/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
   It is considered beerware. Prost. Skol. Cheers or whatever.
   Some of the stuff below is stolen from Fefes example libowfat httpd.

   $Id$ */

/* System */
#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <pthread.h>
#include <pwd.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#ifdef WANT_SYSLOGS
#include <syslog.h>
#endif

/* Libowfat */
#include "io.h"

/* Opentracker */
#include "ot_accesslist.h"
#include "ot_config.h"
#include "ot_hex.h"
#include "ot_http.h"
#include "ot_ip.h"
#include "ot_livesync.h"
#include "ot_mutex.h"
#include "ot_random.h"
#include "ot_scan.h"
#include "ot_fdstate.h"
#include "ot_socket.h"
#include "ot_stats.h"
#include "ot_udp.h"
#include "trackerlogic.h"

/* Globals */
time_t              g_now_seconds;
uint32_t            g_tracker_id;
volatile int        g_opentracker_running = 1;
int                 g_self_pipe[2];


static void         panic(const char *routine) __attribute__((noreturn));
static void         panic(const char *routine) {
  fprintf(stderr, "%s: %s\n", routine, strerror(errno));
  exit(111);
}

static void signal_handler(int s) {
  if (s == SIGINT) {
    /* Any new interrupt signal quits the application */
    signal(SIGINT, SIG_DFL);

    /* Tell all other threads to not acquire any new lock on a bucket
       but cancel their operations and return */
    g_opentracker_running = 0;

    trackerlogic_deinit();

#ifdef WANT_SYSLOGS
    closelog();
#endif

    exit(0);
  }
}

static void defaul_signal_handlers(void) {
  sigset_t signal_mask;
  sigemptyset(&signal_mask);
  sigaddset(&signal_mask, SIGPIPE);
  sigaddset(&signal_mask, SIGHUP);
  sigaddset(&signal_mask, SIGINT);
  sigaddset(&signal_mask, SIGALRM);
  pthread_sigmask(SIG_BLOCK, &signal_mask, NULL);
}

static void install_signal_handlers(void) {
  struct sigaction sa;
  sigset_t         signal_mask;
  sigemptyset(&signal_mask);

  sa.sa_handler = signal_handler;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = SA_RESTART;
  if ((sigaction(SIGINT, &sa, NULL) == -1) || (sigaction(SIGALRM, &sa, NULL) == -1))
    panic("install_signal_handlers");

  sigaddset(&signal_mask, SIGINT);
  pthread_sigmask(SIG_UNBLOCK, &signal_mask, NULL);
}


static ssize_t header_complete(char *request, ssize_t byte_count) {
  ssize_t i = 0, state = 0;

  for (i = 1; i < byte_count; i += 2)
    if (request[i] <= 13) {
      i--;
      for (state = 0; i < byte_count; ++i) {
        char c = request[i];
        if (c == '\r' || c == '\n')
          state = (state >> 2) | ((c << 6) & 0xc0);
        else
          break;
        if (state >= 0xa0 || state == 0x99)
          return i + 1;
      }
    }
  return 0;
}

static void handle_dead(const int64_t sock) {
  struct http_data *cookie = fdstate_cookie(sock);
  if (cookie) {
    if (cookie->batch)
      batch_reset(cookie->batch);
    free(cookie->batch);
    buf_reset(&cookie->request);
    if (cookie->flag & (STRUCT_HTTP_FLAG_WAITINGFORTASK | STRUCT_HTTP_FLAG_CHUNKED_IN_TRANSFER))
      mutex_workqueue_canceltask(sock);
    free(cookie);
  }
  /* The generation has to move before the kernel can reissue the number */
  fdstate_close(sock);
  io_close(sock);
}

static void handle_read(const int64_t sock, struct ot_workstruct *ws) {
  struct http_data *cookie     = fdstate_cookie(sock);
  ssize_t           byte_count = io_tryread(sock, ws->inbuf, G_INBUF_SIZE);

  if (byte_count == 0 || byte_count == -3) {
    handle_dead(sock);
    return;
  }

  if (byte_count == -1)
    return;

  ws->request      = NULL;
  ws->request_size = 0;
  ws->header_size  = 0;
  ws->keep_alive   = 0;

  /* If we get the whole request in one packet, handle it without copying */
  if (!cookie->request.data) {
    if ((ws->header_size = header_complete(ws->inbuf, byte_count))) {
      ws->request      = ws->inbuf;
      ws->request_size = byte_count;
      http_handle_request(sock, ws);
    } else if (buf_cat(&cookie->request, ws->inbuf, (size_t)byte_count))
      handle_dead(sock);
    return;
  }

  if (buf_cat(&cookie->request, ws->inbuf, (size_t)byte_count) || cookie->request.size > G_INBUF_SIZE) {
    http_issue_error(sock, ws, CODE_HTTPERROR_500);
    return;
  }

  while ((ws->header_size = header_complete(cookie->request.data, (ssize_t)cookie->request.size))) {
    ws->request      = cookie->request.data;
    ws->request_size = (ssize_t)cookie->request.size;
    http_handle_request(sock, ws);
#ifdef WANT_KEEPALIVE
    if (!ws->keep_alive)
#endif
      return;
  }
}

static void handle_write(const int64_t sock) {
  struct http_data *cookie = fdstate_cookie(sock);
  int               chunked = 0;

  if (cookie) {
    if (cookie->flag & STRUCT_HTTP_FLAG_CHUNKED_IN_TRANSFER)
      chunked = 1;

    if (cookie->batch) {
      if (batch_send(sock, cookie->batch) == BATCH_FAILED) {
        handle_dead(sock);
        return;
      }
      if (batch_pending(cookie->batch))
        return;
    }
  }

  /* In a chunked transfer, wait for the next piece once everything queued has gone out */
  if (chunked)
    io_dontwantwrite(sock);
  else
    handle_dead(sock);
}

static void handle_accept(const int64_t serversocket) {
  struct http_data *cookie;
  int64_t           sock;
  ot_ip6            ip;
  uint16_t          port;

  while ((sock = socket_accept(serversocket, ip, &port)) != -1) {

    /* Put fd into a non-blocking mode */
    io_nonblock(sock);

    if (!io_fd(sock) || !(cookie = (struct http_data *)malloc(sizeof(struct http_data)))) {
      io_close(sock);
      continue;
    }
    memset(cookie, 0, sizeof(struct http_data));
    memcpy(cookie->ip, ip, sizeof(ot_ip6));

    fdstate_open(sock, cookie, g_now_seconds + OT_CLIENT_TIMEOUT);
    io_wantread(sock);

    stats_issue_event(EVENT_ACCEPT, FLAG_TCP, (uintptr_t)ip);

  }
  io_eagain(serversocket);
}

static void *server_mainloop(void *args) {
  struct ot_workstruct ws;
  time_t               next_timeout_check = g_now_seconds + OT_CLIENT_TIMEOUT_CHECKINTERVAL;
  struct iovec        *iovector;
  size_t               iovec_entries;
  int                  is_partial;

  (void)args;

  /* Initialize our "thread local storage" */
  ws.inbuf  = malloc(G_INBUF_SIZE);
  ws.outbuf = malloc(G_OUTBUF_SIZE);
#ifdef _DEBUG_HTTPERROR
  ws.debugbuf = malloc(G_DEBUGBUF_SIZE);
#endif

  if (!ws.inbuf || !ws.outbuf)
    panic("Initializing worker failed");

  random_bytes(ws.rand48_state, sizeof(ws.rand48_state));

  for (;;) {
    int64_t sock;

    io_wait();

    while ((sock = io_canread()) != -1) {
      const void *cookie = fdstate_cookie(sock);
      if ((intptr_t)cookie == FLAG_TCP)
        handle_accept(sock);
      else if ((intptr_t)cookie == FLAG_UDP)
        handle_udp6(sock, &ws);
      else if ((intptr_t)cookie == FLAG_SELFPIPE)
        io_tryread(sock, ws.inbuf, G_INBUF_SIZE);
      else
        handle_read(sock, &ws);
    }

    while ((sock = mutex_workqueue_popresult(&iovec_entries, &iovector, &is_partial)) != -1)
      http_sendiovecdata(sock, &ws, iovec_entries, iovector, is_partial);

    while ((sock = io_canwrite()) != -1)
      handle_write(sock);

    if (g_now_seconds > next_timeout_check) {
      int cursor = 0;

      while ((sock = fdstate_next_expired(g_now_seconds, &cursor)) != -1)
        handle_dead(sock);
      next_timeout_check = g_now_seconds + OT_CLIENT_TIMEOUT_CHECKINTERVAL;
    }

    livesync_ticker();
  }
  return 0;
}


static void listen_bind_one(ot_listen *entry) {
  socket_sharing sharing = entry->shared ? SOCKET_SHARED : SOCKET_EXCLUSIVE;

#ifdef _DEBUG
  {
    const char *protos[] = {"TCP", "UDP", "UDP mcast"};
    char  _debug[512];
    int   off  = snprintf(_debug, sizeof(_debug), "Binding socket type %s to address [", protos[entry->proto]);
    off       += ip_format(_debug + off, entry->ip);
    snprintf(_debug + off, sizeof(_debug) - off, "]:%d...", entry->port);
    fputs(_debug, stderr);
  }
#endif

#ifdef WANT_SYNC_LIVE
  if (entry->proto == FLAG_MCA) {
    livesync_bind_mcast(entry->ip, entry->port);
#ifdef _DEBUG
    fputs(" success.\n", stderr);
#endif
    return;
  }
#endif

  if (entry->proto == FLAG_TCP) {
    if ((entry->sock = socket_tcp_listen(entry->ip, entry->port, sharing)) == -1)
      panic("socket_tcp_listen");
  } else {
    if ((entry->sock = socket_udp_bind(entry->ip, entry->port, sharing)) == -1)
      panic("socket_udp_bind");
  }

  if (!io_fd(entry->sock))
    panic("io_fd");

  fdstate_open(entry->sock, (void *)entry->proto, 0);
  io_wantread(entry->sock);

#ifdef _DEBUG
  fputs(" success.\n", stderr);
#endif
}

/* Bound in the order the entries were given.
   Note: On macOS SO_REUSEPORT delivers everything to the socket that bound last. */
static void listen_bind_all(void) {
  size_t     count, i;
  ot_listen *entries = config_listen_entries(&count);

  for (i = 0; i < count; ++i)
    listen_bind_one(entries + i);
}

static void listen_start_udp_workers(void) {
  size_t     count, i;
  ot_listen *entries = config_listen_entries(&count);

  udp_init();

  for (i = 0; i < count; ++i) {
    ot_listen *entry = entries + i;

    if (entry->proto != FLAG_UDP || entry->workers <= 0)
      continue;

    io_block(entry->sock);
    udp_workers_install(entry->sock, (unsigned int)entry->workers);
  }
}

void load_state(const char *const state_filename) {
  FILE              *state_filehandle;
  char               inbuf[512];
  ot_hash  infohash;
  uint64_t base, downcount;
  int      consumed;

  state_filehandle = fopen(state_filename, "r");

  if (state_filehandle == NULL) {
    fprintf(stderr, "Warning: Can't open config file: %s.", state_filename);
    return;
  }

  /* We do ignore anything that is not of the form "^[:xdigit:]:\d+:\d+" */
  while (fgets(inbuf, sizeof(inbuf), state_filehandle)) {
    size_t i;

    if (!hex_tohash(infohash, inbuf))
      continue;
    i = 2 * sizeof(ot_hash);

    if (inbuf[i++] != ':' || !(consumed = scan_udec(inbuf + i, &base, UINT64_MAX)))
      continue;
    i += consumed;
    if (inbuf[i++] != ':' || !(consumed = scan_udec(inbuf + i, &downcount, UINT64_MAX)))
      continue;
    add_torrent_from_saved_state(infohash, base, downcount);
  }

  fclose(state_filehandle);
}

int drop_privileges(const char *const serveruser, const char *const serverdir) {
  struct passwd *pws = NULL;

#ifdef _DEBUG
  if (!geteuid())
    fprintf(stderr, "Dropping to user %s.\n", serveruser);
  if (serverdir)
    fprintf(stderr, "ch%s'ing to directory %s.\n", geteuid() ? "dir" : "root", serverdir);
#endif

  /* Grab pws entry before chrooting */
  pws = getpwnam(serveruser);
  endpwent();

  if (geteuid() == 0) {
    /* Running as root: chroot and drop privileges */
    if (serverdir && chroot(serverdir)) {
      fprintf(stderr, "Could not chroot to %s, because: %s\n", serverdir, strerror(errno));
      return -1;
    }

    if (chdir("/"))
      panic("chdir() failed after chrooting: ");

    /* If we can't find server user, revert to nobody's default uid */
    if (!pws) {
      fprintf(stderr, "Warning: Could not get password entry for %s. Reverting to uid -2.\n", serveruser);
      if (setegid((gid_t)-2) || setgid((gid_t)-2) || setuid((uid_t)-2) || seteuid((uid_t)-2))
        panic("Could not set uid to value -2");
    } else {
      if (setegid(pws->pw_gid) || setgid(pws->pw_gid) || setuid(pws->pw_uid) || seteuid(pws->pw_uid))
        panic("Could not set uid to specified value");
    }

    if (geteuid() == 0 || getegid() == 0)
      panic("Still running with root privileges?!");
  } else {
    /* Normal user, just chdir() */
    if (serverdir && chdir(serverdir)) {
      fprintf(stderr, "Could not chroot to %s, because: %s\n", serverdir, strerror(errno));
      return -1;
    }
  }

  return 0;
}

/* Maintain our copy of the clock. time() on BSDs is very expensive. */
static void *time_caching_worker(void *args) {
  (void)args;
  while (1) {
    g_now_seconds = time(NULL);
    sleep(5);
  }
  return NULL;
}

int main(int argc, char **argv) {
  pthread_t thread_id; /* time cacher */

  random_init();
  if (fdstate_init() == -1)
    panic("fdstate_init");
  config_parse(argc, argv);

  listen_bind_all();

  defaul_signal_handlers();

#ifdef WANT_SYSLOGS
  openlog("opentracker", 0, LOG_USER);
  setlogmask(LOG_UPTO(LOG_INFO));
#endif

  if (drop_privileges(g_serveruser ? g_serveruser : "nobody", g_serverdir) == -1)
    panic("drop_privileges failed, exiting. Last error");

  g_now_seconds = time(NULL);
  pthread_create(&thread_id, NULL, time_caching_worker, NULL);

  /* Create our self pipe which allows us to interrupt mainloops
     io_wait in case some data is available to send out */
  if (pipe(g_self_pipe) == -1)
    panic("selfpipe failed: ");
  if (!io_fd(g_self_pipe[0]))
    panic("selfpipe io_fd failed: ");
  if (!io_fd(g_self_pipe[1]))
    panic("selfpipe io_fd failed: ");
  fdstate_open(g_self_pipe[0], (void *)FLAG_SELFPIPE, 0);
  io_wantread(g_self_pipe[0]);

  /* Init all sub systems. This call may fail with an exit() */
  trackerlogic_init();

#ifdef _DEBUG_RANDOMTORRENTS
  fprintf(stderr, "DEBUG: Generating %d random peers on random torrents. This may take a while. (Setting RANDOMTORRENTS in trackerlogic.h)\n", RANDOMTORRENTS);
  trackerlogic_add_random_torrents(RANDOMTORRENTS);
  fprintf(stderr, "... done.\n");
#endif

  if (g_statefile)
    load_state(g_statefile);

  install_signal_handlers();

  listen_start_udp_workers();

  server_mainloop(0);

  fdstate_deinit();
  return 0;
}