printer YANG FEATURE initial implementation of YANG printer
diff --git a/src/printer_internal.h b/src/printer_internal.h
new file mode 100644
index 0000000..4d61285
--- /dev/null
+++ b/src/printer_internal.h
@@ -0,0 +1,80 @@
+/**
+ * @file printer_internal.h
+ * @author Radek Krejci <rkrejci@cesnet.cz>
+ * @brief Internal structures and functions for libyang
+ *
+ * Copyright (c) 2015-2019 CESNET, z.s.p.o.
+ *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://opensource.org/licenses/BSD-3-Clause
+ */
+
+#ifndef LY_PRINTER_INTERNAL_H_
+#define LY_PRINTER_INTERNAL_H_
+
+#include "printer_schema.h"
+
+typedef enum LYOUT_TYPE {
+ LYOUT_FD, /**< file descriptor */
+ LYOUT_STREAM, /**< FILE stream */
+ LYOUT_MEMORY, /**< memory */
+ LYOUT_CALLBACK /**< print via provided callback */
+} LYOUT_TYPE;
+
+struct lyout {
+ LYOUT_TYPE type;
+ union {
+ int fd;
+ FILE *f;
+ struct {
+ char *buf;
+ size_t len;
+ size_t size;
+ } mem;
+ struct {
+ ssize_t (*f)(void *arg, const void *buf, size_t count);
+ void *arg;
+ } clb;
+ } method;
+
+ /* buffer for holes */
+ char *buffered;
+ size_t buf_len;
+ size_t buf_size;
+
+ /* hole counter */
+ size_t hole_count;
+};
+
+struct ext_substmt_info_s {
+ const char *name;
+ const char *arg;
+ int flags;
+#define SUBST_FLAG_YIN 0x1 /**< has YIN element */
+#define SUBST_FLAG_ID 0x2 /**< the value is identifier -> no quotes */
+};
+
+/* filled in printer.c */
+extern struct ext_substmt_info_s ext_substmt_info[];
+
+
+/**
+ * @brief
+ */
+LY_ERR yang_print_parsed(struct lyout *out, const struct lys_module *module);
+
+/**
+ * @brief
+ */
+LY_ERR yang_print_compiled(struct lyout *out, const struct lys_module *module);
+
+LY_ERR ly_print(struct lyout *out, const char *format, ...);
+
+void ly_print_flush(struct lyout *out);
+
+LY_ERR ly_write(struct lyout *out, const char *buf, size_t count);
+
+#endif /* LY_PRINTER_INTERNAL_H_ */