CODEWITHSUNDEEP
csocketsclient
Bob3825
Bob3825

Reputation: 11

C - read() never blocks on the server side

I'm creating a game for a project, with a highscore server where the game can send commands to save a new highscore, get the top 10 score and so on. The problem I'm having is that after the game send a couple of command to the server, and they are executed perfectly fine, the call read() just keeps receiving null, even though the game isn't sending anything!!

I've searched around for a solution and I checked the following and they are OK:

1- when any socket is created, I check if (sockfd==-1) and print an error and exit
2- I enabled blocking mode explicitly on every socket
3- I tested all the sockets

if(n < 0){  
   perror("Read Error:");
}

and it never enters here, but i changed to 

if(n == 0){  
   perror("Read Error:");
}

and i get bad address!! Any help on how to have the read function to wait til the game actually executes a send?

Here is the send and read code that fails:

Server:

listen(sock, 5);
clientlength = sizeof(client_add); 
newsock = accept(sock, (struct sockaddr *) &client_add, &clientlength);
if(newsock < 0){
  printf("Couldn't accept\n");
}
while(1){
  bzero(buffer, 300);
  ioctl(newsock, FIONBIO, 0);  
  n= read(newsock, buffer, 299);
  if(n == 0){  
    perror("Read Error:");
  } 
  if(n<0){
    printf("Error while reading from socket\n");
  }
  printf("Received: %s\n",buffer);
  //send to function that processes the string 
  dothemagic(buffer);
}

An example of a sent msg:

strcpy(buffer, "gettop5");   
n = write(sock,buffer,strlen(buffer));
if (n < 0){ 
  printf("Writing to socket was unsuccessful\n");
}

Upvotes: 1

Views: 125

Answers (1)

loreb
loreb

Reputation: 1357

The big problem is that your printf/perror only prints a message, but then execution continues (with the zeroed buffer...); you should instead print an error and then break from the loop/exit the program/whatever is appropriate. And like wildplasser pointed out, n==0 is not an error.

If you still can't figure it out, try with short, self contained, correct example -- it's impressive how often you'll realize the problem just by putting a sscce together!

Upvotes: 1

Related Questions