lnrpc: add betweenness centrality to GetNodeMetrics (new RPC call)

This commit extends the RPC interface with GetNodeMetrics will contain
all graph node metrics in the future. Currently only holds betweennes
centrality per node.

rpcserver.go

@@ -354,6 +354,10 @@ func mainRPCServerPermissions() map[string][]bakery.Op {
 			Entity: "info",
 			Action: "read",
 		}},
+		"/lnrpc.Lightning/GetNodeMetrics": {{
+			Entity: "info",
+			Action: "read",
+		}},
 		"/lnrpc.Lightning/GetChanInfo": {{
 			Entity: "info",
 			Action: "read",
@@ -4561,14 +4565,16 @@ func (r *rpcServer) DescribeGraph(ctx context.Context,
 			nodeAddrs = append(nodeAddrs, nodeAddr)
 		}
 
-		resp.Nodes = append(resp.Nodes, &lnrpc.LightningNode{
+		lnNode := &lnrpc.LightningNode{
 			LastUpdate: uint32(node.LastUpdate.Unix()),
 			PubKey:     hex.EncodeToString(node.PubKeyBytes[:]),
 			Addresses:  nodeAddrs,
 			Alias:      node.Alias,
 			Color:      routing.EncodeHexColor(node.Color),
 			Features:   invoicesrpc.CreateRPCFeatures(node.Features),
-		})
+		}
+
+		resp.Nodes = append(resp.Nodes, lnNode)
 
 		return nil
 	})
@@ -4657,6 +4663,57 @@ func marshalDbEdge(edgeInfo *channeldb.ChannelEdgeInfo,
 	return edge
 }
 
+// GetNodeMetrics returns all available node metrics calculated from the
+// current channel graph.
+func (r *rpcServer) GetNodeMetrics(ctx context.Context,
+	req *lnrpc.NodeMetricsRequest) (*lnrpc.NodeMetricsResponse, error) {
+
+	// Get requested metric types.
+	getCentrality := false
+	for _, t := range req.Types {
+		if t == lnrpc.NodeMetricType_BETWEENNESS_CENTRALITY {
+			getCentrality = true
+		}
+	}
+
+	// Only centrality can be requested for now.
+	if !getCentrality {
+		return nil, nil
+	}
+
+	resp := &lnrpc.NodeMetricsResponse{
+		BetweennessCentrality: make(map[string]*lnrpc.FloatValue),
+	}
+
+	// Obtain the pointer to the global singleton channel graph, this will
+	// provide a consistent view of the graph due to bolt db's
+	// transactional model.
+	graph := r.server.chanDB.ChannelGraph()
+
+	// Calculate betweenness centrality if requested. Note that depending on the
+	// graph size, this may take up to a few minutes.
+	channelGraph := autopilot.ChannelGraphFromDatabase(graph)
+	centralityMetric := autopilot.NewBetweennessCentralityMetric()
+	if err := centralityMetric.Refresh(channelGraph); err != nil {
+		return nil, err
+	}
+
+	// Fill normalized and non normalized centrality.
+	centrality := centralityMetric.GetMetric(true)
+	for nodeID, val := range centrality {
+		resp.BetweennessCentrality[hex.EncodeToString(nodeID[:])] = &lnrpc.FloatValue{
+			NormalizedValue: val,
+		}
+	}
+
+	centrality = centralityMetric.GetMetric(false)
+	for nodeID, val := range centrality {
+		resp.BetweennessCentrality[hex.EncodeToString(nodeID[:])].Value = val
+	}
+
+	return resp, nil
+}
+
 // GetChanInfo returns the latest authenticated network announcement for the
 // given channel identified by its channel ID: an 8-byte integer which uniquely
 // identifies the location of transaction's funding output within the block