#include "pcap.h"

 main()

 {

     pcap_if_t *alldevs;

     pcap_if_t *d;

     int i=;

     char errbuf[PCAP_ERRBUF_SIZE];

     /* 获取本地机器设备列表 */

     if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING, NULL /* auth is not needed */, &alldevs, errbuf) == -)

     {

         fprintf(stderr,"Error in pcap_findalldevs_ex: %s\n", errbuf);

         exit();

     }

     /* 打印列表 */

     for(d= alldevs; d != NULL; d= d->next)

     {

         printf("%d. %s", ++i, d->name);

         if (d->description)

             printf(" (%s)\n", d->description);

         else

             printf(" (No description available)\n");

     }

     if (i == )

     {

         printf("\nNo interfaces found! Make sure WinPcap is installed.\n");

         return;

     }

     /* 不再需要设备列表了，释放它 */

     pcap_freealldevs(alldevs);

 }

 #ifdef _MSC_VER

 /*

  * we do not want the warnings about the old deprecated and unsecure CRT functions

  * since these examples can be compiled under *nix as well

  */

 #define _CRT_SECURE_NO_WARNINGS

 #endif

 #include "pcap.h"

 /* 4 bytes IP address */

 typedef struct ip_address

 {

     u_char byte1;

     u_char byte2;

     u_char byte3;

     u_char byte4;

 }ip_address;

 /* IPv4 header */

 typedef struct ip_header

 {

     u_char    ver_ihl;        // Version (4 bits) + Internet header length (4 bits)

     u_char    tos;            // Type of service

     u_short tlen;            // Total length

     u_short identification; // Identification

     u_short flags_fo;        // Flags (3 bits) + Fragment offset (13 bits)

     u_char    ttl;            // Time to live

     u_char    proto;            // Protocol

     u_short crc;            // Header checksum

     ip_address    saddr;        // Source address

     ip_address    daddr;        // Destination address

     u_int    op_pad;            // Option + Padding

 }ip_header;

 /* UDP header*/

 typedef struct udp_header

 {

     u_short sport;            // Source port

     u_short dport;            // Destination port

     u_short len;            // Datagram length

     u_short crc;            // Checksum

 }udp_header;

 /* prototype of the packet handler */

 void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data);

 int main()

 {

     pcap_if_t *alldevs;

     pcap_if_t *d;

     int inum;

     int i=;

     pcap_t *adhandle;

     char errbuf[PCAP_ERRBUF_SIZE];

     u_int netmask;

     char packet_filter[] = "ip and udp";

     struct bpf_program fcode;

     /* Retrieve the device list */

     if(pcap_findalldevs(&alldevs, errbuf) == -)

     {

         fprintf(stderr,"Error in pcap_findalldevs: %s\n", errbuf);

         exit();

     }

     /* Print the list */

     for(d=alldevs; d; d=d->next)

     {

         printf("%d. %s", ++i, d->name);

         if (d->description)

             printf(" (%s)\n", d->description);

         else

             printf(" (No description available)\n");

     }

     if(i==)

     {

         printf("\nNo interfaces found! Make sure WinPcap is installed.\n");

         return -;

     }

     printf("Enter the interface number (1-%d):",i);

     scanf("%d", &inum);

     /* Check if the user specified a valid adapter */

     if(inum <  || inum > i)

     {

         printf("\nAdapter number out of range.\n");

         /* Free the device list */

         pcap_freealldevs(alldevs);

         return -;

     }

     /* Jump to the selected adapter */

     for(d=alldevs, i=; i< inum- ;d=d->next, i++);

     /* Open the adapter */

     if ((adhandle= pcap_open_live(d->name,    // name of the device

                              ,            // portion of the packet to capture.

                                             // 65536 grants that the whole packet will be captured on all the MACs.

                              ,                // promiscuous mode (nonzero means promiscuous)

                              ,            // read timeout

                              errbuf            // error buffer

                              )) == NULL)

     {

         fprintf(stderr,"\nUnable to open the adapter. %s is not supported by WinPcap\n");

         /* Free the device list */

         pcap_freealldevs(alldevs);

         return -;

     }

     /* Check the link layer. We support only Ethernet for simplicity. */

     if(pcap_datalink(adhandle) != DLT_EN10MB)

     {

         fprintf(stderr,"\nThis program works only on Ethernet networks.\n");

         /* Free the device list */

         pcap_freealldevs(alldevs);

         return -;

     }

     if(d->addresses != NULL)

         /* Retrieve the mask of the first address of the interface */

         netmask=((struct sockaddr_in *)(d->addresses->netmask))->sin_addr.S_un.S_addr;

     else

         /* If the interface is without addresses we suppose to be in a C class network */

         netmask=0xffffff; 

     //compile the filter

     if (pcap_compile(adhandle, &fcode, packet_filter, , netmask) < )

     {

         fprintf(stderr,"\nUnable to compile the packet filter. Check the syntax.\n");

         /* Free the device list */

         pcap_freealldevs(alldevs);

         return -;

     }

     //set the filter

     if (pcap_setfilter(adhandle, &fcode)<)

     {

         fprintf(stderr,"\nError setting the filter.\n");

         /* Free the device list */

         pcap_freealldevs(alldevs);

         return -;

     }

     printf("\nlistening on %s...\n", d->description);

     /* At this point, we don't need any more the device list. Free it */

     pcap_freealldevs(alldevs);

     /* start the capture */

     pcap_loop(adhandle, , packet_handler, NULL);

     return ;

 }

 /* Callback function invoked by libpcap for every incoming packet */

 void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data)

 {

     struct tm *ltime;

     char timestr[];

     ip_header *ih;

     udp_header *uh;

     u_int ip_len;

     u_short sport,dport;

     time_t local_tv_sec;

     /*

      * unused parameter

      */

     (VOID)(param);

     /* convert the timestamp to readable format */

     local_tv_sec = header->ts.tv_sec;

     ltime=localtime(&local_tv_sec);

     strftime( timestr, sizeof timestr, "%H:%M:%S", ltime);

     /* print timestamp and length of the packet */

     printf("%s.%.6d len:%d ", timestr, header->ts.tv_usec, header->len);

     /* retireve the position of the ip header */

     ih = (ip_header *) (pkt_data +

         ); //length of ethernet header

     /* retireve the position of the udp header */

     ip_len = (ih->ver_ihl & 0xf) * ;

     uh = (udp_header *) ((u_char*)ih + ip_len);

     /* convert from network byte order to host byte order */

     sport = ntohs( uh->sport );

     dport = ntohs( uh->dport );

     /* print ip addresses and udp ports */

     printf("%d.%d.%d.%d.%d -> %d.%d.%d.%d.%d\n",

         ih->saddr.byte1,

         ih->saddr.byte2,

         ih->saddr.byte3,

         ih->saddr.byte4,

         sport,

         ih->daddr.byte1,

         ih->daddr.byte2,

         ih->daddr.byte3,

         ih->daddr.byte4,

         dport);

 }