graph/db: add buildCachedChanPolicies helper

Here we just remove some code duplication by adding a
buildCachedChanPolicies helper.

graph/db/sql_store.go

@@ -1275,26 +1275,11 @@ func (s *SQLStore) ForEachChannelCacheable(cb func(*models.CachedEdgeInfo,
 			return err
 		}
 
-		var pol1, pol2 *models.CachedEdgePolicy
-		if dbPol1 != nil {
-			policy1, err := buildChanPolicy(
-				*dbPol1, edge.ChannelID, nil, node2,
-			)
-			if err != nil {
-				return err
-			}
-
-			pol1 = models.NewCachedPolicy(policy1)
-		}
-		if dbPol2 != nil {
-			policy2, err := buildChanPolicy(
-				*dbPol2, edge.ChannelID, nil, node1,
-			)
-			if err != nil {
-				return err
-			}
-
-			pol2 = models.NewCachedPolicy(policy2)
+		pol1, pol2, err := buildCachedChanPolicies(
+			dbPol1, dbPol2, edge.ChannelID, node1, node2,
+		)
+		if err != nil {
+			return err
 		}
 
 		if err := cb(edge, pol1, pol2); err != nil {
@@ -2646,58 +2631,50 @@ func (s *SQLStore) ChannelView() ([]EdgePoint, error) {
 		edgePoints []EdgePoint
 	)
 
-	handleChannel := func(db SQLQueries,
-		channel sqlc.ListChannelsPaginatedRow) error {
-
-		pkScript, err := genMultiSigP2WSH(
-			channel.BitcoinKey1, channel.BitcoinKey2,
-		)
-		if err != nil {
-			return err
-		}
-
-		op, err := wire.NewOutPointFromString(channel.Outpoint)
-		if err != nil {
-			return err
-		}
-
-		edgePoints = append(edgePoints, EdgePoint{
-			FundingPkScript: pkScript,
-			OutPoint:        *op,
-		})
-
-		return nil
-	}
-
 	err := s.db.ExecTx(ctx, sqldb.ReadTxOpt(), func(db SQLQueries) error {
-		lastID := int64(-1)
-		for {
-			rows, err := db.ListChannelsPaginated(
-				ctx, sqlc.ListChannelsPaginatedParams{
-					Version: int16(ProtocolV1),
-					ID:      lastID,
-					Limit:   s.cfg.QueryCfg.MaxPageSize,
-				},
+		handleChannel := func(_ context.Context,
+			channel sqlc.ListChannelsPaginatedRow) error {
+
+			pkScript, err := genMultiSigP2WSH(
+				channel.BitcoinKey1, channel.BitcoinKey2,
 			)
 			if err != nil {
 				return err
 			}
 
-			if len(rows) == 0 {
-				break
+			op, err := wire.NewOutPointFromString(channel.Outpoint)
+			if err != nil {
+				return err
 			}
 
-			for _, row := range rows {
-				err := handleChannel(db, row)
-				if err != nil {
-					return err
-				}
+			edgePoints = append(edgePoints, EdgePoint{
+				FundingPkScript: pkScript,
+				OutPoint:        *op,
+			})
 
-				lastID = row.ID
-			}
+			return nil
 		}
 
-		return nil
+		queryFunc := func(ctx context.Context, lastID int64,
+			limit int32) ([]sqlc.ListChannelsPaginatedRow, error) {
+
+			return db.ListChannelsPaginated(
+				ctx, sqlc.ListChannelsPaginatedParams{
+					Version: int16(ProtocolV1),
+					ID:      lastID,
+					Limit:   limit,
+				},
+			)
+		}
+
+		extractCursor := func(row sqlc.ListChannelsPaginatedRow) int64 {
+			return row.ID
+		}
+
+		return sqldb.ExecutePaginatedQuery(
+			ctx, s.cfg.QueryCfg, int64(-1), queryFunc,
+			extractCursor, handleChannel,
+		)
 	}, func() {
 		edgePoints = nil
 	})
@@ -3071,26 +3048,11 @@ func forEachNodeDirectedChannel(ctx context.Context, db SQLQueries,
 			return err
 		}
 
-		var p1, p2 *models.CachedEdgePolicy
-		if dbPol1 != nil {
-			policy1, err := buildChanPolicy(
-				*dbPol1, edge.ChannelID, nil, node2,
-			)
-			if err != nil {
-				return err
-			}
-
-			p1 = models.NewCachedPolicy(policy1)
-		}
-		if dbPol2 != nil {
-			policy2, err := buildChanPolicy(
-				*dbPol2, edge.ChannelID, nil, node1,
-			)
-			if err != nil {
-				return err
-			}
-
-			p2 = models.NewCachedPolicy(policy2)
+		p1, p2, err := buildCachedChanPolicies(
+			dbPol1, dbPol2, edge.ChannelID, node1, node2,
+		)
+		if err != nil {
+			return err
 		}
 
 		// Determine the outgoing and incoming policy for this
@@ -4276,6 +4238,34 @@ func getAndBuildChanPolicies(ctx context.Context, db SQLQueries,
 	return pol1, pol2, nil
 }
 
+// buildCachedChanPolicies builds models.CachedEdgePolicy instances from the
+// provided sqlc.GraphChannelPolicy objects. If a provided policy is nil,
+// then nil is returned for it.
+func buildCachedChanPolicies(dbPol1, dbPol2 *sqlc.GraphChannelPolicy,
+	channelID uint64, node1, node2 route.Vertex) (*models.CachedEdgePolicy,
+	*models.CachedEdgePolicy, error) {
+
+	var p1, p2 *models.CachedEdgePolicy
+	if dbPol1 != nil {
+		policy1, err := buildChanPolicy(*dbPol1, channelID, nil, node2)
+		if err != nil {
+			return nil, nil, err
+		}
+
+		p1 = models.NewCachedPolicy(policy1)
+	}
+	if dbPol2 != nil {
+		policy2, err := buildChanPolicy(*dbPol2, channelID, nil, node1)
+		if err != nil {
+			return nil, nil, err
+		}
+
+		p2 = models.NewCachedPolicy(policy2)
+	}
+
+	return p1, p2, nil
+}
+
 // buildChanPolicy builds a models.ChannelEdgePolicy instance from the
 // provided sqlc.GraphChannelPolicy and other required information.
 func buildChanPolicy(dbPolicy sqlc.GraphChannelPolicy, channelID uint64,