261 lines
6.8 KiB
Go
261 lines
6.8 KiB
Go
// Copyright 2018 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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"fmt"
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"math/rand"
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"net"
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"strings"
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"time"
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"github.com/ethereum/go-ethereum/common/mclock"
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"github.com/ethereum/go-ethereum/crypto"
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"github.com/ethereum/go-ethereum/log"
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"github.com/ethereum/go-ethereum/p2p/enode"
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"github.com/ethereum/go-ethereum/p2p/enr"
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lru "github.com/hashicorp/golang-lru"
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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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linkCache linkCache
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trees map[string]*clientTree
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entries *lru.Cache
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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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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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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.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, urls ...string) (*Client, error) {
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c := &Client{
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cfg: cfg.withDefaults(),
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clock: mclock.System{},
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trees: make(map[string]*clientTree),
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}
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var err error
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if c.entries, err = lru.New(c.cfg.CacheLimit); err != nil {
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return nil, err
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}
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for _, url := range urls {
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if err := c.AddTree(url); err != nil {
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return nil, err
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}
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}
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return c, nil
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}
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// SyncTree downloads the entire node tree at the given URL. This doesn't add the tree for
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// later use, but any previously-synced entries are reused.
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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, 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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// AddTree adds a enrtree:// URL to crawl.
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func (c *Client) 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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ct, err := c.ensureTree(le)
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if err != nil {
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return err
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}
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c.linkCache.add(ct)
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return nil
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}
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func (c *Client) ensureTree(le *linkEntry) (*clientTree, error) {
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if tree, ok := c.trees[le.domain]; ok {
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if !tree.matchPubkey(le.pubkey) {
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return nil, fmt.Errorf("conflicting public keys for domain %q", le.domain)
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}
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return tree, nil
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}
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ct := newClientTree(c, le)
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c.trees[le.domain] = ct
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return ct, nil
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}
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// RandomNode retrieves the next random node.
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func (c *Client) RandomNode(ctx context.Context) *enode.Node {
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for {
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ct := c.randomTree()
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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(ctx)
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if err != nil {
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if err == ctx.Err() {
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return nil // context canceled.
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}
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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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// randomTree returns a random tree.
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func (c *Client) randomTree() *clientTree {
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if !c.linkCache.valid() {
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c.gcTrees()
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}
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limit := rand.Intn(len(c.trees))
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for _, ct := range c.trees {
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if limit == 0 {
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return ct
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}
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limit--
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}
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return nil
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}
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// gcTrees rebuilds the 'trees' map.
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func (c *Client) gcTrees() {
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trees := make(map[string]*clientTree)
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for t := range c.linkCache.all() {
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trees[t.loc.domain] = t
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}
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c.trees = trees
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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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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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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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cacheKey := truncateHash(hash)
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if e, ok := c.entries.Get(cacheKey); ok {
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return e.(entry), nil
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}
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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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// 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 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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