socket.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>     /* inet_ntoa */
#include <netdb.h>         /* gethostname */
#include <sys/socket.h>

#include "socket.h"

/*
 * Initialize a server address associated with the given port.
 */
struct sockaddr_in *init_server_addr(int port) {
    struct sockaddr_in *addr = malloc(sizeof(struct sockaddr_in));

    // Allow sockets across machines.
    addr->sin_family = PF_INET;
    // The port the process will listen on.
    addr->sin_port = htons(port);
    // Clear this field; sin_zero is used for padding for the struct.
    memset(&(addr->sin_zero), 0, 8);

    // Listen on all network interfaces.
    addr->sin_addr.s_addr = INADDR_ANY;

    return addr;
}

/*
 * Create and setup a socket for a server to listen on.
 */
int setup_server_socket(struct sockaddr_in *self, int num_queue) {
    int soc = socket(PF_INET, SOCK_STREAM, 0);
    if (soc < 0) {
        perror("socket");
        exit(1);
    }

    // Make sure we can reuse the port immediately after the
    // server terminates. Avoids the "address in use" error
    int on = 1;
    int status = setsockopt(soc, SOL_SOCKET, SO_REUSEADDR,
        (const char *) &on, sizeof(on));
    if (status < 0) {
        perror("setsockopt");
        exit(1);
    }

    // Associate the process with the address and a port
    if (bind(soc, (struct sockaddr *)self, sizeof(*self)) < 0) {
        // bind failed; could be because port is in use.
        perror("bind");
        exit(1);
    }

    // Set up a queue in the kernel to hold pending connections.
    if (listen(soc, num_queue) < 0) {
        // listen failed
        perror("listen");
        exit(1);
    }

    return soc;
}


/*
 * Wait for and accept a new connection.
 * Return -1 if the accept call failed.
 */
int accept_connection(int listenfd) {
    struct sockaddr_in peer;
    unsigned int peer_len = sizeof(peer);
    peer.sin_family = PF_INET;

    fprintf(stderr, "Waiting for a new connection...\n");
    int client_socket = accept(listenfd, (struct sockaddr *)&peer, &peer_len);
    if (client_socket < 0) {
        perror("accept");
        return -1;
    } else {
        fprintf(stderr,
            "New connection accepted from %s:%d\n",
            inet_ntoa(peer.sin_addr),
            ntohs(peer.sin_port));
        return client_socket;
    }
}


/******************************************************************************
 * Client-specific functions
 *****************************************************************************/
/*
 * Create a socket and connect to the server indicated by the port and hostname
 */
int connect_to_server(int port, const char *hostname) {
    int soc = socket(PF_INET, SOCK_STREAM, 0);
    if (soc < 0) {
        perror("socket");
        exit(1);
    }
    struct sockaddr_in addr;

    // Allow sockets across machines.
    addr.sin_family = PF_INET;
    // The port the server will be listening on.
    addr.sin_port = htons(port);
    // Clear this field; sin_zero is used for padding for the struct.
    memset(&(addr.sin_zero), 0, 8);

    // Lookup host IP address.
    struct hostent *hp = gethostbyname(hostname);
    if (hp == NULL) {
        fprintf(stderr, "unknown host %s\n", hostname);
        exit(1);
    }

    addr.sin_addr = *((struct in_addr *) hp->h_addr);

    // Request connection to server.
    if (connect(soc, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
        perror("connect");
        exit(1);
    }

    return soc;
}