C-IPC/server.c

#include "bits/types/struct_timeval.h"
#include "sys/ipc.h"
#include "sys/shm.h"
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/msg.h>
#include <sys/sem.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

// commands.h already is included by util.h
#include "util/util.h"

#define send(queue_id, msgbuf_ptr) msgsnd(queue_id, msgbuf_ptr, sizeof(*(msgbuf_ptr)) - sizeof(long), 0)

typedef struct {
  char sender[COMMAND_LENGTH];
  char command[COMMAND_LENGTH];
  char message[MESSAGE_LENGTH];
  char message_id[COMMAND_LENGTH];
} saved_message_t;

typedef struct {
  char id[COMMAND_LENGTH];
  bool logged_in;
  char *muted_clients;
  char nickname[COMMAND_LENGTH]; // Nicknames cannot contain special characters
                                 // like # (reserved for groups)
  int queue_id;
  long last_seen;
  // Things for keeping track of the saved messages
  saved_message_t saved_messages[20];
  int saved_message_count;
} Client_t;

typedef struct {
  Client_t **members;
  char name[COMMAND_LENGTH - 1]; // In the command one char is used for # to indicate a group
  int client_count;
} Group_t;

static void handle_hearbeat_timeouts(Client_t *clients, int client_count, int semaphore_id) {
  struct sembuf sem_op = {
      .sem_num = 0,
      .sem_op = -1,
      .sem_flg = 0,
  };
  while (1) {
    sem_op.sem_op = 1;
    semop(semaphore_id, &sem_op, 1);
    struct timeval tv;
    gettimeofday(&tv, NULL);
    for (int i = 0; i < client_count; i++) {
      if (clients[i].logged_in && (tv.tv_sec - clients[i].last_seen) > HEARTBEAT_TIMEOUT) {
        printf("Client %s has timed out due to missed heartbeats\n", clients[i].id);
        clients[i].logged_in = false;
        clients[i].queue_id = -1;
      }
    }
    sem_op.sem_op = 1;
    semop(semaphore_id, &sem_op, 1);
    sleep(HEARTBEAT_TIMEOUT);
  }
}

int main(int argc, char **argv) {
  server_config_t config;
  // If we are given a path, try to load the config from there
  if (argc >= 2) {
    load_config(&config, argv[1]);
  } else {
    fprintf(stderr, "No config file provided, using default location example.conf\n");
    load_config(&config, "./example.conf");
  }

  int client_count = config.client_count;
  int group_count = config.group_count;
  int clients_memory_id = shmget(IPC_PRIVATE, sizeof(Client_t) * client_count, IPC_CREAT | 0666);
  Client_t *clients = shmat(clients_memory_id, NULL, 0);
  Group_t *groups = malloc(sizeof(Group_t) * group_count);

  int semaphore_id = semget(IPC_PRIVATE, 1, IPC_CREAT | 0666);
  semctl(semaphore_id, 0, SETVAL, 1);

  for (int i = 0; i < client_count; i++) {
    strncpy(clients[i].id, config.clients[i].client_id, COMMAND_LENGTH - 1);
    clients[i].logged_in = false;
    clients[i].muted_clients = NULL;
    strncpy(clients[i].nickname, config.clients[i].nickname, COMMAND_LENGTH - 1);
    clients[i].queue_id = -1;
    clients[i].last_seen = 0;
    clients[i].saved_message_count = 0;
  }

  for (int i = 0; i < group_count; i++) {
    strncpy(groups[i].name, config.groups[i].name, COMMAND_LENGTH - 2);
    groups[i].client_count = config.groups[i].member_count;
    groups[i].members = malloc(sizeof(Client_t *) * config.groups[i].member_count);
    for (int j = 0; j < config.groups[i].member_count; j++) {
      // Find the client with the given id
      for (int k = 0; k < client_count; k++) {
        if (strncmp(clients[k].id, config.groups[i].member_ids[j], COMMAND_LENGTH) == 0) {
          groups[i].members[j] = &clients[k];
          break;
        }
      }
    }
  }

  // No longer useful after copying the data over
  for (int i = 0; i < group_count; i++) {
    for (int j = 0; j < config.groups[i].member_count; j++) {
      free(config.groups[i].member_ids[j]);
    }
  }
  free(config.clients);
  free(config.groups);

  int server_queue_id = msgget(IPC_PRIVATE, 0666 | IPC_CREAT);

  if (server_queue_id == -1) {
    perror("msgget failed");
    return 1;
  }

  int id_file_handle = open("/home/piotr/server_queue_id", O_WRONLY | O_CREAT | O_TRUNC, 0666);
  if (!id_file_handle) {
    perror("Failed to open file");
    return 1;
  }

  if (write(id_file_handle, &server_queue_id, sizeof(int)) == -1) {
    perror("Failed to write server queue id to file");
    return 1;
  }
  close(id_file_handle);

  if (fork() == 0) {
    handle_hearbeat_timeouts(clients, client_count, semaphore_id);
    return 0;
  }

  printf("Server ready.\n");

  msgbuf_t msgbuf;
  while (1) {
    // Read from the ipc, then handle the command
    int read_status = msgrcv(server_queue_id, &msgbuf, sizeof(msgbuf) - sizeof(long), 0, 0);

    switch (msgbuf.mtype) {
    case Login: {
      printf("Received login request for id: %s\n", msgbuf.sender);
      Client_t *client = NULL;
      for (int i = 0; i < client_count; i++) {
        if (strncmp(clients[i].id, msgbuf.sender, COMMAND_LENGTH) == 0) {
          client = &clients[i];
          break;
        }
      }

      // Reuse the buffer to get the client's message queue id
      int msg_queue_id = atoi(msgbuf.command);
      if (client == NULL) {
        printf("User not found: %s\n", msgbuf.sender);
        msgbuf_t response = {
            .mtype = Login,
            .stype = ERR_USER_NOT_FOUND,
        };

        send(msg_queue_id, &response);
        continue;
      }

      if (client->logged_in) {
        printf("User already logged in: %s\n", msgbuf.sender);
        msgbuf_t response = {
            .mtype = Login,
            .stype = ERR_ALREADY_LOGGED_IN,
        };

        send(msg_queue_id, &response);
        continue;
      }

      client->logged_in = true;
      client->queue_id = msg_queue_id;
      struct timeval tv;
      gettimeofday(&tv, NULL);
      client->last_seen = tv.tv_sec;
      msgbuf_t response = {
          .mtype = Login,
          .command = "",
          .stype = ACK_ACCEPTED,
      };
      strncpy(response.command, client->nickname, COMMAND_LENGTH);

      printf("User accepted: %s\n", msgbuf.sender);
      send(msg_queue_id, &response);

      // Check if there are any saved messages for this client
      if (client->saved_message_count > 0) {
        response.mtype = Inbox;
        snprintf(response.command, COMMAND_LENGTH, "0");
        send(client->queue_id, &response);
      }
      break;
    }
    case Message: {
      // Find the client that sent the message then forward it to all the
      // specified recipients
      Client_t *client = NULL;
      for (int i = 0; i < client_count; i++) {
        if (strncmp(clients[i].id, msgbuf.sender, COMMAND_LENGTH) == 0) {
          client = &clients[i];
          break;
        }
      }

      printf("Received message from client id %s to %s\n", msgbuf.sender, msgbuf.command);

      if (client == NULL || !client->logged_in) {
        // Client not found or not logged in
        printf("Sender not found or not logged in");
        msgbuf_t response = {
            .mtype = Message,
            .stype = ERR_NOT_LOGGED_IN,
        };
        send(read_status, &response);
        continue;
      }

      // Now we have to decode if we are to forward this message to a user or a
      // group. A group is indicated by a #  at the start of the command
      char target_type = msgbuf.command[0];
      Client_t **recipients = malloc(sizeof(Client_t *) * client_count - 1); // We won't send to ourselves so one less

      if (target_type != '#') {
        for (int i = 0; i < client_count; i++) {
          if (strncmp(clients[i].nickname, msgbuf.command, COMMAND_LENGTH) == 0) {
            recipients[0] = &clients[i];
            break;
          }
        }
      } else {
        // Target is a group, find it first
        Group_t *target_group = NULL;
        for (int i = 0; i < group_count; i++) {
          if (strncmp(groups[i].name, msgbuf.command + 1, COMMAND_LENGTH - 1) == 0) {
            target_group = &groups[i];
            break;
          }
        }

        // Target group not found
        if (target_group == NULL) {
          printf("Target group %s not found\n", msgbuf.command + 1);
          msgbuf_t response = {
              .mtype = Message,
              .stype = ERR_USER_NOT_FOUND,
          };
          send(client->queue_id, &response);
          continue;
        }

        // Forward the message to all group members except the sender
        int recipient_idx = 0;
        for (int i = 0; i < target_group->client_count; i++) {
          if (strncmp(target_group->members[i]->id, client->id, COMMAND_LENGTH) == 0) {
            continue;
          }
          recipients[recipient_idx++] = target_group->members[i];
        }

        if (recipient_idx < client_count - 1) {
          recipients[recipient_idx] = NULL;
        }
      }

      // Now forward the message to all recipients
      for (int i = 0; i < client_count - 1; i++) {
        Client_t *target_client = recipients[i];
        // Just the empty pointer so no more recipients
        if (target_client == NULL)
          break;

        // Check if the target is online or not, if they are not, store the
        // message
        if (!target_client->logged_in) {
          saved_message_t *saved_msg = NULL;
          if (target_client->saved_message_count >= 20) {
            // Discard the oldest one and shift the rest to make room
            for (int i = 1; i < target_client->saved_message_count; i++) {
              target_client->saved_messages[i - 1] = target_client->saved_messages[i];
            }
            saved_msg = &target_client->saved_messages[target_client->saved_message_count - 1];
          } else {
            // There is room for a new message
            saved_msg = &target_client->saved_messages[target_client->saved_message_count++];
          }

          get_id(saved_msg->message_id);
          strncpy(saved_msg->sender, client->nickname, COMMAND_LENGTH);
          strncpy(saved_msg->message, msgbuf.message, MESSAGE_LENGTH);
          msgbuf_t response = {
              .mtype = Message,
              .stype = ACK_ACCEPTED,
          };
          send(client->queue_id, &response);
          printf("Message saved for offline client %s\n", target_client->id);
          continue;
        }

        printf("Forwarding message from user %s to %s\n", client->nickname, target_client->nickname);
        msgbuf_t forward_msg = {
            .mtype = Message,
            .sender = "",
        };
        strncpy(forward_msg.sender, client->nickname, COMMAND_LENGTH);
        strncpy(forward_msg.message, msgbuf.message, MESSAGE_LENGTH);
        send(target_client->queue_id, &forward_msg);

        forward_msg.stype = ACK_ACCEPTED;
        forward_msg.mtype = Signal;
        send(client->queue_id, &forward_msg);

        printf("Forwarding message: %s\n", msgbuf.message);
      }
      break;
    }
    case Logout: {
      for (int i = 0; i < client_count; i++) {
        if (strncmp(clients[i].id, msgbuf.sender, COMMAND_LENGTH) == 0 && clients[i].logged_in) {
          clients[i].logged_in = false;
          clients[i].queue_id = -1;
          printf("Client %s logged out\n", msgbuf.sender);
          break;
        }
      }
      break;
    }
    case Hearbeat:
      for (int i = 0; i < client_count; i++) {
        if (strncmp(clients[i].id, msgbuf.sender, COMMAND_LENGTH) == 0 && clients[i].logged_in) {
          // Take the semaphore to update last_seen
          struct sembuf sem_op = {
              .sem_num = 0,
              .sem_op = -1,
              .sem_flg = 0,
          };
          semop(semaphore_id, &sem_op, 1);
          struct timeval tv;
          gettimeofday(&tv, NULL);
          clients[i].last_seen = tv.tv_sec;

          // Free the semaphore
          sem_op.sem_op = 1;
          semop(semaphore_id, &sem_op, 1);
        }
      }
      break;
    case List: {
      Client_t *client = NULL;
      for (int i = 0; i < client_count; i++) {
        if (strncmp(clients[i].id, msgbuf.sender, COMMAND_LENGTH) == 0) {
          client = &clients[i];
          break;
        }
      }

      if (client == NULL || !client->logged_in) {
        continue;
      }

      char list_buffer[MESSAGE_LENGTH] = "";

      if (strncmp(msgbuf.command, "groups", COMMAND_LENGTH) == 0) {
        for (int i = 0; i < group_count; i++) {
          bool isMember = false;
          for (int j = 0; j < groups[i].client_count; j++) {
            if (strncmp(groups[i].members[j]->id, client->id, COMMAND_LENGTH) == 0) {
              isMember = true;
              break;
            }
          }

          char line[COMMAND_LENGTH + 4 + 9];
          // Tell the user if they are in the group or not
          snprintf(line, COMMAND_LENGTH + 4 + 9, "- %s%s\n", groups[i].name, isMember ? " (member)" : "");
          strncat(list_buffer, line, MESSAGE_LENGTH - strlen(list_buffer) - 1);
        }

        msgbuf_t response = {
            .mtype = List,
            .command = "groups",
        };
        strncpy(response.message, list_buffer, MESSAGE_LENGTH);
        send(client->queue_id, &response);
        continue;
      }

      // Parse the command parameter
      // Just check if the user wants the active clients
      // Not worth checking if the other option is valid
      bool active_only = false;
      if (strncmp(msgbuf.command, "active", COMMAND_LENGTH) == 0) {
        active_only = true;
      }

      for (int i = 0; i < client_count; i++) {
        if (active_only && !clients[i].logged_in)
          continue;

        // Even a tiny bit of formatting, we fancy like that
        char line[COMMAND_LENGTH + 4];
        snprintf(line, COMMAND_LENGTH + 4, "- %s\n", clients[i].nickname);
        strncat(list_buffer, line, MESSAGE_LENGTH - strlen(list_buffer) - 1);
      }

      msgbuf_t response = {
          .mtype = List,
          .command = "",
      };

      strncpy(response.command, active_only ? "active" : "all", COMMAND_LENGTH);
      strncpy(response.message, list_buffer, MESSAGE_LENGTH);
      send(client->queue_id, &response);
      break;
    }
    case Inbox: {
      Client_t *client = NULL;
      for (int i = 0; i < client_count; i++) {
        if (strncmp(clients[i].id, msgbuf.sender, COMMAND_LENGTH) == 0) {
          client = &clients[i];
          break;
        }
      }

      if (client == NULL || !client->logged_in)
        continue;

      msgbuf_t response = {
          .mtype = Inbox,
          .sender = "",
          .command = "",
          .message = "",
      };

      // Now, for all the stored messages, send them one by one, incrementing
      // the counter in command
      for (int i = 0; i < client->saved_message_count; i++) {
        snprintf(response.command, COMMAND_LENGTH, "%d", i + 1);
        strncpy(response.sender, client->saved_messages[i].sender, COMMAND_LENGTH);
        strncpy(response.message, client->saved_messages[i].message, MESSAGE_LENGTH);
        send(client->queue_id, &response);
      }

      // Now send ACK_DELIVERED to senders
      for (int i = 0; i < client->saved_message_count; i++) {
        saved_message_t *saved_msg = &client->saved_messages[i];
        Client_t *original_sender = NULL;
        for (int j = 0; j < client_count; j++) {
          if (strncmp(clients[j].nickname, saved_msg->sender, COMMAND_LENGTH) == 0) {
            original_sender = &clients[j];
            break;
          }
        }

        // Technically, the first check should never fail, as we can't remove
        // users dynamically but I'll leave it here anyway
        if (original_sender == NULL || !original_sender->logged_in) {
          continue;
        }

        msgbuf_t ack_msg = {
            .mtype = Signal,
            .sender = "",
            .command = "",
            .stype = ACK_DELIVERED,
        };
        strncpy(ack_msg.sender, client->nickname, COMMAND_LENGTH);
        send(original_sender->queue_id, &ack_msg);
      }
      client->saved_message_count = 0;
      break;
    }
    case Mute:
    case Unmute:
      break;
    case Signal:
      // Signals are sent from server to client, not the other way around
      // so we ignore them here lol
      break;
    }
  }

  return 0;
}