Fix race in iterator

Makefile

@@ -1,4 +1,4 @@
 .PHONY: test
 test:
-	go test ./...
+	go test -race -cpu 5 ./...
 

stream/iterator.go

@@ -5,15 +5,6 @@ import (
 	"math/big"
 )
 
-type NodeIterator struct {
-	*ReadItem
-	LastError      error
-	needFeedback   bool
-	items          chan *ReadItem
-	feedback       chan error
-	feedbackClosed bool
-}
-
 type ReadItem struct {
 	Path      []interface{}
 	TokenType ReaderToken
@@ -152,6 +143,15 @@ func (s *ReadItem) ToFloat() (res float64, ok bool) {
 	return res, ok
 }
 
+type NodeIterator struct {
+	*ReadItem
+	LastError      error
+	needFeedback   bool
+	items          chan *ReadItem
+	feedback       chan error
+	feedbackClosed bool
+}
+
 // Read from a NodeReader using a channel of ReadItem.
 func Iterate(r NodeReader, res_error *error) *NodeIterator {
 	it := make(chan *ReadItem)
@@ -160,12 +160,10 @@ func Iterate(r NodeReader, res_error *error) *NodeIterator {
 
 	go func() {
 		err := r.Read(func(path []interface{}, tokenType ReaderToken, value interface{}) error {
-			res.needFeedback = true
 			item := &ReadItem{path, tokenType, value}
 			it <- item
 			return <-feedback
 		})
-		res.needFeedback = false
 		close(it)
 		if err != nil && res_error != nil {
 			res.LastError = err
@@ -182,13 +180,15 @@ func (s *NodeIterator) Iter() bool {
 
 	item := <-s.items
 	if item == nil {
+		s.needFeedback = false
 		if !s.feedbackClosed {
 			close(s.feedback)
 			s.feedbackClosed = true
 		}
 		return false
 	}
 
+	s.needFeedback = true
 	s.ReadItem = item
 	return true
 }