add last handshake metric (#1)

* feat: add latest handshake metric

* docs: add last handshake metric

Author: rogercoll

README.md

@@ -20,6 +20,7 @@ receivers:
 ```
 peer.usage.rx_bytes
 peer.usage.tx_bytes
+peer.last_handshake
 ```
 
 ## Attributes

metrics.go

@@ -19,7 +19,6 @@ func peerToMetrics(ts time.Time, deviceName string, peer *wgtypes.Peer) pmetric.
 	resourceAttr := rs.Resource().Attributes()
 	resourceAttr.PutStr("peer.device.name", deviceName)
 	resourceAttr.PutStr("peer.name", peer.PublicKey.String())
-
 	ms := rs.ScopeMetrics().AppendEmpty().Metrics()
 	appendPeerMetrics(ms, peer, pbts)
 
@@ -29,6 +28,7 @@ func peerToMetrics(ts time.Time, deviceName string, peer *wgtypes.Peer) pmetric.
 func appendPeerMetrics(ms pmetric.MetricSlice, peer *wgtypes.Peer, ts pcommon.Timestamp) {
 	gaugeI(ms, "usage.rx_bytes", "By", peer.ReceiveBytes, ts)
 	gaugeI(ms, "usage.tx_bytes", "By", peer.TransmitBytes, ts)
+	gaugeI(ms, "last_handshake", "s", int64(peer.LastHandshakeTime.Second()), ts)
 }
 
 func initMetric(ms pmetric.MetricSlice, name, unit string) pmetric.Metric {

metrics_test.go

@@ -36,7 +36,7 @@ func assertPeerToMetrics(t *testing.T, peer *wgtypes.Peer, md pmetric.Metrics) {
 	assert.Equal(t, rsm.ScopeMetrics().Len(), 1)
 
 	metrics := rsm.ScopeMetrics().At(0).Metrics()
-	assert.Equal(t, metrics.Len(), 2)
+	assert.Equal(t, metrics.Len(), 3)
 }
 
 func getPeer() (*wgtypes.Peer, error) {