looprpc: add simple pagination to the ListSwaps command

This commit adds the ability to set a max_swaps and an index_offset
flag to the ListSwaps command. These new fields are applied AFTER
the initial filtering step. The response also now passes additional
information about the index count and total swaps filtered.

Author: kornpow

cmd/loop/swaps.go

@@ -35,6 +35,14 @@ var listSwapsCommand = cli.Command{
 		labelFlag,
 		channelFlag,
 		lastHopFlag,
+		cli.Uint64Flag{
+			Name:  "max_swaps",
+			Usage: "Max number of swaps to return after filtering",
+		},
+		cli.Uint64Flag{
+			Name:  "index_offset",
+			Usage: "index to start listing filtered swaps from",
+		},
 	},
 }
 
@@ -102,6 +110,8 @@ func listSwaps(ctx *cli.Context) error {
 	resp, err := client.ListSwaps(
 		context.Background(), &looprpc.ListSwapsRequest{
 			ListSwapFilter: filter,
+			IndexOffset:    uint32(ctx.Uint("index_offset")),
+			MaxSwaps:       uint32(ctx.Uint("max_swaps")),
 		},
 	)
 	if err != nil {

loopd/swapclient_server.go

@@ -579,15 +579,42 @@ func (s *swapClientServer) ListSwaps(ctx context.Context,
 		if !filterSwap(&swp, req.ListSwapFilter) {
 			continue
 		}
-
 		rpcSwap, err := s.marshallSwap(ctx, &swp)
 		if err != nil {
 			return nil, err
 		}
 		rpcSwaps = append(rpcSwaps, rpcSwap)
 		idx++
 	}
-	return &looprpc.ListSwapsResponse{Swaps: rpcSwaps}, nil
+
+	filteredSwapCount := len(rpcSwaps)
+	endIndex := filteredSwapCount
+
+	// Calculate the endIndex if necessary
+	if req.MaxSwaps > 0 {
+		endIndex = int(req.IndexOffset + req.MaxSwaps)
+		if endIndex > filteredSwapCount {
+			endIndex = filteredSwapCount
+		}
+	}
+
+	// If starting indexOffset is more than the total return empty
+	if int(req.IndexOffset) >= filteredSwapCount {
+		rpcSwaps = []*looprpc.SwapStatus{}
+	}
+
+	// finally, only slice the slice if indexes are in range
+	if int(req.IndexOffset) < filteredSwapCount {
+		rpcSwaps = rpcSwaps[req.IndexOffset:endIndex]
+	}
+
+	response := looprpc.ListSwapsResponse{
+		Swaps:              rpcSwaps,
+		FirstIndexOffset:   req.IndexOffset,
+		LastIndexOffset:    uint32(endIndex),
+		TotalFilteredSwaps: uint32(filteredSwapCount),
+	}
+	return &response, nil
 }
 
 // filterSwap filters the given swap based on the provided filter.