aboutsummaryrefslogtreecommitdiffstats
path: root/les/retrieve.go
blob: bc8763f3e67a3cf09c7bf5d5699d16aa51493f9b (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
// Copyright 2017 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 light implements on-demand retrieval capable state and chain objects
// for the Ethereum Light Client.
package les

import (
    "context"
    "crypto/rand"
    "encoding/binary"
    "fmt"
    "sync"
    "time"

    "github.com/dexon-foundation/dexon/common/mclock"
    "github.com/dexon-foundation/dexon/light"
)

var (
    retryQueue         = time.Millisecond * 100
    softRequestTimeout = time.Millisecond * 500
    hardRequestTimeout = time.Second * 10
)

// retrieveManager is a layer on top of requestDistributor which takes care of
// matching replies by request ID and handles timeouts and resends if necessary.
type retrieveManager struct {
    dist       *requestDistributor
    peers      *peerSet
    serverPool peerSelector

    lock     sync.RWMutex
    sentReqs map[uint64]*sentReq
}

// validatorFunc is a function that processes a reply message
type validatorFunc func(distPeer, *Msg) error

// peerSelector receives feedback info about response times and timeouts
type peerSelector interface {
    adjustResponseTime(*poolEntry, time.Duration, bool)
}

// sentReq represents a request sent and tracked by retrieveManager
type sentReq struct {
    rm       *retrieveManager
    req      *distReq
    id       uint64
    validate validatorFunc

    eventsCh chan reqPeerEvent
    stopCh   chan struct{}
    stopped  bool
    err      error

    lock   sync.RWMutex // protect access to sentTo map
    sentTo map[distPeer]sentReqToPeer

    lastReqQueued bool     // last request has been queued but not sent
    lastReqSentTo distPeer // if not nil then last request has been sent to given peer but not timed out
    reqSrtoCount  int      // number of requests that reached soft (but not hard) timeout
}

// sentReqToPeer notifies the request-from-peer goroutine (tryRequest) about a response
// delivered by the given peer. Only one delivery is allowed per request per peer,
// after which delivered is set to true, the validity of the response is sent on the
// valid channel and no more responses are accepted.
type sentReqToPeer struct {
    delivered bool
    valid     chan bool
}

// reqPeerEvent is sent by the request-from-peer goroutine (tryRequest) to the
// request state machine (retrieveLoop) through the eventsCh channel.
type reqPeerEvent struct {
    event int
    peer  distPeer
}

const (
    rpSent = iota // if peer == nil, not sent (no suitable peers)
    rpSoftTimeout
    rpHardTimeout
    rpDeliveredValid
    rpDeliveredInvalid
)

// newRetrieveManager creates the retrieve manager
func newRetrieveManager(peers *peerSet, dist *requestDistributor, serverPool peerSelector) *retrieveManager {
    return &retrieveManager{
        peers:      peers,
        dist:       dist,
        serverPool: serverPool,
        sentReqs:   make(map[uint64]*sentReq),
    }
}

// retrieve sends a request (to multiple peers if necessary) and waits for an answer
// that is delivered through the deliver function and successfully validated by the
// validator callback. It returns when a valid answer is delivered or the context is
// cancelled.
func (rm *retrieveManager) retrieve(ctx context.Context, reqID uint64, req *distReq, val validatorFunc, shutdown chan struct{}) error {
    sentReq := rm.sendReq(reqID, req, val)
    select {
    case <-sentReq.stopCh:
    case <-ctx.Done():
        sentReq.stop(ctx.Err())
    case <-shutdown:
        sentReq.stop(fmt.Errorf("Client is shutting down"))
    }
    return sentReq.getError()
}

// sendReq starts a process that keeps trying to retrieve a valid answer for a
// request from any suitable peers until stopped or succeeded.
func (rm *retrieveManager) sendReq(reqID uint64, req *distReq, val validatorFunc) *sentReq {
    r := &sentReq{
        rm:       rm,
        req:      req,
        id:       reqID,
        sentTo:   make(map[distPeer]sentReqToPeer),
        stopCh:   make(chan struct{}),
        eventsCh: make(chan reqPeerEvent, 10),
        validate: val,
    }

    canSend := req.canSend
    req.canSend = func(p distPeer) bool {
        // add an extra check to canSend: the request has not been sent to the same peer before
        r.lock.RLock()
        _, sent := r.sentTo[p]
        r.lock.RUnlock()
        return !sent && canSend(p)
    }

    request := req.request
    req.request = func(p distPeer) func() {
        // before actually sending the request, put an entry into the sentTo map
        r.lock.Lock()
        r.sentTo[p] = sentReqToPeer{false, make(chan bool, 1)}
        r.lock.Unlock()
        return request(p)
    }
    rm.lock.Lock()
    rm.sentReqs[reqID] = r
    rm.lock.Unlock()

    go r.retrieveLoop()
    return r
}

// deliver is called by the LES protocol manager to deliver reply messages to waiting requests
func (rm *retrieveManager) deliver(peer distPeer, msg *Msg) error {
    rm.lock.RLock()
    req, ok := rm.sentReqs[msg.ReqID]
    rm.lock.RUnlock()

    if ok {
        return req.deliver(peer, msg)
    }
    return errResp(ErrUnexpectedResponse, "reqID = %v", msg.ReqID)
}

// reqStateFn represents a state of the retrieve loop state machine
type reqStateFn func() reqStateFn

// retrieveLoop is the retrieval state machine event loop
func (r *sentReq) retrieveLoop() {
    go r.tryRequest()
    r.lastReqQueued = true
    state := r.stateRequesting

    for state != nil {
        state = state()
    }

    r.rm.lock.Lock()
    delete(r.rm.sentReqs, r.id)
    r.rm.lock.Unlock()
}

// stateRequesting: a request has been queued or sent recently; when it reaches soft timeout,
// a new request is sent to a new peer
func (r *sentReq) stateRequesting() reqStateFn {
    select {
    case ev := <-r.eventsCh:
        r.update(ev)
        switch ev.event {
        case rpSent:
            if ev.peer == nil {
                // request send failed, no more suitable peers
                if r.waiting() {
                    // we are already waiting for sent requests which may succeed so keep waiting
                    return r.stateNoMorePeers
                }
                // nothing to wait for, no more peers to ask, return with error
                r.stop(light.ErrNoPeers)
                // no need to go to stopped state because waiting() already returned false
                return nil
            }
        case rpSoftTimeout:
            // last request timed out, try asking a new peer
            go r.tryRequest()
            r.lastReqQueued = true
            return r.stateRequesting
        case rpDeliveredInvalid:
            // if it was the last sent request (set to nil by update) then start a new one
            if !r.lastReqQueued && r.lastReqSentTo == nil {
                go r.tryRequest()
                r.lastReqQueued = true
            }
            return r.stateRequesting
        case rpDeliveredValid:
            r.stop(nil)
            return r.stateStopped
        }
        return r.stateRequesting
    case <-r.stopCh:
        return r.stateStopped
    }
}

// stateNoMorePeers: could not send more requests because no suitable peers are available.
// Peers may become suitable for a certain request later or new peers may appear so we
// keep trying.
func (r *sentReq) stateNoMorePeers() reqStateFn {
    select {
    case <-time.After(retryQueue):
        go r.tryRequest()
        r.lastReqQueued = true
        return r.stateRequesting
    case ev := <-r.eventsCh:
        r.update(ev)
        if ev.event == rpDeliveredValid {
            r.stop(nil)
            return r.stateStopped
        }
        if r.waiting() {
            return r.stateNoMorePeers
        }
        r.stop(light.ErrNoPeers)
        return nil
    case <-r.stopCh:
        return r.stateStopped
    }
}

// stateStopped: request succeeded or cancelled, just waiting for some peers
// to either answer or time out hard
func (r *sentReq) stateStopped() reqStateFn {
    for r.waiting() {
        r.update(<-r.eventsCh)
    }
    return nil
}

// update updates the queued/sent flags and timed out peers counter according to the event
func (r *sentReq) update(ev reqPeerEvent) {
    switch ev.event {
    case rpSent:
        r.lastReqQueued = false
        r.lastReqSentTo = ev.peer
    case rpSoftTimeout:
        r.lastReqSentTo = nil
        r.reqSrtoCount++
    case rpHardTimeout:
        r.reqSrtoCount--
    case rpDeliveredValid, rpDeliveredInvalid:
        if ev.peer == r.lastReqSentTo {
            r.lastReqSentTo = nil
        } else {
            r.reqSrtoCount--
        }
    }
}

// waiting returns true if the retrieval mechanism is waiting for an answer from
// any peer
func (r *sentReq) waiting() bool {
    return r.lastReqQueued || r.lastReqSentTo != nil || r.reqSrtoCount > 0
}

// tryRequest tries to send the request to a new peer and waits for it to either
// succeed or time out if it has been sent. It also sends the appropriate reqPeerEvent
// messages to the request's event channel.
func (r *sentReq) tryRequest() {
    sent := r.rm.dist.queue(r.req)
    var p distPeer
    select {
    case p = <-sent:
    case <-r.stopCh:
        if r.rm.dist.cancel(r.req) {
            p = nil
        } else {
            p = <-sent
        }
    }

    r.eventsCh <- reqPeerEvent{rpSent, p}
    if p == nil {
        return
    }

    reqSent := mclock.Now()
    srto, hrto := false, false

    r.lock.RLock()
    s, ok := r.sentTo[p]
    r.lock.RUnlock()
    if !ok {
        panic(nil)
    }

    defer func() {
        // send feedback to server pool and remove peer if hard timeout happened
        pp, ok := p.(*peer)
        if ok && r.rm.serverPool != nil {
            respTime := time.Duration(mclock.Now() - reqSent)
            r.rm.serverPool.adjustResponseTime(pp.poolEntry, respTime, srto)
        }
        if hrto {
            pp.Log().Debug("Request timed out hard")
            if r.rm.peers != nil {
                r.rm.peers.Unregister(pp.id)
            }
        }

        r.lock.Lock()
        delete(r.sentTo, p)
        r.lock.Unlock()
    }()

    select {
    case ok := <-s.valid:
        if ok {
            r.eventsCh <- reqPeerEvent{rpDeliveredValid, p}
        } else {
            r.eventsCh <- reqPeerEvent{rpDeliveredInvalid, p}
        }
        return
    case <-time.After(softRequestTimeout):
        srto = true
        r.eventsCh <- reqPeerEvent{rpSoftTimeout, p}
    }

    select {
    case ok := <-s.valid:
        if ok {
            r.eventsCh <- reqPeerEvent{rpDeliveredValid, p}
        } else {
            r.eventsCh <- reqPeerEvent{rpDeliveredInvalid, p}
        }
    case <-time.After(hardRequestTimeout):
        hrto = true
        r.eventsCh <- reqPeerEvent{rpHardTimeout, p}
    }
}

// deliver a reply belonging to this request
func (r *sentReq) deliver(peer distPeer, msg *Msg) error {
    r.lock.Lock()
    defer r.lock.Unlock()

    s, ok := r.sentTo[peer]
    if !ok || s.delivered {
        return errResp(ErrUnexpectedResponse, "reqID = %v", msg.ReqID)
    }
    valid := r.validate(peer, msg) == nil
    r.sentTo[peer] = sentReqToPeer{true, s.valid}
    s.valid <- valid
    if !valid {
        return errResp(ErrInvalidResponse, "reqID = %v", msg.ReqID)
    }
    return nil
}

// stop stops the retrieval process and sets an error code that will be returned
// by getError
func (r *sentReq) stop(err error) {
    r.lock.Lock()
    if !r.stopped {
        r.stopped = true
        r.err = err
        close(r.stopCh)
    }
    r.lock.Unlock()
}

// getError returns any retrieval error (either internally generated or set by the
// stop function) after stopCh has been closed
func (r *sentReq) getError() error {
    return r.err
}

// genReqID generates a new random request ID
func genReqID() uint64 {
    var rnd [8]byte
    rand.Read(rnd[:])
    return binary.BigEndian.Uint64(rnd[:])
}