（作者：燕云 出处：http://www.cnblogs.com/SwordTao/
欢迎转载，但也请保留这段声明，谢谢！）
君不见 黄河之水 天上来 奔流到海不复回
君不见 高堂明镜 悲白发 朝如青丝暮成雪
人生得意须尽欢 莫使金樽空对月
——将进酒
pcap文件格式，为多数的tcpdump、wireshark等重量级的数据包抓取、分析应用程序所直接支持，所以，为我们的程序中嵌入此类文件的解析与生成功能，很是值得。
具体信息请看wireshark wiki：http://wiki.wireshark.org/Development/LibpcapFileFormat
笔者本来想借助开源的tcpreplay与libpcap中的代码片段来快速实现此目的，没想到被两个bug，卡住了几个小时，真是欲速则不达！
第一处：tcpreplay，如果不是因为宏SEEK_SET恰巧等于0 ......
不要多说，虽不致命，但祸患无穷。
第二处：libpcap，关于packet header的结构定义，struct
timeval长度为16字节，而实际上这段区域长度为8字节，所以，这个结构体根本不能正常工作。只会更糟！
无碍，我们继续，最终的pcap文件解析函数原型：
上图是即为解析的核心函数原型，对照着第一个图一起看会很清晰！下面进行测试 :)
1 int main()
2 {
3 struct pcap_file_header phdr;
4 char * filePathPtr="log.pcap";
5 int fd;
6 int i;
7 int packet_counter;
8 struct packet pkt;
9
10 if ( ( fd=open(filePathPtr,O_RDONLY) )==-1 )
11 {
12 printf("error: open file error %s \n",filePathPtr);
13 return 1;
14 }
15 if( is_pcap_file_format(fd,&phdr))
16 {
17 print_pcap_file_header(&phdr);
18 }
19 else
20 {
21 printf("error: file %s format not support \n",filePathPtr);
22 return 1;
23 }
24 packet_counter=0;
25 while(1)
26 {
27 if(pcap_file_get_next_packet(fd,&pkt))
28 {
29 packet_counter++;
30 printf("snaplen: %d actual_len: %d packet_counter: %d \n",pkt.len,pkt.actual_len,packet_counter);
31 for(i=0; i<pkt.len; ++i)
32 {
33 printf(" %02x", pkt.data[i]);
34 if( (i + 1) % 16 == 0 )
35 {
36 printf("\n");
37 }
38 }
39 printf("\n\n");
40 }
41 else
42 {
43 printf("done\n");
44 break;
45 }
46 }
47 close(fd);
48 }
nice ! pcap文件解析已完成，接下来进行流量重放：
其中，函数 build_send_ethernet_packet
是我们的老朋友了，无需多言，重点是 pcap_ip_repaly
的实现：
1 int pcap_ip_repaly( char * pcapFilePathPtr, int usecDelayPerPacket, char * devName)
2 {
3 struct pcap_file_header phdr;
4 struct ethernet_ip_hdr * hdrPtr;
5 int packet_counter;
6 struct packet pkt;
7 int fd;
8 int i;
9
10
11 if ( ( fd=open(pcapFilePathPtr,O_RDONLY) )==-1 )
12 {
13 fprintf(stderr,"error: open file error %s",pcapFilePathPtr);
14 return 1;
15 }
16
17 if( is_pcap_file_format(fd,&phdr) )
18 {
19 print_pcap_file_header(&phdr);
20 }
21 else
22 {
23 fprintf(stderr, "error: the file %s is not .pcap format\n",pcapFilePathPtr);
24 return 1;
25 }
26
27 packet_counter=0;
28 while(1)
29 {
30 if(pcap_file_get_next_packet(fd,&pkt))
31 {
32 usleep(usecDelayPerPacket);
33 packet_counter++;
34 //analyze packet and send it
35 hdrPtr=(struct ethernet_ip_hdr *) pkt.data;
36 if( hdrPtr->ether_type==0x0008) //filter: ip type: 0x0800 -> little endian 0x0008
37 {
38 // print packet information
39 printf("ether: %02x:%02x:%02x:%02x:%02x:%02x ->",hdrPtr->ether_shost[0],hdrPtr->ether_shost[1]
40 ,hdrPtr->ether_shost[2],hdrPtr->ether_shost[3],hdrPtr->ether_shost[4],hdrPtr->ether_shost[5]);
41 printf(" %02x:%02x:%02x:%02x:%02x:%02x ",hdrPtr->ether_dhost[0],hdrPtr->ether_dhost[1]
42 ,hdrPtr->ether_dhost[2],hdrPtr->ether_dhost[3],hdrPtr->ether_dhost[4],hdrPtr->ether_dhost[5]);
43 printf("ip: %d.%d.%d.%d ->",hdrPtr->ip_src[0],hdrPtr->ip_src[1],hdrPtr->ip_src[2],hdrPtr->ip_src[3]);
44 printf(" %d.%d.%d.%d \n",hdrPtr->ip_dst[0],hdrPtr->ip_dst[1],hdrPtr->ip_dst[2],hdrPtr->ip_dst[3]);
45 if(pkt.len==pkt.actual_len)
46 {
47 printf("whole packet:padPtr is %x,padLength is %d \n",pkt.data+14,pkt.len-14);
48 if (build_send_ethernet_packet(devName,1, hdrPtr->ether_dhost,
49 hdrPtr->ether_shost,0x0800,pkt.data+14,pkt.len-14)
50 ==0
51 )
52 printf("resend packet success :) \n");
53 else
54 printf("resend packet fail :( \n");
55 }
56 else
57 {
58 fprintf(stderr,"this packet is not entire,cannot resend :(");
59 }
60
61 }
62 else
63 {
64 if(hdrPtr->ether_type==0x0608) //filter: ip type: 0x0806 -> little endian 0x0608
65 {printf("arp packet \n");}
66 else if(hdrPtr->ether_type==0x3508) //filter: ip type: 0x0835 -> little endian 0x3508
67 {printf("rarp packet \n");}
68 else
69 {printf("unknown packet type\n");}
70 }
71 //print packet
72 printf("snaplen: %d actual_len: %d packet_counter: %d \n",pkt.len,pkt.actual_len,packet_counter);
73 for(i=0; i<pkt.len; ++i)
74 {
75 printf(" %02x", pkt.data[i]);
76 if( (i + 1) % 16 == 0 )
77 {
78 printf("\n");
79 }
80 }
81 printf("\n\n");
82 }
83 else
84 {
85 break;
86 }
87 }
88
89 close(fd);
90 return 0;
91
92 }
int pcap_ip_repaly( char * pcapFilePathPtr, int usecDelayPerPacket, char * devName)
char * pcapFilePathPtr : 待解析 pcap 文件路径
int usecDelayPerPacket : 每隔多少us发一个包。。即控制发包速率
char * devName : 你想让哪个网卡做坏事？写上他的”真名“吧！
进行测试：
int main()
{
return pcap_ip_repaly("log.pcap",0,"eth0");
}
附录：
全部代码
1 #include <sys/time.h>
2 #include <sys/types.h>
3 #include <stdio.h>
4 #include <fcntl.h>
5 #include <unistd.h>
6 #include <sys/types.h>
7 #include <sys/time.h>
8 #include <sys/types.h>
9 #include <stdint.h>
10 #include <libnet.h>
11
12
13 #define PCAP_MAGIC 0xa1b2c3d4 /* magic constants for various pcap file types */
14 #define DEFAULT_MTU 1500 /* Max Transmission Unit of standard ethernet
15 * don‘t forget *frames* are MTU + L2 header! */
16 #define MAXPACKET 16436 /* MTU of Linux loopback */
17 #define MAX_SNAPLEN 65535 /* tell libpcap to capture the entire packet */
18
19 struct pcap_file_header {
20 unsigned int magic;
21 unsigned short int version_major;
22 unsigned short int version_minor;
23 int thiszone; /* gmt to local correction */
24 unsigned int sigfigs; /* accuracy of timestamps */
25 unsigned int snaplen; /* max length saved portion of each pkt */
26 unsigned int linktype; /* data link type (LINKTYPE_*) */
27 };
28 struct pcap_pkthdr {
29 time_t ts;//struct timeval ts; /* time stamp */
30 unsigned int caplen; /* length of portion present */
31 unsigned int len; /* length this packet (off wire) */
32 };
33
34 struct packet {
35 unsigned char data[MAXPACKET]; /* pointer to packet contents */
36 unsigned int len; /* length of data (snaplen) */
37 unsigned int actual_len; /* actual length of the packet */
38 time_t ts; /* timestamp */
39 };
40
41 struct ethernet_ip_hdr
42 {
43 uint8_t ether_dhost[6];/* destination ethernet address */
44 uint8_t ether_shost[6];/* source ethernet address */
45 uint16_t ether_type; /* protocol */
46 uint8_t ip_ver_hdrlen;
47 uint8_t ip_tos;
48 uint16_t ip_total_len; /* total length */
49 uint16_t ip_id; /* identification */
50 uint16_t ip_frag;
51 uint8_t ip_ttl; /* time to live */
52 uint8_t ip_proto; /* protocol */
53 uint16_t ip_hdrCRC; /* checksum */
54 uint8_t ip_src[4];
55 uint8_t ip_dst[4];
56 };
57
58 /* return flag if this is a pcap file */
59 /*
60 retCode
61 0 fail
62 1 success
63 */
64 int is_pcap_file_format(int fd,struct pcap_file_header * pcapFileHdrPtr)
65 {
66
67 if (lseek(fd, 0, SEEK_SET) != 0)
68 {
69 fprintf(stderr,"Unable to seek to start of file\n");
70 return 0;
71 }
72
73 if (read(fd, (void *) pcapFileHdrPtr, sizeof( struct pcap_file_header )) != sizeof( struct pcap_file_header ))
74 {
75 fprintf(stderr,"Unable to read whole pcap file hdr of file\n");
76 return 0;
77 }
78
79 switch (pcapFileHdrPtr->magic)
80 {
81 case PCAP_MAGIC:
82 break;
83 default:
84 {
85 fprintf(stderr,"Unable to resolve the magic number %d \n",pcapFileHdrPtr->magic);
86 return 0;
87 }
88 }
89
90 /* version, snaplen, & linktype magic */
91 if (pcapFileHdrPtr->version_major != 2)
92 {
93 fprintf(stderr,"Unable to resolve the version_major number %d \n",pcapFileHdrPtr->version_major);
94 return 0;
95 }
96
97
98 if (pcapFileHdrPtr->linktype != 1)
99 {
100 fprintf(stderr,"Only could resolve the ethernet linktype packet, not %d \n",pcapFileHdrPtr->linktype);
101 return 0;
102 }
103
104 return 1;
105 }
106
107 void print_pcap_file_header(struct pcap_file_header * pcapFileHdrPtr)
108 {
109 printf("magic number: %X \n",pcapFileHdrPtr->magic);
110 printf("version_major: %d \n",pcapFileHdrPtr->version_major);
111 printf("version_minor: %d \n",pcapFileHdrPtr->version_minor);
112 printf("gmt to local correction: %d \n",pcapFileHdrPtr->thiszone);
113 printf("accuracy of timestamps: %d \n",pcapFileHdrPtr->sigfigs);
114 printf("max snap length: %d \n",pcapFileHdrPtr->snaplen);
115 printf("linktype(1 for ethernet): %d \n",pcapFileHdrPtr->linktype);
116 }
117
118 int
119 pcap_file_get_next_packet(int fd, struct packet *pkt)
120 {
121 struct pcap_pkthdr p1, *p;
122
123 if (read(fd, &p1, sizeof(p1)) != sizeof(p1))
124 return 0;
125 p = &p1;
126
127 pkt->len = p->caplen;
128 /* stupid OpenBSD, won‘t let me just assign things, so I‘ve got
129 * to use a memcpy() instead
130 */
131 memcpy(&(pkt->ts), &(p->ts), sizeof(time_t));
132 pkt->actual_len = p->len;
133
134 if (read(fd, &pkt->data, pkt->len) != pkt->len)
135 return 0;
136
137 return pkt->len;
138 }
139
140 int pcap_file_print( char * pcapFilePathPtr )
141 {
142 struct pcap_file_header phdr;
143 int packet_counter;
144 struct packet pkt;
145 int fd;
146 int i;
147
148
149 if ( ( fd=open(pcapFilePathPtr,O_RDONLY) )==-1 )
150 {
151 fprintf(stderr,"error: open file error %s",pcapFilePathPtr);
152 return 1;
153 }
154
155 if( is_pcap_file_format(fd,&phdr) )
156 {
157 print_pcap_file_header(&phdr);
158 }
159 else
160 {
161 fprintf(stderr, "error: the file %s is not .pcap format\n",pcapFilePathPtr);
162 return 1;
163 }
164
165 packet_counter=0;
166 while(1)
167 {
168 if(pcap_file_get_next_packet(fd,&pkt))
169 {
170 packet_counter++;
171 printf("snaplen: %d actual_len: %d packet_counter: %d \n",pkt.len,pkt.actual_len,packet_counter);
172 for(i=0; i<pkt.len; ++i)
173 {
174 printf(" %02x", pkt.data[i]);
175 if( (i + 1) % 16 == 0 )
176 {
177 printf("\n");
178 }
179 }
180 printf("\n\n");
181 }
182 else
183 {
184 break;
185 }
186 }
187
188 close(fd);
189 return 0;
190
191 }
192
193
194
195 int build_send_ethernet_packet(const char * dev,const unsigned int sendTimes,
196 const unsigned char * dst_mac,const unsigned char * src_mac,
197 const uint16_t protoType,const unsigned char * padPtr,const unsigned int padLength
198 )
199 {
200 libnet_t *net_t = NULL;
201 char err_buf[LIBNET_ERRBUF_SIZE];
202 libnet_ptag_t p_tag;
203 unsigned int i=0;
204
205 //init the libnet context structure
206 net_t = libnet_init(LIBNET_LINK_ADV, dev, err_buf);
207 if(net_t == NULL)
208 {
209 fprintf(stderr,"libnet_init error:%s\n",err_buf);
210 return 1;
211 }
212
213 //build the ethernet packet
214 p_tag = libnet_build_ethernet(//create ethernet header
215 dst_mac,//dest mac addr
216 src_mac,//source mac addr
217 protoType,//protocol type
218 padPtr,//payload
219 padLength,//payload length
220 net_t,//libnet context
221 0//0 to build a new one
222 );
223 if(-1 == p_tag)
224 {
225 fprintf(stderr,"libnet_build_ethernet error!\n");
226 fprintf(stderr,"BuildAndSendEthernetPacket: %s",net_t->err_buf);
227 goto FAIL;
228 }
229
230 for(i=0;i<sendTimes;i++)
231 if(-1 == libnet_write(net_t))
232 {
233 fprintf(stderr,"B libnet_write error!\n");
234 fprintf(stderr,"BuildAndSendEthernetPacket: %s",net_t->err_buf);
235 goto FAIL;
236 }
237
238 libnet_destroy(net_t);
239 return 0;
240 FAIL:
241 libnet_destroy(net_t);
242 return 1;
243 }244
245
246 int pcap_ip_repaly( char * pcapFilePathPtr, int usecDelayPerPacket, char * devName)
247 {
248 struct pcap_file_header phdr;
249 struct ethernet_ip_hdr * hdrPtr;
250 int packet_counter;
251 struct packet pkt;
252 int fd;
253 int i;
254
255
256 if ( ( fd=open(pcapFilePathPtr,O_RDONLY) )==-1 )
257 {
258 fprintf(stderr,"error: open file error %s",pcapFilePathPtr);
259 return 1;
260 }
261
262 if( is_pcap_file_format(fd,&phdr) )
263 {
264 print_pcap_file_header(&phdr);
265 }
266 else
267 {
268 fprintf(stderr, "error: the file %s is not .pcap format\n",pcapFilePathPtr);
269 return 1;
270 }
271
272 packet_counter=0;
273 while(1)
274 {
275 if(pcap_file_get_next_packet(fd,&pkt))
276 {
277 usleep(usecDelayPerPacket);
278 packet_counter++;
279 //analyze packet and send it
280 hdrPtr=(struct ethernet_ip_hdr *) pkt.data;
281 if( hdrPtr->ether_type==0x0008) //filter: ip type: 0x0800 -> little endian 0x0008
282 {
283 // print packet information
284 printf("ether: %02x:%02x:%02x:%02x:%02x:%02x ->",hdrPtr->ether_shost[0],hdrPtr->ether_shost[1]
285 ,hdrPtr->ether_shost[2],hdrPtr->ether_shost[3],hdrPtr->ether_shost[4],hdrPtr->ether_shost[5]);
286 printf(" %02x:%02x:%02x:%02x:%02x:%02x ",hdrPtr->ether_dhost[0],hdrPtr->ether_dhost[1]
287 ,hdrPtr->ether_dhost[2],hdrPtr->ether_dhost[3],hdrPtr->ether_dhost[4],hdrPtr->ether_dhost[5]);
288 printf("ip: %d.%d.%d.%d ->",hdrPtr->ip_src[0],hdrPtr->ip_src[1],hdrPtr->ip_src[2],hdrPtr->ip_src[3]);
289 printf(" %d.%d.%d.%d \n",hdrPtr->ip_dst[0],hdrPtr->ip_dst[1],hdrPtr->ip_dst[2],hdrPtr->ip_dst[3]);
290 if(pkt.len==pkt.actual_len)
291 {
292 printf("whole packet:padPtr is %x,padLength is %d \n",pkt.data+14,pkt.len-14);
293 if (build_send_ethernet_packet(devName,1, hdrPtr->ether_dhost,
294 hdrPtr->ether_shost,0x0800,pkt.data+14,pkt.len-14)
295 ==0
296 )
297 printf("resend packet success :) \n");
298 else
299 printf("resend packet fail :( \n");
300 }
301 else
302 {
303 fprintf(stderr,"this packet is not entire,cannot resend :(");
304 }
305
306 }
307 else
308 {
309 if(hdrPtr->ether_type==0x0608) //filter: ip type: 0x0806 -> little endian 0x0608
310 {printf("arp packet \n");}
311 else if(hdrPtr->ether_type==0x3508) //filter: ip type: 0x0835 -> little endian 0x3508
312 {printf("rarp packet \n");}
313 else
314 {printf("unknown packet type\n");}
315 }
316 //print packet
317 printf("snaplen: %d actual_len: %d packet_counter: %d \n",pkt.len,pkt.actual_len,packet_counter);
318 for(i=0; i<pkt.len; ++i)
319 {
320 printf(" %02x", pkt.data[i]);
321 if( (i + 1) % 16 == 0 )
322 {
323 printf("\n");
324 }
325 }
326 printf("\n\n");
327 }
328 else
329 {
330 break;
331 }
332 }
333
334 close(fd);
335 return 0;
336
337 }
338
339 int main()
340 {
341 return pcap_ip_repaly("/home/yun/Codes/wp.pcap",0,"eth0");
342 }
如有问题或者建议，欢迎留言讨论 :)