demonstrate DNS request receiving

1 files changed, 103 insertions, 0 deletions

diff --git a/src/receive.c b/src/receive.c
new file mode 100644
index 0000000..eb5fdb2
--- /dev/null
+++ b/src/receive.c
@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2009 - 2012 Marco Peereboom <marco@peereboom.us>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <err.h>
+
+#include <netinet/in.h>
+
+#include <arpa/inet.h>
+
+#include <ldns/ldns.h>
+
+#define INBUF_SIZE 4096
+#define PORT 53
+
+struct sockaddr		paddr;
+socklen_t		plen = (socklen_t)sizeof(paddr);
+
+int
+udp_bind(int sock, uint16_t port)
+{
+	struct sockaddr_in		addr;
+	in_addr_t			maddr = INADDR_ANY;
+
+	addr.sin_family = AF_INET;
+	addr.sin_port = (in_port_t) htons((uint16_t)port);
+	addr.sin_addr.s_addr = maddr;
+	return (bind(sock, (struct sockaddr*)&addr, (socklen_t) sizeof(addr)));
+}
+
+int
+socket_create(uint16_t port) {
+	int so = socket(AF_INET, SOCK_DGRAM, 0);
+	if (so == -1)
+		err(1, "can't open socket");
+	if (udp_bind(so, port))
+		err(1, "can't udp bind");
+	return so;
+}
+
+void
+printpacket(ldns_pkt *pkt)
+{
+	char			*str = ldns_pkt2str(pkt);
+	
+	if (str) {
+		printf("%s", str);
+		LDNS_FREE(str);
+	} else
+		warnx("could not convert packet to string");
+}
+
+void receive_and_print(int so) {
+	uint8_t			inbuf[INBUF_SIZE];
+	ssize_t			nb;
+	ldns_status		status;
+	ldns_pkt		*query_pkt;
+	
+	nb = recvfrom(so, inbuf, INBUF_SIZE, 0, &paddr, &plen);
+	if (nb == -1) {
+		if (errno == EINTR || errno == EAGAIN)
+			return;
+		else
+			err(EXIT_FAILURE, "recvfrom");
+	}
+
+	status = ldns_wire2pkt(&query_pkt, inbuf, (size_t)nb);
+	if (status != LDNS_STATUS_OK) {
+		warnx("bad packet: %s", ldns_get_errorstr_by_id(status));
+		return;
+	} else {
+		puts("received packet:");
+		printpacket(query_pkt);
+	}
+
+	ldns_pkt_free(query_pkt);
+}
+
+int main(int argc, char **argv) {
+	int so;
+	
+	if (geteuid())
+		errx(1, "need root privileges");
+
+	so = socket_create(PORT);
+
+	while (1)
+		receive_and_print(so);
+}