+ const char *prefix = _find_prefix ("replyto");
+ int prefix_len = strlen (prefix);
+ Xapian::TermIterator i;
+ std::string in_reply_to;
+
+ if (message->in_reply_to)
+ return message->in_reply_to;
+
+ i = message->doc.termlist_begin ();
+ i.skip_to (prefix);
+
+ if (i != message->doc.termlist_end ())
+ in_reply_to = *i;
+
+ /* It's perfectly valid for a message to have no In-Reply-To
+ * header. For these cases, we return an empty string. */
+ if (i == message->doc.termlist_end () ||
+ strncmp (in_reply_to.c_str (), prefix, prefix_len))
+ {
+ message->in_reply_to = talloc_strdup (message, "");
+ return message->in_reply_to;
+ }
+
+ message->in_reply_to = talloc_strdup (message,
+ in_reply_to.c_str () + prefix_len);
+
+#if DEBUG_DATABASE_SANITY
+ i++;
+
+ in_reply_to = *i;
+
+ if (i != message->doc.termlist_end () &&
+ strncmp ((*i).c_str (), prefix, prefix_len))
+ {
+ INTERNAL_ERROR ("Message %s has duplicate In-Reply-To IDs: %s and %s\n",
+ notmuch_message_get_message_id (message),
+ message->in_reply_to,
+ (*i).c_str () + prefix_len);
+ }
+#endif
+
+ return message->in_reply_to;