-extern void reply_with_error (const char *fs, ...);
-extern void reply_with_perror (const char *fs, ...);
+extern void reply_with_error (const char *fs, ...)
+ __attribute__((format (printf,1,2)));
+extern void reply_with_perror (const char *fs, ...)
+ __attribute__((format (printf,1,2)));
+
+/* daemon functions that receive files (FileIn) should call
+ * receive_file for each FileIn parameter.
+ */
+typedef int (*receive_cb) (void *opaque, const void *buf, int len);
+extern int receive_file (receive_cb cb, void *opaque);
+
+/* daemon functions that receive files (FileIn) can call this
+ * to cancel incoming transfers (eg. if there is a local error),
+ * but they MUST then call reply_with_error or reply_with_perror.
+ */
+extern void cancel_receive (void);