Issue #161: add a json_object_to_fd() function.

json_util.h

@@ -67,7 +67,18 @@ extern int json_object_to_file(const char *filename, struct json_object *obj);
 extern int json_object_to_file_ext(const char *filename, struct json_object *obj, int flags);
 
 /**
- * Return the last error from json_object_to_file{,_ext} or
+ * Convert the json_object to a string and write it to the file descriptor.
+ * Handles partial writes and will keep writing until done, or an error
+ * occurs.
+ *
+ * @param flags flags to pass to json_object_to_json_string_ext()
+ * @return -1 if something fails.  See json_util_get_last_err() for details.
+ */
+extern int json_object_to_fd(int fd, struct json_object *obj, int flags);
+
+/**
+ * Return the last error from json_object_to_file{,_ext},
+ * json_object_to_fd() or
  * json_object_from_{file,fd}, or NULL if there is none.
  */
 const char *json_util_get_last_err(void);