此程序应从脱机转储文件中捕获数据包并对其进行解码。这里我遇到了ntohs（）函数的问题（它接近结束，头文件描述在开头）。为什么它不起作用？ OS win7 x86，VS 2010 express。
#include "pcap.h"
#define SIZE_ETHERNET 14
#define ETHER_ADDR_LEN 6
/* 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;
typedef struct ethernet_address{
u_char byte1;
u_char byte2;
u_char byte3;
u_char byte4;
u_char byte5;
u_char byte6;
}ethernet_address;
/* Ethernet header */
typedef struct ethernet_header {
ethernet_address ether_dhost; /* Destination host address */
ethernet_address ether_shost; /* Source host address */
u_short ether_type; /* IP? ARP? RARP? etc */
};
/* TCP header */
typedef struct tcp_header {
u_short th_sport; /* source port */
u_short th_dport; /* destination port */
u_char th_offx2; /* data offset, rsvd */
#define TH_OFF(th) (((th)->th_offx2 & 0xf0) >> 4)
u_char th_flags;
#define TH_FIN 0x01
#define TH_SYN 0x02
#define TH_RST 0x04
#define TH_PUSH 0x08
#define TH_ACK 0x10
#define TH_URG 0x20
#define TH_ECE 0x40
#define TH_CWR 0x80
#define TH_FLAGS (TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG|TH_ECE|TH_CWR)
u_short th_win; /* window */
u_short th_sum; /* checksum */
u_short th_urp; /* urgent pointer */
}tcp_header;
/* prototype of the packet handler */
void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data);
/* Packet count */
int num = 1;
int main(int argc, char **argv)
{
pcap_t *adhandle;
char errbuf[PCAP_ERRBUF_SIZE];
char source[PCAP_BUF_SIZE];
u_int netmask;
char packet_filter[] = "";
struct bpf_program fcode;
if(argc != 2){
printf("usage: %s filename", argv[0]);
return -1;
}
/* Create the source string according to the new WinPcap syntax */
if ( pcap_createsrcstr( source, // variable that will keep the source string
PCAP_SRC_FILE, // we want to open a file
NULL, // remote host
NULL, // port on the remote host
argv[1], // name of the file we want to open
errbuf // error buffer
) != 0)
{
fprintf(stderr,"\nError creating a source string\n");
return -1;
}
/* Open the adapter */
if ( (adhandle= pcap_open(source, // name of the device
65536, // portion of the packet to capture.
// 65536 grants that the whole packet will be captured on all the MACs.
PCAP_OPENFLAG_PROMISCUOUS, // promiscuous mode
1000, // read timeout
NULL, // remote authentication
errbuf // error buffer
) ) == NULL)
{
fprintf(stderr,"\nUnable to open the adapter. %s is not supported by WinPcap\n");
return -1;
}
/* 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");
return -1;
}
/* 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, 1, netmask) <0 )
{
fprintf(stderr,"\nUnable to compile the packet filter. Check the syntax.\n");
return -1;
}
//set the filter
if (pcap_setfilter(adhandle, &fcode)<0)
{
fprintf(stderr,"\nError setting the filter.\n");
return -1;
}
/* start the capture */
pcap_loop(adhandle, 0, packet_handler, NULL);
return 0;
}
/* 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[16];
time_t local_tv_sec;
u_int ip_len;
u_short sport,dport;
ip_header *ih;
const struct ethernet_header *ethh; /* The ethernet header */
/*
* Unused variable
*/
(VOID)(param);
printf("Packet %d\n", num);
num++;
/* convert the timestamp to readable format */
local_tv_sec = header->ts.tv_sec;
localtime_s(<ime, &local_tv_sec);
strftime( timestr, sizeof timestr, "%H:%M:%S", <ime);
/* print timestamp and length of the packet */
// printf("%s.%.6d len:%d ", timestr, header->ts.tv_usec, header->len);
/* retireve the position of the ethernet header */
ethh = (struct ethernet_header*)(pkt_data);
/* retireve the position of the ip header */
ih = (ip_header *) (pkt_data + 14); //length of ethernet header
/* retireve the position of the udp header */
ip_len = (ih->ver_ihl & 0xf) * 4;
/* print ip addresses and ports */
printf("Eth Src: %x:%x:%x:%x:%x:%x >>> Dest: %x:%x:%x:%x:%x:%x\nIP Src: %d.%d.%d.%d >>> Dest: %d.%d.%d.%d\n",
ethh->ether_shost.byte1,
ethh->ether_shost.byte2,
ethh->ether_shost.byte3,
ethh->ether_shost.byte4,
ethh->ether_shost.byte5,
ethh->ether_shost.byte6,
ethh->ether_dhost.byte1,
ethh->ether_dhost.byte2,
ethh->ether_dhost.byte3,
ethh->ether_dhost.byte4,
ethh->ether_dhost.byte5,
ethh->ether_dhost.byte6,
ih->saddr.byte1,
ih->saddr.byte2,
ih->saddr.byte3,
ih->saddr.byte4,
ih->daddr.byte1,
ih->daddr.byte2,
ih->daddr.byte3,
ih->daddr.byte4
);
/* Panage protocols */
if(ih->proto == 0x11)
{
udp_header *uh;
uh = (udp_header *) ((u_char*)ih + ip_len);
printf("UDP Src: %d >>> Dest: %d\n", uh->sport,uh->dport);
}
else if(ih->proto == 0x06)
{
tcp_header *tcp = NULL;
/* convert from network byte order to host byte order */
tcp = (tcp_header *) ((u_char*)ih + ip_len);
/*HERE*/ sport = ntohs(tcp->th_sport);
/*HERE*/ dport = ntohs(tcp->th_dport);
printf("TCP Src: %d >>> Dest: %d\n", sport,dport);
}
}
错误日志：
1>------ Build started: Project: cw1, Configuration: Debug Win32 ------
1> cw1.c
1>cw1.obj : error LNK2019: unresolved external symbol __imp__ntohs@4 referenced in function _packet_handler
1>C:\Users\Medardas\Desktop\ComputerScience\C.SC251 - CW1\cw1\Debug\cw1.exe : fatal error LNK1120: 1 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
答案 0 :(得分：1)
尝试添加<arpa/inet.h>或<netinet/in.h>。如果做不到这一点，请检查链接器设置。
答案 1 :(得分：0)
这是一个链接器错误。咨询documentation of the function。在该页面的底部（所有这些页面都以相同的方式布局），您将找到所需的头，lib和DLL的详细信息。在这种情况下，您需要链接Ws2_32.lib。