Add sync/p2p metric for number of messages received by topic (#3341)

* Add going msg metric

* fmt

* rename

beacon-chain/sync/BUILD.bazel

@@ -48,6 +48,8 @@ go_library(
         "@com_github_libp2p_go_libp2p_core//:go_default_library",
         "@com_github_libp2p_go_libp2p_core//network:go_default_library",
         "@com_github_pkg_errors//:go_default_library",
+        "@com_github_prometheus_client_golang//prometheus:go_default_library",
+        "@com_github_prometheus_client_golang//prometheus/promauto:go_default_library",
         "@com_github_prysmaticlabs_go_ssz//:go_default_library",
         "@com_github_sirupsen_logrus//:go_default_library",
     ],

beacon-chain/sync/metrics.go

@@ -1,3 +1,18 @@
 package sync
 
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
 // TODO(3147): Add metrics for RPC & subscription success/error.
+
+var (
+	messageReceivedCounter = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "p2p_message_recieved_total",
+			Help: "Count of messages received.",
+		},
+		[]string{"topic"},
+	)
+)

beacon-chain/sync/subscriber.go

@@ -12,10 +12,10 @@ import (
 	"github.com/prysmaticlabs/prysm/beacon-chain/p2p"
 )
 
-var oneYear = 365 * 24 * time.Hour
+const oneYear = 365 * 24 * time.Hour
 
 // prefix to add to keys, so that we can represent invalid objects
-var invalid = "invalidObject"
+const invalid = "invalidObject"
 
 // subHandler represents handler for a given subscription.
 type subHandler func(context.Context, proto.Message) error
@@ -132,6 +132,8 @@ func (r *RegularSync) subscribe(topic string, validate validator, handle subHand
 				continue
 			}
 
+			messageReceivedCounter.WithLabelValues(topic + r.p2p.Encoding().ProtocolSuffix()).Inc()
+
 			go pipeline(msg.Data)
 		}
 	}