用C语言(必须用socket函数)完整编写一个监听网络流量的程序,并对截取的报文进行tcp头部解析,提取数据
时间: 2024-05-14 17:15:33 浏览: 6
这是一个较为复杂的任务,需要涉及到网络编程、TCP/IP协议等多个领域的知识。以下是一个简单的代码示例,仅供参考。
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#define BUFFER_SIZE 1024
int main(int argc, char *argv[]) {
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[BUFFER_SIZE];
if (argc < 3) {
fprintf(stderr, "Usage: %s hostname port\n", argv[0]);
exit(1);
}
portno = atoi(argv[2]);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) {
perror("ERROR opening socket");
exit(1);
}
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr, "ERROR, no such host\n");
exit(1);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *) server->h_addr, (char *) &serv_addr.sin_addr.s_addr, server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
perror("ERROR connecting");
exit(1);
}
while (1) {
bzero(buffer, BUFFER_SIZE);
n = read(sockfd, buffer, BUFFER_SIZE - 1);
if (n < 0) {
perror("ERROR reading from socket");
exit(1);
}
printf("Received %d bytes:\n", n);
printf("%s\n", buffer);
// 解析TCP头部
struct tcphdr *tcph = (struct tcphdr *) buffer;
printf("Source port: %d\n", ntohs(tcph->source));
printf("Destination port: %d\n", ntohs(tcph->dest));
printf("Sequence number: %u\n", ntohl(tcph->seq));
printf("Acknowledgement number: %u\n", ntohl(tcph->ack_seq));
printf("Data offset: %d\n", tcph->doff);
printf("Flags: ");
if (tcph->urg) printf("U ");
if (tcph->ack) printf("A ");
if (tcph->psh) printf("P ");
if (tcph->rst) printf("R ");
if (tcph->syn) printf("S ");
if (tcph->fin) printf("F ");
printf("\n");
printf("Window size: %d\n", ntohs(tcph->window));
printf("Checksum: %d\n", ntohs(tcph->check));
printf("Urgent pointer: %d\n", ntohs(tcph->urg_ptr));
// 提取数据
char *data = buffer + tcph->doff * 4;
printf("Data: %s\n", data);
}
close(sockfd);
return 0;
}
```
该程序使用了 `socket()` 函数创建了一个 TCP 套接字,并使用 `connect()` 函数连接到指定的主机和端口。接着进入一个无限循环,每次从套接字中读取数据,并解析 TCP 头部,输出其中的各个字段。最后通过简单的指针操作提取出数据。需要注意的是,TCP 消息可能会被分成多个分片进行传输,因此需要合并多次读取到的数据,才能完整解析 TCP 头部和数据。