cmd: start work on an ifquery command

cmd/ifquery.c

@@ -0,0 +1,71 @@
+/*
+ * cmd/ifquery.c
+ * Purpose: look up information in /etc/network/interfaces
+ *
+ * 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"
+
+
+void
+print_interface(struct lif_interface *iface)
+{
+	if (iface->is_auto)
+		printf("auto %s\n", iface->ifname);
+
+	printf("iface %s", iface->ifname);
+
+	if (iface->is_loopback)
+		printf(" inet loopback\n");
+	else if (iface->is_dhcp)
+		printf(" inet dhcp\n");
+	else
+		printf("\n");
+
+	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);
+	}
+}
+
+
+int
+main(int argc, char *argv[])
+{
+	struct lif_dict collection;
+
+	lif_interface_collection_init(&collection);
+
+	struct lif_interface *if_lo = lif_interface_collection_find(&collection, "lo");
+	print_interface(if_lo);
+
+	return EXIT_SUCCESS;
+}