Add pagination types and helper func

types/query/pagination.go

@@ -0,0 +1,83 @@
+package query
+
+import (
+	"github.com/cosmos/cosmos-sdk/store/types"
+)
+
+// Paginate does pagination of the results in the prefixStore based on the
+// provided PageRequest. onResult should be used to do actual unmarshaling.
+//
+// Ex:
+//		prefixStore := prefix.NewStore(store, someRequestParam)
+//		var results []Result
+//		pageRes, err := query.Paginate(accountStore, req.Page, func(key []byte, value []byte) error {
+//			var result Result
+//			err := Unmarshal(value, &balance)
+//			results = append(results, result)
+//			...
+//		})
+func Paginate(
+	prefixStore types.KVStore,
+	req *PageRequest,
+	onResult func(key []byte, value []byte) error,
+) (*PageResponse, error) {
+	offset := req.Offset
+	key := req.Key
+	limit := req.Limit
+
+	if len(key) != 0 {
+		iterator := prefixStore.Iterator(key, nil)
+		defer iterator.Close()
+
+		var count uint64
+		var nextKey []byte
+
+		for ; iterator.Valid(); iterator.Next() {
+			if count == limit {
+				nextKey = iterator.Key()
+				break
+			}
+
+			err := onResult(iterator.Key(), iterator.Value())
+			if err != nil {
+				return nil, err
+			}
+
+			count++
+		}
+
+		return &PageResponse{
+			NextKey: nextKey,
+		}, nil
+	} else {
+		iterator := prefixStore.Iterator(nil, nil)
+		defer iterator.Close()
+
+		end := offset + limit
+		var count uint64
+		var nextKey []byte
+
+		for ; iterator.Valid(); iterator.Next() {
+			count++
+
+			if count < offset {
+				continue
+			} else if count <= end {
+				err := onResult(iterator.Key(), iterator.Value())
+				if err != nil {
+					return nil, err
+				}
+			} else if !req.CountTotal {
+				nextKey = iterator.Key()
+				break
+			}
+		}
+
+		res := &PageResponse{NextKey: nextKey}
+		if req.CountTotal {
+			res.Total = count
+		}
+
+		return res, nil
+	}
+}