+/* Generate a compressed version of 'message_id' of the form:
+ *
+ * notmuch-sha1-<sha1_sum_of_message_id>
+ */
+static char *
+_message_id_compressed (void *ctx, const char *message_id)
+{
+ char *sha1, *compressed;
+
+ sha1 = notmuch_sha1_of_string (message_id);
+
+ compressed = talloc_asprintf (ctx, "notmuch-sha1-%s", sha1);
+ free (sha1);
+
+ return compressed;
+}
+