[FAB-1355] Make gossip JoinChannel use block utils

As mention in comment to CR 3175, get chain id out
of the block should be abstracted out to the utility
package. This commit takes care to replace chain id
code from gossip join channel functionality by common
utility function.

Change-Id: I62708190c41e8a5174bfd41546e751604f80659e
Signed-off-by: Artem Barger <bartem@il.ibm.com>

gossip/service/gossip_service.go

@@ -18,9 +18,7 @@ package service
 
 import (
 	"sync"
-	"fmt"
 
-	pb "github.com/golang/protobuf/proto"
 	"github.com/hyperledger/fabric/core/committer"
 	"github.com/hyperledger/fabric/gossip/comm"
 	gossipCommon "github.com/hyperledger/fabric/gossip/common"
@@ -30,6 +28,7 @@ import (
 	"github.com/hyperledger/fabric/gossip/proto"
 	"github.com/hyperledger/fabric/gossip/state"
 	"github.com/hyperledger/fabric/protos/common"
+	"github.com/hyperledger/fabric/protos/utils"
 	"google.golang.org/grpc"
 )
 
@@ -79,26 +78,13 @@ func (g *gossipServiceImpl) JoinChannel(commiter committer.Committer, block *com
 	g.lock.Lock()
 	defer g.lock.Unlock()
 
-	if block.Data == nil || block.Data.Data == nil || len(block.Data.Data) == 0 {
-		return fmt.Errorf("Cannot join channel, configuration block is empty")
-	}
-
-	envelope := &common.Envelope{}
-	if err := pb.Unmarshal(block.Data.Data[0], envelope); err != nil {
-		return err
-	}
-
-	payload := &common.Payload{}
-	if err := pb.Unmarshal(envelope.Payload, payload); err != nil {
+	if chainID, err := utils.GetChainIDFromBlock(block); err != nil {
 		return err
+	} else {
+		// Initialize new state provider for given committer
+		g.chains[chainID] = state.NewGossipStateProvider(g.gossip, g.comm, commiter)
 	}
 
-	chainID := payload.Header.ChainHeader.ChainID
-	if len(chainID) == 0 {
-		return fmt.Errorf("Cannot join channel, with empty chainID")
-	}
-	// Initialize new state provider for given committer
-	g.chains[chainID] = state.NewGossipStateProvider(g.gossip, g.comm, commiter)
 	return nil
 }