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

@@ -564,7 +564,9 @@ func (s *swapClientServer) ListSwaps(ctx context.Context,
 
 	var (
 		rpcSwaps = []*looprpc.SwapStatus{}
-		idx      = 0
+		idx      = uint32(0)
+		lastIdx  = uint32(0)
+		maxSwaps = int(req.MaxSwaps)
 	)
 
 	s.swapsLock.Lock()
@@ -580,14 +582,29 @@ func (s *swapClientServer) ListSwaps(ctx context.Context,
 			continue
 		}
 
-		rpcSwap, err := s.marshallSwap(ctx, &swp)
-		if err != nil {
-			return nil, err
+		// Check if this swap is within our pagination window.
+		if idx >= req.IndexOffset {
+			// If maxSwaps is 0, we return all swaps.
+			// Otherwise, check if we've reached our limit.
+			if maxSwaps == 0 || len(rpcSwaps) < maxSwaps {
+				rpcSwap, err := s.marshallSwap(ctx, &swp)
+				if err != nil {
+					return nil, err
+				}
+				rpcSwaps = append(rpcSwaps, rpcSwap)
+				lastIdx = idx
+			}
+
 		}
-		rpcSwaps = append(rpcSwaps, rpcSwap)
 		idx++
 	}
-	return &looprpc.ListSwapsResponse{Swaps: rpcSwaps}, nil
+
+	response := looprpc.ListSwapsResponse{
+		Swaps:              rpcSwaps,
+		LastIndexOffset:    lastIdx,
+		TotalFilteredSwaps: idx,
+	}
+	return &response, nil
 }
 
 // filterSwap filters the given swap based on the provided filter.

looprpc/client.pb.go

@@ -675,6 +675,12 @@ enum FailureReason {
 message ListSwapsRequest {
     // Optional filter to only return swaps that match the filter.
     ListSwapsFilter list_swap_filter = 1;
+
+    // Allow specifying an starting index when returning filtered swaps.
+    uint32 index_offset = 2;
+
+    // Set a maximum number of swaps to return in the response.
+    uint32 max_swaps = 3;
 }
 
 message ListSwapsFilter {
@@ -711,6 +717,16 @@ message ListSwapsResponse {
     The list of all currently known swaps and their status.
     */
     repeated SwapStatus swaps = 1;
+
+    // The last returned swap index returned.
+    uint32 last_index_offset = 2;
+
+    /*
+    The total number of swaps found after filtering, but before any pagination
+    takes place. The caller can use this field as they iterate over all swaps
+    using pagination.
+    */
+    uint32 total_filtered_swaps = 4;
 }
 
 message SwapInfoRequest {

looprpc/client.proto

@@ -625,6 +625,22 @@
             "in": "query",
             "required": false,
             "type": "boolean"
+          },
+          {
+            "name": "index_offset",
+            "description": "Allow specifying an starting index when returning filtered swaps.",
+            "in": "query",
+            "required": false,
+            "type": "integer",
+            "format": "int64"
+          },
+          {
+            "name": "max_swaps",
+            "description": "Set a maximum number of swaps to return in the response.",
+            "in": "query",
+            "required": false,
+            "type": "integer",
+            "format": "int64"
           }
         ],
         "tags": [
@@ -1415,6 +1431,16 @@
             "$ref": "#/definitions/looprpcSwapStatus"
           },
           "description": "The list of all currently known swaps and their status."
+        },
+        "last_index_offset": {
+          "type": "integer",
+          "format": "int64",
+          "description": "The last returned swap index returned."
+        },
+        "total_filtered_swaps": {
+          "type": "integer",
+          "format": "int64",
+          "description": "The total number of swaps found after filtering, but before any pagination\ntakes place. The caller can use this field as they iterate over all swaps\nusing pagination."
         }
       }
     },