Kernel/LibC/Networking: Be able to send UDP messages

Now it can send UDP messages to a specific IP address and libc has
enough to create a basic UDP ECHO server, that is kinda cool.

1 files changed, 67 insertions, 0 deletions

diff --git a/network/ipv4.c b/network/ipv4.c
index e7ef2c2..099aa0d 100644
--- a/network/ipv4.c
+++ b/network/ipv4.c
@@ -1,11 +1,78 @@
 #include <assert.h>
+#include <kmalloc.h>
+#include <network/arp.h>
 #include <network/bytes.h>
+#include <network/ethernet.h>
 #include <network/ipv4.h>
 #include <network/udp.h>
 #include <string.h>
 
+uint16_t ip_checksum(void *vdata, size_t length) {
+  // Cast the data pointer to one that can be indexed.
+  char *data = (char *)vdata;
+
+  // Initialise the accumulator.
+  uint32_t acc = 0xffff;
+
+  // Handle complete 16-bit blocks.
+  for (size_t i = 0; i + 1 < length; i += 2) {
+    uint16_t word;
+    memcpy(&word, data + i, 2);
+    acc += ntohs(word);
+    if (acc > 0xffff) {
+      acc -= 0xffff;
+    }
+  }
+
+  // Handle any partial block at the end of the data.
+  if (length & 1) {
+    uint16_t word = 0;
+    memcpy(&word, data + length - 1, 1);
+    acc += ntohs(word);
+    if (acc > 0xffff) {
+      acc -= 0xffff;
+    }
+  }
+
+  // Return the checksum in network byte order.
+  return htons(~acc);
+}
+
+extern uint8_t ip_address[4];
+void send_ipv4_packet(uint32_t ip, uint8_t protocol, const uint8_t *payload,
+                      uint16_t length) {
+  uint8_t header[20] = {0};
+  header[0] = (4 /*version*/ << 4) | (5 /*IHL*/);
+  *((uint16_t *)(header + 2)) = htons(length + 20);
+  header[8 /*TTL*/] = 0xF8;
+  header[9] = protocol;
+
+  memcpy(header + 12 /*src_ip*/, ip_address, sizeof(uint8_t[4]));
+  memcpy(header + 16, &ip, sizeof(uint8_t[4]));
+
+  *((uint16_t *)(header + 10 /*checksum*/)) = ip_checksum(header, 20);
+  uint16_t packet_length = length + 20;
+  uint8_t *packet = kmalloc(packet_length);
+  memcpy(packet, header, 20);
+  memcpy(packet + 20, payload, length);
+
+  uint8_t mac[6];
+  uint8_t ip_copy[4]; // TODO: Do I need to do this?
+  memcpy(ip_copy, &ip, sizeof(uint8_t[4]));
+  get_mac_from_ip(ip_copy, mac);
+  send_ethernet_packet(mac, 0x0800, packet, packet_length);
+  kfree(packet);
+}
+
 void handle_ipv4(const uint8_t *payload, uint32_t packet_length) {
   assert(packet_length > 4);
+
+  uint16_t saved_checksum = *(uint16_t *)(payload + 10);
+  *(uint16_t *)(payload + 10) = 0;
+  uint16_t calc_checksum = ip_checksum((uint8_t *)payload, 20);
+  *(uint16_t *)(payload + 10) = saved_checksum;
+  assert(calc_checksum == saved_checksum);
+
   uint8_t version = (*payload & 0xF0) >> 4;
   uint8_t IHL = (*payload & 0xF);
   kprintf("version: %x\n", version);