py: Change stream protocol API: fns return uint; is_text for text.
diff --git a/py/obj.h b/py/obj.h
index d0284e6..4745b76 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -228,13 +228,14 @@
 void mp_get_buffer_raise(mp_obj_t obj, mp_buffer_info_t *bufinfo, int flags);
 
 // Stream protocol
+#define MP_STREAM_ERROR (-1)
 typedef struct _mp_stream_p_t {
-    // On error, functions should return -1 and fill in *errcode (values are
-    // implementation-dependent, but will be exposed to user, e.g. via exception).
-    mp_int_t (*read)(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode);
-    mp_int_t (*write)(mp_obj_t obj, const void *buf, mp_uint_t size, int *errcode);
+    // On error, functions should return MP_STREAM_ERROR and fill in *errcode (values
+    // are implementation-dependent, but will be exposed to user, e.g. via exception).
+    mp_uint_t (*read)(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode);
+    mp_uint_t (*write)(mp_obj_t obj, const void *buf, mp_uint_t size, int *errcode);
     // add seek() ?
-    int is_bytes : 1;
+    int is_text : 1; // default is bytes, set this for text stream
 } mp_stream_p_t;
 
 struct _mp_obj_type_t {