无法通过 sockets 发送或接收数据

Question

I tried making a simple server-client socket communication but something seems to no work properly with the server. I get this error whenever I send or receive:

Socket operation on non-socket: Socket operation on non-socket

Strangely enough, this only appears whenever the server is sending. the client seems to be ok:

//server
#include <iostream>
#include <sys/socket.h>
#include <string.h>
#include <netinet/in.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <arpa/inet.h>

using namespace std;

int main(){
    const int PORT = 5000;
    int serverfd, clientfd, opt=1, n_send, n_recv;
    sockaddr_in server_address, client_address;
    char recvbuf[1024], sendbuf[1024];
    bzero(&server_address , sizeof(server_address));
    inet_pton(AF_INET, "127.0.0.1",&server_address.sin_addr);
    int x = INADDR_ANY;
    server_address.sin_family = AF_INET;
    server_address.sin_port = htons(PORT);

    socklen_t addrSize = sizeof(server_address);

    if((serverfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }
    if((setsockopt(serverfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) < 0){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }
    if((bind(serverfd, (sockaddr*)&server_address, sizeof(server_address)))< 0){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }
    if((listen(serverfd, 1))< 0){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }
    if((clientfd = accept(serverfd, (sockaddr *)&server_address, (socklen_t*)&addrSize) < 0)){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }

    while (true){
        cout << "SAY TO CLIENT: ";
        bzero(sendbuf, sizeof(sendbuf));
        cin >> sendbuf;
        cout << endl;
        send(clientfd, sendbuf, strlen(sendbuf), 0);
        errno = 0;
        bzero(recvbuf, sizeof(recvbuf));
        if((n_recv = recv(clientfd, recvbuf, sizeof(recvbuf), MSG_WAITALL))< 0){
            perror(strerror(errno));
            exit(EXIT_FAILURE);
        }
        cout << recvbuf << endl;
    }

    return 0;
}

//client
#include <iostream>
#include <sys/socket.h>
#include <string.h>
#include <netinet/in.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <arpa/inet.h>

using namespace std;

int main(){
    const int PORT = 5000;
    int sockfd, n_send, n_recv;
    char recvbuf[1024], sendbuf[1024];
    sockaddr_in server_address;
    bzero(&server_address, sizeof(server_address));
    server_address.sin_family= AF_INET;
    server_address.sin_port = htons(PORT);
    inet_pton(AF_INET, "127.0.0.1", &server_address.sin_addr);
    if((sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }
    if(connect(sockfd, (sockaddr *) &server_address, sizeof(server_address))<0){
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }
    while (true){
        if((n_recv = recv(sockfd, recvbuf, sizeof(recvbuf), MSG_WAITALL)) < 0){
            perror(strerror(errno));
            exit(EXIT_FAILURE);
        }
        cout << "Server: " << recvbuf << endl;
        cout << "Say to server: ";
        cin >> sendbuf;
        cout << endl;
        if((n_send = send(sockfd, sendbuf, sizeof(sendbuf), 0)) < 0){
            perror(strerror(errno));
            exit(EXIT_FAILURE);
        }
    }
    return 0;
}

Answer 1

clientfd is assigned a non-socket value. If we change the whitespace in your if :

if((clientfd =
     accept(serverfd, (sockaddr *)&server_address, (socklen_t*)&addrSize) < 0
   )) {
        perror(strerror(errno));
        exit(EXIT_FAILURE);
    }

Because of the way you wrote it, the result of accept (the presumably valid socket) is checked, and that result is set to clientFd . Note that your parenthesis placement doesn't match your other lines.