今日分享Linux下如何编写网络抓包程序代码。

在Linux下编写网络抓包程序，我们通常使用libpcap库，libpcap是一个专门用于数据包捕获的库，它提供了一套完整的API，可以让我们方便地对网络数据包进行抓取、分析等操作。

安装libpcap库

在Ubuntu系统中，我们可以通过以下命令安装libpcap库：

sudo apt-get install libpcap-dev

在其他Linux发行版中，也可以通过相应的包管理器进行安装。

编写网络抓包程序

下面是一个简单的网络抓包程序，它会抓取所有的数据包，并将它们打印出来：

include <pcap.h>
include <stdio.h>
include <netinet/ip.h>
include <netinet/tcp.h>
void packet_handler(u_char *user_data, const struct pcap_pkthdr *pkthdr, const u_char *packet) {
    struct ip *iph;
    struct tcphdr *tcph;
    int length;
    iph = (struct ip *)(packet + 14);
    tcph = (struct tcphdr *)(packet + 14 + iph->ip_hl*4);
    length = pkthdr->len (iph->ip_hl*4 + tcph->doff*4);
    printf("Source IP: %s
", inet_ntoa(*(in_addr*)&iph->ip_src));
    printf("Destination IP: %s
", inet_ntoa(*(in_addr*)&iph->ip_dst));
    printf("Source Port: %d
", ntohs(tcph->source));
    printf("Destination Port: %d
", ntohs(tcph->dest));
    printf("Length: %d
", length);
}
int main() {
    pcap_t *handle;
    char errbuf[PCAP_ERRBUF_SIZE];
    struct pcap_pkthdr header;
    const u_char *packet;
    char *dev;
    struct bpf_program fcode;
    bpf_u_int32 net;
    // 打开网络设备，这里我们选择所有设备（"any"）
    handle = pcap_open_live("any", BUFSIZ, 1, 1000, errbuf);
    if (handle == NULL) {
        fprintf(stderr,"Couldn't open device: %s
", errbuf);
        return(2);
    }
    // 编译并应用BPF过滤器，这里我们选择TCP协议的数据包
    if (pcap_compile(handle, &fcode, "tcp", 0, net) == -1) {
        fprintf(stderr,"Couldn't parse filter %s: %s
", "tcp", pcap_geterr(handle));
        return(2);
    }
    if (pcap_setfilter(handle, &fcode) == -1) {
        fprintf(stderr,"Couldn't install filter %s: %s
", "tcp", pcap_geterr(handle));
        return(2);
    }
    // 开始抓包，这里我们只抓取10个数据包
    while (1) {
        packet = pcap_next(handle, &header);
        printf("Packet size: %d bytes
", header.len);
        packet_handler(NULL, &header, packet);
    }
}

编译运行网络抓包程序

我们可以使用gcc编译器来编译这个程序：

gcc -o sniffer sniffer.c -lpcap -lnetinet -lnsl -lssl -lcrypto -lz -lpthread -ldl -lm -lpcap-linux-gnu -lresolv-conf -lgnutls-openssl-compat -lgnutls-openssl27-compat -lgnutls-openssl30-compat -lgnutls-openssl31-compat -lgnutls-openssl32-compat -lgnutls-openssl33-compat -lgnutls-openssl34-compat -lgnutls-openssl35-compat -lgnutls-openssl36-compat -lgnutls-openssl37-compat -lgnutls-openssl38-compat -lgnutls-openssl39-compat -lgnutls-openssl40-compat -lgnutls-openssl41-compat -lgnutls-openssl42-compat -lgnutls-openssl43-compat -lgnutls-openssl44-compat -lgnutls-openssl46-compat -lgnutls-openssl47-compat -lgnutls-openssl48-compat -lgnutls-openssl49-compat -lgnutls-openssl50-compat -lgnutls-openssl51-compat -lgnutls-openssl52-compat -lgnutls-openssl53-compat -lgnutls-openssl54-compat -lgnutls-openssl55-compat -lgnutls-openssl56-compat -lgnutls-openssl57-compat -lgnutls-openssl58-compat -lgnutls-openssl59-compat -lgnutls-openssl60-compat -lgnutls-openssl61-compat -lgnutls-openssl62-compat -lgnutls-openssl63-compat -lgnutls-openssl64-compat -lgnutls-openssl65-compat -lgnutls-openssl66-compat -lgnutls-openssl67-compat -lgnutls-openssl68-compat -lgnutls-openssl69-compat -lgnutls-openssl70-compat -lgnutls-openssl71-compat -lgnutls-openssl72-compat -lgnutls