Question

当我尝试将数据从tcp服务器发送到tcp客户端时，我一直收到“错误的文件描述符”错误。这对套接字来说意味着什么？我已经在这一段时间了，我不知道我的代码有什么问题。它与我两天前使用的代码基本相同，代码运行正常。我希望有人能告诉我在尝试通过套接字发送时文件描述符不正确的常见原因以及如何检查/修复它们。任何帮助表示赞赏。我将在下面发布一些代码以防万一。

/*Waits to connect a client. Returns true if successful*/
bool TcpServer::launchServer() {
int status;

struct addrinfo hints;
struct addrinfo *servinfo;  //will point to the results

//store the connecting address and size
struct sockaddr_storage their_addr;
socklen_t their_addr_size;


memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET;  //ipv4
hints.ai_socktype = SOCK_STREAM; //tcp

//get server info, put into servinfo
if ((status = getaddrinfo("192.168.2.3", port, &hints, &servinfo)) != 0) {
    printf("\ngetaddrinfo error: %m", errno);
    return false;
}

//make socket
fd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (fd < 0) {
    printf("\nserver socket failure %m", errno);
    return false;
}

//allow reuse of port
int yes=1;
if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,(char*) &yes,sizeof(int)) == -1) {
    perror("setsockopt");
    return false;
}

//bind
if(bind (fd, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
    printf("\nBind error %m", errno);
    return false;
}

//free up space
freeaddrinfo(servinfo);

//listen
if(listen(fd, 5) < 0) {
    printf("\nListen error %m", errno);
    return false;
}
their_addr_size = sizeof(their_addr);


//accept
comm_fd = accept(fd, (struct sockaddr*)&their_addr, &their_addr_size);
if( comm_fd < 0) {
    printf("\nAccept error %m", errno);
    return false;
}

return true;
}   //END LAUNCHSERVER






void TcpServer::communicate() {


fd_set read_flags,write_flags; // the flag sets to be used
struct timeval waitd = {10, 0};          // the max wait time for an event
int sel;        // holds return value for select();
int numRead;    //holds return value for read()
int numSent;    //holds return value for send()
char in[255];   //in buffer
char out[255];  //out buffer

//clear buffersz
memset(&in, 0, 255);
memset(&out, 0, 255);


while(!done) {
    FD_ZERO(&read_flags);
    FD_ZERO(&write_flags);
    FD_SET(comm_fd, &read_flags);
    FD_SET(comm_fd, &write_flags);
    FD_SET(STDIN_FILENO, &read_flags);
    FD_SET(STDIN_FILENO, &write_flags);

    //call select
    sel = select(comm_fd+1, &read_flags, &write_flags, (fd_set*)0, &waitd);

    //if an error with select
    if(sel < 0)
        continue;

    //if socket ready for reading
    if(FD_ISSET(comm_fd, &read_flags)) {

        //clear set
        FD_CLR(comm_fd, &read_flags);

        memset(&in, 0, 255);

        numRead = recv(comm_fd, in, 255, 0);
        //if an error, exit
        if(numRead < 0) {
            printf("\nError reading %m", errno);
            myAgent->getRobot()->pauseSensorStream();
            done = true;
        }   //end if error
        //if connection closed, exit
        else if(numRead == 0) {
            printf("\nClosing socket");
            close(comm_fd);
            done = true;
        }   //end if connection closed
        //if message, call getsendback
        else if(in[0] != '\0') {
            //std::cout<<"\nClient: "<<in;
            getSendBack(in);
        }   //end if message
    }   //end if ready for read


    //if stdin is ready for reading
    if(FD_ISSET(STDIN_FILENO, &read_flags))
        fgets(out, 255, stdin);


    //if socket ready for writing
    if(FD_ISSET(comm_fd, &write_flags)) {

        //printf("\nSocket ready for write");
        FD_CLR(comm_fd, &write_flags);

        //check validity by checking for a digit
        if(isdigit(out[0])) {

            //create message to send
            std::stringstream tosend;
            tosend<<"@ "<<out;
            //std::cout<<"\ntosend: "<<tosend.str();

            //send
            //********ERROR HAPPENS HERE PRINTS OUT MESSAGE BELOW******
            numSent = send(comm_fd, tosend.str().c_str(), tosend.str().length(), 0);
        }   //end if valid message
        //if error, exit
        if(numSent < 0) {
            printf("\nError sending %m", errno);
            done = true;
        }   //end if error
        //wait for message to get there, then clear
        usleep(5000);
        memset(&out, 0, 255);
    }   //end if
}   //end while
}   //END COMMUNICATE

客户端代码基本相同。

Answer 1

当errno为EBADF时，您的程序会打印“Bad file descriptor”。从发送的手册页：

EBADF =指定了无效的描述符。

我非常确定在send（）调用之前套接字已关闭。这可能发生，因为程序可以在“连接关闭”分支后进入“准备写入”分支。

尝试以下方法：

else if(numRead == 0) {
    printf("\nClosing socket");
    close(comm_fd);
    break;
}

而不是：

    else if(numRead == 0) {
        printf("\nClosing socket");
        close(comm_fd);
        done = true;
    }

Answer 2

你回答了自己的问题。如果没有显式初始化numSent和numRead，你会得到垃圾，这可能恰好是numSent的负数，如果out []数组中没有数字，会导致错误。

带有BSD套接字的错误文件描述符

2 个答案: