udpsvd: more work on it. works in limited testing.

1 files changed, 156 insertions, 0 deletions

diff --git a/ipsvd/udp_io.c b/ipsvd/udp_io.c
new file mode 100644
index 0000000..68999d4
--- /dev/null
+++ b/ipsvd/udp_io.c
@@ -0,0 +1,156 @@
+/* Thus far used only by udpsvd.c */
+
+void socket_want_pktinfo(int fd);
+ssize_t send_to_from(int fd, void *buf, size_t len, int flags,
+		const struct sockaddr *from, const struct sockaddr *to,
+		socklen_t tolen);
+ssize_t recv_from_to(int fd, void *buf, size_t len, int flags,
+		struct sockaddr *from, struct sockaddr *to,
+		socklen_t sa_size);
+
+/*
+ * This asks kernel to let us know dst addr/port of incoming packets
+ * We don't check for errors here. Not supported == won't be used
+ */
+void
+socket_want_pktinfo(int fd)
+{
+#ifdef IP_PKTINFO
+	setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &const_int_1, sizeof(int));
+#endif
+#ifdef IPV6_PKTINFO
+	setsockopt(fd, IPPROTO_IPV6, IPV6_PKTINFO, &const_int_1, sizeof(int));
+#endif
+}
+
+
+ssize_t
+send_to_from(int fd, void *buf, size_t len, int flags,
+		const struct sockaddr *from, const struct sockaddr *to,
+		socklen_t tolen)
+{
+#ifndef IP_PKTINFO
+	return sendto(fd, buf, len, flags, to, tolen);
+#else
+	struct iovec iov[1];
+	struct msghdr msg;
+	char cbuf[LSA_SIZEOF_SA];
+	/* actually, max(sizeof(in_pktinfo),sizeof(in6_pktinfo)) */
+	struct cmsghdr* cmsgptr;
+
+	if (from->sa_family != AF_INET
+#if ENABLE_FEATURE_IPV6
+	 && from->sa_family != AF_INET6
+#endif
+	) {
+		/* ANY local address */
+		return sendto(fd, buf, len, flags, to, tolen);
+	}
+	
+	/* man recvmsg and man cmsg is needed to make sense of code below */
+
+	iov[0].iov_base = buf;
+	iov[0].iov_len = len;
+
+	memset(cbuf, 0, sizeof(cbuf));
+
+	memset(&msg, 0, sizeof(msg));
+	msg.msg_name = (void *)(struct sockaddr *)to; /* or compiler will annoy us */
+	msg.msg_namelen = tolen;
+	msg.msg_iov = iov;
+	msg.msg_iovlen = 1;
+	msg.msg_control = cbuf;
+	msg.msg_controllen = sizeof(cbuf);
+	msg.msg_flags = flags;
+
+	cmsgptr = CMSG_FIRSTHDR(&msg);
+	if (to->sa_family == AF_INET && from->sa_family == AF_INET) {
+		struct in_pktinfo *pktptr;
+		cmsgptr->cmsg_level = IPPROTO_IP;
+		cmsgptr->cmsg_type = IP_PKTINFO;
+		cmsgptr->cmsg_len = CMSG_LEN(sizeof(struct in_pktinfo));
+		pktptr = (struct in_pktinfo *)(CMSG_DATA(cmsgptr));
+		/* pktptr->ipi_ifindex = 0; -- already done by memset(cbuf...) */
+		pktptr->ipi_spec_dst = ((struct sockaddr_in*)from)->sin_addr;
+	}
+#if ENABLE_FEATURE_IPV6 && defined(IP6_PKTINFO)
+	else if (to->sa_family == AF_INET6 && from->sa_family == AF_INET6) {
+		struct in6_pktinfo *pktptr;
+		cmsgptr->cmsg_level = IPPROTO_IPV6;
+		cmsgptr->cmsg_type = IP6_PKTINFO;
+		cmsgptr->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo));
+		pktptr = (struct in6_pktinfo *)(CMSG_DATA(cmsgptr));
+		/* pktptr->ipi6_ifindex = 0; -- already done by memset(cbuf...) */
+		pktptr->ipi6_addr = ((struct sockaddr_in6*)from)->sin6_addr;
+	}
+#endif
+	return sendmsg(fd, &msg, flags);
+#endif
+}
+
+/* NB: this will never set port# in *to! */
+ssize_t
+recv_from_to(int fd, void *buf, size_t len, int flags,
+		struct sockaddr *from, struct sockaddr *to,
+		socklen_t sa_size)
+{
+#ifndef IP_PKTINFO
+	return recvfrom(fd, buf, len, flags, from, &sa_size);
+#else
+	/* man recvmsg and man cmsg is needed to make sense of code below */
+	struct iovec iov[1];
+	union {
+		char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo))];
+		char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
+	} u;
+	struct cmsghdr *cmsgptr;
+	struct msghdr msg;
+	socklen_t recv_length;
+
+	iov[0].iov_base = buf;
+	iov[0].iov_len = len;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.msg_name = (struct sockaddr *)from;
+	msg.msg_namelen = sa_size;
+	msg.msg_iov = iov;
+	msg.msg_iovlen = 1;
+	msg.msg_control = &u;
+	msg.msg_controllen = sizeof(u);
+
+	recv_length = recvmsg(fd, &msg, flags);
+	if (recv_length < 0)
+		return recv_length;
+
+	/* Here we try to retrieve destination IP and memorize it */
+	memset(to, 0, sa_size);
+	for (cmsgptr = CMSG_FIRSTHDR(&msg);
+			cmsgptr != NULL;
+			cmsgptr = CMSG_NXTHDR(&msg, cmsgptr)
+	) {
+		if (cmsgptr->cmsg_level == IPPROTO_IP
+		 && cmsgptr->cmsg_type == IP_PKTINFO
+		) {
+#define pktinfo(cmsgptr) ( (struct in_pktinfo*)(CMSG_DATA(cmsgptr)) )
+			to->sa_family = AF_INET;
+			((struct sockaddr_in*)to)->sin_addr = pktinfo(cmsgptr)->ipi_addr;
+			/* ((struct sockaddr_in*)to)->sin_port = 123; */
+#undef pktinfo
+			break;
+		}
+#if ENABLE_FEATURE_IPV6 && defined(IP6_PKTINFO)
+		if (cmsgptr->cmsg_level == IPPROTO_IPV6
+		 && cmsgptr->cmsg_type == IP6_PKTINFO
+		) {
+#define pktinfo(cmsgptr) ( (struct in6_pktinfo*)(CMSG_DATA(cmsgptr)) )
+			to->sa_family = AF_INET6;
+			((struct sockaddr_in6*)to)->sin6_addr = pktinfo(cmsgptr)->ipi6_addr;
+			/* ((struct sockaddr_in6*)to)->sin6_port = 123; */
+#undef pktinfo
+			break;
+		}
+#endif
+	}
+	return recv_length;
+#endif
+}