optional message fields

src/transport.c

@@ -595,6 +595,7 @@ DYNAMIC_API void free_message(message *msg)
         free_stringlist(msg->references);
         free_stringlist(msg->keywords);
         free(msg->comments);
+        free_stringpair_map(msg->opt_fields);
         free(msg);
     }
 }
@@ -721,6 +722,12 @@ DYNAMIC_API message * message_dup(const message *src)
             goto enomem;
     }
 
+    if (src->opt_fields) {
+        msg->opt_fields = stringpair_map_dup(src->opt_fields);
+        if (msg->opt_fields == NULL)
+            goto enomem;
+    }
+
     msg->enc_format = src->enc_format;
 
     return msg;

src/transport.h

@@ -332,6 +332,7 @@ typedef struct _message {
                                             // refered
     stringlist_t *keywords;                 // list of UTF-8 strings with keywords
     char *comments;                         // UTF-8 string with comments
+    stringpair_map_t *opt_fields;           // optional fields
     PEP_enc_format enc_format;              // format of encrypted data
 } message;