C/C++ TCP Socket Server Read

Question

I want to create a server and client, running on linux such that

1. Connection is established
2. Client sends a message to the server
3. Server sends a response to the client
4. End connection

Using http://www.thegeekstuff.com/2011/12/c-socket-programming/, this is what I came up with.

TCPSockets.cpp

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

int createConnection(char *ipaddr)
{
    int sockfd = 0;
    struct sockaddr_in serv_addr;

    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("\n Error : Could not create socket \n");
        return -1;
    }

    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(5000);

    if(inet_pton(AF_INET, ipaddr, &serv_addr.sin_addr)<=0)
    {
        printf("\n inet_pton error occured\n");
        return -1;
    }

    if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
       printf("\n Error : Connect Failed \n");
       return -1;
    }

    return sockfd;
}

void receiveMessage(int sockfd)
{
    int n = 0;
    char recvBuff[1024];

    memset(recvBuff, '0',sizeof(recvBuff));

    while ( (n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) > 0)
    {
        std::cout<<"recvBuff="<<recvBuff<<std::endl;
        recvBuff[n] = 0;
        if(fputs(recvBuff, stdout) == EOF)
        {
            printf("\n Error : Fputs error\n");
        }
    }

    if(n < 0)
    {
        printf("\n Read error \n");
    }
}

int createListeningSocket()
{
    int listenfd = 0;
    struct sockaddr_in serv_addr;

    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(5000);

    bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

    listen(listenfd, 10);

    return listenfd;
}

void sendMessage(int connfd, char * format) {
    char sendBuff[1025];
    memset(sendBuff, '0', sizeof(sendBuff));

    snprintf(sendBuff, sizeof(sendBuff), format);
    write(connfd, sendBuff, strlen(sendBuff));
}

Server.cpp

#include "TCPSockets.cpp"

int main(int argc, char *argv[]) {
    std::cout<<"Creating socket..."<<std::endl;
    int listeningSocketDescriptor = createListeningSocket();
    std::cout<<"Socket created."<<std::endl;

    std::cout<<"Waiting for connection..."<<std::endl;
    int clientSocketDescriptor = accept(listeningSocketDescriptor, (struct sockaddr*)NULL, NULL);
    std::cout<<"Connection made."<<std::endl;

    std::cout<<"Waiting for message..."<<std::endl;
    receiveMessage(listeningSocketDescriptor);
    std::cout<<"Message received."<<std::endl;

    std::cout<<"Sending message..."<<std::endl;
    sendMessage(clientSocketDescriptor, "From server!");
    std::cout<<"Message sent."<<std::endl;

    std::cout<<"Closing client socket..."<<std::endl;
    close(clientSocketDescriptor);
    std::cout<<"Client socket closed."<<std::endl;

    close(listeningSocketDescriptor);

    return 0;
}

Client.cpp

#include "TCPSockets.cpp"

int main(int argc, char *argv[]) {
    if(argc != 2)
    {
        printf("\n Usage: %s <ip of server> \n",argv[0]);
        return 1;
    }

    std::cout<<"Creating connection..."<<std::endl;
    int socketDescriptor = createConnection(argv[1]);
    if (socketDescriptor < 0)
    {
        return 1;
    }
    std::cout<<"Connection created."<<std::endl;

    std::cout<<"Sending message..."<<std::endl;
    sendMessage(socketDescriptor, "From client!");
    std::cout<<"Message sent."<<std::endl;

    std::cout<<"Waiting for response..."<<std::endl;
    receiveMessage(socketDescriptor);
    std::cout<<"Response received."<<std::endl;

    return 0;
}

Everything works except the server receiving a message. What am I doing wrong?

Answer 1

Your code is:

int clientSocketDescriptor = accept(listeningSocketDescriptor, 
                                              (struct sockaddr*)NULL, NULL);
receiveMessage(listeningSocketDescriptor);

But you should read bytes from a client socket descriptor returned from accept():

int cs = accept(listeningSocketDescriptor, (struct sockaddr*)NULL, NULL);
receiveMessage(cs);

not from the listeningSocketDescriptor.