1 files changed, 116 insertions, 0 deletions
diff --git a/libs/libnet/dns.c b/libs/libnet/dns.c
new file mode 100644
index 0000000..f20f33a
--- /dev/null
+++ b/libs/libnet/dns.c
@@ -0,0 +1,116 @@
+// MIT License, Copyright (c) 2020 Marvin Borner
+// TODO: Less magic, auto xld splitting
+// TODO: DNS cache
+
+#include <def.h>
+#include <libnet/net.h>
+#include <libnet/socket.h>
+#include <mem.h>
+#include <print.h>
+#include <random.h>
+#include <str.h>
+
+static u32 dns_ip_addr = ip(1, 1, 1, 1);
+
+struct dns_packet {
+	u16 qid;
+	u16 flags;
+	u16 questions;
+	u16 answers;
+	u16 authorities;
+	u16 additional;
+	u8 data[];
+} __attribute__((packed));
+
+static u32 part_count(const char *name)
+{
+	u32 cnt = 0;
+	for (u32 i = 0; i < strlen(name); i++) {
+		if (name[i] == '.')
+			cnt++;
+	}
+	return cnt + 1;
+}
+
+static u32 part_len(const char *name, u32 index)
+{
+	const char *data = name;
+
+	u32 cnt = 0;
+	for (u32 i = 0; i < strlen(name); i++) {
+		if (cnt == index) {
+			data += i;
+			break;
+		}
+
+		if (name[i] == '.')
+			cnt++;
+	}
+
+	for (cnt = 0; cnt < strlen(data); cnt++) {
+		if (data[cnt] == '.' || data[cnt] == '\0')
+			break;
+	}
+
+	return cnt;
+}
+
+static void dns_make_packet(struct dns_packet *packet, const char *name)
+{
+	packet->qid = htons(rand());
+	packet->flags = htons(0x0100); // Standard query
+	packet->questions = htons(1);
+	packet->answers = htons(0);
+	packet->authorities = htons(0);
+	packet->additional = htons(0);
+
+	u8 *data = packet->data;
+	u32 cnt = 0;
+	for (u32 i = 0; i < part_count(name) * 2; i += 2) {
+		data[cnt] = part_len(name, i / 2);
+		memcpy(&data[cnt + 1], &name[cnt], data[cnt]);
+		cnt += data[cnt] + 1;
+	}
+
+	packet->data[cnt + 0] = 0x00; // Name end
+	packet->data[cnt + 2] = 0x01; // A
+	packet->data[cnt + 4] = 0x01; // IN
+}
+
+static u32 dns_handle_packet(struct dns_packet *packet)
+{
+	u16 flags = htons(packet->flags);
+	u8 reply_code = flags & 0xf;
+	if (reply_code != DNS_NOERROR) {
+		printf("DNS error: %d\n", reply_code);
+		return 0;
+	}
+
+	u8 *start = &packet->data[1] + strlen((char *)&packet->data[1]);
+	printf("TTL of %s: %ds\n", &packet->data[1], (u32)start[14]);
+	u8 *ip = &start[17];
+	printf("IP: %d.%d.%d.%d\n", ip[0], ip[1], ip[2], ip[3]);
+	return ip(ip[0], ip[1], ip[2], ip[3]);
+}
+
+u32 dns_request(const char *name)
+{
+	struct socket *socket = net_open(S_UDP);
+	if (!socket || !net_connect(socket, dns_ip_addr, 53, NET_TIMEOUT) || part_count(name) == 1)
+		return 0;
+
+	u32 length = sizeof(struct dns_packet) + strlen(name) + part_count(name) + 4;
+	struct dns_packet *packet = malloc(length);
+	memset(packet, 0, length);
+	dns_make_packet(packet, name);
+	net_send(socket, packet, length);
+	free(packet);
+
+	u8 buf[1024] = { 0 };
+	int l = net_receive(socket, buf, 1024, NET_TIMEOUT);
+	net_close(socket);
+	if (l > 0)
+		return dns_handle_packet((void *)buf);
+	else
+		return 0;
+}