File content as of revision 61:aad055f1b0d1:

#include <stdint.h>

#include    "log.h"
#include    "net.h"
#include "action.h"
#include    "ip4.h"
#include   "dhcp.h"
#include  "echo4.h"

#define ECHO_REPLY   0
#define UNREACHABLE  3
#define REDIRECT     5
#define ECHO_REQUEST 8

__packed struct header
{
    uint8_t  type;
    uint8_t  code;
    uint16_t checksum;
};
static uint8_t  type;
static uint8_t  code;
static uint16_t checksum;
static uint16_t calculated;

static void logType(uint16_t type)
{
    switch (type)
    {
        case ECHO_REPLY:   Log ("Echo Reply"           ); break;
        case ECHO_REQUEST: Log ("Echo Request"         ); break;
        default:           LogF("Unknown type %d", type); break;
    }
}
static void logHeader()
{            
    if (NetTraceVerbose)
    {
        Log ("ICMP4 header\r\n");
        LogF("  Type           "); logType(type); Log("\r\n");
        LogF("  Code           %u\r\n",    code);
        LogF("  Checksum (hex) %04hX\r\n", checksum);
        LogF("  Calculated     %04hX\r\n", calculated);
    }
    else
    {
        Log("ICMP4 header ");
        logType(type);        
        Log("\r\n");
    }
}
static void readHeader(void* pPacket, int size)
{
    struct header* pHeader = (struct header*)pPacket;
          type =             pHeader->type;
          code =             pHeader->code;
      checksum = NetToHost16(pHeader->checksum);
    calculated = NetCheckSum(size, pPacket);
}
static void writeHeader(void* pPacket, int size)
{    
    struct header* pHeader = (struct header*)pPacket;
    pHeader->type     = type;
    pHeader->code     = code;
    pHeader->checksum = 0;
    pHeader->checksum = NetCheckSum(size, pPacket);
    calculated = 0;
}
static void (*pTraceBack)(void);
static void trace()
{
    pTraceBack();
    logHeader();
}
int Icmp4HandleReceivedPacket(void (*traceback)(void), void* pPacketRx, int sizeRx, void* pPacketTx, int* pSizeTx, uint32_t* pSrcIp, uint32_t* pDstIp)
{
    pTraceBack = traceback;

    readHeader(pPacketRx, sizeRx);
    
    int dataLengthRx =           sizeRx - sizeof(struct header);
    int dataLengthTx =         *pSizeTx - sizeof(struct header);
    char* pPayloadRx = (char*)pPacketRx + sizeof(struct header);
    char* pPayloadTx = (char*)pPacketTx + sizeof(struct header);
    
    int action = DO_NOTHING;
    switch (type)
    {
        case ECHO_REQUEST:
            action = Echo4HandleRequest(trace, &type, &code, pPayloadRx, dataLengthRx, pPayloadTx, &dataLengthTx);
            break;
        case UNREACHABLE:
            return DO_NOTHING;
        case REDIRECT:
            return DO_NOTHING;
        default:
            LogTimeF("ICMP4 packet type %d unknown\r\n", type);
            return DO_NOTHING;
    }
    if (!action) return DO_NOTHING;
    
    *pDstIp = *pSrcIp;
    *pSrcIp = DhcpLocalIp;

    *pSizeTx = sizeof(struct header) + dataLengthTx;
    
    writeHeader(pPacketTx, *pSizeTx);
    
    if (ActionGetTracePart(action)) logHeader();
    
    return action;
}