Split into multiple files

For multiple reasons the program is now split:
- Make future porting to OpenBSD easier
- Assign header includes to individiual functions
- Make future program extensions easier
- Recompile only changed parts

ip.c

@@ -0,0 +1,69 @@
+#include <err.h>
+#include <ifaddrs.h>
+#include <netdb.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "util.h"
+
+const char *
+ipv4(const char *iface)
+{
+	struct ifaddrs *ifaddr, *ifa;
+	int s;
+	char host[NI_MAXHOST];
+
+	if (getifaddrs(&ifaddr) == -1) {
+		warn("Failed to get IPv4 address for interface %s", iface);
+		return NULL;
+	}
+
+	for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
+		if (ifa->ifa_addr == NULL) {
+			continue;
+		}
+		s = getnameinfo(ifa->ifa_addr, sizeof(struct sockaddr_in), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
+		if ((strcmp(ifa->ifa_name, iface) == 0) && (ifa->ifa_addr->sa_family == AF_INET)) {
+			if (s != 0) {
+				warnx("Failed to get IPv4 address for interface %s", iface);
+				return NULL;
+			}
+			return bprintf("%s", host);
+		}
+	}
+
+	freeifaddrs(ifaddr);
+
+	return NULL;
+}
+
+const char *
+ipv6(const char *iface)
+{
+	struct ifaddrs *ifaddr, *ifa;
+	int s;
+	char host[NI_MAXHOST];
+
+	if (getifaddrs(&ifaddr) == -1) {
+		warn("Failed to get IPv6 address for interface %s", iface);
+		return NULL;
+	}
+
+	for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
+		if (ifa->ifa_addr == NULL) {
+			continue;
+		}
+		s = getnameinfo(ifa->ifa_addr, sizeof(struct sockaddr_in6), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
+		if ((strcmp(ifa->ifa_name, iface) == 0) && (ifa->ifa_addr->sa_family == AF_INET6)) {
+			if (s != 0) {
+				warnx("Failed to get IPv6 address for interface %s", iface);
+				return NULL;
+			}
+			return bprintf("%s", host);
+		}
+	}
+
+	freeifaddrs(ifaddr);
+
+	return NULL;
+}