关于socket客户端发送数据正常，而服务器收到的数据为空

Question

我写了一个简单的聊天程序，服务器和客户端接受发送数据都通过定义的同一个结构体，为什么在本机测试，开两个终端都没有问题，客户端和服务器分开在不同的电脑上测试时，客户端发送数据正常，而此时服务器收到的结构体里的数据为空是怎么回事？服务器用的epoll单线程，客户端用的双线程

Answer 1

服务器代码

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include"message.h"

#define PORT 6666 //服务器端口
#define LISTEN_SIZE 1024 //连接请求队列的最大长度
#define EPOLL_SIZE 1024 //监听的客户端的最大数目
#define BUF_MAX 257 //读取缓存区最大字节

time_t timep; //记录当前时间

typedef struct cli_data //记录在线用户信息的结构体
{
int cli_fd; //记录连接的用户套接字
char username[21]; //记录账号，最大20位
struct cli_data* next;
}cli_data;
typedef struct user //记录用户账号信息的结构体
{
char username[21];
char pwd[21];
}user;
typedef struct group
{
char username[100][21];
int groupfd[100];
char groupname[21];
int n;
}group;
group taolun[100]; //全局讨论组
char* my_time() //输出当前时间
{
time(&timep);
char* p=ctime(&timep);
return p;
}

cli_data* head; //创建头结点
cli_data* create() //创建一个带头节点的链表，储存已连接的用户
{
cli_data* head;
head=(cli_data*)malloc(sizeof(struct cli_data));
head->next=NULL;
return head;
}
cli_data* insert() //插入链表
{

cli_data* temp=head;
cli_data* new;
new=(cli_data*)malloc(sizeof(cli_data));
new->next=NULL;

while(temp->next!=NULL)
{
    temp=temp->next;
}  
temp->next=new;

return new;

}
void delete(cli_data* head,int cli_fd) //链表的删除
{
cli_data* temp,*last;
temp=head->next;
last=head;
while(temp!=NULL&&temp->cli_fd!=cli_fd)
{
last=temp;
temp=temp->next;
}
if(temp!=NULL&&temp->cli_fd==cli_fd)
{
last->next=temp->next;
free(temp);
}
}
void my_err(char* string)
{
perror(string);
exit(1);
}
void my_path(char*dir,char* filename,char* path) //将目录和文件名连接成一个路径
{
strcpy(path,dir);
strcat(path,"/");
strcat(path,filename);
}
void send_message(struct message recv_buf,int conn_fd) //向客户端发送信息
{
struct message send_buf;
send_buf=recv_buf;
int n=send_buf.n;
int fd;
struct user user_data;
int ret=0; //用来表示注册账号是否存在或账号密码信息是否匹配
FILE* fp;
cli_data* temp; //在线用户链表临时指针
char path[256]; //储存文件路径
char friendname[21]; //储存用户好友用户名
int i=0;
fp=fopen("passwd.txt","a+");
fclose(fp);

switch(n)
{
    case 0:  {  //注册账号
    if((fd=open("passwd.txt",O_RDWR|O_APPEND))<0)
    {
        my_err("open");
    }
    while(read(fd,&user_data,sizeof(struct user))>0)
    {
        if(strcmp(user_data.username,send_buf.username)==0)
        {
            send_buf.n=-2;
            ret=1;
            break;
        }
    }
    if(!ret)
    {
        strcpy(user_data.username,recv_buf.username);
        strcpy(user_data.pwd,recv_buf.pwd1);
        send_buf.n=22;
        if(write(fd,&user_data,sizeof(struct user))<0)
        {
            my_err("write");
        }
        close(fd);

        int fd,stdoutfd;
        fd=open("log_file",O_RDWR|O_CREAT|O_APPEND);
        stdoutfd=dup(1);
        printf("a user register,username:%s,time:%s",user_data.username,my_time());
        dup2(fd,1);
        printf("a user register,username:%s,time:%s",user_data.username,my_time());
        dup2(stdoutfd,1);
        close(fd);
        close(stdoutfd);


        mkdir(user_data.username,07777);  //创建用户所属目录
        my_path(user_data.username,user_data.username,path);
        fd=open(path,O_RDWR|O_CREAT|O_APPEND,0777);
        if(fd<0)
        {
            printf("创建用户好友文件失败\n");
        }
        close(fd);




    }
    if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
    {
        printf("向客户端发送数据失败\n");
    }
    break;
}

    case 1:  {//登陆 
    if((fd=open("passwd.txt",O_RDONLY))<0)
    {
        my_err("open");
    }
    while(read(fd,&user_data,sizeof(struct user))>0)
    {
        if(strcmp(user_data.username,send_buf.username)==0)
        {
            if(strcmp(user_data.pwd,send_buf.pwd1)==0)
            {
                ret=1;
                break;
            }
        }
    }
    if(ret)
    send_buf.n=11;
    else
    send_buf.n=-1;
    if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
    {
        printf("向客户端发送数据失败\n");
        return;
    }
    if(send_buf.n==11)
    {
      int fd,stdoutfd;
      fd=open("log_file",O_CREAT|O_RDWR|O_APPEND);
      printf("a user is login,username:%s,time:%s",send_buf.username,my_time());
      stdoutfd=dup(1);
      dup2(fd,1);
      printf("a user is login,username:%s,time:%s",send_buf.username,my_time());
      dup2(stdoutfd,1);
      close(fd);
      close(stdoutfd);

      temp=insert();
      temp->cli_fd=conn_fd;
      strcpy(temp->username,send_buf.username);

      my_path("lixian",send_buf.username,path);  //发送离线消息
      fd=open(path,O_RDONLY);
      if(fd>0)
      {
          send_buf.n=6;
          while(read(fd,send_buf.time,sizeof(send_buf.time))!=0)
          {
              read(fd,send_buf.from,sizeof(send_buf.from));
              read(fd,send_buf.chat,sizeof(send_buf.chat));
              if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
              {
                  printf("向客服端发送离线消息失败\n");
                  return;
              }
          }
          close(fd);
          fd=open(path,O_RDWR|O_CREAT|O_TRUNC);
          close(fd);
      }
    }

    break;
}


    case 3:   { //添加好友
    temp=head->next;

    my_path(send_buf.from,send_buf.from,path);           //防止重复添加好友
    fd=open(path,O_RDONLY);
    if(fd<0)
    {
        printf("打开用户好友文件失败\n");
        return;
    }
    while(read(fd,friendname,sizeof(friendname))!=0)
    {
        if(strcmp(friendname,send_buf.to)==0)
        {
            send_buf.n=-3;
            if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
            {
                printf("向客户端发送数据失败\n");
                return;
            }
            close(fd);
            return;
        }
    }
    while(temp!=NULL)
    {

        if(strcmp(temp->username,send_buf.to)==0)  //找到指定在线好友
        { 
           ret=1;
            break;
        }
        temp=temp->next;
    }
    if(ret)
    {


        int to_fd=temp->cli_fd;        //向另一用户征求是否同意添加好友


        send(to_fd,&send_buf,sizeof(struct message),0);
        recv(to_fd,&send_buf,sizeof(struct message),0);


        if(send_buf.n==33)
        {
            my_path(send_buf.from,send_buf.from,path);//写入用户好友文件
            fd=open(path,O_RDWR|O_APPEND);
            if(write(fd,&send_buf.to,sizeof(send_buf.to))<0)
            {
              printf("写入用户好友失败\n");
              send_buf.n=-3;
            }
            close(fd);
           my_path(send_buf.from,send_buf.to,path);   //创建用户与该好友的聊天记录文件
           fd=open(path,O_RDWR|O_CREAT|O_TRUNC,0777);
           close(fd);


            my_path(send_buf.to,send_buf.to,path);    //写入另一用户好友文件
            fd=open(path,O_RDWR|O_APPEND);
            write(fd,&send_buf.from,sizeof(send_buf.from));
            close(fd);
            my_path(send_buf.to,send_buf.from,path);  //创建另一用户与该好友的聊天记录文件
            fd=open(path,O_RDWR|O_CREAT|O_TRUNC,0777);
            close(fd);

        }
    }

    else
    send_buf.n=-3;
    if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
    {
        printf("send error\n");
    }
    break;
}

    case 4:   {//查看好友列表 
    my_path(recv_buf.username,recv_buf.username,path);  //连接用户好友文件路径
    fd=open(path,O_RDONLY);
    while(read(fd,send_buf.friendname[i++],sizeof(recv_buf.username))!=0);
    send_buf.friendname[i][0]='\0';

    if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
    {
        printf("send error\n");

    }
    break;}

    case 44:    { //查看在线好友
    my_path(recv_buf.username,recv_buf.username,path);  //连接用户好友文件路径
    fd=open(path,O_RDONLY);


    while(read(fd,friendname,sizeof(friendname))!=0)
    {
        int n=0;
        temp=head->next;
        while(temp!=NULL)
        {
            if(strcmp(temp->username,friendname)==0)
            {
                n=1;
                break;
            }
            else
            temp=temp->next;
        }
        if(n)
        {
            strcpy(send_buf.friendname[i++],friendname);
        }

    }
    send_buf.friendname[i][0]='\0';
    if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
    {
       printf("send error\n");                                                    
    }
    break;
   }

    case 5:    //删除好友
   {
       int i=0;
       int ret=0;
       my_path(send_buf.from,send_buf.from,path);
       fd=open(path,O_RDONLY);
       if(fd<0)
       {
           printf("打开用户好友文件失败\n");
           send_buf.n=-5;
       }
       while(read(fd,send_buf.friendname[i++],sizeof(send_buf.username))!=0)
       send_buf.friendname[i][0]='\0';
       i=0;
       close(fd);
       while(strlen(send_buf.friendname[i])!=0)
       {
           if(strcmp(send_buf.friendname[i],send_buf.to)==0)
           {
               strcpy(send_buf.friendname[i],"\n");
               ret++;
           }
           i++;
       }
       fd=open(path,O_RDWR|O_CREAT|O_TRUNC);
       if(fd<0)
       {
           printf("打开用户好友文件失败\n");
           send_buf.n=-5;

       }
       i=0;
       while(strlen(send_buf.friendname[i])!=0)
       {
           if(strcmp(send_buf.friendname[i],"\n")!=0)
           {
               if(write(fd,send_buf.friendname[i],sizeof(send_buf.username))<0)
               {
                   printf("写入用户好友文件失败\n");
                   send_buf.n=-5;
               }
           }
           i++;

       }
       close(fd);


       i=0;
       my_path(send_buf.to,send_buf.to,path);
       fd=open(path,O_RDONLY);      //读取删除对象的好友列表
       if(fd<0)
       {
           printf("打开删除对象好友文件失败\n");
           send_buf.n=-5;
       }
       while(read(fd,send_buf.friendname[i++],sizeof(send_buf.username))!=0);
       send_buf.friendname[i][0]='\0';
       close(fd);
       i=0;

       while(strlen(send_buf.friendname[i])!=0)
       {
           if(strcmp(send_buf.friendname[i],send_buf.from)==0)
           strcpy(send_buf.friendname[i],"\n");
           i++;
       }
       i=0;
       fd=open(path,O_RDWR|O_CREAT|O_TRUNC);
       if(fd<0)
       {
           printf("打开删除对象好友文件失败\n");
           send_buf.n=-5;
       }
       while(strlen(send_buf.friendname[i])!=0)
       {
           if(strcmp(send_buf.friendname[i],"\n")!=0)
           {
               if(write(fd,send_buf.friendname[i],sizeof(send_buf.username))<0)
               {
                   printf("写入删除对象好友文件失败\n");
                   send_buf.n=-5;
               }
           }
           i++;
       }
       close(fd);
       ret++;
       if(ret==2)
       send_buf.n=55;
       else
       send_buf.n=-5;

       if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
       {
           printf("向客户端发送信息失败\n");
           return;
       }
       break;
   }

   case 6:   //私聊
   {

       int i=0,ret=0;
       my_path(send_buf.from,send_buf.from,path);
       fd=open(path,O_RDONLY);
       while(read(fd,send_buf.friendname[i++],sizeof(send_buf.username))!=0);
       send_buf.friendname[i][0]='\0';
       close(fd);
       i=0;
       while(strlen(send_buf.friendname[i])!=0)
       {
           if(strcmp(send_buf.friendname[i],send_buf.to)==0)
           {
               ret=1;
               break;

           }
           i++;
       }
       if(ret)
       {
           temp=head->next;
           while(temp!=NULL)
           {
               if(strcmp(temp->username,send_buf.to)==0)
               {
                   my_path(send_buf.from,send_buf.to,path);
                   fd=open(path,O_RDWR|O_CREAT|O_APPEND);
                   if(fd<0)
                   {
                       printf("打开记录用户聊天记录文件失败\n");
                   }

                   if(send(temp->cli_fd,&send_buf,sizeof(struct message),0)<0)
                   {
                       printf("发送用户消息失败\n");
                       return;
                   }
                   else
                   {
                       int stdoutfd=dup(1);
                       dup2(fd,1);
                       printf("%s",send_buf.time);
                       printf("我@%s:%s\n",send_buf.to,send_buf.chat);
                       dup2(stdoutfd,1);
                       close(fd);

                       my_path(send_buf.to,send_buf.from,path);
                       open(path,O_RDWR|O_CREAT|O_APPEND);
                       if(fd<0)
                       {
                           printf("打开记录用户聊天记录文件失败\n");
                           return;
                       }
                       dup2(fd,1);
                       printf("%s",send_buf.time);
                       printf("%s@我:%s\n",send_buf.from,send_buf.chat);
                       dup2(stdoutfd,1);
                       close(fd);
                       close(stdoutfd);

                       return;
                   }

               }
               temp=temp->next;
           }
           my_path("lixian",send_buf.to,path);

           fd=open(path,O_RDWR|O_CREAT|O_APPEND,0777);
           if(fd<0)
           {
               printf("打开指定用户离线消息文件\n");
               return;
           }
           write(fd,send_buf.time,sizeof(send_buf.time));
           write(fd,send_buf.from,sizeof(send_buf.from));
           write(fd,send_buf.chat,sizeof(send_buf.chat));
           close(fd);

       }
       else
       {
           send_buf.n=-6;
           if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
           {
               printf("向客户端发送信息失败\n");
               return;
           }
       }
       break;

   }

   case 77:   //创建讨论组
   {
       int i=1;
       while(taolun[i].n!=0)
       i++;
       if(i<100)
       {
           taolun[i].n=1;
           send_buf.groupi=i;
           strcpy(taolun[i].username[0],send_buf.from);
           strcpy(taolun[i].groupname,send_buf.groupname);
           taolun[i].groupfd[0]=conn_fd;
       }
       else
       send_buf.n=-77;

       if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
       {
           printf("向客户发送信息失败\n");
           return;
       }
       break;

   }

   case 777:   //邀请在线好友加入讨论组
   {
       int ret=0;
       int i=0;
       my_path(send_buf.from,send_buf.from,path);
       fd=open(path,O_RDONLY);
       if(fd<0)
       {
           printf("打开用户好友文件失败\n");
           send_buf.n=-777;
       }
       while(read(fd,send_buf.friendname[i],sizeof(send_buf.username))!=0)
       {
           if(strcmp(send_buf.to,send_buf.friendname[i])==0)
           {
               ret=1;
               break;
           }
       }
       if(ret)
       {
           temp=head->next;
           while(temp!=NULL)
           {
               if(strcmp(send_buf.to,temp->username)==0)
               {
                   int j=0,k=send_buf.groupi;
                   send(temp->cli_fd,&send_buf,sizeof(struct message),0);
                   while(taolun[k].groupfd[j]!=0)
                   {
                       j++;
                   }
                   taolun[k].groupfd[j]=temp->cli_fd;
                   strcpy(taolun[k].username[j],send_buf.to);
                   return;
               }
               temp=temp->next;
           }
       }
       send_buf.n=-777;
       send(conn_fd,&send_buf,sizeof(struct message),0);
       break;
   }

   case 7:  //群聊
   {

       int i=send_buf.groupi,j=0;
       while(taolun[i].groupfd[j]!=0)
       {
           if(taolun[i].groupfd[j]!=conn_fd&&taolun[i].groupfd[j]!=-1)
           {
               send(taolun[i].groupfd[j],&send_buf,sizeof(struct message),0);
           }
           j++;
       }
       break;
   }

   case -7: //退出讨论组
   {
       int i=send_buf.groupi,j=0;
       while(taolun[i].groupfd[j]!=conn_fd)
       {
           j++;
       }
       if(j==0)
       {
           j=1;
           send_buf.n=-7777;
           while(taolun[i].groupfd[j]!=0&&taolun[i].groupfd[j]!=-1)
           {
               send(taolun[i].groupfd[j],&send_buf,sizeof(struct message),0);
               j++;
           }
           taolun[i].n=0;
           memset(&taolun[i],0,sizeof(taolun[i]));
       }
       else
       taolun[i].groupfd[j]=-1;
       break;
   }

   case 7777:  //查看讨论组成员
   {
       int i=send_buf.groupi,j=0,k=0;;
       while(taolun[i].groupfd[j]!=0&&taolun[i].groupfd[j]!=-1)
       {
           strcpy(send_buf.friendname[k++],taolun[i].username[j]);
           j++;
       }
       send_buf.friendname[k][0]='\0';
       send(conn_fd,&send_buf,sizeof(struct message),0);
       break;

   }

   case 8:   //查看与好友聊天记录
   {
       int j=0,ret=0;
       send_buf.n=-8;
       temp=head->next;
       my_path(send_buf.from,send_buf.from,path);
       fd=open(path,O_RDONLY);
       while(read(fd,send_buf.friendname[j++],sizeof(send_buf.username))!=0);
       send_buf.friendname[j][0]='\0';
       j=0;
       while(strlen(send_buf.friendname[j])!=0)
       {
           if(strcmp(send_buf.to,send_buf.friendname[j])==0)
           {
              ret=1;
              break;
           }
           j++;

       }
       if(ret)
       {
           FILE * fp;
           j=0;
           my_path(send_buf.from,send_buf.to,path);
           fp=fopen(path,"r+");
           while(!feof(fp))
           {
               fgets(send_buf.chathistory[j],10000,fp);
               j++;
               if(j==100)
               break;
           }
           send_buf.n=8;
       }
       if(send(conn_fd,&send_buf,sizeof(struct message),0)<0)
       {
           printf("向客户端发送数据失败\n");
           return;
       }

   }

}

}
int main()
{
int sock_fd,conn_fd; //储存套接字
struct sockaddr_in cli_addr,serv_addr;
struct message recv_buf; //读取缓存区
socklen_t cli_len;
int epollfd;
struct epoll_event event;
struct epoll_event* events;
int fd;

memset(taolun,0,sizeof(taolun));

fd=open("log_file",O_RDWR|O_CREAT|O_APPEND);
close(fd);


//创建一个套接字
sock_fd=socket(AF_INET,SOCK_STREAM,0);
if(sock_fd<0)
{
    my_err("socket");
}
//设置该套接字使之可以重新绑定端口
int optval=1;
if(setsockopt(sock_fd,SOL_SOCKET,SO_REUSEADDR,(void*)&optval,sizeof(int))<0)
{
    my_err("setsockopt");
}
//初始化服务器端地址结构
memset(&serv_addr,0,sizeof(struct sockaddr_in));
serv_addr.sin_family=AF_INET;
serv_addr.sin_port=htons(PORT);
serv_addr.sin_addr.s_addr=htonl(INADDR_ANY);
if(bind(sock_fd,(struct sockaddr*)&serv_addr,sizeof(struct sockaddr_in))<0)
{
    my_err("bind");
}
//将套接字转化为监听套接字
if(listen(sock_fd,LISTEN_SIZE)<0)
{
    my_err("listen");
}
cli_len=sizeof(struct sockaddr_in);
events=(struct epoll_event*)malloc(sizeof(struct epoll_event)*EPOLL_SIZE);
//创建一个监听描述符epoll,并将监听套接字加入
epollfd=epoll_create(EPOLL_SIZE);
if(epollfd==-1)
{
    my_err("epoll_create");
}
event.events = EPOLLIN;
event.data.fd = sock_fd;
if(epoll_ctl(epollfd,EPOLL_CTL_ADD,sock_fd,&event)<0)
{
    my_err("epoll_ctl");
}

mkdir("lixian",0777);  //创建离线消息目录

head=create();  //创建链表
while(1)
{
    int sum=0,i;
    sum=epoll_wait(epollfd,events,EPOLL_SIZE,-1);
    for(i=0;i<sum;i++)
    {
        if(events[i].data.fd==sock_fd)    //有请求连接
        {
            int fd,stdoutfd;
            fd=open("log_file",O_RDWR|O_CREAT|O_APPEND);
            stdoutfd=dup(1);

            conn_fd=accept(sock_fd,(struct sockaddr*)&cli_addr,&cli_len);
            if(conn_fd<0)
            {
                my_err("accept");
            }

            event.events = EPOLLIN | EPOLLRDHUP;
            event.data.fd = conn_fd;
            if(epoll_ctl(epollfd,EPOLL_CTL_ADD,conn_fd,&event)<0)   //将新连接的套接字加入监听
            {
                my_err("epoll_ctl");
            }
            printf("a connet is connected,ip is %s,time:%s",inet_ntoa(cli_addr.sin_addr),my_time());
            dup2(fd,1);
            printf("a connet is connected,ip is %s,time:%s",inet_ntoa(cli_addr.sin_addr),my_time());
            dup2(stdoutfd,1);
            close(fd);
            close(stdoutfd);

        }
        else if(events[i].events&EPOLLIN)    //有可读的套接字
        {

            memset(&recv_buf,0,sizeof(struct message));  
            recv(events[i].data.fd,&recv_buf,sizeof(struct message),0);
            send_message(recv_buf,events[i].data.fd);

        }
        if(events[i].events&EPOLLRDHUP)
        {
            int fd,stdoutfd;
            fd=open("log_file",O_RDWR|O_CREAT|O_APPEND);
            stdoutfd=dup(1);
            delete(head,events[i].data.fd);
            printf("a connet is quit,ip is %s,time:%s",inet_ntoa(cli_addr.sin_addr),my_time());
            dup2(fd,1);
            printf("a connet is quit,ip is %s,time:%s",inet_ntoa(cli_addr.sin_addr),my_time());
            dup2(stdoutfd,1);
            close(fd);
            close(stdoutfd);
            epoll_ctl(epollfd,EPOLL_CTL_DEL,events[i].data.fd,&event);
            close(events[i].data.fd);
        }
    }
}
return 0;

}