client

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <errno.h>
#include <getopt.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <sys/socket.h>
#include <sys/types.h>

struct Server {
  char ip[255];
  int port;
};

uint64_t MultModulo(uint64_t a, uint64_t b, uint64_t mod) {
  uint64_t result = 0;
  a = a % mod;
  while (b > 0) {
    if (b % 2 == 1)
      result = (result + a) % mod;
    a = (a * 2) % mod;
    b /= 2;
  }

  return result % mod;
}

bool ConvertStringToUI64(const char *str, uint64_t *val) {
  char *end = NULL;
  unsigned long long i = strtoull(str, &end, 10);
  if (errno == ERANGE) {
    fprintf(stderr, "Out of uint64_t range: %s\n", str);
    return false;
  }

  if (errno != 0)
    return false;

  *val = i;
  return true;
}

int main(int argc, char **argv) {
  uint64_t k = -1;
  uint64_t mod = -1;
  char servers[255] = {'\0'}; // max filename length = 255


  while (true) {
    int current_optind = optind ? optind : 1;

    static struct option options[] = {{"k", required_argument, 0, 0},
                                      {"mod", required_argument, 0, 0},
                                      {"servers", required_argument, 0, 0},
                                      {0, 0, 0, 0}};

    int option_index = 0;
    int c = getopt_long(argc, argv, "", options, &option_index);

    if (c == -1)
      break;

    switch (c) {
    case 0: {
      switch (option_index) {
      case 0:
        ConvertStringToUI64(optarg, &k);
        if (k < 1)
        {
            printf("k must be positive");
            return 1;
        }
        break;
      case 1:
        ConvertStringToUI64(optarg, &mod);
        if (mod < 1)
        {
            printf("mod must be positive");
            return 1;
        }
        break;
      case 2:
        memcpy(servers, optarg, strlen(optarg));
        break;
      default:
        printf("Index %d is out of options\n", option_index);
      }
    } break;

    case '?':
      printf("Arguments error\n");
      break;
    default:
      fprintf(stderr, "getopt returned character code 0%o?\n", c);
    }
  }

  if (k == -1 || mod == -1 || !strlen(servers)) {
    fprintf(stderr, "Using: %s --k 1000 --mod 5 --servers /path/to/file\n",
            argv[0]);
    return 1;
  }

  FILE *serversFile;

  serversFile = fopen(servers, "r");
  if (serversFile == NULL)
  {
      printf("Could not open servers file");
      return 1;
  }
  char buff[255];
  int port;
  unsigned int servers_num = 0;
  while (fscanf(serversFile, "%s %d\n", buff, &port)!=EOF) servers_num++;
  rewind(serversFile);
  struct Server *to = malloc(sizeof(struct Server) * servers_num);
  int count = 0;
  while (fscanf(serversFile, "%s %d\n", buff, &port)!=EOF && count != 20)
  {
      to[count].port = port;
      memcpy(to[count].ip, buff, sizeof(buff));
      count++;
  }


  uint64_t result = 1;
  int sockets[servers_num];
  for (int i = 0; i < servers_num; i++) {
    struct hostent *hostname = gethostbyname(to[i].ip);
    if (hostname == NULL) {
      fprintf(stderr, "gethostbyname failed with %s\n", to[i].ip);
      exit(1);
    }

    struct sockaddr_in server;
    server.sin_family = AF_INET;
    server.sin_port = htons(to[i].port);
    server.sin_addr.s_addr = *((unsigned long *)hostname->h_addr_list[0]);

    sockets[i] = socket(AF_INET, SOCK_STREAM, 0);
    if (sockets[i] < 0) {
      fprintf(stderr, "Socket creation failed!\n");
      exit(1);
    }

    if (connect(sockets[i], (struct sockaddr *)&server, sizeof(server)) < 0) {
      fprintf(stderr, "Connection failed\n");
      exit(1);
    }
    uint64_t begin = 2 + i*k/servers_num;
    uint64_t end = (i+1)*k/servers_num;

    char task[sizeof(uint64_t) * 3];
    memcpy(task, &begin, sizeof(uint64_t));
    memcpy(task + sizeof(uint64_t), &end, sizeof(uint64_t));
    memcpy(task + 2 * sizeof(uint64_t), &mod, sizeof(uint64_t));

    if (send(sockets[i], task, sizeof(task), 0) < 0) {
      fprintf(stderr, "Send failed\n");
      exit(1);
    }
  }

for (int i = 0; i < servers_num; i++)
{
    char response[sizeof(uint64_t)];
    if (recv(sockets[i], response, sizeof(response), 0) < 0) {
      fprintf(stderr, "Recieve failed\n");
      exit(1);
    }
    uint64_t answer = 0;
    memcpy(&answer, response, sizeof(uint64_t));
    result = (result * answer) % mod;
    close(sockets[i]);
}

  printf("answer: %lu\n", result);
  free(to);

  return 0;
}