pgs/pgs.c

#include "py.h"
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <unistd.h>
#define LISTEN_PORT 2222
#define UPSTREAM_HOST "127.0.0.1"
#define UPSTREAM_PORT 9999
#define MAX_EVENTS 8096
#define BUFFER_SIZE 1024

void set_nonblocking(int fd) {
  int flags = fcntl(fd, F_GETFL, 0);
  if (flags == -1) {
    perror("fcntl get");
    exit(EXIT_FAILURE);
  }
  if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
    perror("fcntl set");
    exit(EXIT_FAILURE);
  }
}

int prepare_upstream() {
  int sockfd = socket(AF_INET, SOCK_STREAM, 0);

  return sockfd;
}

int connect_upstream(const char *host, int port) {
  int sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd == -1) {
    perror("socket");
    return -1;
  }

  set_nonblocking(sockfd);

  struct sockaddr_in server_addr;
  memset(&server_addr, 0, sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(port);
  if (inet_pton(AF_INET, host, &server_addr.sin_addr) <= 0) {
    perror("inet_pton");
    close(sockfd);
    return -1;
  }

  if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) ==
      -1) {
    if (errno != EINPROGRESS) {
      perror("connect");
      close(sockfd);
      return -1;
    }
  }

  return sockfd;
}

int create_listening_socket(int port) {
  int listen_fd = socket(AF_INET, SOCK_STREAM, 0);
  if (listen_fd == -1) {
    perror("socket");
    return -1;
  }

  int opt = 1;
  if (setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) ==
      -1) {
    perror("setsockopt");
    close(listen_fd);
    return -1;
  }

  struct sockaddr_in server_addr;
  memset(&server_addr, 0, sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  server_addr.sin_addr.s_addr = INADDR_ANY;
  server_addr.sin_port = htons(port);

  if (bind(listen_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) ==
      -1) {
    perror("bind");
    close(listen_fd);
    return -1;
  }

  if (listen(listen_fd, SOMAXCONN) == -1) {
    perror("listen");
    close(listen_fd);
    return -1;
  }

  set_nonblocking(listen_fd);
  return listen_fd;
}

typedef struct {
  int client_fd;
  int upstream_fd;
} connection_t;

void close_connection(int epoll_fd, connection_t *conn) {
  if (conn->client_fd != -1) {
    epoll_ctl(epoll_fd, EPOLL_CTL_DEL, conn->client_fd, NULL);
    close(conn->client_fd);
  }
  if (conn->upstream_fd != -1) {
    epoll_ctl(epoll_fd, EPOLL_CTL_DEL, conn->upstream_fd, NULL);
    close(conn->upstream_fd);
  }
}

int forward_data(int from_fd, int to_fd) {
  static char buffer[BUFFER_SIZE];
  // Feels great to do somehow. Better safe than sorry. 
  memset(buffer, 0, BUFFER_SIZE);
  ssize_t bytes_read = recv(from_fd, buffer, sizeof(buffer), 0);
  if (bytes_read > 0) {
    ssize_t bytes_written = send(to_fd, buffer, bytes_read, 0);
    if (bytes_written == -1) {
      perror("write");
    }
  } else if (bytes_read == 0) {
    printf("Connection closed by remote (fd=%d)\n", from_fd);
  } else {
    perror("read");
  }
  return (int)bytes_read;
}

int listen_fd = 0;
int epoll_fd = 0;
void cleanup() {
  close(epoll_fd);
  close(listen_fd);
  py_destruct();
  printf("Graceful exit.\n");
}
void handle_sigint(int sig) {
  printf("\nCtrl+C pressed.\n");
  exit(0);
}

int main() {
  if (signal(SIGINT, handle_sigint) == SIG_ERR) {
    perror("Failed to register signal handler");
    return EXIT_FAILURE;
  }

  listen_fd = create_listening_socket(LISTEN_PORT);
  if (listen_fd == -1) {
    fprintf(stderr, "Failed to create listening socket\n");
    return EXIT_FAILURE;
  }
  atexit(cleanup);
  epoll_fd = epoll_create1(0);
  if (epoll_fd == -1) {
    perror("epoll_create1");
    close(listen_fd);
    return EXIT_FAILURE;
  }

  struct epoll_event event;
  event.events = EPOLLIN;
  event.data.fd = listen_fd;

  if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, listen_fd, &event) == -1) {
    perror("epoll_ctl");
    close(listen_fd);
    close(epoll_fd);
    return EXIT_FAILURE;
  }

  struct epoll_event events[MAX_EVENTS];
  memset(events, 0, sizeof(events));

  printf("Intercepting load balancer listening on port %d\n", LISTEN_PORT);
  connection_t connections[MAX_EVENTS][sizeof(connection_t)] = {0};
  while (1) {
    int num_events = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);
    if (num_events == -1) {
      perror("epoll_wait");
      break;
    }

    for (int i = 0; i < num_events; i++) {
      if (events[i].data.fd == listen_fd) {
        struct sockaddr_in client_addr;
        socklen_t client_len = sizeof(client_addr);
        int client_fd =
            accept(listen_fd, (struct sockaddr *)&client_addr, &client_len);
        if (client_fd == -1) {
          perror("accept");
          continue;
        }
        set_nonblocking(client_fd);

        struct epoll_event client_event;
        client_event.events = EPOLLIN | EPOLLOUT | EPOLLERR | EPOLLHUP;
        client_event.data.ptr = connections[client_fd];
        client_event.data.fd = client_fd;
        connections[client_fd]->upstream_fd = -1;
        connections[client_fd]->client_fd = client_fd;

        //  connections[client_fd]->upstream_fd = upstream_fd;
        // connections[conn->client_fd] = conn;
        // connections[upstream_fd]->client_fd = client_fd;
        // connections[upstream_fd]->upstream_fd = upstream_fd;

        epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_fd, &client_event);

      } else {
        // Handle data forwarding for existing connections
        connection_t *conn = connections[events[i].data.fd];
        if (events[i].events & (EPOLLHUP | EPOLLERR)) {
          printf("Connection closed: client_fd=%d, upstream_fd=%d\n",
                 conn->client_fd, conn->upstream_fd);
          close_connection(epoll_fd, conn);
        } else if (events[i].events & EPOLLIN) {
          if (conn->upstream_fd == -1) {
            conn->upstream_fd = prepare_upstream();
            int upstream_fd = py_route(conn->client_fd, conn->upstream_fd);

            if (upstream_fd == -1) {
              close(conn->client_fd);
              continue;
            }
            set_nonblocking(upstream_fd);
            struct epoll_event upstream_event;
            upstream_event.events = EPOLLIN | EPOLLOUT | EPOLLERR | EPOLLHUP;
            upstream_event.data.ptr = connections[upstream_fd];
            upstream_event.data.fd = upstream_fd;

            connections[conn->client_fd]->upstream_fd = upstream_fd;
            connections[upstream_fd]->client_fd = conn->client_fd;
            connections[upstream_fd]->upstream_fd = upstream_fd;

            epoll_ctl(epoll_fd, EPOLL_CTL_ADD, upstream_fd, &upstream_event);

            printf("Connected: client_fd=%d, upstream_fd=%d\n",
                   conn->client_fd, conn->upstream_fd);
            continue;
          }

          if (events[i].data.fd == conn->client_fd) {

            if (forward_data(conn->client_fd, conn->upstream_fd) < 1) {
              close_connection(epoll_fd, conn);
            }
          } else if (events[i].data.fd == conn->upstream_fd) {

            if (forward_data(conn->upstream_fd, conn->client_fd) < 1) {
              close_connection(epoll_fd, conn);
            }
          }
        }
      }
    }
  }

  close(listen_fd);
  close(epoll_fd);
  return EXIT_SUCCESS;
}