[C++知识库]C语言使用libpcap输出报文到pcap文件

一、pcap文件格式简介

pcap文件格式由一个文件头，加上若干个分组header + 分组数据组成。

pcap整体文件结构：

?文件头：

?

?

分组header：

?二、libpcap库函数介绍

为了输出pcap文件，将使用到以下的函数：

// 创建一个 pcap_t 句柄用于写入文件
// @param linktype 参见 http://www.tcpdump.org/linktypes.html
// @param snaplen 指定捕获(最大)长度
pcap_t *pcap_open_dead(int linktype, int snaplen);

// 打开文件用于输出，打开文件模式相当于fopen("w")
pcap_dumper_t *pcap_dump_open(pcap_t *p, const char *fname);

// 将 sp 指向的数组输出到 user 打开的文件中
void pcap_dump(u_char *user, struct pcap_pkthdr *h,
               u_char *sp);

// 在不关闭文件的情况下，将输出buffer写入文件，非必须
int pcap_dump_flush(pcap_dumper_t *p);

struct pcap_pkthdr {
	struct timeval ts;	/* time stamp */
	bpf_u_int32 caplen;	/* length of portion present */
	bpf_u_int32 len;	/* length of this packet (off wire) */
};

三、C语言实现

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <pcap/pcap.h>

#define LINKTYPE_ETHERNET 1


int main() {
    char *filename = "output.pcap";
    uint8_t packet1[] = {0x08, 0x00, 0x27, 0xfc, 0x6a, 0xc9, 0x08, 0x00, 0x27, 0xe2, 0x9f, 0xa6, 0x08, 0x00, 0x45, 0x00, 0x05, 0x94, 0x83, 0xf6, 0x00, 0x00, 0x40, 0x01, 0xeb, 0x6e, 0x02, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x02, 0x00, 0x00, 0x55, 0x71, 0x13, 0xc2, 0x00, 0x01, 0x14, 0x2b, 0xd2, 0x59, 0x00, 0x00, 0x00, 0x00, 0x3d, 0x2a, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf, 0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf};
    uint8_t packet2[] = {0x08, 0x00, 0x27, 0xfc, 0x6a, 0xc9, 0x08, 0x00, 0x27, 0xe2, 0x9f, 0xa6, 0x08, 0x00, 0x45, 0x00, 0x05, 0x94, 0x83, 0xf6, 0x00, 0x00, 0x40, 0x01, 0xeb, 0x6e, 0x02, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x02, 0x00, 0x00, 0x55, 0x71, 0x13, 0xc2, 0x00, 0x01, 0x14, 0x2b, 0xd2, 0x59, 0x00, 0x00, 0x00, 0x00, 0x3d, 0x2a, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf, 0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf};

    pcap_t *p;
    p = pcap_open_dead(LINKTYPE_ETHERNET, 65535);

    pcap_dumper_t *pcap_file;
    pcap_file = pcap_dump_open(p, filename);

    // init time
    clock_t time;
    time = clock();

    // write packet 1
    struct pcap_pkthdr pkt_header;
    time = clock();
    pkt_header.ts.tv_sec = time / CLOCKS_PER_SEC;
    pkt_header.ts.tv_usec = time % CLOCKS_PER_SEC;
    pkt_header.caplen = sizeof(packet1);
    pkt_header.len = sizeof(packet1);
    pcap_dump((u_char*)pcap_file, &pkt_header, packet1);

    // write packet 2
    time = clock();
    pkt_header.ts.tv_sec = time / CLOCKS_PER_SEC;
    pkt_header.ts.tv_usec = time % CLOCKS_PER_SEC;
    pkt_header.caplen = sizeof(packet2);
    pkt_header.len = sizeof(packet2);
    pcap_dump((u_char*)pcap_file, &pkt_header, packet2);

    if(pcap_dump_flush(pcap_file) == PCAP_ERROR) {
        printf("Error: can't write output to file.");
    }
    // finishing
    pcap_dump_close(pcap_file);
    pcap_close(p);

    return 0;
}