add testcase for ipv4-mapped ipv6 address

tests/test_v4_in_v6.c

@@ -0,0 +1,42 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+
+static void v4_to_v6(const struct in_addr *v4, struct in6_addr *v6) {
+	memset(v6, 0, sizeof(*v6));
+	v6->s6_addr[10]=0xff;
+	v6->s6_addr[11]=0xff;
+	memcpy(&v6->s6_addr[12], &v4->s_addr, 4);
+}
+
+int main(void) {
+	struct addrinfo *result;
+	struct addrinfo *res;
+	const struct addrinfo hints = { .ai_family = AF_INET };
+	int error, sock;
+
+	/* resolve the domain name into a list of addresses */
+	error = getaddrinfo("www.example.com", NULL, &hints, &result);
+	if (error != 0)	{
+		fprintf(stderr, "error in getaddrinfo: %s\n", gai_strerror(error));
+		return EXIT_FAILURE;
+	}
+	if((sock=socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1) {
+		perror("socket");
+		return EXIT_FAILURE;
+	}
+	struct sockaddr_in6 a = { .sin6_family = AF_INET6,
+	                          .sin6_port = htons(80) };
+	v4_to_v6(&((struct sockaddr_in *)result->ai_addr)->sin_addr, &a.sin6_addr);
+	freeaddrinfo(result);
+
+	if((error = connect(sock, (struct sockaddr *)&a, sizeof(a))) == -1) {
+		perror("connect");
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_SUCCESS;
+}