iOS CFSocket and C Socket

Question

in iOS CFSocket the way handle callback function is as followed

      void receiveData(CFSocketRef s, 
                         CFSocketCallBackType type, 
                         CFDataRef address, 
                         const void *data, 
                         void *info)
{

}


int main ()
{
    CFSocketRef s = CFSocketCreate(NULL, PF_INET, 
                                            SOCK_STREAM, IPPROTO_TCP, 
                                            kCFSocketDataCallBack, 
                                            receiveData, 
                                            NULL);
    struct sockaddr_in      sin; 
    struct hostent           *host;

    host = gethostbyname("localhost");      
    memset(&sin, 0, sizeof(sin));
    memcpy(&(sin.sin_addr), host->h_addr,host->h_length); 
    sin.sin_family = AF_INET;
    sin.sin_port = htons(888);

    CFDataRef address, data;
    UInt8 message[] = "Hello world";
    CFRunLoopSourceRef source;

    address = CFDataCreate(NULL, (UInt8 *)&sin, sizeof(sin));
    data = CFDataCreate(NULL, message, sizeof(message));

    CFSocketConnectToAddress(s, address, 0);
    CFSocketSendData(s, NULL, data, 0);

}

in CFSocket when we do a CFSocketCreate we put the callback function in the SocketCreate function.

But for C Code the Socket and read from Socket is as followed.

 sockfd = socket(AF_INET, SOCK_STREAM, 0);

if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0) 
    error("ERROR connecting");
printf("Please enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0) 
     error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);

I don't how to implement the callback read function inside the C Code. The callback function would be implemented every time something come into the buffer.

Answer 1

As you noted BSD sockets is not callback based, you need to poll from read to receive new data. You can call this periodically on the main thread or create a custom thread for reading data repeatedly.

CFSocket wraps BSD sockets at a higher level. It has some nice features, I believe that it automatically handles threading, and sleeps the thread until data is received. Reimplemnenting these features would not be a trivial process.

Good resources:

http://beej.us/guide/bgnet/

BSD Sockets - How to use non-blocking sockets?

http://man7.org/linux/man-pages/man2/poll.2.html