lander/src/event_loop/event_loop.c

#include <errno.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <poll.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#include "event_loop.h"
#include "log.h"

static int event_loop_fd_set_nb(int fd) {
  int flags = fcntl(fd, F_GETFL);

  flags |= O_NONBLOCK;

  fcntl(fd, F_SETFL, flags);

  return 0;
}

event_loop *event_loop_init() {
  event_loop *el = calloc(sizeof(event_loop), 1);

  // No idea if this is a good starter value
  el->connections = calloc(sizeof(event_loop_conn), 16);
  el->connection_count = 16;

  return el;
}

int event_loop_put(event_loop *el, event_loop_conn *conn) {
  if ((size_t)conn->fd >= el->connection_count) {
    event_loop_conn **resized =
        realloc(el->connections, sizeof(event_loop_conn) * (conn->fd + 1));

    if (resized == NULL) {
      return -1;
    }

    el->connections = resized;
    el->connection_count = conn->fd + 1;
  }

  el->connections[conn->fd] = conn;

  return 0;
}

int event_loop_accept(event_loop *el, int fd) {
  struct sockaddr_in client_addr;
  socklen_t socklen = sizeof(client_addr);
  int connfd = accept(fd, (struct sockaddr *)&client_addr, &socklen);

  if (connfd < 0) {
    return -1;
  }

  // set the new connection fd to nonblocking mode
  int res = event_loop_fd_set_nb(connfd);

  if (res < 0) {
    close(connfd);

    return -2;
  }

  // creating the struct Conn
  event_loop_conn *conn = event_loop_conn_init(el);

  // Close the connectoin if we fail to allocate a connection struct
  if (conn == NULL) {
    close(connfd);

    return -3;
  }

  conn->fd = connfd;
  conn->state = event_loop_conn_state_req;

  res = event_loop_put(el, conn);

  if (res != 0) {
    close(connfd);

    return -4;
  }

  debug("Connection established on fd %i", connfd);

  return 0;
}

void event_loop_run(event_loop *el, int port) {
  int fd = socket(AF_INET, SOCK_STREAM, 0);

  if (fd < 0) {
    critical(1, "Failed to open listening socket, errno: %i", errno);
  }

  int val = 1;
  setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));

  // bind
  struct sockaddr_in addr = {.sin_family = AF_INET,
                             .sin_port = ntohs(port),
                             .sin_addr.s_addr = ntohl(0)};

  int res = bind(fd, (const struct sockaddr *)&addr, sizeof(addr));

  if (res) {
    critical(1, "Failed to bind listening socket, errno: %i", errno);
  }

  debug("Listening socket bound to fd %i", fd);

  res = listen(fd, SOMAXCONN);

  if (res) {
    critical(1, "Failed to start listening on listening socket, errno: %i",
             errno);
  }

  // The listening socket is always poll'ed in non-blocking mode as well
  res = event_loop_fd_set_nb(fd);

  if (res != 0) {
    critical(1, "Failed to set listening socket to non-blocking, errno: %i",
             errno);
  }

  // TODO don't hardcode the number 32
  struct pollfd *poll_args = calloc(sizeof(struct pollfd), 32);
  size_t poll_args_count;

  // for convenience, the listening fd is put in the first position
  struct pollfd pfd = {fd, POLLIN, 0};
  poll_args[0] = pfd;

  event_loop_conn *conn;
  int events;

  info("Starting event loop on port %i", port);

  while (1) {
    poll_args_count = 1;

    // connection fds
    for (size_t i = 0; i < el->connection_count; i++) {
      conn = el->connections[i];

      if (conn == NULL) {
        continue;
      }

      events = (conn->state == event_loop_conn_state_req) ? POLLIN : POLLOUT;
      events |= POLLERR;

      struct pollfd pfd = {conn->fd, events, 0};

      poll_args[poll_args_count] = pfd;
      poll_args_count++;

      // We do at most 32 connections at a time for now
      if (poll_args_count == 32)
        break;
    }

    // poll for active fds
    // the timeout argument doesn't matter here
    int rv = poll(poll_args, (nfds_t)poll_args_count, 0);

    if (rv < 0) {
      critical(1, "Poll failed, errno: %i", errno);
    }

    // process active connections
    for (size_t i = 1; i < poll_args_count; i++) {
      if (poll_args[i].revents) {
        conn = el->connections[poll_args[i].fd];

        event_loop_conn_io(el, conn);

        if (conn->state == event_loop_conn_state_end) {
          // client closed normally, or something bad happened.
          // destroy this connection
          el->connections[conn->fd] = NULL;

          close(conn->fd);
          debug("Connection closed on fd %i", conn->fd);
          event_loop_conn_free(el, conn);
        }
      }
    }

    // try to accept a new connection if the listening fd is active
    if (poll_args[0].revents) {
      event_loop_accept(el, fd);
    }
  }
}