diff --git a/src/parser_internal.h b/src/parser_internal.h
index d90c504..f60e5bd 100644
--- a/src/parser_internal.h
+++ b/src/parser_internal.h
@@ -32,53 +32,75 @@
  * @brief Parser input structure specifying where the data are read.
  */
 struct ly_in {
-    LY_IN_TYPE type;     /**< type of the output to select the output method */
-    const char *current;
-    const char *start;
-    size_t length;
+    LY_IN_TYPE type;        /**< type of the output to select the output method */
+    const char *current;    /**< Current position in the input data */
+    const char *func_start; /**< Input data position when the last parser function was executed */
+    const char *start;      /**< Input data start */
+    size_t length;          /**< mmap() length (if used) */
     union {
-        int fd;          /**< file descriptor for LY_IN_FD type */
-        FILE *f;         /**< file structure for LY_IN_FILE and LY_IN_FILEPATH types */
+        int fd;             /**< file descriptor for LY_IN_FD type */
+        FILE *f;            /**< file structure for LY_IN_FILE and LY_IN_FILEPATH types */
         struct {
-            int fd;      /**< file descriptor for LY_IN_FILEPATH */
-            char *filepath;   /**< stored original filepath */
-        } fpath;         /**< filepath structure for LY_IN_FILEPATH */
-    } method;            /**< type-specific information about the output */
+            int fd;         /**< file descriptor for LY_IN_FILEPATH */
+            char *filepath; /**< stored original filepath */
+        } fpath;            /**< filepath structure for LY_IN_FILEPATH */
+    } method;               /**< type-specific information about the output */
 };
 
 /**
+ * @brief Read bytes from an input.
+ *
+ * @param[in] in Input structure.
+ * @param[in] buf Destination buffer.
+ * @param[in] count Number of bytes to read.
+ * @return LY_SUCCESS on success,
+ * @return LY_EDENIED on EOF.
+ */
+LY_ERR ly_in_read(struct ly_in *in, void *buf, size_t count);
+
+/**
+ * @brief Just skip bytes in an input.
+ *
+ * @param[in] in Input structure.
+ * @param[in] count Number of bytes to skip.
+ * @return LY_SUCCESS on success,
+ * @return LY_EDENIED on EOF.
+ */
+LY_ERR ly_in_skip(struct ly_in *in, size_t count);
+
+/**
  * @brief Parse submodule from YANG data.
  * @param[in,out] ctx Parser context.
  * @param[in] ly_ctx Context of YANG schemas.
  * @param[in] main_ctx Parser context of main module.
- * @param[in] data Input data to be parsed.
+ * @param[in] in Input structure.
  * @param[out] submod Pointer to the parsed submodule structure.
  * @return LY_ERR value - LY_SUCCESS, LY_EINVAL or LY_EVALID.
  */
 LY_ERR yang_parse_submodule(struct lys_yang_parser_ctx **context, struct ly_ctx *ly_ctx, struct lys_parser_ctx *main_ctx,
-                            const char *data, struct lysp_submodule **submod);
+                            struct ly_in *in, struct lysp_submodule **submod);
 
 /**
  * @brief Parse module from YANG data.
  * @param[in] ctx Parser context.
- * @param[in] data Input data to be parsed.
- * @param[in, out] mod Prepared module structure where the parsed information, including the parsed
+ * @param[in] in Input structure.
+ * @param[in,out] mod Prepared module structure where the parsed information, including the parsed
  * module structure, will be filled in.
  * @return LY_ERR value - LY_SUCCESS, LY_EINVAL or LY_EVALID.
  */
-LY_ERR yang_parse_module(struct lys_yang_parser_ctx **context, const char *data, struct lys_module *mod);
+LY_ERR yang_parse_module(struct lys_yang_parser_ctx **context, struct ly_in *in, struct lys_module *mod);
 
 /**
  * @brief Parse module from YIN data.
  *
  * @param[in,out] yin_ctx Context created during parsing, is used to finalize lysp_model after it's completly parsed.
- * @param[in] data Input data to be parsed.
+ * @param[in] in Input structure.
  * @param[in,out] mod Prepared module structure where the parsed information, including the parsed
  * module structure, will be filled in.
  *
  * @return LY_ERR values.
  */
-LY_ERR yin_parse_module(struct lys_yin_parser_ctx **yin_ctx, const char *data, struct lys_module *mod);
+LY_ERR yin_parse_module(struct lys_yin_parser_ctx **yin_ctx, struct ly_in *in, struct lys_module *mod);
 
 /**
  * @brief Parse submodule from YIN data.
@@ -86,11 +108,11 @@
  * @param[in,out] yin_ctx Context created during parsing, is used to finalize lysp_model after it's completly parsed.
  * @param[in] ctx Libyang context.
  * @param[in] main_ctx Parser context of main module.
- * @param[in,out] data Input data to be parsed.
+ * @param[in] in Input structure.
  * @param[in,out] submod Submodule structure where the parsed information, will be filled in.
  * @return LY_ERR values.
  */
 LY_ERR yin_parse_submodule(struct lys_yin_parser_ctx **yin_ctx, struct ly_ctx *ctx, struct lys_parser_ctx *main_ctx,
-                           const char *data, struct lysp_submodule **submod);
+                           struct ly_in *in, struct lysp_submodule **submod);
 
 #endif /* LY_PARSER_INTERNAL_H_ */