client not connecting with server C (Socket programming)

Question

I have a very simple client and server code:

client

int sockfd = 0;
    int bytesReceived = 0;
    char recvBuff[BUFSIZE];
    memset(recvBuff, '0', sizeof(recvBuff));
    struct sockaddr_in serv_addr;
    printf("here i am\n");
    /* Create a socket first */
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0))< 0){
        printf("\n Error : Could not create socket \n");
        return 1;
    }
    fprintf(stderr, "connection stats\n");
    fprintf(stderr, "connecting to %d - %s \n",port,server);
    /* Initialize sockaddr_in data structure */
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(port); // port
    serv_addr.sin_addr.s_addr = server;
    printf(" attempting connection %s:%d\n", server, port);
    /* Attempt a connection */
     int con =  connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
     printf("Error %d\n", con);
    exit(-1);

And server

   int listenfd = 0;
    int connfd = 0;
    struct sockaddr_in serv_addr;
    char sendBuff[BUFSIZE];
    int numrv;

    listenfd = socket(AF_INET, SOCK_STREAM, 0);

    printf("Socket retrieve success\n");

    memset(&serv_addr, '0', sizeof(serv_addr));
    memset(sendBuff, '0', sizeof(sendBuff));
    printf("here 2\n");
    serv_addr.sin_family = AF_INET;
    printf("here 3\n");
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    printf("here 4\n");
    serv_addr.sin_port = htons(port);
    printf("here 5\n");
    int optval = 1;
    printf(" opening port %d\n", port);
    setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR,
               (const void *) &optval, sizeof(int));
    bind(listenfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));
    printf("binded\n");


    while (1) {
        connfd = accept(listenfd, (struct sockaddr *) NULL, NULL);
        printf("connfd %d", connfd);


        close(connfd);
        sleep(1);


    }

Client output:

here i am
connecting to 8888 - localhost 
 attempting connection localhost:8888

Server output

Socket retrieve success
here 2
here 3
here 4
here 5
 opening port 8888
binded

And after like few minutes of wait.. I observe the following: Client:

here i am
connecting to 8888 - localhost 
 attempting connection localhost:8888
Error -1

Server:

Socket retrieve success
here 2
here 3
here 4
here 5
 opening port 8888
binded
connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd -1connfd

which by -1, I can guess that the connection has failed. I am not sure what I am missing?

You should put a \n after connfd %d, or else printf's output will be buffered and you won't see it right when it happens. You could also call fflush to print buffered output — Eregrith
– Eregrith, Commented May 26, 2015 at 8:22
@Eregrith: You are correct.. so basically, the connect fails instantaneously.. But I am not sure.. why server is not accepting client connection.. — frazman
– frazman, Commented May 26, 2015 at 8:28
Have a look at errno and perror maybe that can help, cross it with the connect() manual — Eregrith
– Eregrith, Commented May 26, 2015 at 8:32
In theory connect should block, but this depends on your environment. Try not exiting from the client immediately, but send some data and wait some time (100ms) in a loop. — vbence
– vbence, Commented May 26, 2015 at 8:32

alk · Accepted Answer · 2015-05-26 09:37:10Z

2

The server misses to call listen() on the bound socket prior to calling accept() on it.

Also this

serv_addr.sin_addr.s_addr = server;

should have issued a warning by the compiler. You cannot assign a C-"string" (what I assume server is) to an in_addr_t (what serv_addr.sin_addr.s_addr is).

Fix this by doing:

serv_addr.sin_addr.s_addr = inet_addr(server);

or better add error checking to this, like so:

{
  in_addr_t in_addr = inet_addr(server);
  if (INADDR_NONE == in_addr)
  {
    perror("inet_addr() failed");
    abort(); /* or whatever error handling you choose. */
  }

  serv_addr.sin_addr.s_addr = in_addr;
}

edited May 26, 2015 at 9:37

answered May 26, 2015 at 8:37

alk

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4 Comments

frazman Over a year ago

Yepp.. that did solves.. so now the server is waiting for incoming connections.. but client is not able to connect to it.. am i missing anything on my client code?

frazman Over a year ago

Ok.. So I am able to make this work.. Instead of localhost, if I have serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1"); Then it works fine? But I actually have string localhost? Is there a way to initialize localhost..instead of 127.0.0.1

frazman Over a year ago

I get PING localhost (127.0.0.1) 56(84) bytes of data. 64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.011 ms 64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.018 ms But when I use localhost instead of 127.0.0.1, the client connection fails (returns -1)

alk Over a year ago

@Fraz: You need to go via getaddrinfo() to pull the ip-address for a symbolic name.

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