libs/common: refactor libs common 3 (#4232)

* libs/common: refactor libs common 3

- move nil.go into types folder and make private
- move service & baseservice out of common into service pkg

ref #4147

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* add changelog entry

types/encoding_helper.go

@@ -1,13 +1,9 @@
 package types
 
-import (
-	cmn "github.com/tendermint/tendermint/libs/common"
-)
-
 // cdcEncode returns nil if the input is nil, otherwise returns
 // cdc.MustMarshalBinaryBare(item)
 func cdcEncode(item interface{}) []byte {
-	if item != nil && !cmn.IsTypedNil(item) && !cmn.IsEmpty(item) {
+	if item != nil && !isTypedNil(item) && !isEmpty(item) {
 		return cdc.MustMarshalBinaryBare(item)
 	}
 	return nil

types/event_bus.go

@@ -5,9 +5,9 @@ import (
 	"fmt"
 
 	"github.com/tendermint/tendermint/abci/types"
-	cmn "github.com/tendermint/tendermint/libs/common"
 	"github.com/tendermint/tendermint/libs/log"
 	tmpubsub "github.com/tendermint/tendermint/libs/pubsub"
+	"github.com/tendermint/tendermint/libs/service"
 )
 
 const defaultCapacity = 0
@@ -31,7 +31,7 @@ type Subscription interface {
 // are proxied to underlying pubsub server. All events must be published using
 // EventBus to ensure correct data types.
 type EventBus struct {
-	cmn.BaseService
+	service.BaseService
 	pubsub *tmpubsub.Server
 }
 
@@ -45,7 +45,7 @@ func NewEventBusWithBufferCapacity(cap int) *EventBus {
 	// capacity could be exposed later if needed
 	pubsub := tmpubsub.NewServer(tmpubsub.BufferCapacity(cap))
 	b := &EventBus{pubsub: pubsub}
-	b.BaseService = *cmn.NewBaseService(nil, "EventBus", b)
+	b.BaseService = *service.NewBaseService(nil, "EventBus", b)
 	return b
 }
 

types/utils.go

@@ -0,0 +1,29 @@
+package types
+
+import "reflect"
+
+// Go lacks a simple and safe way to see if something is a typed nil.
+// See:
+//  - https://dave.cheney.net/2017/08/09/typed-nils-in-go-2
+//  - https://groups.google.com/forum/#!topic/golang-nuts/wnH302gBa4I/discussion
+//  - https://github.com/golang/go/issues/21538
+func isTypedNil(o interface{}) bool {
+	rv := reflect.ValueOf(o)
+	switch rv.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice:
+		return rv.IsNil()
+	default:
+		return false
+	}
+}
+
+// Returns true if it has zero length.
+func isEmpty(o interface{}) bool {
+	rv := reflect.ValueOf(o)
+	switch rv.Kind() {
+	case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
+		return rv.Len() == 0
+	default:
+		return false
+	}
+}