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
use std::cmp::Ordering;
use std::collections::{BinaryHeap, HashMap, HashSet, VecDeque};
use std::fmt;
use ethcore::header::Header;
use light::net::ReqId;
use light::request::Headers as HeadersRequest;
use network::PeerId;
use util::{Bytes, H256};
use super::response;
const SCAFFOLD_ATTEMPTS: usize = 3;
pub trait ResponseContext {
fn responder(&self) -> PeerId;
fn req_id(&self) -> &ReqId;
fn data(&self) -> &[Bytes];
fn punish_responder(&self);
}
#[derive(Debug, Clone)]
pub enum AbortReason {
BadScaffold(Vec<PeerId>),
NoResponses,
TargetReached,
}
#[derive(PartialEq, Eq)]
struct SubchainRequest {
subchain_parent: (u64, H256),
headers_request: HeadersRequest,
subchain_end: (u64, H256),
downloaded: VecDeque<Header>,
}
impl PartialOrd for SubchainRequest {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
self.subchain_parent.0
.partial_cmp(&other.subchain_parent.0)
.map(Ordering::reverse)
}
}
impl Ord for SubchainRequest {
fn cmp(&self, other: &Self) -> Ordering {
self.subchain_parent.0.cmp(&other.subchain_parent.0).reverse()
}
}
pub struct Fetcher {
sparse: VecDeque<Header>,
requests: BinaryHeap<SubchainRequest>,
complete_requests: HashMap<H256, SubchainRequest>,
pending: HashMap<ReqId, SubchainRequest>,
scaffold_contributors: Vec<PeerId>,
ready: VecDeque<Header>,
end: (u64, H256),
target: (u64, H256),
}
impl Fetcher {
fn new(sparse_headers: Vec<Header>, contributors: Vec<PeerId>, target: (u64, H256)) -> SyncRound {
let mut requests = BinaryHeap::with_capacity(sparse_headers.len() - 1);
for pair in sparse_headers.windows(2) {
let low_rung = &pair[0];
let high_rung = &pair[1];
let diff = high_rung.number() - low_rung.number();
if diff < 2 { continue }
let needed_headers = HeadersRequest {
start: high_rung.parent_hash().clone().into(),
max: diff as usize - 1,
skip: 0,
reverse: true,
};
requests.push(SubchainRequest {
headers_request: needed_headers,
subchain_end: (high_rung.number() - 1, *high_rung.parent_hash()),
downloaded: VecDeque::new(),
subchain_parent: (low_rung.number(), low_rung.hash()),
});
}
let end = match sparse_headers.last().map(|h| (h.number(), h.hash())) {
Some(end) => end,
None => return SyncRound::abort(AbortReason::BadScaffold(contributors), VecDeque::new()),
};
SyncRound::Fetch(Fetcher {
sparse: sparse_headers.into(),
requests: requests,
complete_requests: HashMap::new(),
pending: HashMap::new(),
scaffold_contributors: contributors,
ready: VecDeque::new(),
end: end,
target: target,
})
}
fn collect_ready(&mut self) {
loop {
let start_hash = match self.sparse.front() {
Some(first) => first.hash(),
None => break,
};
match self.complete_requests.remove(&start_hash) {
None => break,
Some(complete_req) => {
self.ready.push_back(self.sparse.pop_front().expect("first known to exist; qed"));
self.ready.extend(complete_req.downloaded);
}
}
}
if self.sparse.len() == 1 {
self.ready.push_back(self.sparse.pop_back().expect("sparse known to have one entry; qed"))
}
trace!(target: "sync", "{} headers ready to drain", self.ready.len());
}
fn process_response<R: ResponseContext>(mut self, ctx: &R) -> SyncRound {
let mut request = match self.pending.remove(ctx.req_id()) {
Some(request) => request,
None => return SyncRound::Fetch(self),
};
trace!(target: "sync", "Received response for subchain ({} -> {})",
request.subchain_parent.0 + 1, request.subchain_end.0);
let headers = ctx.data();
if headers.len() == 0 {
trace!(target: "sync", "Punishing peer {} for empty response", ctx.responder());
ctx.punish_responder();
self.requests.push(request);
return SyncRound::Fetch(self);
}
match response::decode_and_verify(headers, &request.headers_request) {
Err(e) => {
trace!(target: "sync", "Punishing peer {} for invalid response ({})", ctx.responder(), e);
ctx.punish_responder();
self.requests.push(request);
SyncRound::Fetch(self)
}
Ok(headers) => {
let mut parent_hash = None;
for header in headers {
if parent_hash.as_ref().map_or(false, |h| h != &header.hash()) {
trace!(target: "sync", "Punishing peer {} for parent mismatch", ctx.responder());
ctx.punish_responder();
self.requests.push(request);
return SyncRound::Fetch(self);
}
parent_hash = Some(header.parent_hash().clone());
request.headers_request.start = header.parent_hash().clone().into();
request.headers_request.max -= 1;
request.downloaded.push_front(header);
}
let subchain_parent = request.subchain_parent.1;
if request.headers_request.max == 0 {
if parent_hash.map_or(true, |hash| hash != subchain_parent) {
let abort = AbortReason::BadScaffold(self.scaffold_contributors);
return SyncRound::abort(abort, self.ready);
}
self.complete_requests.insert(subchain_parent, request);
self.collect_ready();
}
(SyncRound::Fetch(self))
}
}
}
fn requests_abandoned(mut self, abandoned: &[ReqId]) -> SyncRound {
for abandoned in abandoned {
match self.pending.remove(abandoned) {
None => {},
Some(req) => self.requests.push(req),
}
}
SyncRound::Fetch(self)
}
fn dispatch_requests<D>(mut self, mut dispatcher: D) -> SyncRound
where D: FnMut(HeadersRequest) -> Option<ReqId>
{
while let Some(pending_req) = self.requests.pop() {
match dispatcher(pending_req.headers_request.clone()) {
Some(req_id) => {
trace!(target: "sync", "Assigned request for subchain ({} -> {})",
pending_req.subchain_parent.0 + 1, pending_req.subchain_end.0);
self.pending.insert(req_id, pending_req);
}
None => {
self.requests.push(pending_req);
break;
}
}
}
SyncRound::Fetch(self)
}
fn drain(mut self, headers: &mut Vec<Header>, max: Option<usize>) -> SyncRound {
let max = ::std::cmp::min(max.unwrap_or(usize::max_value()), self.ready.len());
headers.extend(self.ready.drain(0..max));
if self.sparse.is_empty() && self.ready.is_empty() {
trace!(target: "sync", "sync round complete. Starting anew from {:?}", self.end);
SyncRound::begin(self.end, self.target)
} else {
SyncRound::Fetch(self)
}
}
}
fn scaffold_params(diff: u64) -> (u64, usize) {
const ROUND_SKIP: u64 = 255;
const ROUND_PIVOTS: usize = 256;
let rem = diff % (ROUND_SKIP + 1);
if diff <= ROUND_SKIP {
(0, rem as usize)
} else {
let pivots_to_target = (diff / (ROUND_SKIP + 1)) + if rem == 0 { 0 } else { 1 };
let num_pivots = ::std::cmp::min(pivots_to_target, ROUND_PIVOTS as u64) as usize;
(ROUND_SKIP, num_pivots)
}
}
pub struct RoundStart {
start_block: (u64, H256),
target: (u64, H256),
pending_req: Option<(ReqId, HeadersRequest)>,
sparse_headers: Vec<Header>,
contributors: HashSet<PeerId>,
attempt: usize,
skip: u64,
pivots: usize,
}
impl RoundStart {
fn new(start: (u64, H256), target: (u64, H256)) -> Self {
let (skip, pivots) = scaffold_params(target.0 - start.0);
trace!(target: "sync", "Beginning sync round: {} pivots and {} skip from block {}",
pivots, skip, start.0);
RoundStart {
start_block: start,
target: target,
pending_req: None,
sparse_headers: Vec::new(),
contributors: HashSet::new(),
attempt: 0,
skip: skip,
pivots: pivots,
}
}
fn failed_attempt(mut self) -> SyncRound {
self.attempt += 1;
if self.attempt >= SCAFFOLD_ATTEMPTS {
return if self.sparse_headers.len() > 1 {
Fetcher::new(self.sparse_headers, self.contributors.into_iter().collect(), self.target)
} else {
let fetched_headers = if self.skip == 0 {
self.sparse_headers.into()
} else {
VecDeque::new()
};
SyncRound::abort(AbortReason::NoResponses, fetched_headers)
}
} else {
SyncRound::Start(self)
}
}
fn process_response<R: ResponseContext>(mut self, ctx: &R) -> SyncRound {
let req = match self.pending_req.take() {
Some((id, ref req)) if ctx.req_id() == &id => { req.clone() }
other => {
self.pending_req = other;
return SyncRound::Start(self);
}
};
match response::decode_and_verify(ctx.data(), &req) {
Ok(headers) => {
if self.sparse_headers.len() == 0
&& headers.get(0).map_or(false, |x| x.parent_hash() != &self.start_block.1) {
trace!(target: "sync", "Wrong parent for first header in round");
ctx.punish_responder();
}
self.contributors.insert(ctx.responder());
self.sparse_headers.extend(headers);
if self.sparse_headers.len() == self.pivots {
return if self.skip == 0 {
SyncRound::abort(AbortReason::TargetReached, self.sparse_headers.into())
} else {
trace!(target: "sync", "Beginning fetch of blocks between {} sparse headers",
self.sparse_headers.len());
Fetcher::new(
self.sparse_headers,
self.contributors.into_iter().collect(),
self.target
)
}
}
}
Err(e) => {
trace!(target: "sync", "Punishing peer {} for malformed response ({})", ctx.responder(), e);
ctx.punish_responder();
}
};
self.failed_attempt()
}
fn requests_abandoned(mut self, abandoned: &[ReqId]) -> SyncRound {
match self.pending_req.take() {
Some((id, req)) => {
if abandoned.iter().any(|r| r == &id) {
self.pending_req = None;
self.failed_attempt()
} else {
self.pending_req = Some((id, req));
SyncRound::Start(self)
}
}
None => SyncRound::Start(self),
}
}
fn dispatch_requests<D>(mut self, mut dispatcher: D) -> SyncRound
where D: FnMut(HeadersRequest) -> Option<ReqId>
{
if self.pending_req.is_none() {
let start = (self.start_block.0 + 1)
+ self.sparse_headers.len() as u64 * (self.skip + 1);
let max = self.pivots - self.sparse_headers.len();
let headers_request = HeadersRequest {
start: start.into(),
max: max,
skip: self.skip,
reverse: false,
};
if let Some(req_id) = dispatcher(headers_request.clone()) {
trace!(target: "sync", "Requesting scaffold: {} headers forward from {}, skip={}",
max, start, self.skip);
self.pending_req = Some((req_id, headers_request));
}
}
SyncRound::Start(self)
}
}
pub enum SyncRound {
Start(RoundStart),
Fetch(Fetcher),
Abort(AbortReason, VecDeque<Header>),
}
impl SyncRound {
fn abort(reason: AbortReason, remaining: VecDeque<Header>) -> Self {
trace!(target: "sync", "Aborting sync round: {:?}. To drain: {}", reason, remaining.len());
SyncRound::Abort(reason, remaining)
}
pub fn begin(start: (u64, H256), target: (u64, H256)) -> Self {
if target.0 <= start.0 {
SyncRound::abort(AbortReason::TargetReached, VecDeque::new())
} else {
SyncRound::Start(RoundStart::new(start, target))
}
}
pub fn process_response<R: ResponseContext>(self, ctx: &R) -> Self {
match self {
SyncRound::Start(round_start) => round_start.process_response(ctx),
SyncRound::Fetch(fetcher) => fetcher.process_response(ctx),
other => other,
}
}
pub fn requests_abandoned(self, abandoned: &[ReqId]) -> Self {
match self {
SyncRound::Start(round_start) => round_start.requests_abandoned(abandoned),
SyncRound::Fetch(fetcher) => fetcher.requests_abandoned(abandoned),
other => other,
}
}
pub fn dispatch_requests<D>(self, dispatcher: D) -> Self
where D: FnMut(HeadersRequest) -> Option<ReqId>
{
match self {
SyncRound::Start(round_start) => round_start.dispatch_requests(dispatcher),
SyncRound::Fetch(fetcher) => fetcher.dispatch_requests(dispatcher),
other => other,
}
}
pub fn drain(self, v: &mut Vec<Header>, max: Option<usize>) -> Self {
match self {
SyncRound::Fetch(fetcher) => fetcher.drain(v, max),
SyncRound::Abort(reason, mut remaining) => {
let len = ::std::cmp::min(max.unwrap_or(usize::max_value()), remaining.len());
v.extend(remaining.drain(..len));
SyncRound::Abort(reason, remaining)
}
other => other,
}
}
}
impl fmt::Debug for SyncRound {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match *self {
SyncRound::Start(ref state) => write!(f, "Scaffolding from {:?}", state.start_block),
SyncRound::Fetch(ref fetcher) => write!(f, "Filling scaffold up to {:?}", fetcher.end),
SyncRound::Abort(ref reason, ref remaining) =>
write!(f, "Aborted: {:?}, {} remain", reason, remaining.len()),
}
}
}
#[cfg(test)]
mod tests {
use super::scaffold_params;
#[test]
fn scaffold_config() {
assert_eq!(scaffold_params(1), (0, 1));
assert_eq!(scaffold_params(6), (0, 6));
assert_eq!(scaffold_params(1000), (255, 4));
assert_eq!(scaffold_params(1024), (255, 4));
}
}