client.c

#include <stdio.h>
#include <string.h>
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <netdb.h>
#include <stdint.h>
#include <errno.h>
#include <arpa/inet.h>

#include "shared.h"

/* Given a socket, a host, and a port, configure a socket and send the message
 * "hello". Wait for a response and print it as if it was a string. */
int communicate(int sck, char * host, char * port);

int main(int argc, char * argv[]) {
  if (argc < 2) {
    fprintf(stderr, "usage:\n\t%s [remote address] [remote port]\n", argv[0]);
    return -1;
  }

  char * remote_addr = argv[1];
  char * remote_port = argv[2];

  int sck;

  if (0 > (sck = setup_socket())) {
    fprintf(stderr, "Failed to bind socket. Error: %d\n", sck);
    return sck;
  }

  return communicate(sck, remote_addr, remote_port);
}

int communicate(int sck, char * host, char * port) {
  uint8_t msg[] = "hello";
  uint8_t buffer[128] = {0};
  struct hostent * he;
  struct sockaddr_in remote;
  struct sockaddr_storage from;
  socklen_t from_len = sizeof(from);

  if (NULL == (he = gethostbyname(host))) {
    return -1;
  }

  remote.sin_family = AF_INET;
  remote.sin_port = htons(atoi(port));
  remote.sin_addr = *(struct in_addr *)he->h_addr;
  memset(remote.sin_zero, 0, sizeof(remote.sin_zero));

  /* Send the broadcast packet. */
  int len = sendto(sck, msg, sizeof(msg), 0, (struct sockaddr *)&remote, sizeof(remote));

  if (0 > len) {
    fprintf(stderr, "Unable to 'sendto': %s\n", strerror(errno));
    return -2;
  }
  while (1) {
    len = recvfrom(sck, buffer, sizeof(buffer), 0, (struct sockaddr *)&from, &from_len);

    if (EWOULDBLOCK == errno) {
      // recv timed out. exit normally.
      return 0;
    } else if (0 > len) {
      fprintf(stderr, "Unable to 'recvfrom': %s (%d)\n", strerror(errno), errno);
      return -3;
    }

    char addr[40] = {0};

    const char * ptr = inet_ntop(
                          from.ss_family,
                          get_in_addr((struct sockaddr *)&from),
                          addr,
                          sizeof(addr));

    printf("Message from %s:%u of length %d: 0x",
        ptr,
        ntohs((*((struct sockaddr_in *)&from)).sin_port),
        len);

    for (int i = 0; i < len; i++) {
        printf("%02X", buffer[i]);
    }
    printf("\n");
  }

  return 0;
}