source: libpacketdump/ip_6.cc @ 2d96bf2

#include <stdio.h>
#include <inttypes.h>
#include <dlfcn.h>
#include <map>
#include "libpacketdump.h"
#include <netinet/tcp.h>
#include <netinet/in.h>
#include <assert.h>
#include <netdb.h>

#define SAFE(x) \
        ((unsigned int)len>=((char*)&tcp->x-(char*)tcp+sizeof(tcp->x))) 
#define DISPLAY_EXP(x,fmt,exp) \
        if (SAFE(x)) \
                printf(fmt,exp); \
        else \
                return; 

#define DISPLAY(x,fmt) DISPLAY_EXP(x,fmt,tcp->x)

#define DISPLAYS(x,fmt) DISPLAY_EXP(x,fmt,htons(tcp->x))
#define DISPLAYL(x,fmt) DISPLAY_EXP(x,fmt,htonl(tcp->x))
#define DISPLAYIP(x,fmt) DISPLAY_EXP(x,fmt,inet_ntoa(*(struct in_addr*)&tcp->x))

int get_next_option(unsigned char **ptr,int *len,
                        unsigned char *type,
                        unsigned char *optlen,
                        unsigned char **data)
{
        if (*len<=0)
                return 0;
        *type=**ptr;
        switch(*type) {
                case 0:
                        return 0;
                case 1:
                        (*ptr)++;
                        (*len)--;
                        return 1;
                default:
                        *optlen = *(*ptr+1);
                        (*len)-=*optlen;
                        (*data)=(*ptr+2);
                        (*ptr)+=*optlen+2;
                        if (*len<0)
                                return 0;
                        return 1;
        }
}

extern "C"
void decode(int link_type,char *packet,int len)
{
        struct tcphdr *tcp = (struct tcphdr*)packet;
        printf(" TCP:");
        if (SAFE(source)) {
                struct servent *ent=getservbyport(tcp->source,"tcp");
                if(ent) {
                        printf(" Source %i (%s)",htons(tcp->source),ent->s_name);
                } else {
                        printf(" Source %i",htons(tcp->source));
                }
        }
        else {
                printf("\n");
                return;
        }
        if (SAFE(dest)) {
                struct servent *ent=getservbyport(tcp->dest,"tcp");
                if(ent) {
                        printf(" Dest %i (%s)",htons(tcp->dest),ent->s_name);
                } else {
                        printf(" Dest %i",htons(tcp->dest));
                }
        }
        else {
                printf("\n");
                return;
        }
        printf("\n TCP:");
        DISPLAYL(seq," Seq %u");
        printf("\n TCP:");
        DISPLAYL(ack_seq," Ack %u");
        if ((char*)&tcp->window-(char *)tcp>len) {
                printf("\n");
                return;
        }
        printf("\n TCP:");
        printf(" DOFF %i",tcp->doff);
        printf(" Flags:");
        if (tcp->fin) printf(" FIN");
        if (tcp->syn) printf(" SYN");
        if (tcp->rst) printf(" RST");
        if (tcp->psh) printf(" PSH");
        if (tcp->ack) printf(" ACK");
        if (tcp->urg) printf(" URG");
        DISPLAYS(window," Window %i");
        printf("\n TCP:");
        DISPLAYS(check," Checksum %i");
        DISPLAYS(urg_ptr," Urgent %i");
        unsigned char *pkt = (unsigned char*)packet+sizeof(*tcp);
        int plen = (len-sizeof *tcp) <? (tcp->doff*4-sizeof *tcp);
        unsigned char type,optlen,*data;
        while(get_next_option(&pkt,&plen,&type,&optlen,&data)) {
                printf("\n TCP: ");
                switch(type) {
                        case 0:
                                printf("End of options");
                                break;
                        case 1:
                                printf("NOP");
                                break;
                        case 2:
                                printf("MSS %i",htons(*(uint32_t *)(data)));
                                break;
                        case 3:
                                printf("Winscale %i",data[0]);
                                break;
                        case 4:
                                printf("SACK");
                                break;
                        case 5:
                                printf("SACK Information");
                                int i;
                                i=0;
                                while(i+8<optlen) {
                                        printf("\n TCP:  %u-%u",
                                                htonl(*(uint32_t*)&data[i]),
                                                htonl(*(uint32_t*)&data[i+4]));
                                        i+=8;
                                }
                                break;
                        case 8:
                                printf("Timestamp %u %u",
                                                htonl(*(uint32_t *)&data[0]),
                                                htonl(*(uint32_t *)&data[4])
                                      );
                                break;
                        default:
                                printf("Unknown option %i",type);
                }
        }
        printf("\n");
        if (htons(tcp->source) < htons(tcp->dest)) 
                decode_next(packet+tcp->doff*4,len-tcp->doff*4,"tcp",htons(tcp->source));
        else
                decode_next(packet+tcp->doff*4,len-tcp->doff*4,"tcp",htons(tcp->dest));
        return;
}