fix: added Conetent method for value interface

Signed-off-by: Junjie Gao <[email protected]>

internal/encoding/asn1/asn1.go

@@ -32,11 +32,17 @@ var (
 
 // value represents an ASN.1 value.
 type value interface {
-	// Encode encodes the value to the value writer in DER.
-	Encode(*bytes.Buffer) error
+	// EncodeMetadata encodes the identifier and length in DER to the buffer.
+	EncodeMetadata(*bytes.Buffer) error
 
 	// EncodedLen returns the length in bytes of the encoded data.
 	EncodedLen() int
+
+	// Content returns the content of the value.
+	// For primitive values, it returns the content octets.
+	// For constructed values, it returns nil because the content is
+	// the data of all members.
+	Content() []byte
 }
 
 // ConvertToDER converts BER-encoded ASN.1 data structures to DER-encoded.
@@ -49,9 +55,17 @@ func ConvertToDER(ber []byte) ([]byte, error) {
 	// get the total length from the root value and allocate a buffer
 	buf := bytes.NewBuffer(make([]byte, 0, flatValues[0].EncodedLen()))
 	for _, v := range flatValues {
-		if err = v.Encode(buf); err != nil {
+		if err = v.EncodeMetadata(buf); err != nil {
 			return nil, err
 		}
+
+		if v.Content() != nil {
+			// primitive value
+			_, err = buf.Write(v.Content())
+			if err != nil {
+				return nil, err
+			}
+		}
 	}
 
 	return buf.Bytes(), nil
@@ -60,7 +74,9 @@ func ConvertToDER(ber []byte) ([]byte, error) {
 // decode decodes BER-encoded ASN.1 data structures.
 //
 // r is the input byte slice.
-// The returned value is the flat ASN.1 values slice.
+// The returned value, which is the flat slice of ASN.1 values, contains the
+// nodes from a depth-first traversal. To get the DER of `r`, encode the values
+// in the returned slice in order.
 func decode(r []byte) ([]value, error) {
 	// prepare the first value
 	identifier, content, r, err := decodeMetadata(r)

internal/encoding/asn1/constructed.go

@@ -23,8 +23,8 @@ type constructedValue struct {
 	rawContent []byte // the raw content of BER
 }
 
-// Encode encodes the constructed value to the value writer in DER.
-func (v constructedValue) Encode(w *bytes.Buffer) error {
+// EncodeMetadata encodes the constructed value to the value writer in DER.
+func (v *constructedValue) EncodeMetadata(w *bytes.Buffer) error {
 	_, err := w.Write(v.identifier)
 	if err != nil {
 		return err
@@ -36,6 +36,11 @@ func (v constructedValue) Encode(w *bytes.Buffer) error {
 }
 
 // EncodedLen returns the length in bytes of the encoded data.
-func (v constructedValue) EncodedLen() int {
+func (v *constructedValue) EncodedLen() int {
 	return len(v.identifier) + encodedLengthSize(v.length) + v.length
 }
+
+// Content returns the content of the value.
+func (v *constructedValue) Content() []byte {
+	return nil
+}

internal/encoding/asn1/primitive.go

@@ -21,20 +21,24 @@ type primitiveValue struct {
 	content    []byte
 }
 
-// Encode encodes the primitive value to the value writer in DER.
-func (v primitiveValue) Encode(w *bytes.Buffer) error {
+// EncodeMetadata encodes the primitive value to the value writer in DER.
+func (v *primitiveValue) EncodeMetadata(w *bytes.Buffer) error {
 	_, err := w.Write(v.identifier)
 	if err != nil {
 		return err
 	}
 	if err = encodeLength(w, len(v.content)); err != nil {
 		return err
 	}
-	_, err = w.Write(v.content)
-	return err
+	return nil
 }
 
 // EncodedLen returns the length in bytes of the encoded data.
-func (v primitiveValue) EncodedLen() int {
+func (v *primitiveValue) EncodedLen() int {
 	return len(v.identifier) + encodedLengthSize(len(v.content)) + len(v.content)
 }
+
+// Content returns the content of the value.
+func (v *primitiveValue) Content() []byte {
+	return v.content
+}