1 files changed, 64 insertions, 0 deletions
diff --git a/src/local_ip.c b/src/local_ip.c
new file mode 100644
index 00000000..3707559f
--- /dev/null
+++ b/src/local_ip.c
@@ -0,0 +1,64 @@
+/*
+ * Test if an IP address is assigned to the local system
+ *
+ * This uses the fact Linux will not allow binding to an address that
+ * is not on the system.  It is much faster than scanning all the
+ * interface addresses.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+int main(int argc, char **argv)
+{
+	int af, s;
+
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s x.x.x.x\n", argv[0]);
+		return -1;
+	}
+
+	af = strchr(argv[1], ':') ? AF_INET6 : AF_INET;
+	s = socket(af, SOCK_STREAM, 0);
+	if (s < 0) {
+		perror("socket");
+		return -1;
+	}
+
+	if (af == AF_INET) {
+		struct sockaddr_in sin = {
+			.sin_family = AF_INET,
+		};
+
+		if (inet_pton(af, argv[1], &sin.sin_addr) <= 0) {
+			fprintf(stderr, "%s: invalid address\n", argv[1]);
+			return -1;
+		}
+
+		if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
+			if (errno == EADDRNOTAVAIL)
+				return 1;
+			perror("bind");
+			return -1;
+		}
+	} else {
+		struct sockaddr_in6 sin6;
+
+		if (inet_pton(af, argv[1], &sin6.sin6_addr) <= 0) {
+			fprintf(stderr, "%s: invalid address\n", argv[1]);
+			return -1;
+		}
+
+		if (bind(s, (struct sockaddr *)&sin6, sizeof(sin6)) < 0) {
+			if (errno == EADDRNOTAVAIL)
+				return 1;
+			perror("bind");
+			return -1;
+		}
+	}
+	return 0;
+}