diff --git a/include/eport.h b/include/eport.h
index 7754f15..e6d26f9 100644
--- a/include/eport.h
+++ b/include/eport.h
@@ -23,10 +23,20 @@
 
 #include <ejabbermsg.h>
 
-size_t eport_read(FILE *, char *, size_t);
+/* returns -1 in case of error, see errno than, or bytes ridden otherwise */
+ssize_t eport_read(FILE *, char *, size_t);
 
-size_t eport_write(FILE *, char *, size_t);
+/* returns -1 in case of error, see errno than, or bytes written otherwise */
+ssize_t eport_write(FILE *, char *, size_t);
 
+/* returns -1 in case of error, otherwise returns a number of
+ * elements ridden from the message data
+ * message structure shall be preallocated, but pointers within it are not,
+ * e.g. all contents are set by this function.
+ * pointer is a message data content with size.
+ * NOTE: this function modifies the message data content, however freeing and
+ * allocation shall be done outside of this function.
+ */
 int eport_ejabberd_msgread(char *, size_t, struct ejabber_msg *);
 
 #endif /* __EPORT_H__ */