4.p2p点对点通信

参考链接：Linux 网络编程详解三（p2p点对点聊天）https://www.cnblogs.com/zhanggaofeng/p/6131783.html?from=singlemessage&isappinstalled=0

服务器

void handler(int signo){                                                                                                         
  if(signo==SIGUSR1){                                                                                                           
    printf("child process exit\n");                                                                                              
    exit(1);                                                                                                                     
  }                                                                                                                              
}
int main(){                                                                                                                      
  int listenfd=socket(PF_INET,SOCK_STREAM,0);                                                                                    
                                                                                                                                 
  struct sockaddr_in addr;                                                                                                       
  addr.sin_family=AF_INET;                                                                                                       
  addr.sin_port=htons(8001);                                                                                                     
  addr.sin_addr.s_addr=inet_addr("127.0.0.1");                                                                                   
  int optval=1;                                                                                                                  
  setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&optval,sizeof(optval));                                                           
  bind(listenfd,(struct sockaddr*)&addr,sizeof(addr));                                                                           
  listen(listenfd,5);                                                                                                            
                                                                                                                                 
  struct sockaddr_in peer_addr;                                                                                                  
  socklen_t peer_addr_len;                                                                                                       
  int newconn=accept(listenfd,(struct sockaddr*)&peer_addr,&peer_addr_len);                                                      
  if(newconn==-1){                                                                                                               
    perror("connect fail");                                                                                                      
    close(newconn);              
    return -1;                                                                                                
  }                                                                                                                              
  else                                                                                                                           
    printf("accept by %s\n", inet_ntoa(peer_addr.sin_addr));                                                                                   
  pid_t pid=fork();        
  if(pid==-1){
    perror("fork");
    return -1;
  }                                                                                                      
  if(pid>0){ //父进程接收客户端信息，打屏                                                                                                                  
    while(1){                                                                                                                    
      char buf[1024];                                                                                                            
      int ret=read(newconn,buf,sizeof(buf));                                                                                     
      if(ret>0)                                                                                                                  
        fputs(buf,stdout);   //write(STDOUT_FILENO, buf, ret);  //打印到屏幕上                                                                                                   
      else if(ret==0){                                                                                                           
        printf("peer have close\n");   
        close(newconn);                                                                                          
        break;                                                                                                                   
      }                                                                                                                          
      else{ //recv error                                                                                                         
        printf("read<0,error\n");                                                                                                
        break;                                                                                                                   
      }                                                                                                                          
      memset(buf,0,sizeof(buf));                                                                                                 
    }            
    //发送信号，关闭子进程                                                                                                                
    kill(pid,SIGUSR1); // kill signal                                                                                           
    close(listenfd);                                                                                                             
    close(newconn);   
     
    //wait子进程
    int ret=0;
    while(1)
    {
        ret=wait(NULL);
        printf("子进程pid=%d\n",ret);
        if(ret==-1)
        {
            if(errno==EINTR)
                continue;
            break;
        }
    }     
                                                                                                         
  }                                                                                                                              
  else if(pid==0){  //子进程读取用户输入，发送给客户端                                                                                                             
    close(listenfd); //关闭服务器监听套接字                                                                                                            
    signal(SIGUSR1,handler);  //安装信号                                                                                                  
                                                                                                                                 
    char buf[1024];                                                                                                              
    while(fgets(buf,sizeof(buf),stdin)!=NULL){ //while(read(STDIN_FILENO, sendbuf, 1024) == -1)                                                                                   
      write(newconn,buf,strlen(buf));                                                                                            
      memset(buf,0,sizeof(buf));
    }
  }
}

客户端

int main(){
  int sockfd=socket(PF_INET,SOCK_STREAM,0);                                                                                      
                                                                                                                                 
  struct sockaddr_in svr_addr;                                                                                                   
  svr_addr.sin_family=AF_INET;                                                                                                   
  svr_addr.sin_port=htons(8001);                                                                                                 
  svr_addr.sin_addr.s_addr=inet_addr("127.0.0.1");                                                                               
                                                                                                                                 
  int ret=connect(sockfd,(struct sockaddr*)&svr_addr,sizeof(svr_addr));                                                          
  if(ret==-1){                                                                                                                   
    perror("connect");                                                                                                           
    exit(1);                                                                                                                     
  }                                                                                                                              
  else                                                                                                                           
    printf("connect server sucess\n");                                                                                           
                                                                                                                                 
  pid_t pid=fork();  
  if (pid == -1){
      perror("fork() err");
      return -1;
  }                                                                                                              
  if(pid>0){ //父进程
    char buf[1024]={0};                                                                                                          
    while(fgets(buf,sizeof(buf),stdin)!=NULL){                                                                                   
      write(sockfd,buf,strlen(buf));                                                                                             
      memset(buf,0,sizeof(buf));                                                                                                 
    }                                                                                                                            
  }                  
  else if(pid==0){//子进程接收信息，打屏
    while(1){                                                                                                                    
      char buf[1024];                                                                                                            
      int ret=read(sockfd,buf,sizeof(buf));                                                                                      
      if(ret>0)                                                                                                                  
        fputs(buf,stdout); //打屏                                                                                                      
      else if(ret==0){                                                                                                           
        printf("peer have close\n");   
        close(sockfd);                                                                                          
        break;                                                                                                                   
      }                                                                                                                          
      else{                                                                                                                      
        printf("read<0,error\n");                                                                                                
        break;                                                                                                                   
      }                                                                                                                          
      memset(buf,0,sizeof(buf));                                                                                                 
    }                                                                                                                            
    close(sockfd);                                                                                                               
    kill(getppid(),SIGKILL);                                                                                                     
    exit(1);                                                                                                                     
  }                                                                                                                                                                                                                                               
  return 0;                                                                                                                      
}