fw/udp.c (902aa40) - mips_sys · BlinkenArea

udp.c

/* MIPS I system
 * Copyright 2011-2012 Stefan Schuermans <stefan@blinkenarea.org>
 * Copyleft GNU public license V2 or later
 *          http://www.gnu.org/copyleft/gpl.html
 */

#include "config.h"
#include "checksum.h"
#include "ethernet.h"
#include "dhcp.h"
#include "ip.h"
#include "macros.h"
#include "nethelp.h"
#include "udp.h"

// some kind of "token bucket" for UDP echo
#define UDP_ECHO_TICKS 10 ///< allowed rate of UDP echo replies (in 200ms)
static unsigned int udp_echo_tick_cnt = 0; ///< tick counter
#define UDP_ECHO_REPLIES_MAX 3 ///< maximum value for udp_echo_replies
static unsigned int udp_echo_replies = 0; // # of allowed UDP echo replies

/// tick procedure - call every 200ms
void udp_tick200(void)
{
  // count ticks
  udp_echo_tick_cnt++;
  // time to allow one reply more
  if (udp_echo_tick_cnt >= UDP_ECHO_TICKS) {
    udp_echo_tick_cnt = 0;

// increase reply count if not at maximum
    if (udp_echo_replies < UDP_ECHO_REPLIES_MAX)
      udp_echo_replies++;
  }
}

/**
 * @brief process a received UDP echo packet
 * @param[in] ptr pointer to data of packet
 * @param[in] sz size of packet
 */
static void udp_echo_recv(void *ptr, unsigned int sz)
{
  struct udp_packet *udp_pack;

udp_pack = ptr;

// source port is UDP echo port
  if (udp_pack->udp_hdr.src_port == htons(7))
    // ignore this packet
    //  - UDP echo answer to another UDP echo port will result
    //    in endless echoing
    return;

// only reply with allowed packet rate
  if (udp_echo_replies <= 0)
    return;
  udp_echo_replies--;

// send an UDP echo
  //  - use same buffer to send reply
  //  - this saves us from allocating a new buffer
  //  - this saves us from copying the data
  udp_pack->udp_hdr.dest_port = udp_pack->udp_hdr.src_port; // to source port
  udp_pack->udp_hdr.src_port = htons(7); // UDP echo port
  ip_cpy( udp_pack->ip_hdr.dest, udp_pack->ip_hdr.src); // to source IP
  udp_send(udp_pack, sz);
}

/**
 * @brief process a received UDP packet
 * @param[in] ptr pointer to data of packet
 * @param[in] sz size of packet
 */
void udp_recv(void *ptr, unsigned int sz)
{
  struct udp_packet *udp_pack;
  unsigned int len;

// packet too short
  if (sz < sizeof(struct udp_packet))
    return;

udp_pack = ptr;

// ignore packets sent from or to port 0 (not allowed by RFC)
  if (udp_pack->udp_hdr.src_port == htons(0) ||
      udp_pack->udp_hdr.dest_port == htons(0))
    return;

// check total length
  len = sizeof(struct ethernet_header) + sizeof(struct ip_header) +
        ntohs(udp_pack->udp_hdr.length); // length according to UDP header
  if (sz < len) // packet is truncated
    return;
  sz = len; // remove IP padding from packet (maybe sz > len)

// test checksum
  if (checksum(&udp_pack->ip_hdr.src,
                sz - sizeof(struct ethernet_header)
                   - sizeof(struct ip_header ) + 8,
                0x0011,
                ntohs(udp_pack->udp_hdr.length)))
    return;

// branch according to destination port
  switch (ntohs(udp_pack->udp_hdr.dest_port)) {
    // UDP echo
    case 7:
      udp_echo_recv(ptr, sz);
      break;
    // DHCP
    case 68:
      dhcp_recv(ptr, sz);
      break;
  }
}

/**
 * @brief send a UDP packet
 * @param[in] ptr pointer to data of packet
 * @param[in] sz size of packet
 *
 * ptr must point to a udp_packet
 * with ip_hdr.proto ip_hdr.dest, udp_hdr.src_port and udp_hdr.dest_port
 * already initialized
 */
void udp_send(void *ptr, unsigned int sz)
{
  struct udp_packet *udp_pack;
  unsigned int chk;

// packet too short
  if (sz < sizeof(struct udp_packet))
    return;

udp_pack = ptr;

// fill in header values
  udp_pack->udp_hdr.length = htons(sz - sizeof(struct ethernet_header)
                                      - sizeof(struct ip_header));
  udp_pack->udp_hdr.chk = 0x0000;
  /* put IP already here into IP header
     because it is needed for calculation of UDP checksum */
  ip_cpy(udp_pack->ip_hdr.src, config_ip.ip);

// generate checksum
  chk = checksum(&udp_pack->ip_hdr.src,
                 sz - sizeof(struct ethernet_header )
                    - sizeof(struct ip_header ) + 8,
                 0x0011,
                 ntohs(udp_pack->udp_hdr.length));
  udp_pack->udp_hdr.chk = htons(chk);

// send UDP packet
  udp_pack->ip_hdr.proto = 0x11; // UDP
  ip_send(udp_pack, sz);
}

mips_sys

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