How to gob encode struct with unexported pointer? - go

Question

I have a struct that I can successfully gob encode and decode as follows:
type Node struct {
Value int
Next *Node
}
myNode := Node{
Value: 1,
Next: &Node{
Value: 2,
},
}
var buf bytes.Buffer
enc := gob.NewEncoder(&buf)
dec := gob.NewDecoder(&buf)
if err := enc.Encode(&myNode); err != nil {
panic(err)
}
var decodedNode Node
if err := dec.Decode(&decodedNode); err != nil {
panic(err)
}
I'd like to now hide the fields of Node:
type Node struct {
value int
next *Node
}
Because the fields are no longer exported I have to now write custom GobEncode and GobDecode functions:
func (d *Node) GobEncode() ([]byte, error) {
var buf bytes.Buffer
encoder := gob.NewEncoder(&buf)
if err := encoder.Encode(d.value); err != nil {
return nil, err
}
if err := encoder.Encode(d.next); err != nil {
return nil, err
}
return buf.Bytes(), nil
}
func (d *Node) GobDecode(b []byte) error {
buf := bytes.NewBuffer(b)
decoder := gob.NewDecoder(buf)
if err := decoder.Decode(&d.value); err != nil {
return err
}
if err := decoder.Decode(&d.next); err != nil {
return err
}
return nil
}
This doesn't work because of a nil value in Node.next:
panic: gob: cannot encode nil pointer of type *main.Node [recovered]
panic: gob: cannot encode nil pointer of type *main.Node [recovered]
panic: gob: cannot encode nil pointer of type *main.Node
I'm re-using gob.NewEncoder inside my custom function because I'm trying to re-use as much of the encode package as possible.
Any suggestions for getting this working?