aboutsummaryrefslogtreecommitdiffstats
path: root/p2p/discover/table.go
blob: 67f7ec46fb7b6ee87ff0e5e10595b00c9754f39b (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
// Copyright 2015 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 discover implements the Node Discovery Protocol.
//
// The Node Discovery protocol provides a way to find RLPx nodes that
// can be connected to. It uses a Kademlia-like protocol to maintain a
// distributed database of the IDs and endpoints of all listening
// nodes.
package discover

import (
    "crypto/rand"
    "encoding/binary"
    "net"
    "sort"
    "sync"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
)

const (
    alpha      = 3  // Kademlia concurrency factor
    bucketSize = 16 // Kademlia bucket size
    hashBits   = len(common.Hash{}) * 8
    nBuckets   = hashBits + 1 // Number of buckets

    maxBondingPingPongs = 16
    maxFindnodeFailures = 5
)

type Table struct {
    mutex   sync.Mutex        // protects buckets, their content, and nursery
    buckets [nBuckets]*bucket // index of known nodes by distance
    nursery []*Node           // bootstrap nodes
    db      *nodeDB           // database of known nodes

    bondmu    sync.Mutex
    bonding   map[NodeID]*bondproc
    bondslots chan struct{} // limits total number of active bonding processes

    nodeAddedHook func(*Node) // for testing

    net  transport
    self *Node // metadata of the local node
}

type bondproc struct {
    err  error
    n    *Node
    done chan struct{}
}

// transport is implemented by the UDP transport.
// it is an interface so we can test without opening lots of UDP
// sockets and without generating a private key.
type transport interface {
    ping(NodeID, *net.UDPAddr) error
    waitping(NodeID) error
    findnode(toid NodeID, addr *net.UDPAddr, target NodeID) ([]*Node, error)
    close()
}

// bucket contains nodes, ordered by their last activity.
// the entry that was most recently active is the last element
// in entries.
type bucket struct {
    lastLookup time.Time
    entries    []*Node
}

func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string) *Table {
    // If no node database was given, use an in-memory one
    db, err := newNodeDB(nodeDBPath, Version, ourID)
    if err != nil {
        glog.V(logger.Warn).Infoln("Failed to open node database:", err)
        db, _ = newNodeDB("", Version, ourID)
    }
    tab := &Table{
        net:       t,
        db:        db,
        self:      newNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
        bonding:   make(map[NodeID]*bondproc),
        bondslots: make(chan struct{}, maxBondingPingPongs),
    }
    for i := 0; i < cap(tab.bondslots); i++ {
        tab.bondslots <- struct{}{}
    }
    for i := range tab.buckets {
        tab.buckets[i] = new(bucket)
    }
    return tab
}

// Self returns the local node.
// The returned node should not be modified by the caller.
func (tab *Table) Self() *Node {
    return tab.self
}

// ReadRandomNodes fills the given slice with random nodes from the
// table. It will not write the same node more than once. The nodes in
// the slice are copies and can be modified by the caller.
func (tab *Table) ReadRandomNodes(buf []*Node) (n int) {
    tab.mutex.Lock()
    defer tab.mutex.Unlock()
    // TODO: tree-based buckets would help here
    // Find all non-empty buckets and get a fresh slice of their entries.
    var buckets [][]*Node
    for _, b := range tab.buckets {
        if len(b.entries) > 0 {
            buckets = append(buckets, b.entries[:])
        }
    }
    if len(buckets) == 0 {
        return 0
    }
    // Shuffle the buckets.
    for i := uint32(len(buckets)) - 1; i > 0; i-- {
        j := randUint(i)
        buckets[i], buckets[j] = buckets[j], buckets[i]
    }
    // Move head of each bucket into buf, removing buckets that become empty.
    var i, j int
    for ; i < len(buf); i, j = i+1, (j+1)%len(buckets) {
        b := buckets[j]
        buf[i] = &(*b[0])
        buckets[j] = b[1:]
        if len(b) == 1 {
            buckets = append(buckets[:j], buckets[j+1:]...)
        }
        if len(buckets) == 0 {
            break
        }
    }
    return i + 1
}

func randUint(max uint32) uint32 {
    if max == 0 {
        return 0
    }
    var b [4]byte
    rand.Read(b[:])
    return binary.BigEndian.Uint32(b[:]) % max
}

// Close terminates the network listener and flushes the node database.
func (tab *Table) Close() {
    if tab.net != nil {
        tab.net.close()
    }
    tab.db.close()
}

// Bootstrap sets the bootstrap nodes. These nodes are used to connect
// to the network if the table is empty. Bootstrap will also attempt to
// fill the table by performing random lookup operations on the
// network.
func (tab *Table) Bootstrap(nodes []*Node) {
    tab.mutex.Lock()
    // TODO: maybe filter nodes with bad fields (nil, etc.) to avoid strange crashes
    tab.nursery = make([]*Node, 0, len(nodes))
    for _, n := range nodes {
        cpy := *n
        cpy.sha = crypto.Sha3Hash(n.ID[:])
        tab.nursery = append(tab.nursery, &cpy)
    }
    tab.mutex.Unlock()
    tab.refresh()
}

// Lookup performs a network search for nodes close
// to the given target. It approaches the target by querying
// nodes that are closer to it on each iteration.
// The given target does not need to be an actual node
// identifier.
func (tab *Table) Lookup(targetID NodeID) []*Node {
    var (
        target         = crypto.Sha3Hash(targetID[:])
        asked          = make(map[NodeID]bool)
        seen           = make(map[NodeID]bool)
        reply          = make(chan []*Node, alpha)
        pendingQueries = 0
    )
    // don't query further if we hit ourself.
    // unlikely to happen often in practice.
    asked[tab.self.ID] = true

    tab.mutex.Lock()
    // update last lookup stamp (for refresh logic)
    tab.buckets[logdist(tab.self.sha, target)].lastLookup = time.Now()
    // generate initial result set
    result := tab.closest(target, bucketSize)
    tab.mutex.Unlock()

    // If the result set is empty, all nodes were dropped, refresh
    if len(result.entries) == 0 {
        tab.refresh()
        return nil
    }

    for {
        // ask the alpha closest nodes that we haven't asked yet
        for i := 0; i < len(result.entries) && pendingQueries < alpha; i++ {
            n := result.entries[i]
            if !asked[n.ID] {
                asked[n.ID] = true
                pendingQueries++
                go func() {
                    // Find potential neighbors to bond with
                    r, err := tab.net.findnode(n.ID, n.addr(), targetID)
                    if err != nil {
                        // Bump the failure counter to detect and evacuate non-bonded entries
                        fails := tab.db.findFails(n.ID) + 1
                        tab.db.updateFindFails(n.ID, fails)
                        glog.V(logger.Detail).Infof("Bumping failures for %x: %d", n.ID[:8], fails)

                        if fails >= maxFindnodeFailures {
                            glog.V(logger.Detail).Infof("Evacuating node %x: %d findnode failures", n.ID[:8], fails)
                            tab.del(n)
                        }
                    }
                    reply <- tab.bondall(r)
                }()
            }
        }
        if pendingQueries == 0 {
            // we have asked all closest nodes, stop the search
            break
        }
        // wait for the next reply
        for _, n := range <-reply {
            if n != nil && !seen[n.ID] {
                seen[n.ID] = true
                result.push(n, bucketSize)
            }
        }
        pendingQueries--
    }
    return result.entries
}

// refresh performs a lookup for a random target to keep buckets full, or seeds
// the table if it is empty (initial bootstrap or discarded faulty peers).
func (tab *Table) refresh() {
    seed := true

    // If the discovery table is empty, seed with previously known nodes
    tab.mutex.Lock()
    for _, bucket := range tab.buckets {
        if len(bucket.entries) > 0 {
            seed = false
            break
        }
    }
    tab.mutex.Unlock()

    // If the table is not empty, try to refresh using the live entries
    if !seed {
        // The Kademlia paper specifies that the bucket refresh should
        // perform a refresh in the least recently used bucket. We cannot
        // adhere to this because the findnode target is a 512bit value
        // (not hash-sized) and it is not easily possible to generate a
        // sha3 preimage that falls into a chosen bucket.
        //
        // We perform a lookup with a random target instead.
        var target NodeID
        rand.Read(target[:])

        result := tab.Lookup(target)
        if len(result) == 0 {
            // Lookup failed, seed after all
            seed = true
        }
    }

    if seed {
        // Pick a batch of previously know seeds to lookup with
        seeds := tab.db.querySeeds(10)
        for _, seed := range seeds {
            glog.V(logger.Debug).Infoln("Seeding network with", seed)
        }
        nodes := append(tab.nursery, seeds...)

        // Bond with all the seed nodes (will pingpong only if failed recently)
        bonded := tab.bondall(nodes)
        if len(bonded) > 0 {
            tab.Lookup(tab.self.ID)
        }
        // TODO: the Kademlia paper says that we're supposed to perform
        // random lookups in all buckets further away than our closest neighbor.
    }
}

// closest returns the n nodes in the table that are closest to the
// given id. The caller must hold tab.mutex.
func (tab *Table) closest(target common.Hash, nresults int) *nodesByDistance {
    // This is a very wasteful way to find the closest nodes but
    // obviously correct. I believe that tree-based buckets would make
    // this easier to implement efficiently.
    close := &nodesByDistance{target: target}
    for _, b := range tab.buckets {
        for _, n := range b.entries {
            close.push(n, nresults)
        }
    }
    return close
}

func (tab *Table) len() (n int) {
    for _, b := range tab.buckets {
        n += len(b.entries)
    }
    return n
}

// bondall bonds with all given nodes concurrently and returns
// those nodes for which bonding has probably succeeded.
func (tab *Table) bondall(nodes []*Node) (result []*Node) {
    rc := make(chan *Node, len(nodes))
    for i := range nodes {
        go func(n *Node) {
            nn, _ := tab.bond(false, n.ID, n.addr(), uint16(n.TCP))
            rc <- nn
        }(nodes[i])
    }
    for _ = range nodes {
        if n := <-rc; n != nil {
            result = append(result, n)
        }
    }
    return result
}

// bond ensures the local node has a bond with the given remote node.
// It also attempts to insert the node into the table if bonding succeeds.
// The caller must not hold tab.mutex.
//
// A bond is must be established before sending findnode requests.
// Both sides must have completed a ping/pong exchange for a bond to
// exist. The total number of active bonding processes is limited in
// order to restrain network use.
//
// bond is meant to operate idempotently in that bonding with a remote
// node which still remembers a previously established bond will work.
// The remote node will simply not send a ping back, causing waitping
// to time out.
//
// If pinged is true, the remote node has just pinged us and one half
// of the process can be skipped.
func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) (*Node, error) {
    // Retrieve a previously known node and any recent findnode failures
    node, fails := tab.db.node(id), 0
    if node != nil {
        fails = tab.db.findFails(id)
    }
    // If the node is unknown (non-bonded) or failed (remotely unknown), bond from scratch
    var result error
    if node == nil || fails > 0 {
        glog.V(logger.Detail).Infof("Bonding %x: known=%v, fails=%v", id[:8], node != nil, fails)

        tab.bondmu.Lock()
        w := tab.bonding[id]
        if w != nil {
            // Wait for an existing bonding process to complete.
            tab.bondmu.Unlock()
            <-w.done
        } else {
            // Register a new bonding process.
            w = &bondproc{done: make(chan struct{})}
            tab.bonding[id] = w
            tab.bondmu.Unlock()
            // Do the ping/pong. The result goes into w.
            tab.pingpong(w, pinged, id, addr, tcpPort)
            // Unregister the process after it's done.
            tab.bondmu.Lock()
            delete(tab.bonding, id)
            tab.bondmu.Unlock()
        }
        // Retrieve the bonding results
        result = w.err
        if result == nil {
            node = w.n
        }
    }
    // Even if bonding temporarily failed, give the node a chance
    if node != nil {
        tab.mutex.Lock()
        defer tab.mutex.Unlock()

        b := tab.buckets[logdist(tab.self.sha, node.sha)]
        if !b.bump(node) {
            tab.pingreplace(node, b)
        }
        tab.db.updateFindFails(id, 0)
    }
    return node, result
}

func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) {
    // Request a bonding slot to limit network usage
    <-tab.bondslots
    defer func() { tab.bondslots <- struct{}{} }()

    // Ping the remote side and wait for a pong
    if w.err = tab.ping(id, addr); w.err != nil {
        close(w.done)
        return
    }
    if !pinged {
        // Give the remote node a chance to ping us before we start
        // sending findnode requests. If they still remember us,
        // waitping will simply time out.
        tab.net.waitping(id)
    }
    // Bonding succeeded, update the node database
    w.n = newNode(id, addr.IP, uint16(addr.Port), tcpPort)
    tab.db.updateNode(w.n)
    close(w.done)
}

func (tab *Table) pingreplace(new *Node, b *bucket) {
    if len(b.entries) == bucketSize {
        oldest := b.entries[bucketSize-1]
        if err := tab.ping(oldest.ID, oldest.addr()); err == nil {
            // The node responded, we don't need to replace it.
            return
        }
    } else {
        // Add a slot at the end so the last entry doesn't
        // fall off when adding the new node.
        b.entries = append(b.entries, nil)
    }
    copy(b.entries[1:], b.entries)
    b.entries[0] = new
    if tab.nodeAddedHook != nil {
        tab.nodeAddedHook(new)
    }
}

// ping a remote endpoint and wait for a reply, also updating the node database
// accordingly.
func (tab *Table) ping(id NodeID, addr *net.UDPAddr) error {
    // Update the last ping and send the message
    tab.db.updateLastPing(id, time.Now())
    if err := tab.net.ping(id, addr); err != nil {
        return err
    }
    // Pong received, update the database and return
    tab.db.updateLastPong(id, time.Now())
    tab.db.ensureExpirer()

    return nil
}

// add puts the entries into the table if their corresponding
// bucket is not full. The caller must hold tab.mutex.
func (tab *Table) add(entries []*Node) {
outer:
    for _, n := range entries {
        if n.ID == tab.self.ID {
            // don't add self.
            continue
        }
        bucket := tab.buckets[logdist(tab.self.sha, n.sha)]
        for i := range bucket.entries {
            if bucket.entries[i].ID == n.ID {
                // already in bucket
                continue outer
            }
        }
        if len(bucket.entries) < bucketSize {
            bucket.entries = append(bucket.entries, n)
            if tab.nodeAddedHook != nil {
                tab.nodeAddedHook(n)
            }
        }
    }
}

// del removes an entry from the node table (used to evacuate failed/non-bonded
// discovery peers).
func (tab *Table) del(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) 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
    }
}