open_listenfd.c

#include "simpleServer.h"
#include "globals.h"
//Copied from the Computer Systems textbook.
//This function creates a socket descriptor, and binds
//the socket descriptor the specified port.
//bind() associates the socket descriptor created
//with socket() to the port we want the server to listen on.
//Once the descriptor is bound, the listen() call
//will prepare the socket so that we can call accept() on it
//and get a connection to a user.


int open_listenfd(int port)
{
    int listenfd, optval=1;
    struct sockaddr_in serveraddr;
    
    /* Create a socket descriptor */
    if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){
        return -1;
    }
    
    /* Eliminates "Address already in use" error from bind */
    if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR,
                   (const void *)&optval , sizeof(int)) < 0){
        return -1;
    }
    
    //Reset the serveraddr struct, setting all of it's bytes to zero.
    //Some properties are then set for the struct, you don't
    //need to worry about these.
    //bind() is then called, associating the port number with the
    //socket descriptor.
    bzero((char *) &serveraddr, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
    serveraddr.sin_port = htons((unsigned short)port);
    if (bind(listenfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0){
        return -1;
    }
    
    //Prepare the socket to allow accept() calls. The value 20 is
    //the backlog, this is the maximum number of connections that will be placed
    //on queue until accept() is called again.
    if (listen(listenfd, 20) < 0){
        return -1;
    }
    
    return listenfd;
}