Merge pull request #125 from ifupdown-ng/feature/ifparse

YAML output support

Makefile

@@ -39,8 +39,7 @@ LIBIFUPDOWN_SRC = \
 	libifupdown/lifecycle.c \
 	libifupdown/config-parser.c \
 	libifupdown/config-file.c \
-	libifupdown/compat.c \
+	libifupdown/compat.c
-
 LIBIFUPDOWN_OBJ = ${LIBIFUPDOWN_SRC:.c=.o}
 LIBIFUPDOWN_LIB = libifupdown.a
 
@@ -48,7 +47,8 @@ MULTICALL_SRC = \
 	cmd/multicall.c \
 	cmd/multicall-options.c \
 	cmd/multicall-exec-options.c \
-	cmd/multicall-match-options.c
+	cmd/multicall-match-options.c \
+	cmd/pretty-print-iface.c
 MULTICALL_OBJ = ${MULTICALL_SRC:.c=.o}
 MULTICALL = ifupdown
 
@@ -74,6 +74,22 @@ MULTICALL_${CONFIG_IFCTRSTAT}_OBJ += ${IFCTRSTAT_SRC:.c=.o}
 CMDS_${CONFIG_IFCTRSTAT} += ifctrstat
 CPPFLAGS_${CONFIG_IFCTRSTAT} += -DCONFIG_IFCTRSTAT
 
+# enable ifparse applet (+1 KB)
+CONFIG_IFPARSE ?= Y
+IFPARSE_SRC = cmd/ifparse.c
+MULTICALL_${CONFIG_IFPARSE}_OBJ += ${IFPARSE_SRC:.c=.o}
+CMDS_${CONFIG_IFPARSE} += ifparse
+CPPFLAGS_${CONFIG_IFPARSE} += -DCONFIG_IFPARSE
+
+# enable YAML support (+2 KB)
+CONFIG_YAML ?= Y
+YAML_SRC = \
+	libifupdown/yaml-base.c \
+	libifupdown/yaml-writer.c
+LIBIFUPDOWN_${CONFIG_YAML}_OBJ += ${YAML_SRC:.c=.o}
+CPPFLAGS_${CONFIG_YAML} += -DCONFIG_YAML
+
+LIBIFUPDOWN_OBJ += ${LIBIFUPDOWN_Y_OBJ}
 MULTICALL_OBJ += ${MULTICALL_Y_OBJ}
 CMDS += ${CMDS_Y}
 CPPFLAGS += ${CPPFLAGS_Y}
@@ -156,7 +172,8 @@ MANPAGES_8 = \
 	doc/ifquery.8 \
 	doc/ifup.8 \
 	doc/ifdown.8 \
-	doc/ifctrstat.8
+	doc/ifctrstat.8 \
+	doc/ifparse.8
 
 MANPAGES = ${MANPAGES_5} ${MANPAGES_7} ${MANPAGES_8}
 

cmd/ifparse.c

@@ -0,0 +1,224 @@
+/*
+ * cmd/ifparse.c
+ * Purpose: Redisplay /e/n/i in alternative formats.
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#define _GNU_SOURCE
+#include <fnmatch.h>
+#include <stdio.h>
+#include <string.h>
+#include <getopt.h>
+#include "libifupdown/libifupdown.h"
+
+#ifdef CONFIG_YAML
+# include "libifupdown/yaml-base.h"
+# include "libifupdown/yaml-writer.h"
+#endif
+
+#include "cmd/multicall.h"
+#include "cmd/pretty-print-iface.h"
+
+static bool show_all = false;
+static bool allow_undefined = false;
+
+static void
+set_show_all(const char *arg)
+{
+	(void) arg;
+
+	show_all = true;
+}
+
+static void
+set_allow_undefined(const char *arg)
+{
+	(void) arg;
+
+	allow_undefined = true;
+}
+
+static const char *output_fmt = "ifupdown";
+
+static void
+set_output_fmt(const char *arg)
+{
+	output_fmt = arg;
+}
+
+static struct if_option local_options[] = {
+	{'F', "format", NULL, "output format to use", true, set_output_fmt},
+	{'A', "all", NULL, "show all interfaces", false, set_show_all},
+	{'U', "allow-undefined", NULL, "allow querying undefined (virtual) interfaces", false, set_allow_undefined},
+};
+
+static struct if_option_group local_option_group = {
+	.desc = "Program-specific options",
+	.group_size = ARRAY_SIZE(local_options),
+	.group = local_options
+};
+
+#ifdef CONFIG_YAML
+static void
+prettyprint_interface_yaml(struct lif_interface *iface)
+{
+	struct lif_yaml_node doc = {};
+
+	lif_yaml_document_init(&doc, "interfaces");
+
+	struct lif_yaml_node *iface_node = lif_yaml_node_new_list(iface->ifname);
+	lif_yaml_node_append_child(&doc, iface_node);
+
+	if (iface->is_auto)
+	{
+		struct lif_yaml_node *iface_entry_node = lif_yaml_node_new_boolean("auto", true);
+		lif_yaml_node_append_child(iface_node, iface_entry_node);
+	}
+
+	struct lif_node *iter;
+	LIF_DICT_FOREACH(iter, &iface->vars)
+	{
+		struct lif_dict_entry *entry = iter->data;
+		const char *value = entry->data;
+		char addr_buf[512];
+
+		if (!strcmp(entry->key, "address"))
+		{
+			struct lif_address *addr = entry->data;
+
+			if (!lif_address_unparse(addr, addr_buf, sizeof addr_buf, true))
+				continue;
+
+			value = addr_buf;
+		}
+
+		struct lif_yaml_node *iface_entry_node = lif_yaml_node_new_string(entry->key, value);
+		lif_yaml_node_append_child(iface_node, iface_entry_node);
+	}
+
+	lif_yaml_write(iface_node, stdout, true);
+	lif_yaml_node_free(&doc);
+}
+#endif
+
+struct prettyprint_impl_map {
+	const char *name;
+	void (*handle)(struct lif_interface *iface);
+};
+
+struct prettyprint_impl_map pp_impl_map[] = {
+	{"ifupdown", prettyprint_interface_eni},
+#ifdef CONFIG_YAML
+	{"yaml-raw", prettyprint_interface_yaml},
+#endif
+};
+
+static int
+pp_impl_cmp(const void *a, const void *b)
+{
+	const char *key = a;
+	const struct prettyprint_impl_map *impl = b;
+
+	return strcmp(key, impl->name);
+}
+
+int
+ifparse_main(int argc, char *argv[])
+{
+	struct lif_dict state = {};
+	struct lif_dict collection = {};
+	struct lif_interface_file_parse_state parse_state = {
+		.collection = &collection,
+	};
+
+	lif_interface_collection_init(&collection);
+
+	if (!lif_state_read_path(&state, exec_opts.state_file))
+	{
+		fprintf(stderr, "%s: could not parse %s\n", argv0, exec_opts.state_file);
+		return EXIT_FAILURE;
+	}
+
+	if (!lif_interface_file_parse(&parse_state, exec_opts.interfaces_file))
+	{
+		fprintf(stderr, "%s: could not parse %s\n", argv0, exec_opts.interfaces_file);
+		return EXIT_FAILURE;
+	}
+
+	if (match_opts.property == NULL && lif_lifecycle_count_rdepends(&exec_opts, &collection) == -1)
+	{
+		fprintf(stderr, "%s: could not validate dependency tree\n", argv0);
+		return EXIT_FAILURE;
+	}
+
+	if (!lif_compat_apply(&collection))
+	{
+		fprintf(stderr, "%s: failed to apply compatibility glue\n", argv0);
+		return EXIT_FAILURE;
+	}
+
+	struct prettyprint_impl_map *m = bsearch(output_fmt, pp_impl_map, ARRAY_SIZE(pp_impl_map), sizeof(*m), pp_impl_cmp);
+	if (m == NULL)
+	{
+		fprintf(stderr, "%s: %s: output format not supported\n", argv0, output_fmt);
+		return EXIT_FAILURE;
+	}
+
+	if (show_all)
+	{
+		struct lif_node *n;
+
+		LIF_DICT_FOREACH(n, &collection)
+		{
+			struct lif_dict_entry *entry = n->data;
+
+			m->handle(entry->data);
+		}
+
+		return EXIT_SUCCESS;
+	}
+
+	if (optind >= argc)
+		generic_usage(self_applet, EXIT_FAILURE);
+
+	int idx = optind;
+	for (; idx < argc; idx++)
+	{
+		struct lif_dict_entry *entry = lif_dict_find(&collection, argv[idx]);
+		struct lif_interface *iface = NULL;
+
+		if (entry != NULL)
+			iface = entry->data;
+
+		if (entry == NULL && allow_undefined)
+			iface = lif_interface_collection_find(&collection, argv[idx]);
+
+		if (iface == NULL)
+		{
+			fprintf(stderr, "%s: unknown interface %s\n", argv0, argv[idx]);
+			return EXIT_FAILURE;
+		}
+
+		m->handle(iface);
+	}
+
+	return EXIT_SUCCESS;
+}
+
+struct if_applet ifparse_applet = {
+	.name = "ifparse",
+	.desc = "redisplay interface configuration",
+	.main = ifparse_main,
+	.usage = "ifparse [options] <interfaces>\n  ifparse [options] --all",
+	.manpage = "8 ifparse",
+	.groups = { &global_option_group, &match_option_group, &exec_option_group, &local_option_group },
+};

cmd/ifquery.c

@@ -20,42 +20,7 @@
 #include <getopt.h>
 #include "libifupdown/libifupdown.h"
 #include "cmd/multicall.h"
-
+#include "cmd/pretty-print-iface.h"
-void
-print_interface(struct lif_interface *iface)
-{
-	if (!lif_lifecycle_query_dependents(&exec_opts, iface, iface->ifname))
-		return;
-
-	if (iface->is_auto)
-		printf("auto %s\n", iface->ifname);
-
-	printf("%s %s\n", iface->is_template ? "template" : "iface", iface->ifname);
-
-	struct lif_node *iter;
-	LIF_DICT_FOREACH(iter, &iface->vars)
-	{
-		struct lif_dict_entry *entry = iter->data;
-
-		if (!strcmp(entry->key, "address"))
-		{
-			struct lif_address *addr = entry->data;
-			char addr_buf[512];
-
-			if (!lif_address_unparse(addr, addr_buf, sizeof addr_buf, true))
-			{
-				printf("  # warning: failed to unparse address\n");
-				continue;
-			}
-
-			printf("  %s %s\n", entry->key, addr_buf);
-		}
-		else
-			printf("  %s %s\n", entry->key, (const char *) entry->data);
-	}
-
-	printf("\n");
-}
 
 void
 print_interface_dot(struct lif_dict *collection, struct lif_interface *iface, struct lif_interface *parent)
@@ -147,7 +112,7 @@ list_interfaces(struct lif_dict *collection, struct match_options *opts)
 			continue;
 
 		if (opts->pretty_print)
-			print_interface(iface);
+			prettyprint_interface_eni(iface);
 		else if (opts->dot)
 			print_interface_dot(collection, iface, NULL);
 		else
@@ -330,7 +295,7 @@ ifquery_main(int argc, char *argv[])
 		if (match_opts.property != NULL)
 			print_interface_property(iface, match_opts.property);
 		else
-			print_interface(iface);
+			prettyprint_interface_eni(iface);
 	}
 
 	return EXIT_SUCCESS;

cmd/multicall.c

@@ -36,6 +36,10 @@ extern struct if_applet ifdown_applet;
 extern struct if_applet ifctrstat_applet;
 #endif
 
+#ifdef CONFIG_IFPARSE
+extern struct if_applet ifparse_applet;
+#endif
+
 struct if_applet ifupdown_applet;
 const struct if_applet *self_applet = NULL;
 
@@ -46,6 +50,9 @@ struct if_applet *applet_table[] = {
 #ifdef CONFIG_IFUPDOWN
 	&ifdown_applet,
 #endif
+#ifdef CONFIG_IFPARSE
+	&ifparse_applet,
+#endif
 #ifdef CONFIG_IFQUERY
 	&ifquery_applet,
 #endif

cmd/pretty-print-iface.c

@@ -0,0 +1,56 @@
+/*
+ * cmd/pretty-print-iface.c
+ * Purpose: interface pretty-printer (/e/n/i style)
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include "libifupdown/libifupdown.h"
+#include "cmd/multicall.h"
+#include "cmd/pretty-print-iface.h"
+
+void
+prettyprint_interface_eni(struct lif_interface *iface)
+{
+	if (!lif_lifecycle_query_dependents(&exec_opts, iface, iface->ifname))
+		return;
+
+	if (iface->is_auto)
+		printf("auto %s\n", iface->ifname);
+
+	printf("%s %s\n", iface->is_template ? "template" : "iface", iface->ifname);
+
+	struct lif_node *iter;
+	LIF_DICT_FOREACH(iter, &iface->vars)
+	{
+		struct lif_dict_entry *entry = iter->data;
+
+		if (!strcmp(entry->key, "address"))
+		{
+			struct lif_address *addr = entry->data;
+			char addr_buf[512];
+
+			if (!lif_address_unparse(addr, addr_buf, sizeof addr_buf, true))
+			{
+				printf("  # warning: failed to unparse address\n");
+				continue;
+			}
+
+			printf("  %s %s\n", entry->key, addr_buf);
+		}
+		else
+			printf("  %s %s\n", entry->key, (const char *) entry->data);
+	}
+
+	printf("\n");
+}

cmd/pretty-print-iface.h

@@ -0,0 +1,23 @@
+/*
+ * cmd/pretty-print-iface.h
+ * Purpose: interface pretty-printer (/e/n/i style)
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#ifndef IFUPDOWN_CMD_PRETTY_PRINT_IFACE_H__GUARD
+#define IFUPDOWN_CMD_PRETTY_PRINT_IFACE_H__GUARD
+
+#include "libifupdown/libifupdown.h"
+
+extern void prettyprint_interface_eni(struct lif_interface *iface);
+
+#endif

doc/ifparse.scd

@@ -0,0 +1,62 @@
+ifparse(8)
+
+# NAME
+
+ifparse - redisplay interface configuration in different formats
+
+# SYNOPSIS
+
+*ifparse* [<_options_>...] <_interfaces_...>
+
+*ifparse* -A|--all
+
+# DESCRIPTION
+
+*ifparse* is used to extract information from the interface configuration
+file.  It is intended to be used to translate the interface configuration
+stanzas between different formats.
+
+# OPTIONS
+
+*-a, --auto*
+	Only match interfaces that are marked as _auto_.
+
+*-h, --help*
+	Display supported options to ifquery.
+
+*-i, --interfaces* _FILE_
+	Use _FILE_ as the config database.
+
+*-F, --format* _FORMAT_
+	Use _FORMAT_ to determine what format to use.  *ifupdown* and
+	*yaml-raw* formats are available.
+
+*-I, --include* _PATTERN_
+	Include _PATTERN_ when matching against the config or state
+	database.
+
+*-U, --allow-undefined*
+	Create virtual interfaces for any interfaces not explicitly
+	defined in the configuration file.  This is primarily useful
+	for property queries.
+
+*-S, --state-file* _FILE_
+	Use _FILE_ as the state database.
+
+*-V, --version*
+	Print the ifupdown-ng version and exit.
+
+*-X, --exclude* _PATTERN_
+	Exclude _PATTERN_ when matching against the config or state
+	database.
+
+# SEE ALSO
+
+*ifup*(8)++
+*ifdown*(8)++
+*ifquery*(8)++
+*interfaces*(5)
+
+# AUTHORS
+
+Ariadne Conill <ariadne@dereferenced.org>

libifupdown/list.h

@@ -40,7 +40,7 @@ extern void lif_node_delete(struct lif_node *node, struct lif_list *list);
 	for ((iter) = (head); (iter) != NULL; (iter) = (iter)->next)
 
 #define LIF_LIST_FOREACH_SAFE(iter, iter_next, head) \
-	for ((iter) = (head), (iter_next) = (iter)->next; (iter) != NULL; (iter) = (iter_next), (iter_next) = (iter) != NULL ? (iter)->next : NULL)
+	for ((iter) = (head), (iter_next) = (iter) != NULL ? (iter)->next : NULL; (iter) != NULL; (iter) = (iter_next), (iter_next) = (iter) != NULL ? (iter)->next : NULL)
 
 #define LIF_LIST_FOREACH_REVERSE(iter, tail) \
 	for ((iter) = (tail); (iter) != NULL; (iter) = (iter)->prev)

libifupdown/yaml-base.c

@@ -0,0 +1,127 @@
+/*
+ * libifupdown/yaml-base.c
+ * Purpose: YAML implementation -- base
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#include <string.h>
+#include "libifupdown/libifupdown.h"
+#include "libifupdown/yaml-base.h"
+
+void
+lif_yaml_document_init(struct lif_yaml_node *doc, const char *name)
+{
+	memset(doc, '\0', sizeof *doc);
+	doc->value_type = LIF_YAML_OBJECT;
+
+	if (name != NULL)
+		doc->name = strdup(name);
+}
+
+struct lif_yaml_node *
+lif_yaml_document_new(const char *name)
+{
+	struct lif_yaml_node *doc = calloc(1, sizeof *doc);
+
+	lif_yaml_document_init(doc, name);
+	doc->malloced = true;
+
+	return doc;
+}
+
+struct lif_yaml_node *
+lif_yaml_node_new_boolean(const char *name, bool value)
+{
+	struct lif_yaml_node *node = calloc(1, sizeof *node);
+
+	node->malloced = true;
+	node->value_type = LIF_YAML_BOOLEAN;
+
+	if (name != NULL)
+		node->name = strdup(name);
+
+	node->value.bool_value = value;
+
+	return node;
+}
+
+struct lif_yaml_node *
+lif_yaml_node_new_string(const char *name, const char *value)
+{
+	struct lif_yaml_node *node = calloc(1, sizeof *node);
+
+	node->malloced = true;
+	node->value_type = LIF_YAML_STRING;
+
+	if (name != NULL)
+		node->name = strdup(name);
+
+	if (value != NULL)
+		node->value.str_value = strdup(value);
+
+	return node;
+}
+
+struct lif_yaml_node *
+lif_yaml_node_new_object(const char *name)
+{
+	struct lif_yaml_node *node = calloc(1, sizeof *node);
+
+	node->malloced = true;
+	node->value_type = LIF_YAML_OBJECT;
+
+	if (name != NULL)
+		node->name = strdup(name);
+
+	return node;
+}
+
+struct lif_yaml_node *
+lif_yaml_node_new_list(const char *name)
+{
+	struct lif_yaml_node *node = calloc(1, sizeof *node);
+
+	node->malloced = true;
+	node->value_type = LIF_YAML_LIST;
+
+	if (name != NULL)
+		node->name = strdup(name);
+
+	return node;
+}
+
+void
+lif_yaml_node_free(struct lif_yaml_node *node)
+{
+	struct lif_node *iter, *next;
+
+	LIF_LIST_FOREACH_SAFE(iter, next, node->children.head)
+	{
+		struct lif_yaml_node *iter_node = iter->data;
+
+		lif_yaml_node_free(iter_node);
+	}
+
+	free(node->name);
+
+	if (node->value_type == LIF_YAML_STRING)
+		free(node->value.str_value);
+
+	if (node->malloced)
+		free(node);
+}
+
+void
+lif_yaml_node_append_child(struct lif_yaml_node *parent, struct lif_yaml_node *child)
+{
+	lif_node_insert_tail(&child->node, child, &parent->children);
+}

libifupdown/yaml-base.h

@@ -0,0 +1,52 @@
+/*
+ * libifupdown/yaml-base.h
+ * Purpose: YAML implementation -- base
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#ifndef LIBIFUPDOWN_YAML_BASE_H__GUARD
+#define LIBIFUPDOWN_YAML_BASE_H__GUARD
+
+#include "libifupdown/libifupdown.h"
+
+/* this is a subset of types supported by our implementation */
+enum lif_yaml_value {
+	LIF_YAML_STRING,
+	LIF_YAML_LIST,
+	LIF_YAML_OBJECT,
+	LIF_YAML_BOOLEAN
+};
+
+struct lif_yaml_node {
+	struct lif_node node;
+
+	bool malloced;
+	char *name;
+	enum lif_yaml_value value_type;
+	union {
+		char *str_value;			/* for string nodes */
+		bool bool_value;			/* for boolean nodes */
+	} value;
+	struct lif_list children;	/* for list and object nodes */
+};
+
+extern void lif_yaml_document_init(struct lif_yaml_node *doc, const char *name);
+extern struct lif_yaml_node *lif_yaml_document_new(const char *name);
+
+extern struct lif_yaml_node *lif_yaml_node_new_boolean(const char *name, bool value);
+extern struct lif_yaml_node *lif_yaml_node_new_string(const char *name, const char *value);
+extern struct lif_yaml_node *lif_yaml_node_new_object(const char *name);
+extern struct lif_yaml_node *lif_yaml_node_new_list(const char *name);
+extern void lif_yaml_node_free(struct lif_yaml_node *node);
+extern void lif_yaml_node_append_child(struct lif_yaml_node *parent, struct lif_yaml_node *child);
+
+#endif

libifupdown/yaml-writer.c

@@ -0,0 +1,66 @@
+/*
+ * libifupdown/yaml-writer.c
+ * Purpose: YAML implementation -- writer
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include "libifupdown/libifupdown.h"
+#include "libifupdown/yaml-base.h"
+#include "libifupdown/yaml-writer.h"
+
+static const size_t INDENT_WIDTH = 2;
+
+static void
+lif_yaml_write_node(const struct lif_yaml_node *node, FILE *f, size_t indent, bool type_annotations)
+{
+	const struct lif_node *iter;
+
+	if (node->name != NULL)
+		fprintf(f, "%*s%s: ", (int) indent, "", node->name);
+
+	size_t child_indent = indent + INDENT_WIDTH;
+
+	switch (node->value_type)
+	{
+	case LIF_YAML_BOOLEAN:
+		fprintf(f, "%s%s\n", type_annotations ? "!!bool " : "", node->value.bool_value ? "true" : "false");
+		break;
+	case LIF_YAML_STRING:
+		fprintf(f, "%s%s\n", type_annotations ? "!!str " : "", node->value.str_value);
+		break;
+	case LIF_YAML_OBJECT:
+		fprintf(f, "\n");
+		break;
+	case LIF_YAML_LIST:
+		fprintf(f, "\n");
+		child_indent += INDENT_WIDTH;
+		break;
+	}
+
+	LIF_LIST_FOREACH(iter, node->children.head)
+	{
+		const struct lif_yaml_node *iter_node = iter->data;
+
+		if (node->value_type == LIF_YAML_LIST)
+			fprintf(f, "%*s-\n", (int) (child_indent - INDENT_WIDTH), "");
+
+		lif_yaml_write_node(iter_node, f, child_indent, type_annotations);
+	}
+}
+
+void
+lif_yaml_write(const struct lif_yaml_node *doc, FILE *f, bool type_annotations)
+{
+	lif_yaml_write_node(doc, f, 0, type_annotations);
+}

libifupdown/yaml-writer.h

@@ -0,0 +1,24 @@
+/*
+ * libifupdown/yaml-writer.h
+ * Purpose: YAML implementation -- writer
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#ifndef LIBIFUPDOWN_YAML_WRITER_H__GUARD
+#define LIBIFUPDOWN_YAML_WRITER_H__GUARD
+
+#include "libifupdown/libifupdown.h"
+#include "libifupdown/yaml-base.h"
+
+extern void lif_yaml_write(const struct lif_yaml_node *doc, FILE *f, bool type_annotations);
+
+#endif