aboutsummaryrefslogtreecommitdiffstats
path: root/p2p/server.go
blob: edc1d9d219833c6874c809e4f622f4d58480b5f6 (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
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
// Copyright 2014 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 p2p implements the Ethereum p2p network protocols.
package p2p

import (
    "crypto/ecdsa"
    "errors"
    "fmt"
    "net"
    "sync"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/mclock"
    "github.com/ethereum/go-ethereum/event"
    "github.com/ethereum/go-ethereum/log"
    "github.com/ethereum/go-ethereum/p2p/discover"
    "github.com/ethereum/go-ethereum/p2p/discv5"
    "github.com/ethereum/go-ethereum/p2p/nat"
    "github.com/ethereum/go-ethereum/p2p/netutil"
)

const (
    defaultDialTimeout      = 15 * time.Second
    refreshPeersInterval    = 30 * time.Second
    staticPeerCheckInterval = 15 * time.Second

    // Connectivity defaults.
    maxActiveDialTasks     = 16
    defaultMaxPendingPeers = 50
    defaultDialRatio       = 3

    // Maximum time allowed for reading a complete message.
    // This is effectively the amount of time a connection can be idle.
    frameReadTimeout = 30 * time.Second

    // Maximum amount of time allowed for writing a complete message.
    frameWriteTimeout = 20 * time.Second
)

var errServerStopped = errors.New("server stopped")

// Config holds Server options.
type Config struct {
    // This field must be set to a valid secp256k1 private key.
    PrivateKey *ecdsa.PrivateKey `toml:"-"`

    // MaxPeers is the maximum number of peers that can be
    // connected. It must be greater than zero.
    MaxPeers int

    // MaxPendingPeers is the maximum number of peers that can be pending in the
    // handshake phase, counted separately for inbound and outbound connections.
    // Zero defaults to preset values.
    MaxPendingPeers int `toml:",omitempty"`

    // DialRatio controls the ratio of inbound to dialed connections.
    // Example: a DialRatio of 2 allows 1/2 of connections to be dialed.
    // Setting DialRatio to zero defaults it to 3.
    DialRatio int `toml:",omitempty"`

    // NoDiscovery can be used to disable the peer discovery mechanism.
    // Disabling is useful for protocol debugging (manual topology).
    NoDiscovery bool

    // DiscoveryV5 specifies whether the the new topic-discovery based V5 discovery
    // protocol should be started or not.
    DiscoveryV5 bool `toml:",omitempty"`

    // Name sets the node name of this server.
    // Use common.MakeName to create a name that follows existing conventions.
    Name string `toml:"-"`

    // BootstrapNodes are used to establish connectivity
    // with the rest of the network.
    BootstrapNodes []*discover.Node

    // BootstrapNodesV5 are used to establish connectivity
    // with the rest of the network using the V5 discovery
    // protocol.
    BootstrapNodesV5 []*discv5.Node `toml:",omitempty"`

    // Static nodes are used as pre-configured connections which are always
    // maintained and re-connected on disconnects.
    StaticNodes []*discover.Node

    // Trusted nodes are used as pre-configured connections which are always
    // allowed to connect, even above the peer limit.
    TrustedNodes []*discover.Node

    // Connectivity can be restricted to certain IP networks.
    // If this option is set to a non-nil value, only hosts which match one of the
    // IP networks contained in the list are considered.
    NetRestrict *netutil.Netlist `toml:",omitempty"`

    // NodeDatabase is the path to the database containing the previously seen
    // live nodes in the network.
    NodeDatabase string `toml:",omitempty"`

    // Protocols should contain the protocols supported
    // by the server. Matching protocols are launched for
    // each peer.
    Protocols []Protocol `toml:"-"`

    // If ListenAddr is set to a non-nil address, the server
    // will listen for incoming connections.
    //
    // If the port is zero, the operating system will pick a port. The
    // ListenAddr field will be updated with the actual address when
    // the server is started.
    ListenAddr string

    // If set to a non-nil value, the given NAT port mapper
    // is used to make the listening port available to the
    // Internet.
    NAT nat.Interface `toml:",omitempty"`

    // If Dialer is set to a non-nil value, the given Dialer
    // is used to dial outbound peer connections.
    Dialer NodeDialer `toml:"-"`

    // If NoDial is true, the server will not dial any peers.
    NoDial bool `toml:",omitempty"`

    // If EnableMsgEvents is set then the server will emit PeerEvents
    // whenever a message is sent to or received from a peer
    EnableMsgEvents bool

    // Logger is a custom logger to use with the p2p.Server.
    Logger log.Logger
}

// Server manages all peer connections.
type Server struct {
    // Config fields may not be modified while the server is running.
    Config

    // Hooks for testing. These are useful because we can inhibit
    // the whole protocol stack.
    newTransport func(net.Conn) transport
    newPeerHook  func(*Peer)

    lock    sync.Mutex // protects running
    running bool

    ntab         discoverTable
    listener     net.Listener
    ourHandshake *protoHandshake
    lastLookup   time.Time
    DiscV5       *discv5.Network

    // These are for Peers, PeerCount (and nothing else).
    peerOp     chan peerOpFunc
    peerOpDone chan struct{}

    quit          chan struct{}
    addstatic     chan *discover.Node
    removestatic  chan *discover.Node
    posthandshake chan *conn
    addpeer       chan *conn
    delpeer       chan peerDrop
    loopWG        sync.WaitGroup // loop, listenLoop
    peerFeed      event.Feed
    log           log.Logger
}

type peerOpFunc func(map[discover.NodeID]*Peer)

type peerDrop struct {
    *Peer
    err       error
    requested bool // true if signaled by the peer
}

type connFlag int

const (
    dynDialedConn connFlag = 1 << iota
    staticDialedConn
    inboundConn
    trustedConn
)

// conn wraps a network connection with information gathered
// during the two handshakes.
type conn struct {
    fd net.Conn
    transport
    flags connFlag
    cont  chan error      // The run loop uses cont to signal errors to SetupConn.
    id    discover.NodeID // valid after the encryption handshake
    caps  []Cap           // valid after the protocol handshake
    name  string          // valid after the protocol handshake
}

type transport interface {
    // The two handshakes.
    doEncHandshake(prv *ecdsa.PrivateKey, dialDest *discover.Node) (discover.NodeID, error)
    doProtoHandshake(our *protoHandshake) (*protoHandshake, error)
    // The MsgReadWriter can only be used after the encryption
    // handshake has completed. The code uses conn.id to track this
    // by setting it to a non-nil value after the encryption handshake.
    MsgReadWriter
    // transports must provide Close because we use MsgPipe in some of
    // the tests. Closing the actual network connection doesn't do
    // anything in those tests because NsgPipe doesn't use it.
    close(err error)
}

func (c *conn) String() string {
    s := c.flags.String()
    if (c.id != discover.NodeID{}) {
        s += " " + c.id.String()
    }
    s += " " + c.fd.RemoteAddr().String()
    return s
}

func (f connFlag) String() string {
    s := ""
    if f&trustedConn != 0 {
        s += "-trusted"
    }
    if f&dynDialedConn != 0 {
        s += "-dyndial"
    }
    if f&staticDialedConn != 0 {
        s += "-staticdial"
    }
    if f&inboundConn != 0 {
        s += "-inbound"
    }
    if s != "" {
        s = s[1:]
    }
    return s
}

func (c *conn) is(f connFlag) bool {
    return c.flags&f != 0
}

// Peers returns all connected peers.
func (srv *Server) Peers() []*Peer {
    var ps []*Peer
    select {
    // Note: We'd love to put this function into a variable but
    // that seems to cause a weird compiler error in some
    // environments.
    case srv.peerOp <- func(peers map[discover.NodeID]*Peer) {
        for _, p := range peers {
            ps = append(ps, p)
        }
    }:
        <-srv.peerOpDone
    case <-srv.quit:
    }
    return ps
}

// PeerCount returns the number of connected peers.
func (srv *Server) PeerCount() int {
    var count int
    select {
    case srv.peerOp <- func(ps map[discover.NodeID]*Peer) { count = len(ps) }:
        <-srv.peerOpDone
    case <-srv.quit:
    }
    return count
}

// AddPeer connects to the given node and maintains the connection until the
// server is shut down. If the connection fails for any reason, the server will
// attempt to reconnect the peer.
func (srv *Server) AddPeer(node *discover.Node) {
    select {
    case srv.addstatic <- node:
    case <-srv.quit:
    }
}

// RemovePeer disconnects from the given node
func (srv *Server) RemovePeer(node *discover.Node) {
    select {
    case srv.removestatic <- node:
    case <-srv.quit:
    }
}

// SubscribePeers subscribes the given channel to peer events
func (srv *Server) SubscribeEvents(ch chan *PeerEvent) event.Subscription {
    return srv.peerFeed.Subscribe(ch)
}

// Self returns the local node's endpoint information.
func (srv *Server) Self() *discover.Node {
    srv.lock.Lock()
    defer srv.lock.Unlock()

    if !srv.running {
        return &discover.Node{IP: net.ParseIP("0.0.0.0")}
    }
    return srv.makeSelf(srv.listener, srv.ntab)
}

func (srv *Server) makeSelf(listener net.Listener, ntab discoverTable) *discover.Node {
    // If the server's not running, return an empty node.
    // If the node is running but discovery is off, manually assemble the node infos.
    if ntab == nil {
        // Inbound connections disabled, use zero address.
        if listener == nil {
            return &discover.Node{IP: net.ParseIP("0.0.0.0"), ID: discover.PubkeyID(&srv.PrivateKey.PublicKey)}
        }
        // Otherwise inject the listener address too
        addr := listener.Addr().(*net.TCPAddr)
        return &discover.Node{
            ID:  discover.PubkeyID(&srv.PrivateKey.PublicKey),
            IP:  addr.IP,
            TCP: uint16(addr.Port),
        }
    }
    // Otherwise return the discovery node.
    return ntab.Self()
}

// Stop terminates the server and all active peer connections.
// It blocks until all active connections have been closed.
func (srv *Server) Stop() {
    srv.lock.Lock()
    defer srv.lock.Unlock()
    if !srv.running {
        return
    }
    srv.running = false
    if srv.listener != nil {
        // this unblocks listener Accept
        srv.listener.Close()
    }
    close(srv.quit)
    srv.loopWG.Wait()
}

// sharedUDPConn implements a shared connection. Write sends messages to the underlying connection while read returns
// messages that were found unprocessable and sent to the unhandled channel by the primary listener.
type sharedUDPConn struct {
    *net.UDPConn
    unhandled chan discover.ReadPacket
}

// ReadFromUDP implements discv5.conn
func (s *sharedUDPConn) ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error) {
    packet, ok := <-s.unhandled
    if !ok {
        return 0, nil, fmt.Errorf("Connection was closed")
    }
    l := len(packet.Data)
    if l > len(b) {
        l = len(b)
    }
    copy(b[:l], packet.Data[:l])
    return l, packet.Addr, nil
}

// Close implements discv5.conn
func (s *sharedUDPConn) Close() error {
    return nil
}

// Start starts running the server.
// Servers can not be re-used after stopping.
func (srv *Server) Start() (err error) {
    srv.lock.Lock()
    defer srv.lock.Unlock()
    if srv.running {
        return errors.New("server already running")
    }
    srv.running = true
    srv.log = srv.Config.Logger
    if srv.log == nil {
        srv.log = log.New()
    }
    srv.log.Info("Starting P2P networking")

    // static fields
    if srv.PrivateKey == nil {
        return fmt.Errorf("Server.PrivateKey must be set to a non-nil key")
    }
    if srv.newTransport == nil {
        srv.newTransport = newRLPX
    }
    if srv.Dialer == nil {
        srv.Dialer = TCPDialer{&net.Dialer{Timeout: defaultDialTimeout}}
    }
    srv.quit = make(chan struct{})
    srv.addpeer = make(chan *conn)
    srv.delpeer = make(chan peerDrop)
    srv.posthandshake = make(chan *conn)
    srv.addstatic = make(chan *discover.Node)
    srv.removestatic = make(chan *discover.Node)
    srv.peerOp = make(chan peerOpFunc)
    srv.peerOpDone = make(chan struct{})

    var (
        conn      *net.UDPConn
        sconn     *sharedUDPConn
        realaddr  *net.UDPAddr
        unhandled chan discover.ReadPacket
    )

    if !srv.NoDiscovery || srv.DiscoveryV5 {
        addr, err := net.ResolveUDPAddr("udp", srv.ListenAddr)
        if err != nil {
            return err
        }
        conn, err = net.ListenUDP("udp", addr)
        if err != nil {
            return err
        }
        realaddr = conn.LocalAddr().(*net.UDPAddr)
        if srv.NAT != nil {
            if !realaddr.IP.IsLoopback() {
                go nat.Map(srv.NAT, srv.quit, "udp", realaddr.Port, realaddr.Port, "ethereum discovery")
            }
            // TODO: react to external IP changes over time.
            if ext, err := srv.NAT.ExternalIP(); err == nil {
                realaddr = &net.UDPAddr{IP: ext, Port: realaddr.Port}
            }
        }
    }

    if !srv.NoDiscovery && srv.DiscoveryV5 {
        unhandled = make(chan discover.ReadPacket, 100)
        sconn = &sharedUDPConn{conn, unhandled}
    }

    // node table
    if !srv.NoDiscovery {
        cfg := discover.Config{
            PrivateKey:   srv.PrivateKey,
            AnnounceAddr: realaddr,
            NodeDBPath:   srv.NodeDatabase,
            NetRestrict:  srv.NetRestrict,
            Bootnodes:    srv.BootstrapNodes,
            Unhandled:    unhandled,
        }
        ntab, err := discover.ListenUDP(conn, cfg)
        if err != nil {
            return err
        }
        srv.ntab = ntab
    }

    if srv.DiscoveryV5 {
        var (
            ntab *discv5.Network
            err  error
        )
        if sconn != nil {
            ntab, err = discv5.ListenUDP(srv.PrivateKey, sconn, realaddr, "", srv.NetRestrict) //srv.NodeDatabase)
        } else {
            ntab, err = discv5.ListenUDP(srv.PrivateKey, conn, realaddr, "", srv.NetRestrict) //srv.NodeDatabase)
        }
        if err != nil {
            return err
        }
        if err := ntab.SetFallbackNodes(srv.BootstrapNodesV5); err != nil {
            return err
        }
        srv.DiscV5 = ntab
    }

    dynPeers := srv.maxDialedConns()
    dialer := newDialState(srv.StaticNodes, srv.BootstrapNodes, srv.ntab, dynPeers, srv.NetRestrict)

    // handshake
    srv.ourHandshake = &protoHandshake{Version: baseProtocolVersion, Name: srv.Name, ID: discover.PubkeyID(&srv.PrivateKey.PublicKey)}
    for _, p := range srv.Protocols {
        srv.ourHandshake.Caps = append(srv.ourHandshake.Caps, p.cap())
    }
    // listen/dial
    if srv.ListenAddr != "" {
        if err := srv.startListening(); err != nil {
            return err
        }
    }
    if srv.NoDial && srv.ListenAddr == "" {
        srv.log.Warn("P2P server will be useless, neither dialing nor listening")
    }

    srv.loopWG.Add(1)
    go srv.run(dialer)
    srv.running = true
    return nil
}

func (srv *Server) startListening() error {
    // Launch the TCP listener.
    listener, err := net.Listen("tcp", srv.ListenAddr)
    if err != nil {
        return err
    }
    laddr := listener.Addr().(*net.TCPAddr)
    srv.ListenAddr = laddr.String()
    srv.listener = listener
    srv.loopWG.Add(1)
    go srv.listenLoop()
    // Map the TCP listening port if NAT is configured.
    if !laddr.IP.IsLoopback() && srv.NAT != nil {
        srv.loopWG.Add(1)
        go func() {
            nat.Map(srv.NAT, srv.quit, "tcp", laddr.Port, laddr.Port, "ethereum p2p")
            srv.loopWG.Done()
        }()
    }
    return nil
}

type dialer interface {
    newTasks(running int, peers map[discover.NodeID]*Peer, now time.Time) []task
    taskDone(task, time.Time)
    addStatic(*discover.Node)
    removeStatic(*discover.Node)
}

func (srv *Server) run(dialstate dialer) {
    defer srv.loopWG.Done()
    var (
        peers        = make(map[discover.NodeID]*Peer)
        inboundCount = 0
        trusted      = make(map[discover.NodeID]bool, len(srv.TrustedNodes))
        taskdone     = make(chan task, maxActiveDialTasks)
        runningTasks []task
        queuedTasks  []task // tasks that can't run yet
    )
    // Put trusted nodes into a map to speed up checks.
    // Trusted peers are loaded on startup and cannot be
    // modified while the server is running.
    for _, n := range srv.TrustedNodes {
        trusted[n.ID] = true
    }

    // removes t from runningTasks
    delTask := func(t task) {
        for i := range runningTasks {
            if runningTasks[i] == t {
                runningTasks = append(runningTasks[:i], runningTasks[i+1:]...)
                break
            }
        }
    }
    // starts until max number of active tasks is satisfied
    startTasks := func(ts []task) (rest []task) {
        i := 0
        for ; len(runningTasks) < maxActiveDialTasks && i < len(ts); i++ {
            t := ts[i]
            srv.log.Trace("New dial task", "task", t)
            go func() { t.Do(srv); taskdone <- t }()
            runningTasks = append(runningTasks, t)
        }
        return ts[i:]
    }
    scheduleTasks := func() {
        // Start from queue first.
        queuedTasks = append(queuedTasks[:0], startTasks(queuedTasks)...)
        // Query dialer for new tasks and start as many as possible now.
        if len(runningTasks) < maxActiveDialTasks {
            nt := dialstate.newTasks(len(runningTasks)+len(queuedTasks), peers, time.Now())
            queuedTasks = append(queuedTasks, startTasks(nt)...)
        }
    }

running:
    for {
        scheduleTasks()

        select {
        case <-srv.quit:
            // The server was stopped. Run the cleanup logic.
            break running
        case n := <-srv.addstatic:
            // This channel is used by AddPeer to add to the
            // ephemeral static peer list. Add it to the dialer,
            // it will keep the node connected.
            srv.log.Debug("Adding static node", "node", n)
            dialstate.addStatic(n)
        case n := <-srv.removestatic:
            // This channel is used by RemovePeer to send a
            // disconnect request to a peer and begin the
            // stop keeping the node connected
            srv.log.Debug("Removing static node", "node", n)
            dialstate.removeStatic(n)
            if p, ok := peers[n.ID]; ok {
                p.Disconnect(DiscRequested)
            }
        case op := <-srv.peerOp:
            // This channel is used by Peers and PeerCount.
            op(peers)
            srv.peerOpDone <- struct{}{}
        case t := <-taskdone:
            // A task got done. Tell dialstate about it so it
            // can update its state and remove it from the active
            // tasks list.
            srv.log.Trace("Dial task done", "task", t)
            dialstate.taskDone(t, time.Now())
            delTask(t)
        case c := <-srv.posthandshake:
            // A connection has passed the encryption handshake so
            // the remote identity is known (but hasn't been verified yet).
            if trusted[c.id] {
                // Ensure that the trusted flag is set before checking against MaxPeers.
                c.flags |= trustedConn
            }
            // TODO: track in-progress inbound node IDs (pre-Peer) to avoid dialing them.
            select {
            case c.cont <- srv.encHandshakeChecks(peers, inboundCount, c):
            case <-srv.quit:
                break running
            }
        case c := <-srv.addpeer:
            // At this point the connection is past the protocol handshake.
            // Its capabilities are known and the remote identity is verified.
            err := srv.protoHandshakeChecks(peers, inboundCount, c)
            if err == nil {
                // The handshakes are done and it passed all checks.
                p := newPeer(c, srv.Protocols)
                // If message events are enabled, pass the peerFeed
                // to the peer
                if srv.EnableMsgEvents {
                    p.events = &srv.peerFeed
                }
                name := truncateName(c.name)
                srv.log.Debug("Adding p2p peer", "name", name, "addr", c.fd.RemoteAddr(), "peers", len(peers)+1)
                go srv.runPeer(p)
                peers[c.id] = p
                if p.Inbound() {
                    inboundCount++
                }
            }
            // The dialer logic relies on the assumption that
            // dial tasks complete after the peer has been added or
            // discarded. Unblock the task last.
            select {
            case c.cont <- err:
            case <-srv.quit:
                break running
            }
        case pd := <-srv.delpeer:
            // A peer disconnected.
            d := common.PrettyDuration(mclock.Now() - pd.created)
            pd.log.Debug("Removing p2p peer", "duration", d, "peers", len(peers)-1, "req", pd.requested, "err", pd.err)
            delete(peers, pd.ID())
            if pd.Inbound() {
                inboundCount--
            }
        }
    }

    srv.log.Trace("P2P networking is spinning down")

    // Terminate discovery. If there is a running lookup it will terminate soon.
    if srv.ntab != nil {
        srv.ntab.Close()
    }
    if srv.DiscV5 != nil {
        srv.DiscV5.Close()
    }
    // Disconnect all peers.
    for _, p := range peers {
        p.Disconnect(DiscQuitting)
    }
    // Wait for peers to shut down. Pending connections and tasks are
    // not handled here and will terminate soon-ish because srv.quit
    // is closed.
    for len(peers) > 0 {
        p := <-srv.delpeer
        p.log.Trace("<-delpeer (spindown)", "remainingTasks", len(runningTasks))
        delete(peers, p.ID())
    }
}

func (srv *Server) protoHandshakeChecks(peers map[discover.NodeID]*Peer, inboundCount int, c *conn) error {
    // Drop connections with no matching protocols.
    if len(srv.Protocols) > 0 && countMatchingProtocols(srv.Protocols, c.caps) == 0 {
        return DiscUselessPeer
    }
    // Repeat the encryption handshake checks because the
    // peer set might have changed between the handshakes.
    return srv.encHandshakeChecks(peers, inboundCount, c)
}

func (srv *Server) encHandshakeChecks(peers map[discover.NodeID]*Peer, inboundCount int, c *conn) error {
    switch {
    case !c.is(trustedConn|staticDialedConn) && len(peers) >= srv.MaxPeers:
        return DiscTooManyPeers
    case !c.is(trustedConn) && c.is(inboundConn) && inboundCount >= srv.maxInboundConns():
        return DiscTooManyPeers
    case peers[c.id] != nil:
        return DiscAlreadyConnected
    case c.id == srv.Self().ID:
        return DiscSelf
    default:
        return nil
    }
}

func (srv *Server) maxInboundConns() int {
    return srv.MaxPeers - srv.maxDialedConns()
}

func (srv *Server) maxDialedConns() int {
    if srv.NoDiscovery || srv.NoDial {
        return 0
    }
    r := srv.DialRatio
    if r == 0 {
        r = defaultDialRatio
    }
    return srv.MaxPeers / r
}

type tempError interface {
    Temporary() bool
}

// listenLoop runs in its own goroutine and accepts
// inbound connections.
func (srv *Server) listenLoop() {
    defer srv.loopWG.Done()
    srv.log.Info("RLPx listener up", "self", srv.makeSelf(srv.listener, srv.ntab))

    tokens := defaultMaxPendingPeers
    if srv.MaxPendingPeers > 0 {
        tokens = srv.MaxPendingPeers
    }
    slots := make(chan struct{}, tokens)
    for i := 0; i < tokens; i++ {
        slots <- struct{}{}
    }

    for {
        // Wait for a handshake slot before accepting.
        <-slots

        var (
            fd  net.Conn
            err error
        )
        for {
            fd, err = srv.listener.Accept()
            if tempErr, ok := err.(tempError); ok && tempErr.Temporary() {
                srv.log.Debug("Temporary read error", "err", err)
                continue
            } else if err != nil {
                srv.log.Debug("Read error", "err", err)
                return
            }
            break
        }

        // Reject connections that do not match NetRestrict.
        if srv.NetRestrict != nil {
            if tcp, ok := fd.RemoteAddr().(*net.TCPAddr); ok && !srv.NetRestrict.Contains(tcp.IP) {
                srv.log.Debug("Rejected conn (not whitelisted in NetRestrict)", "addr", fd.RemoteAddr())
                fd.Close()
                slots <- struct{}{}
                continue
            }
        }

        fd = newMeteredConn(fd, true)
        srv.log.Trace("Accepted connection", "addr", fd.RemoteAddr())
        go func() {
            srv.SetupConn(fd, inboundConn, nil)
            slots <- struct{}{}
        }()
    }
}

// SetupConn runs the handshakes and attempts to add the connection
// as a peer. It returns when the connection has been added as a peer
// or the handshakes have failed.
func (srv *Server) SetupConn(fd net.Conn, flags connFlag, dialDest *discover.Node) error {
    self := srv.Self()
    if self == nil {
        return errors.New("shutdown")
    }
    c := &conn{fd: fd, transport: srv.newTransport(fd), flags: flags, cont: make(chan error)}
    err := srv.setupConn(c, flags, dialDest)
    if err != nil {
        c.close(err)
        srv.log.Trace("Setting up connection failed", "id", c.id, "err", err)
    }
    return err
}

func (srv *Server) setupConn(c *conn, flags connFlag, dialDest *discover.Node) error {
    // Prevent leftover pending conns from entering the handshake.
    srv.lock.Lock()
    running := srv.running
    srv.lock.Unlock()
    if !running {
        return errServerStopped
    }
    // Run the encryption handshake.
    var err error
    if c.id, err = c.doEncHandshake(srv.PrivateKey, dialDest); err != nil {
        srv.log.Trace("Failed RLPx handshake", "addr", c.fd.RemoteAddr(), "conn", c.flags, "err", err)
        return err
    }
    clog := srv.log.New("id", c.id, "addr", c.fd.RemoteAddr(), "conn", c.flags)
    // For dialed connections, check that the remote public key matches.
    if dialDest != nil && c.id != dialDest.ID {
        clog.Trace("Dialed identity mismatch", "want", c, dialDest.ID)
        return DiscUnexpectedIdentity
    }
    err = srv.checkpoint(c, srv.posthandshake)
    if err != nil {
        clog.Trace("Rejected peer before protocol handshake", "err", err)
        return err
    }
    // Run the protocol handshake
    phs, err := c.doProtoHandshake(srv.ourHandshake)
    if err != nil {
        clog.Trace("Failed proto handshake", "err", err)
        return err
    }
    if phs.ID != c.id {
        clog.Trace("Wrong devp2p handshake identity", "err", phs.ID)
        return DiscUnexpectedIdentity
    }
    c.caps, c.name = phs.Caps, phs.Name
    err = srv.checkpoint(c, srv.addpeer)
    if err != nil {
        clog.Trace("Rejected peer", "err", err)
        return err
    }
    // If the checks completed successfully, runPeer has now been
    // launched by run.
    clog.Trace("connection set up", "inbound", dialDest == nil)
    return nil
}

func truncateName(s string) string {
    if len(s) > 20 {
        return s[:20] + "..."
    }
    return s
}

// checkpoint sends the conn to run, which performs the
// post-handshake checks for the stage (posthandshake, addpeer).
func (srv *Server) checkpoint(c *conn, stage chan<- *conn) error {
    select {
    case stage <- c:
    case <-srv.quit:
        return errServerStopped
    }
    select {
    case err := <-c.cont:
        return err
    case <-srv.quit:
        return errServerStopped
    }
}

// runPeer runs in its own goroutine for each peer.
// it waits until the Peer logic returns and removes
// the peer.
func (srv *Server) runPeer(p *Peer) {
    if srv.newPeerHook != nil {
        srv.newPeerHook(p)
    }

    // broadcast peer add
    srv.peerFeed.Send(&PeerEvent{
        Type: PeerEventTypeAdd,
        Peer: p.ID(),
    })

    // run the protocol
    remoteRequested, err := p.run()

    // broadcast peer drop
    srv.peerFeed.Send(&PeerEvent{
        Type:  PeerEventTypeDrop,
        Peer:  p.ID(),
        Error: err.Error(),
    })

    // Note: run waits for existing peers to be sent on srv.delpeer
    // before returning, so this send should not select on srv.quit.
    srv.delpeer <- peerDrop{p, err, remoteRequested}
}

// NodeInfo represents a short summary of the information known about the host.
type NodeInfo struct {
    ID    string `json:"id"`    // Unique node identifier (also the encryption key)
    Name  string `json:"name"`  // Name of the node, including client type, version, OS, custom data
    Enode string `json:"enode"` // Enode URL for adding this peer from remote peers
    IP    string `json:"ip"`    // IP address of the node
    Ports struct {
        Discovery int `json:"discovery"` // UDP listening port for discovery protocol
        Listener  int `json:"listener"`  // TCP listening port for RLPx
    } `json:"ports"`
    ListenAddr string                 `json:"listenAddr"`
    Protocols  map[string]interface{} `json:"protocols"`
}

// NodeInfo gathers and returns a collection of metadata known about the host.
func (srv *Server) NodeInfo() *NodeInfo {
    node := srv.Self()

    // Gather and assemble the generic node infos
    info := &NodeInfo{
        Name:       srv.Name,
        Enode:      node.String(),
        ID:         node.ID.String(),
        IP:         node.IP.String(),
        ListenAddr: srv.ListenAddr,
        Protocols:  make(map[string]interface{}),
    }
    info.Ports.Discovery = int(node.UDP)
    info.Ports.Listener = int(node.TCP)

    // Gather all the running protocol infos (only once per protocol type)
    for _, proto := range srv.Protocols {
        if _, ok := info.Protocols[proto.Name]; !ok {
            nodeInfo := interface{}("unknown")
            if query := proto.NodeInfo; query != nil {
                nodeInfo = proto.NodeInfo()
            }
            info.Protocols[proto.Name] = nodeInfo
        }
    }
    return info
}

// PeersInfo returns an array of metadata objects describing connected peers.
func (srv *Server) PeersInfo() []*PeerInfo {
    // Gather all the generic and sub-protocol specific infos
    infos := make([]*PeerInfo, 0, srv.PeerCount())
    for _, peer := range srv.Peers() {
        if peer != nil {
            infos = append(infos, peer.Info())
        }
    }
    // Sort the result array alphabetically by node identifier
    for i := 0; i < len(infos); i++ {
        for j := i + 1; j < len(infos); j++ {
            if infos[i].ID > infos[j].ID {
                infos[i], infos[j] = infos[j], infos[i]
            }
        }
    }
    return infos
}