MINOR: sock_inet: implement sock_inet_get_dst()

This one is common to the TCPv4 and UDPv4 code, it retrieves the
destination address of a socket, taking care of the possiblity that for
an incoming connection the traffic was possibly redirected. The TCP and
UDP definitions were updated to rely on it and remove duplicated code.
diff --git a/src/proto_tcp.c b/src/proto_tcp.c
index 17da403..675c686 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -65,7 +65,7 @@
 	.unbind_all = unbind_all_listeners,
 	.enable_all = enable_all_listeners,
 	.get_src = sock_get_src,
-	.get_dst = tcp_get_dst,
+	.get_dst = sock_inet_get_dst,
 	.pause = tcp_pause_listener,
 	.add = tcpv4_add_listener,
 	.addrcmp = sock_inet4_addrcmp,
@@ -91,7 +91,7 @@
 	.unbind_all = unbind_all_listeners,
 	.enable_all = enable_all_listeners,
 	.get_src = sock_get_src,
-	.get_dst = tcp_get_dst,
+	.get_dst = sock_get_dst,
 	.pause = tcp_pause_listener,
 	.add = tcpv6_add_listener,
 	.addrcmp = sock_inet6_addrcmp,
@@ -581,38 +581,6 @@
 	return SF_ERR_NONE;  /* connection is OK */
 }
 
-
-/*
- * Retrieves the original destination address for the socket <fd>, with <dir>
- * indicating if we're a listener (=0) or an initiator (!=0). In the case of a
- * listener, if the original destination address was translated, the original
- * address is retrieved. It returns 0 in case of success, -1 in case of error.
- * The socket's source address is stored in <sa> for <salen> bytes.
- */
-int tcp_get_dst(int fd, struct sockaddr *sa, socklen_t salen, int dir)
-{
-	if (dir)
-		return getpeername(fd, sa, &salen);
-	else {
-		int ret = getsockname(fd, sa, &salen);
-
-		if (ret < 0)
-			return ret;
-
-#if defined(USE_TPROXY) && defined(SO_ORIGINAL_DST)
-		/* For TPROXY and Netfilter's NAT, we can retrieve the original
-		 * IPv4 address before DNAT/REDIRECT. We must not do that with
-		 * other families because v6-mapped IPv4 addresses are still
-		 * reported as v4.
-		 */
-		if (((struct sockaddr_storage *)sa)->ss_family == AF_INET
-		    && getsockopt(fd, SOL_IP, SO_ORIGINAL_DST, sa, &salen) == 0)
-			return 0;
-#endif
-		return ret;
-	}
-}
-
 /* Returns true if the passed FD corresponds to a socket bound with LI_O_FOREIGN
  * according to the various supported socket options. The socket's address family
  * must be passed in <family>.
diff --git a/src/proto_udp.c b/src/proto_udp.c
index 0bd903f..96b878a 100644
--- a/src/proto_udp.c
+++ b/src/proto_udp.c
@@ -87,7 +87,7 @@
 	.unbind_all = unbind_all_listeners,
 	.enable_all = enable_all_listeners,
 	.get_src = udp6_get_src,
-	.get_dst = udp_get_dst,
+	.get_dst = udp6_get_dst,
 	.pause = udp_pause_listener,
 	.add = udp6_add_listener,
 	.addrcmp = sock_inet6_addrcmp,
@@ -142,34 +142,27 @@
 {
 	int ret;
 
-	if (dir)
-		ret = getpeername(fd, sa, &salen);
-	else {
-		ret = getsockname(fd, sa, &salen);
+	ret = sock_inet_get_dst(fd, sa, salen, dir);
+	if (!ret)
+		sa->sa_family = AF_CUST_UDP4;
 
-		if (ret < 0)
-			return ret;
+	return ret;
+}
 
-#if defined(USE_TPROXY) && defined(SO_ORIGINAL_DST)
-		/* For TPROXY and Netfilter's NAT, we can retrieve the original
-		 * IPv4 address before DNAT/REDIRECT. We must not do that with
-		 * other families because v6-mapped IPv4 addresses are still
-		 * reported as v4.
-		 */
-		if (((struct sockaddr_storage *)sa)->ss_family == AF_INET
-		    && getsockopt(fd, SOL_IP, SO_ORIGINAL_DST, sa, &salen) == 0) {
-			sa->sa_family = AF_CUST_UDP4;
-			return 0;
-		}
-#endif
-	}
+/*
+ * Retrieves the original destination address for the socket <fd>, with <dir>
+ * indicating if we're a listener (=0) or an initiator (!=0). In the case of a
+ * listener, if the original destination address was translated, the original
+ * address is retrieved. It returns 0 in case of success, -1 in case of error.
+ * The socket's source address is stored in <sa> for <salen> bytes.
+ */
+int udp6_get_dst(int fd, struct sockaddr *sa, socklen_t salen, int dir)
+{
+	int ret;
 
-	if (!ret) {
-		if (sa->sa_family == AF_INET)
-			sa->sa_family = AF_CUST_UDP4;
-		else if (sa->sa_family == AF_INET6)
-			sa->sa_family = AF_CUST_UDP6;
-	}
+	ret = sock_get_dst(fd, sa, salen, dir);
+	if (!ret)
+		sa->sa_family = AF_CUST_UDP6;
 
 	return ret;
 }
diff --git a/src/sock_inet.c b/src/sock_inet.c
index 21a024a..b82a920 100644
--- a/src/sock_inet.c
+++ b/src/sock_inet.c
@@ -75,3 +75,34 @@
 
 	return memcmp(&a6->sin6_addr, &b6->sin6_addr, sizeof(a6->sin6_addr));
 }
+
+/*
+ * Retrieves the original destination address for the socket <fd> which must be
+ * of family AF_INET (not AF_INET6), with <dir> indicating if we're a listener
+ * (=0) or an initiator (!=0). In the case of a listener, if the original
+ * destination address was translated, the original address is retrieved. It
+ * returns 0 in case of success, -1 in case of error. The socket's source
+ * address is stored in <sa> for <salen> bytes.
+ */
+int sock_inet_get_dst(int fd, struct sockaddr *sa, socklen_t salen, int dir)
+{
+	if (dir)
+		return getpeername(fd, sa, &salen);
+	else {
+		int ret = getsockname(fd, sa, &salen);
+
+		if (ret < 0)
+			return ret;
+
+#if defined(USE_TPROXY) && defined(SO_ORIGINAL_DST)
+		/* For TPROXY and Netfilter's NAT, we can retrieve the original
+		 * IPv4 address before DNAT/REDIRECT. We must not do that with
+		 * other families because v6-mapped IPv4 addresses are still
+		 * reported as v4.
+		 */
+		if (getsockopt(fd, SOL_IP, SO_ORIGINAL_DST, sa, &salen) == 0)
+			return 0;
+#endif
+		return ret;
+	}
+}