node: allow replacing existing p2p.Reactor(s) (#3846)

* node: allow replacing existing p2p.Reactor(s)

using [`CustomReactors`
option](https://godoc.org/github.com/tendermint/tendermint/node#CustomReactors).
Warning: beware of accidental name clashes. Here is the list of existing
reactors: MEMPOOL, BLOCKCHAIN, CONSENSUS, EVIDENCE, PEX.

* check the absence of "CUSTOM" prefix

* merge 2 tests

* add doc.go to node package

node/doc.go

@@ -0,0 +1,40 @@
+/*
+Package node is the main entry point, where the Node struct, which
+represents a full node, is defined.
+
+Adding new p2p.Reactor(s)
+
+To add a new p2p.Reactor, use the CustomReactors option:
+
+		node, err := NewNode(
+				config,
+				privVal,
+				nodeKey,
+				clientCreator,
+				genesisDocProvider,
+				dbProvider,
+				metricsProvider,
+				logger,
+				CustomReactors(map[string]p2p.Reactor{"CUSTOM": customReactor}),
+		)
+
+Replacing existing p2p.Reactor(s)
+
+To replace the built-in p2p.Reactor, use the CustomReactors option:
+
+		node, err := NewNode(
+				config,
+				privVal,
+				nodeKey,
+				clientCreator,
+				genesisDocProvider,
+				dbProvider,
+				metricsProvider,
+				logger,
+				CustomReactors(map[string]p2p.Reactor{"BLOCKCHAIN": customBlockchainReactor}),
+		)
+
+The list of existing reactors can be found in CustomReactors documentation.
+
+*/
+package node

node/node.go

@@ -48,10 +48,6 @@ import (
 	dbm "github.com/tendermint/tm-cmn/db"
 )
 
-// CustomReactorNamePrefix is a prefix for all custom reactors to prevent
-// clashes with built-in reactors.
-const CustomReactorNamePrefix = "CUSTOM_"
-
 //------------------------------------------------------------------------------
 
 // DBContext specifies config information for loading a new DB.
@@ -144,11 +140,26 @@ func DefaultMetricsProvider(config *cfg.InstrumentationConfig) MetricsProvider {
 // Option sets a parameter for the node.
 type Option func(*Node)
 
-// CustomReactors allows you to add custom reactors to the node's Switch.
+// CustomReactors allows you to add custom reactors (name -> p2p.Reactor) to
+// the node's Switch.
+//
+// WARNING: using any name from the below list of the existing reactors will
+// result in replacing it with the custom one.
+//
+//  - MEMPOOL
+//  - BLOCKCHAIN
+//  - CONSENSUS
+//  - EVIDENCE
+//  - PEX
 func CustomReactors(reactors map[string]p2p.Reactor) Option {
 	return func(n *Node) {
 		for name, reactor := range reactors {
-			n.sw.AddReactor(CustomReactorNamePrefix+name, reactor)
+			if existingReactor := n.sw.Reactor(name); existingReactor != nil {
+				n.sw.Logger.Info("Replacing existing reactor with a custom one",
+					"name", name, "existing", existingReactor, "custom", reactor)
+				n.sw.RemoveReactor(name, existingReactor)
+			}
+			n.sw.AddReactor(name, reactor)
 		}
 	}
 }

node/node_test.go

@@ -288,6 +288,7 @@ func TestNodeNewNodeCustomReactors(t *testing.T) {
 	defer os.RemoveAll(config.RootDir)
 
 	cr := p2pmock.NewReactor()
+	customBlockchainReactor := p2pmock.NewReactor()
 
 	nodeKey, err := p2p.LoadOrGenNodeKey(config.NodeKeyFile())
 	require.NoError(t, err)
@@ -300,7 +301,7 @@ func TestNodeNewNodeCustomReactors(t *testing.T) {
 		DefaultDBProvider,
 		DefaultMetricsProvider(config.Instrumentation),
 		log.TestingLogger(),
-		CustomReactors(map[string]p2p.Reactor{"FOO": cr}),
+		CustomReactors(map[string]p2p.Reactor{"FOO": cr, "BLOCKCHAIN": customBlockchainReactor}),
 	)
 	require.NoError(t, err)
 
@@ -309,6 +310,10 @@ func TestNodeNewNodeCustomReactors(t *testing.T) {
 	defer n.Stop()
 
 	assert.True(t, cr.IsRunning())
+	assert.Equal(t, cr, n.Switch().Reactor("FOO"))
+
+	assert.True(t, customBlockchainReactor.IsRunning())
+	assert.Equal(t, customBlockchainReactor, n.Switch().Reactor("BLOCKCHAIN"))
 }
 
 func state(nVals int, height int64) (sm.State, dbm.DB) {