn("can't create lru", "err", err)
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}
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return &Client{
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cfg: cfg,
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entries: entries,
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clock: mclock.System{},
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ratelimit: rlimit,
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}
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}
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// SyncTree downloads the entire node tree at the given URL.
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func (c *Client) SyncTree(url string) (*Tree, error) {
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le, err := parseLink(url)
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if err != nil {
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return nil, fmt.Errorf("invalid enrtree URL: %v", err)
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}
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ct := newClientTree(c, new(linkCache), le)
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t := &Tree{entries: make(map[string]entry)}
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if err := ct.syncAll(t.entries); err != nil {
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return nil, err
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}
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t.root = ct.root
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return t, nil
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}
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// NewIterator creates an iterator that visits all nodes at the
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// given tree URLs.
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func (c *Client) NewIterator(urls ...string) (enode.Iterator, error) {
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it := c.newRandomIterator()
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for _, url := range urls {
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if err := it.addTree(url); err != nil {
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return nil, err
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}
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}
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return it, nil
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}
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// resolveRoot retrieves a root entry via DNS.
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func (c *Client) resolveRoot(ctx context.Context, loc *linkEntry) (rootEntry, error) {
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e, err, _ := c.singleflight.Do(loc.str, func() (interface{}, error) {
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txts, err := c.cfg.Resolver.LookupTXT(ctx, loc.domain)
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c.cfg.Logger.Trace("Updating DNS discovery root", "tree", loc.domain, "err", err)
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if err != nil {
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return rootEntry{}, err
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}
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for _, txt := range txts {
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if strings.HasPrefix(txt, rootPrefix) {
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return parseAndVerifyRoot(txt, loc)
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}
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}
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return rootEntry{}, nameError{loc.domain, errNoRoot}
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})
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return e.(rootEntry), err
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}
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func parseAndVerifyRoot(txt string, loc *linkEntry) (rootEntry, error) {
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e, err := parseRoot(txt)
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if err != nil {
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return e, err
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}
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if !e.verifySignature(loc.pubkey) {
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return e, entryError{typ: "root", err: errInvalidSig}
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}
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return e, nil
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}
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// resolveEntry retrieves an entry from the cache or fetches it from the network
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// if it isn't cached.
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func (c *Client) resolveEntry(ctx context.Context, domain, hash string) (entry, error) {
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// The rate limit always applies, even when the result might be cached. This is
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// important because it avoids hot-spinning in consumers of node iterators created on
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// this client.
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if err := c.ratelimit.Wait(ctx); err != nil {
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return nil, err
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}
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cacheKey := truncateHash(hash)
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if e, ok := c.entries.Get(cacheKey); ok {
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return e, nil
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}
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ei, err, _ := c.singleflight.Do(cacheKey, func() (interface{}, error) {
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e, err := c.doResolveEntry(ctx, domain, hash)
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if err != nil {
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return nil, err
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}
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c.entries.Add(cacheKey, e)
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return e, nil
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})
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e, _ := ei.(entry)
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return e, err
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}
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// doResolveEntry fetches an entry via DNS.
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func (c *Client) doResolveEntry(ctx context.Context, domain, hash string) (entry, error) {
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wantHash, err := b32format.DecodeString(hash)
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if err != nil {
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return nil, fmt.Errorf("invalid base32 hash")
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}
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name := hash + "." + domain
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txts, err := c.cfg.Resolver.LookupTXT(ctx, hash+"."+domain)
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c.cfg.Logger.Trace("DNS discovery lookup", "name", name, "err", err)
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if err != nil {
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return nil, err
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}
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for _, txt := range txts {
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e, err := parseEntry(txt, c.cfg.ValidSchemes)
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if errors.Is(err, errUnknownEntry) {
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continue
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}
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if !bytes.HasPrefix(crypto.Keccak256([]byte(txt)), wantHash) {
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err = nameError{name, errHashMismatch}
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} else if err != nil {
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err = nameError{name, err}
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}
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return e, err
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}
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return nil, nameError{name, errNoEntry}
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}
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// randomIterator traverses a set of trees and returns nodes found in them.
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type randomIterator struct {
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cur *enode.Node
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ctx context.Context
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cancelFn context.CancelFunc
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c *Client
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mu sync.Mutex
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lc linkCache // tracks tree dependencies
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trees map[string]*clientTree // all trees
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// buffers for syncableTrees
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syncableList []*clientTree
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disabledList []*clientTree
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}
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func (c *Client) newRandomIterator() *randomIterator {
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ctx, cancel := context.WithCancel(context.Background())
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return &randomIterator{
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c: c,
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ctx: ctx,
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cancelFn: cancel,
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trees: make(map[string]*clientTree),
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}
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}
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// Node returns the current node.
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func (it *randomIterator) Node() *enode.Node {
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return it.cur
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}
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// Close closes the iterator.
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func (it *randomIterator) Close() {
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it.cancelFn()
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it.mu.Lock()
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defer it.mu.Unlock()
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it.trees = nil
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}
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// Next moves the iterator to the next node.
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func (it *randomIterator) Next() bool {
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it.cur = it.nextNode()
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return it.cur != nil
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}
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// addTree adds an enrtree:// URL to the iterator.
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func (it *randomIterator) addTree(url string) error {
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le, err := parseLink(url)
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if err != nil {
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return fmt.Errorf("invalid enrtree URL: %v", err)
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}
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it.lc.addLink("", le.str)
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return nil
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}
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// nextNode syncs random tree entries until it finds a node.
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func (it *randomIterator) nextNode() *enode.Node {
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for {
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ct := it.pickTree()
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if ct == nil {
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return nil
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}
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n, err := ct.syncRandom(it.ctx)
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if err != nil {
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if errors.Is(err, it.ctx.Err()) {
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return nil // context canceled.
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}
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it.c.cfg.Logger.Debug("Error in DNS random node sync", "tree", ct.loc.domain, "err", err)
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continue
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}
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if n != nil {
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return n
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}
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}
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}
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// pickTree returns a random tree to sync from.
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func (it *randomIterator) pickTree() *clientTree {
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it.mu.Lock()
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defer it.mu.Unlock()
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// First check if iterator was closed.
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// Need to do this here to avoid nil map access in rebuildTrees.
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if it.trees == nil {
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return nil
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}
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// Rebuild the trees map if any links have changed.
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if it.lc.changed {
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it.rebuildTrees()
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it.lc.changed = false
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}
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for {
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canSync, trees := it.syncableTrees()
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switch {
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case canSync:
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// Pick a random tree.
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return trees[rand.Intn(len(trees))]
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case len(trees) > 0:
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// No sync action can be performed on any tree right now. The only meaningful
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// thing to do is waiting for any root record to get updated.
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if !it.waitForRootUpdates(trees) {
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// Iterator was closed while waiting.
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return nil
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}
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default:
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// There are no trees left, the iterator was closed.
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return nil
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}
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}
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}
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// syncableTrees finds trees on which any meaningful sync action can be performed.
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func (it *randomIterator) syncableTrees() (canSync bool, trees []*clientTree) {
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// Resize tree lists.
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it.syncableList = it.syncableList[:0]
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it.disabledList = it.disabledList[:0]
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// Partition them into the two lists.
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for _, ct := range it.trees {
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if ct.canSyncRandom() {
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it.syncableList = append(it.syncableList, ct)
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} else {
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it.disabledList = append(it.disabledList, ct)
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}
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}
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if len(it.syncableList) > 0 {
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return true, it.syncableList
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}
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return false, it.disabledList
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}
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// waitForRootUpdates waits for the closest scheduled root check time on the given trees.
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func (it *randomIterator) waitForRootUpdates(trees []*clientTree) bool {
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var minTree *clientTree
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var nextCheck mclock.AbsTime
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for _, ct := range trees {
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check := ct.nextScheduledRootCheck()
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if minTree == nil || check < nextCheck {
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minTree = ct
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nextCheck = check
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}
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}
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sleep := nextCheck.Sub(it.c.clock.Now())
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it.c.cfg.Logger.Debug("DNS iterator waiting for root updates", "sleep", sleep, "tree", minTree.loc.domain)
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timeout := it.c.clock.NewTimer(sleep)
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defer timeout.Stop()
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select {
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case <-timeout.C():
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return true
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case <-it.ctx.Done():
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return false // Iterator was closed.
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}
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}
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// rebuildTrees rebuilds the 'trees' map.
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func (it *randomIterator) rebuildTrees() {
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// Delete removed trees.
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for loc := range it.trees {
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if !it.lc.isReferenced(loc) {
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delete(it.trees, loc)
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}
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}
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// Add new trees.
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for loc := range it.lc.backrefs {
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if it.trees[loc] == nil {
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link, _ := parseLink(linkPrefix + loc)
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it.trees[loc] = newClientTree(it.c, &it.lc, link)
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}
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}
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}
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