refactor: version cursor - update payload

internal/domain/validation.go

@@ -241,6 +241,7 @@ var ErrNil error = simpleError{
 	code: "nil",
 }
 
+// ErrInvalidCursor is an error that is returned when a cursor can't be decoded (e.g. is malformed).
 var ErrInvalidCursor error = simpleError{
 	msg:  "invalid cursor",
 	typ:  ErrorTypeIncorrectInput,

internal/domain/version.go

@@ -4,6 +4,7 @@ import (
 	"encoding/base64"
 	"fmt"
 	"net/url"
+	"strings"
 )
 
 const (
@@ -140,13 +141,19 @@ func decodeVersionCursor(encoded string) (VersionCursor, error) {
 		return VersionCursor{}, err
 	}
 
-	decoded, err := base64.StdEncoding.DecodeString(encoded)
+	decodedBytes, err := base64.StdEncoding.DecodeString(encoded)
 	if err != nil {
 		return VersionCursor{}, ErrInvalidCursor
 	}
+	decoded := string(decodedBytes)
+
+	code, ok := strings.CutPrefix(decoded, "code=")
+	if !ok {
+		return VersionCursor{}, ErrInvalidCursor
+	}
 
 	vc, err := NewVersionCursor(NullString{
-		Value: string(decoded),
+		Value: code,
 		Valid: true,
 	})
 	if err != nil {
@@ -169,7 +176,7 @@ func (vc VersionCursor) Encode() string {
 		return ""
 	}
 
-	return base64.StdEncoding.EncodeToString([]byte(vc.code.Value))
+	return base64.StdEncoding.EncodeToString([]byte("code=" + vc.code.Value))
 }
 
 type ListVersionsParams struct {