Refactored decoder responsibilities (#1402)

- improved comment handling
- yaml decoder now responsible for leading content work around

pkg/yqlib/decoder_base64.go

@@ -19,21 +19,22 @@ func NewBase64Decoder() Decoder {
 	return &base64Decoder{finished: false, encoding: *base64.StdEncoding}
 }
 
-func (dec *base64Decoder) Init(reader io.Reader) {
+func (dec *base64Decoder) Init(reader io.Reader) error {
 	dec.reader = reader
 	dec.readAnything = false
 	dec.finished = false
+	return nil
 }
 
-func (dec *base64Decoder) Decode(rootYamlNode *yaml.Node) error {
+func (dec *base64Decoder) Decode() (*CandidateNode, error) {
 	if dec.finished {
-		return io.EOF
+		return nil, io.EOF
 	}
 	base64Reader := base64.NewDecoder(&dec.encoding, dec.reader)
 	buf := new(bytes.Buffer)
 
 	if _, err := buf.ReadFrom(base64Reader); err != nil {
-		return err
+		return nil, err
 	}
 	if buf.Len() == 0 {
 		dec.finished = true
@@ -42,12 +43,15 @@ func (dec *base64Decoder) Decode(rootYamlNode *yaml.Node) error {
 		// otherwise if we've already read some bytes, and now we get
 		// an empty string, then we are done.
 		if dec.readAnything {
-			return io.EOF
+			return nil, io.EOF
 		}
 	}
 	dec.readAnything = true
-	rootYamlNode.Kind = yaml.ScalarNode
-	rootYamlNode.Tag = "!!str"
-	rootYamlNode.Value = buf.String()
-	return nil
+	return &CandidateNode{
+		Node: &yaml.Node{
+			Kind:  yaml.ScalarNode,
+			Tag:   "!!str",
+			Value: buf.String(),
+		},
+	}, nil
 }