rpcserver: calculate and populate medianChanSizeSat in NetworkInfo

rpcserver.go

@@ -3959,6 +3959,7 @@ func (r *rpcServer) GetNetworkInfo(ctx context.Context,
 		totalNetworkCapacity btcutil.Amount
 		minChannelSize       btcutil.Amount = math.MaxInt64
 		maxChannelSize       btcutil.Amount
+		medianChanSize       btcutil.Amount
 	)
 
 	// We'll use this map to de-duplicate channels during our traversal.
@@ -3966,6 +3967,10 @@ func (r *rpcServer) GetNetworkInfo(ctx context.Context,
 	// edges for each channel within the graph.
 	seenChans := make(map[uint64]struct{})
 
+	// We also keep a list of all encountered capacities, in order to
+	// calculate the median channel size.
+	var allChans []btcutil.Amount
+
 	// We'll run through all the known nodes in the within our view of the
 	// network, tallying up the total number of nodes, and also gathering
 	// each node so we can measure the graph diameter and degree stats
@@ -4012,6 +4017,7 @@ func (r *rpcServer) GetNetworkInfo(ctx context.Context,
 			numChannels++
 
 			seenChans[edge.ChannelID] = struct{}{}
+			allChans = append(allChans, edge.Capacity)
 			return nil
 		}); err != nil {
 			return err
@@ -4028,6 +4034,9 @@ func (r *rpcServer) GetNetworkInfo(ctx context.Context,
 		return nil, err
 	}
 
+	// Find the median.
+	medianChanSize = autopilot.Median(allChans)
+
 	// If we don't have any channels, then reset the minChannelSize to zero
 	// to avoid outputting NaN in encoded JSON.
 	if numChannels == 0 {
@@ -4037,7 +4046,6 @@ func (r *rpcServer) GetNetworkInfo(ctx context.Context,
 	// TODO(roasbeef): graph diameter
 
 	// TODO(roasbeef): also add oldest channel?
-	//  * also add median channel size
 	netInfo := &lnrpc.NetworkInfo{
 		MaxOutDegree:         maxChanOut,
 		AvgOutDegree:         float64(numChannels) / float64(numNodes),
@@ -4048,6 +4056,7 @@ func (r *rpcServer) GetNetworkInfo(ctx context.Context,
 
 		MinChannelSize:       int64(minChannelSize),
 		MaxChannelSize:       int64(maxChannelSize),
+		MedianChannelSizeSat: int64(medianChanSize),
 	}
 
 	// Similarly, if we don't have any channels, then we'll also set the