linux tcpdump htonl()如何填写

在使用tcpdump时，htonl()函数通常用于将网络字节序转换为主机字节序。在填写时，需要根据具体的网络协议和数据包格式来确定需要转换的字段。一般而言，需要转换的字段包括IP地址、端口号等。例如，对于TCP数据包中的源端口号和目的端口号，可以使用如下代码进行转换：

(tcp[tcpflags] & tcp-syn != 0) and (dst port %d or src port %d)" % (socket.htons(port), socket.htons(port))

其中，socket.htons()函数用于将主机字节序转换为网络字节序（即将端口号转换为网络字节序），并将其与目的端口号或源端口号进行比较。根据需要转换的字段不同，在填写时需要进行相应的修改。

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linux tcpdump C++ code

Here is an example of a simple C program to use tcpdump on Linux:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>

#define BUFSIZE 1024

int main(int argc, char *argv[]) {
    int sockfd, n;
    char buffer[BUFSIZE];
    struct sockaddr_in servaddr;
    struct iphdr *ip;
    struct tcphdr *tcp;

    if (argc != 2) {
        printf("Usage: %s <interface>\n", argv[0]);
        exit(1);
    }

    if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) < 0) {
        perror("socket");
        exit(1);
    }

    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(0);

    if (bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0) {
        perror("bind");
        exit(1);
    }

    printf("Listening on interface %s...\n", argv[1]);

    while (1) {
        n = recvfrom(sockfd, buffer, BUFSIZE, 0, NULL, NULL);
        if (n < 0) {
            perror("recvfrom");
            exit(1);
        }

        ip = (struct iphdr *) buffer;
        tcp = (struct tcphdr *) (buffer + sizeof(struct iphdr));

        printf("Source IP: %s\n", inet_ntoa(*(struct in_addr *)&ip->saddr));
        printf("Source port: %d\n", ntohs(tcp->source));
        printf("Destination IP: %s\n", inet_ntoa(*(struct in_addr *)&ip->daddr));
        printf("Destination port: %d\n", ntohs(tcp->dest));
        printf("\n");
    }

    close(sockfd);

    return 0;
}

This program creates a raw socket and binds it to the specified interface. It then listens for incoming TCP packets and prints out the source and destination IP addresses and port numbers. Note that this program requires root privileges to run.