blockchain: Reorg reactor (#3561)

* go routines in blockchain reactor

* Added reference to the go routine diagram

* Initial commit

* cleanup

* Undo testing_logger change, committed by mistake

* Fix the test loggers

* pulled some fsm code into pool.go

* added pool tests

* changes to the design

added block requests under peer

moved the request trigger in the reactor poolRoutine, triggered now by a ticker

in general moved everything required for making block requests smarter in the poolRoutine

added a simple map of heights to keep track of what will need to be requested next

added a few more tests

* send errors to FSM in a different channel than blocks

send errors (RemovePeer) from switch on a different channel than the
one receiving blocks
renamed channels
added more pool tests

* more pool tests

* lint errors

* more tests

* more tests

* switch fast sync to new implementation

* fixed data race in tests

* cleanup

* finished fsm tests

* address golangci comments :)

* address golangci comments :)

* Added timeout on next block needed to advance

* updating docs and cleanup

* fix issue in test from previous cleanup

* cleanup

* Added termination scenarios, tests and more cleanup

* small fixes to adr, comments and cleanup

* Fix bug in sendRequest()

If we tried to send a request to a peer not present in the switch, a
missing continue statement caused the request to be blackholed in a peer
that was removed and never retried.

While this bug was manifesting, the reactor kept asking for other
blocks that would be stored and never consumed. Added the number of
unconsumed blocks in the math for requesting blocks ahead of current
processing height so eventually there will be no more blocks requested
until the already received ones are consumed.

* remove bpPeer's didTimeout field

* Use distinct err codes for peer timeout and FSM timeouts

* Don't allow peers to update with lower height

* review comments from Ethan and Zarko

* some cleanup, renaming, comments

* Move block execution in separate goroutine

* Remove pool's numPending

* review comments

* fix lint, remove old blockchain reactor and duplicates in fsm tests

* small reorg around peer after review comments

* add the reactor spec

* verify block only once

* review comments

* change to int for max number of pending requests

* cleanup and godoc

* Add configuration flag fast sync version

* golangci fixes

* fix config template

* move both reactor versions under blockchain

* cleanup, golint, renaming stuff

* updated documentation, fixed more golint warnings

* integrate with behavior package

* sync with master

* gofmt

* add changelog_pending entry

* move to improvments

* suggestion to changelog entry

docs/spec/reactors/block_sync/impl.md

@@ -1,4 +1,6 @@
-## Blockchain Reactor
+## Blockchain Reactor v0 Modules
+
+### Blockchain Reactor
 
 - coordinates the pool for syncing
 - coordinates the store for persistence
@@ -8,7 +10,7 @@
 - starts the pool.Start() and its poolRoutine()
 - registers all the concrete types and interfaces for serialisation
 
-### poolRoutine
+#### poolRoutine
 
 - listens to these channels:
   - pool requests blocks from a specific peer by posting to requestsCh, block reactor then sends
@@ -22,7 +24,7 @@
 - implements Receive which is called by the switch/peer
   - calls AddBlock on the pool when it receives a new block from a peer
 
-## Block Pool
+### Block Pool
 
 - responsible for downloading blocks from peers
 - makeRequestersRoutine()
@@ -36,6 +38,7 @@
     - we receive a block
       - gotBlockCh is strange
 
-## Block Store
 
-- persists blocks to disk
+### Go Routines in Blockchain Reactor
+
+![Go Routines Diagram](img/bc-reactor-routines.png)