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recvfrom 函数的问题

时间：2010-08-31

来源：互联网

第一次用网络编程，使用了原始套接字的UDP。想实现的功能是服务器接受到来自客户端的数据然后返回给客户端，但是会出现以下问题：
（1）在recvfrom函数接时，得到的客户端的地址信息（struct sockaddr_in client）中的端口号为0，以至于，服务器返回数据的sendto函数不能执行成功。
（2）只要服务器接收到来自客户端的信息，客户端就不停的在循环、不停的打印出消息，而且消息的内容始终是第一条的消息。

代码如下所示，请各位指正！谢谢！

//头文件header.h
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <unistd.h>
#include <pthread.h>
//#include <linux/ip.h>
#define IP_HEAD_LEN 20 //IP header length
#define UDP_HEAD_LEN 8 //UDP header length
#define PACKET_LEN 1500 //Packet length(decided by ethnet packet length)
#define UDP_LEN PACKET_LEN - IP_HEAD_LEN //UDP length(include UDP head and data)
#define MSG_LEN UDP_LEN - UDP_HEAD_LEN //paylod length(data)
#define SERVER_PORT 4567 //server default port
#define CLIENT_PORT 4567 //client default port
#define MAX_ROUTE_HOP 64 //Max route hops
#define MAX_USER 5
/*
*user information structure
*/
typedef struct user
{
int sockfd;
struct sockaddr_in addr;
}USER;
/* Pseudo Header Structure */
typedef struct psd_hdr //定义UDP/TCP伪报头
{
struct in_addr saddr; //源地址
struct in_addr daddr; //目的地址
unsigned char mbz; //全零
unsigned char proto; //协议类型
unsigned short len; //UDP/TCP长度
}PSD_HEADER;
/* UDP Header　Structure */
typedef struct _udphdr //定义UDP报头
{
unsigned short uh_sport; //16位源端口
unsigned short uh_dport; //16位目的端口
unsigned short uh_len; //16位长度
unsigned short uh_sum; //16位校验和
}UDP_HEADER;
/* TCP Header Structure
*/
typedef struct _tcphdr //定义TCP报头
{
unsigned short th_sport; //16位源端口
unsigned short th_dport; //16位目的端口
unsigned int th_seq; //32位序列号
unsigned int th_ack; //32位确认号
unsigned char th_lenres; //4位首部长度/4位保留字
unsigned char th_flag; //6位标志位
unsigned short th_win; //16位窗口大小
unsigned short th_sum; //16位校验和
unsigned short th_urp; //16位紧急数据偏移量
}TCP_HEADER;
/*IP HEADER Structure
*/
typedef struct _iphdr //定义IP报头
{
unsigned char h_lenver; //version and header len
unsigned char tos; //type of service 8bit
unsigned short t_len; //total length 16bit
unsigned short id; //identification 16bit
unsigned short off;
unsigned char ttl;
unsigned char proto;
unsigned short sum;
struct in_addr srcIP;
struct in_addr dstIP;
}IP_HEADER;
//服务器
#include "header.h"
static unsigned short checksum(int numwords, unsigned short *buff);
void RemovHead(int type, char *buf);
struct sockaddr_in user[MAX_USER]; //user structure array
int main()
{
int sockfd,i; //i用作循环
struct sockaddr_in server,client;
struct hostent *ht;
IP_HEADER iphead;
UDP_HEADER udphead;
PSD_HEADER psdhead;
struct in_addr my_addr;
struct in_addr serv_addr;
char hostname[20],qstr[] = "quit";
char msg_tx[PACKET_LEN],buf[PACKET_LEN]; /*message and buffer to send */
char msg_rx[PACKET_LEN];
int on=1;
int add_len = sizeof(struct sockaddr);
for(i=0; i<MAX_USER; i++)
{
user[i].sin_addr.s_addr = 0;
}
printf("\nEnter the server's IP:\n");
scanf("%s",hostname);
//创建原始套接字
if((sockfd = socket(AF_INET,SOCK_RAW,IPPROTO_UDP)) == -1)
{
perror("socket");
exit(1);
}
//设置套接字选项
if(setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL,&on, sizeof(on)) < 0)
{
printf("setsockopt error!\n");
close(sockfd);
exit(1);
}
//获得host信息
if((ht = gethostbyname(hostname)) == NULL)
{
perror("gethostbyname");
exit(1);
}
//填充sockaddr_in结构体
memcpy(&server.sin_addr,ht->h_addr,ht->h_length);
server.sin_family = AF_INET;
server.sin_port=htons(SERVER_PORT);
bzero(&(server.sin_zero),8);
//帮定套接字
if(bind(sockfd, (struct sockaddr*)&server,sizeof(server)) < 0)
{
perror("bind");
exit(1);
}
printf("socket success...\n");
//ip头部填充
iphead.h_lenver = (4<<4|sizeof(IP_HEADER)/sizeof(unsigned long));
iphead.tos = 0;
iphead.id = htons((unsigned short)rand());
iphead.off = 0;
iphead.ttl = MAX_ROUTE_HOP;
iphead.proto = IPPROTO_UDP;
iphead.sum = 0;
iphead.srcIP = server.sin_addr; //测试用的环路地址127.0.0.1
iphead.dstIP = server.sin_addr;
//udp头部填充
udphead.uh_sport = htons(CLIENT_PORT);
udphead.uh_dport = htons(SERVER_PORT);
udphead.uh_sum = 0;
//udp伪首部填充
psdhead.saddr = iphead.srcIP;
psdhead.daddr = iphead.dstIP;
psdhead.mbz = 0;
psdhead.proto = iphead.proto;
//接收消息
printf("You can receive data now!\n");
int len = -1;
int msg_rx_num = 0;
int msg_tx_num = 0;
IP_HEADER *pip = (IP_HEADER*)malloc(sizeof(IP_HEADER));
UDP_HEADER *pudp = (UDP_HEADER*)malloc(sizeof(UDP_HEADER));
while(1)
{
//usleep(2000000);
memset(msg_rx, 0, MSG_LEN);
memset(buf, 0, MSG_LEN);
len = recvfrom(sockfd,msg_rx,sizeof(msg_rx),0,(struct sockaddr*)&client,&add_len);
if(len < 0)
{
printf("不是来自rawclient的消息");
}
else
{
printf("\nsockfd =%d----------------------------------------------------\n",sockfd);
printf("\n客户端口:%d",client.sin_port);
printf("\t客户IP:%d",client.sin_addr.s_addr);
/*打印、调试============================================================*/
pip = (IP_HEADER*)msg_rx;
pudp = (UDP_HEADER*)(msg_rx + pip->t_len);
printf("协议：%d,校验和：%d\n",pip->proto,pip->sum);
printf("源地址：%d",pip->srcIP.s_addr);
printf("\t目的地址：%d\n",pip->dstIP.s_addr);
printf("源端口：%d,目的端口：%d,长度：%d\n",
ntohs(pudp->uh_sport),ntohs(pudp->uh_dport),ntohs(pudp->uh_len));
char tmp[MSG_LEN];
memcpy(buf,msg_rx+sizeof(IP_HEADER)+sizeof(UDP_HEADER),sizeof(buf));
printf("接收到第%d条消息：%s\n",msg_rx_num++,buf);
//转发＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
char *ptr = msg_tx;
memset(msg_tx, 0, MSG_LEN);
iphead.t_len = htons(sizeof(IP_HEADER)+sizeof(UDP_HEADER)+strlen(buf));
udphead.uh_len = htons(sizeof(UDP_HEADER)+strlen(buf));
psdhead.len = udphead.uh_len;
//组包、发送
memcpy(ptr,&iphead,sizeof(IP_HEADER));
ptr += sizeof(IP_HEADER);
memcpy(ptr,&udphead,sizeof(UDP_HEADER));
ptr += sizeof(UDP_HEADER);
memcpy(ptr,buf,strlen(buf));
usleep(2000000);
int len=-1;
if ((len = sendto(sockfd,msg_tx,PACKET_LEN,0,(struct sockaddr *)&client,add_len)) < 0)
{
perror("sendto");
}
}
printf("\n=====================================================================\n");
}
free(pudp);
pip = NULL;
free(pip);
pudp = NULL;
close(sockfd);
}
//客户端
#include "header.h"
int main()
{
int sockfd;
struct sockaddr_in server,client;
struct hostent *ht;
IP_HEADER *iphead = (IP_HEADER*)malloc(sizeof(IP_HEADER));
UDP_HEADER *udphead = (UDP_HEADER*)malloc(sizeof(UDP_HEADER));
PSD_HEADER *psdhead = (PSD_HEADER*)malloc(sizeof(PSD_HEADER));
struct in_addr my_addr;
struct in_addr serv_addr;
char hostname[20],qstr[] = "quit";
char msg_tx[MSG_LEN];
char msg_rx[MSG_LEN],buf[PACKET_LEN]; /*message and buffer to send */
int on=1;
int add_len = sizeof(struct sockaddr);
//pthread_t tid;
printf("Enter the server's IP:\n");
scanf("%s",hostname);
//create a socket for communicatting
if((sockfd = socket(AF_INET,SOCK_RAW,IPPROTO_UDP)) == -1)
{
perror("socket");
exit(1);
}
//set the socket option
if(setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL,&on, sizeof(on)) < 0)
{
printf("setsockopt error!");
close(sockfd);
exit(1);
}
//get host form IP address
if((ht = gethostbyname(hostname)) == NULL)
{
perror("gethostbyname");
exit(1);
}
printf("socket success...");
//copy IP of server to server's struct
memcpy(&server.sin_addr,ht->h_addr,ht->h_length);
server.sin_family = AF_INET;
server.sin_port=htons(SERVER_PORT);
bzero(&(server.sin_addr),8);
memset(buf, 0x00, MSG_LEN);
//ip header
iphead->h_lenver = (4<<4|sizeof(IP_HEADER)/sizeof(unsigned long));
iphead->tos = 0;
iphead->id = htons((unsigned short)rand());
iphead->off = 0;
iphead->ttl = MAX_ROUTE_HOP;
iphead->proto = IPPROTO_UDP;
iphead->sum = 0;
iphead->srcIP = server.sin_addr; //测试用的环路地址127.0.0.1
iphead->dstIP = server.sin_addr;
//udp header
udphead->uh_sport = htons(CLIENT_PORT);
udphead->uh_dport = htons(SERVER_PORT);
udphead->uh_sum = 0;
//psd header
psdhead->saddr = iphead->srcIP;
psdhead->daddr = iphead->dstIP;
psdhead->mbz = 0;
psdhead->proto = iphead->proto;
//psdhead->len = udphead->uh_len;
//send message
printf("\nYou can talk now!\n");
int msg_tx_num = 0;
int msg_rx_num = 0;
printf("input msg_tx\n");
scanf("%s",msg_tx);
while(1)
{
char *ptr = buf;
printf("input msg_tx\n");
scanf("%s",msg_tx);
memset(buf, 0x00, sizeof(buf));
iphead->t_len = htons(sizeof(IP_HEADER)+sizeof(UDP_HEADER)+strlen(msg_tx));
udphead->uh_len = htons(sizeof(UDP_HEADER)+strlen(msg_tx));
psdhead->len = udphead->uh_len;
//form a packet to send
memcpy(ptr,iphead,sizeof(IP_HEADER));
ptr += sizeof(IP_HEADER);
memcpy(ptr,udphead,sizeof(UDP_HEADER));
ptr += sizeof(UDP_HEADER);
memcpy(ptr,msg_tx,strlen(msg_tx));
int len=-1;
if ((len =sendto(sockfd,buf,PACKET_LEN,0,(struct sockaddr *)(&server),sizeof(struct sockaddr))) < 0)
{
perror("sendto");
}
else
{
printf("\n发送：%d,%s\n",msg_tx_num++,msg_tx);
/*打印消息，以便调试*/
IP_HEADER *pip;
UDP_HEADER *pudp;
pip = (IP_HEADER*)buf;
pudp = (UDP_HEADER*)(buf+20);
printf("\n协议：%d,校验和：%d,源地址：%ld,目的地址：%ld\n",
pip->proto,pip->sum,(long int)(pip->srcIP.s_addr),(long int)(pip->dstIP.s_addr));
printf("源端口：%d,目的端口：%d,长度：%d\n",
pudp->uh_sport,pudp->uh_dport,pudp->uh_len);
}
memset(buf,0x00,sizeof(buf));
memset(msg_rx,0x00,sizeof(msg_rx));
usleep(2000000);
len = -1;
if((len = recvfrom(sockfd,msg_rx,PACKET_LEN,0,(struct sockaddr*)(&server),&add_len)) > 0)
{
char tmp[MSG_LEN];
memcpy(tmp,buf+sizeof(IP_HEADER)+sizeof(UDP_HEADER),MSG_LEN);
printf("%s",tmp);
}
printf("\n=====================================================================\n");
}
}

复制代码

作者: whyliyi 发布时间: 2010-08-31

(gdb) p client
$3 = {sin_family = 2, sin_port = 0, sin_addr = {s_addr = 57701834},
sin_zero = "\000\000\000\000\000\000\000"}

上边是单步调试的结果，sin_port = 0,这是为什么？

作者: whyliyi 发布时间: 2010-08-31

代码好长啊！

作者: ecjtubaowp 发布时间: 2010-08-31

recvfrom 函数的问题

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