Backward sync support for SyncManager. (status-im#3131)

* Unbundle SyncQueue from sync_manager.nim.
Unbundle Peer scores constants to peer_scores.nim.
Add Forward/Backward enum.

* Further improvements and tests.

* Adopt getRewindPoint() and fix MissingParent handler.

* Remove unused procedures.
Refactor `result` usage.
Fix resetWait().

* Add all the tests and fix the issue with rewind point.

* Fix get() issue.

* Fix flaky tests.

* test fixes

Co-authored-by: Jacek Sieka <[email protected]>

AllTests-mainnet.md

@@ -298,22 +298,26 @@ OK: 2/2 Fail: 0/2 Skip: 0/2
 OK: 4/4 Fail: 0/4 Skip: 0/4
 ## SyncManager test suite
 ```diff
-+ [SyncQueue] Async pending and resetWait() test                                             OK
-+ [SyncQueue] Async unordered push start from zero                                           OK
-+ [SyncQueue] Async unordered push with not full start from non-zero                         OK
-+ [SyncQueue] Full and incomplete success/fail start from non-zero                           OK
-+ [SyncQueue] Full and incomplete success/fail start from zero                               OK
-+ [SyncQueue] One smart and one stupid + debt split + empty                                  OK
-+ [SyncQueue] Smart and stupid success/fail                                                  OK
-+ [SyncQueue] Start and finish slots equal                                                   OK
-+ [SyncQueue] Two full requests success/fail                                                 OK
++ [SyncQueue#Backward] Async unordered push test                                             OK
++ [SyncQueue#Backward] Async unordered push with rewind test                                 OK
++ [SyncQueue#Backward] Pass through established limits test                                  OK
++ [SyncQueue#Backward] Smoke test                                                            OK
++ [SyncQueue#Backward] Start and finish slots equal                                          OK
++ [SyncQueue#Backward] Two full requests success/fail                                        OK
++ [SyncQueue#Backward] getRewindPoint() test                                                 OK
++ [SyncQueue#Forward] Async unordered push test                                              OK
++ [SyncQueue#Forward] Async unordered push with rewind test                                  OK
++ [SyncQueue#Forward] Pass through established limits test                                   OK
++ [SyncQueue#Forward] Smoke test                                                             OK
++ [SyncQueue#Forward] Start and finish slots equal                                           OK
++ [SyncQueue#Forward] Two full requests success/fail                                         OK
++ [SyncQueue#Forward] getRewindPoint() test                                                  OK
 + [SyncQueue] checkResponse() test                                                           OK
 + [SyncQueue] contains() test                                                                OK
 + [SyncQueue] getLastNonEmptySlot() test                                                     OK
-+ [SyncQueue] getRewindPoint() test                                                          OK
 + [SyncQueue] hasEndGap() test                                                               OK
 ```
-OK: 14/14 Fail: 0/14 Skip: 0/14
+OK: 18/18 Fail: 0/18 Skip: 0/18
 ## Zero signature sanity checks
 ```diff
 + SSZ serialization roundtrip of SignedBeaconBlockHeader                                     OK
@@ -373,4 +377,4 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 OK: 1/1 Fail: 0/1 Skip: 0/1
 
 ---TOTAL---
-OK: 205/207 Fail: 0/207 Skip: 2/207
+OK: 209/211 Fail: 0/211 Skip: 2/211

beacon_chain/sync/peer_scores.nim

@@ -0,0 +1,28 @@
+# beacon_chain
+# Copyright (c) 2018-2021 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+{.push raises: [Defect].}
+
+const
+  PeerScoreNoStatus* = -100
+    ## Peer did not answer `status` request.
+  PeerScoreStaleStatus* = -50
+    ## Peer's `status` answer do not progress in time.
+  PeerScoreUseless* = -10
+    ## Peer's latest head is lower then ours.
+  PeerScoreGoodStatus* = 50
+    ## Peer's `status` answer is fine.
+  PeerScoreNoBlocks* = -100
+    ## Peer did not respond in time on `blocksByRange` request.
+  PeerScoreGoodBlocks* = 100
+    ## Peer's `blocksByRange` answer is fine.
+  PeerScoreBadBlocks* = -1000
+    ## Peer's response contains incorrect blocks.
+  PeerScoreBadResponse* = -1000
+    ## Peer's response is not in requested range.
+  PeerScoreMissingBlocks* = -200
+    ## Peer response contains too many empty blocks.