
/*
 * Copyright (C) 2020 Jens Elkner.  All rights reserved.
 *
 * License: MIT - see https://opensource.org/licenses/MIT
 */

#include "acme.h"
#include "ns_ioalib_impl.h"

#define GET_ACME_PREFIX "GET /.well-known/acme-challenge/"
#define GET_ACME_PREFIX_LEN 32

static int is_acme_req(char *req, size_t len) {
  static const char *A = "                                             -  0123456789       ABCDEFGHIJKLMNOPQRSTUVWXYZ  "
                         "  _ abcdefghijklmnopqrstuvwxyz     ";
  int c, i, k;

  // Check first request line. Should be like: GET path HTTP/1.x
  if (strncmp(req, GET_ACME_PREFIX, GET_ACME_PREFIX_LEN))
    return -1;
  // Usually (for LE) the "method path" is 32 + 43 = 55 chars. But other
  // implementations may choose longer pathes. We define PATHMAX = 127 chars
  // to be prepared for "DoS" attacks (STUN msg size max. is ~ 64K).
  len -= 21; // min size of trailing headers
  if (len > 131)
    len = 131;
  for (i = GET_ACME_PREFIX_LEN; i < (int)len; i++) {
    // find the end of the path
    if (req[i] != ' ')
      continue;
    // consider path < 10 chars invalid. Also we wanna see a "trailer".
    if (i < (GET_ACME_PREFIX_LEN + 10) || strncmp(req + i, " HTTP/1.", 8))
      return -2;
    // finally check for allowed chars
    for (k = GET_ACME_PREFIX_LEN; k < i; k++) {
      c = req[k];
      if ((c > 127) || (A[c] == ' '))
        return -3;
    }
    // all checks passed: sufficient for us to answer with a redirect
    return i;
  }
  return -4; // end of path not found
}

int try_acme_redirect(char *req, size_t len, const char *url, ioa_socket_handle s) {
  static const char *HTML = "<html><head><title>301 Moved Permanently</title></head>\
		<body><h1>301 Moved Permanently</h1></body></html>";
  char http_response[1024];
  size_t plen, rlen;

  if (url == NULL || url[0] == '\0' || req == NULL || s == 0)
    return 1;
  if (len < (GET_ACME_PREFIX_LEN + 32) || len > (512 - GET_ACME_PREFIX_LEN) ||
      (plen = is_acme_req(req, len)) < (GET_ACME_PREFIX_LEN + 1))
    return 2;

  req[plen] = '\0';

  snprintf(http_response, sizeof(http_response) - 1,
           "HTTP/1.1 301 Moved Permanently\r\n"
           "Content-Type: text/html\r\n"
           "Content-Length: %zu\r\n"
           "Connection: close\r\n"
           "Location: %s%s\r\n"
           "\r\n%s",
           strlen(HTML), url, req + GET_ACME_PREFIX_LEN, HTML);

  rlen = strlen(http_response);

#ifdef LIBEV_OK
  ioa_network_buffer_handle nbh_acme = ioa_network_buffer_allocate(s->e);
  uint8_t *data = ioa_network_buffer_data(nbh_acme);
  memcpy(data, http_response, rlen);
  ioa_network_buffer_set_size(nbh_acme, rlen);
  send_data_from_ioa_socket_nbh(s, NULL, nbh_acme, TTL_IGNORE, TOS_IGNORE, NULL);
#else
  if (write(s->fd, http_response, rlen) == -1) {
    TURN_LOG_FUNC(TURN_LOG_LEVEL_WARNING, "Sending redirect to '%s%s' failed", url, req + GET_ACME_PREFIX_LEN);
  } else if (((turn_turnserver *)s->session->server)->verbose) {
    TURN_LOG_FUNC(TURN_LOG_LEVEL_INFO, "ACME redirected to %s%s\n", url, req + GET_ACME_PREFIX_LEN);
  }
#endif

  req[plen] = ' ';

  return 0;
}
