modules/remotebackend/pipeconnector.cc

/*
 * This file is part of PowerDNS or dnsdist.
 * Copyright -- PowerDNS.COM B.V. and its contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * In addition, for the avoidance of any doubt, permission is granted to
 * link this program with OpenSSL and to (re)distribute the binaries
 * produced as the result of such linking.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "remotebackend.hh"

PipeConnector::PipeConnector(std::map<std::string, std::string> optionsMap) :
  d_pid(-1)
{
  if (optionsMap.count("command") == 0) {
    g_log << Logger::Error << "Cannot find 'command' option in connection string" << endl;
    throw PDNSException();
  }
  this->command = optionsMap.find("command")->second;
  this->options = optionsMap;
  d_timeout = 2000;

  if (optionsMap.find("timeout") != optionsMap.end()) {
    d_timeout = std::stoi(optionsMap.find("timeout")->second);
  }

  d_fd1[0] = d_fd1[1] = -1;
  d_fd2[0] = d_fd2[1] = -1;
}

PipeConnector::~PipeConnector()
{
  int status;
  // just in case...
  if (d_pid == -1)
    return;

  if (!waitpid(d_pid, &status, WNOHANG)) {
    kill(d_pid, 9);
    waitpid(d_pid, &status, 0);
  }

  if (d_fd1[1]) {
    close(d_fd1[1]);
  }
}

void PipeConnector::launch()
{
  // no relaunch
  if (d_pid > 0 && checkStatus())
    return;

  std::vector<std::string> v;
  split(v, command, boost::is_any_of(" "));

  std::vector<const char*> argv(v.size() + 1);
  argv[v.size()] = 0;

  for (size_t n = 0; n < v.size(); n++)
    argv[n] = v[n].c_str();

  signal(SIGPIPE, SIG_IGN);

  if (access(argv[0], X_OK)) // check before fork so we can throw
    throw PDNSException("Command '" + string(argv[0]) + "' cannot be executed: " + stringerror());

  if (pipe(d_fd1) < 0 || pipe(d_fd2) < 0)
    throw PDNSException("Unable to open pipe for coprocess: " + string(strerror(errno)));

  if ((d_pid = fork()) < 0)
    throw PDNSException("Unable to fork for coprocess: " + stringerror());
  else if (d_pid > 0) { // parent speaking
    close(d_fd1[0]);
    setCloseOnExec(d_fd1[1]);
    close(d_fd2[1]);
    setCloseOnExec(d_fd2[0]);
    if (!(d_fp = std::unique_ptr<FILE, int (*)(FILE*)>(fdopen(d_fd2[0], "r"), fclose)))
      throw PDNSException("Unable to associate a file pointer with pipe: " + stringerror());
    if (d_timeout)
      setbuf(d_fp.get(), 0); // no buffering please, confuses poll
  }
  else if (!d_pid) { // child
    signal(SIGCHLD, SIG_DFL); // silence a warning from perl
    close(d_fd1[1]);
    close(d_fd2[0]);

    if (d_fd1[0] != 0) {
      dup2(d_fd1[0], 0);
      close(d_fd1[0]);
    }

    if (d_fd2[1] != 1) {
      dup2(d_fd2[1], 1);
      close(d_fd2[1]);
    }

    // stdin & stdout are now connected, fire up our coprocess!

    if (execv(argv[0], const_cast<char* const*>(argv.data())) < 0) // now what
      exit(123);

    /* not a lot we can do here. We shouldn't return because that will leave a forked process around.
       no way to log this either - only thing we can do is make sure that our parent catches this soonest! */
  }

  Json::array parameters;
  Json msg = Json(Json::object{
    {"method", "initialize"},
    {"parameters", Json(options)},
  });

  this->send(msg);
  msg = nullptr;
  if (this->recv(msg) == false) {
    g_log << Logger::Error << "Failed to initialize coprocess" << std::endl;
  }
}

int PipeConnector::send_message(const Json& input)
{
  auto line = input.dump();
  launch();

  line.append(1, '\n');

  unsigned int sent = 0;
  int bytes;

  // writen routine - socket may not accept al data in one go
  while (sent < line.size()) {
    bytes = write(d_fd1[1], line.c_str() + sent, line.length() - sent);
    if (bytes < 0)
      throw PDNSException("Writing to coprocess failed: " + std::string(strerror(errno)));

    sent += bytes;
  }
  return sent;
}

int PipeConnector::recv_message(Json& output)
{
  std::string receive;
  std::string err;
  std::string s_output;
  launch();

  while (1) {
    receive.clear();
    if (d_timeout) {
      int ret = waitForData(fileno(d_fp.get()), 0, d_timeout * 1000);
      if (ret < 0)
        throw PDNSException("Error waiting on data from coprocess: " + stringerror());
      if (!ret)
        throw PDNSException("Timeout waiting for data from coprocess");
    }

    if (!stringfgets(d_fp.get(), receive))
      throw PDNSException("Child closed pipe");

    s_output.append(receive);
    // see if it can be parsed
    output = Json::parse(s_output, err);
    if (output != nullptr)
      return s_output.size();
  }
  return 0;
}

bool PipeConnector::checkStatus()
{
  int status;
  int ret = waitpid(d_pid, &status, WNOHANG);
  if (ret < 0)
    throw PDNSException("Unable to ascertain status of coprocess " + itoa(d_pid) + " from " + itoa(getpid()) + ": " + string(strerror(errno)));
  else if (ret) {
    if (WIFEXITED(status)) {
      int exitStatus = WEXITSTATUS(status);
      throw PDNSException("Coprocess exited with code " + itoa(exitStatus));
    }
    if (WIFSIGNALED(status)) {
      int sig = WTERMSIG(status);
      string reason = "CoProcess died on receiving signal " + itoa(sig);
#ifdef WCOREDUMP
      if (WCOREDUMP(status))
        reason += ". Dumped core";
#endif

      throw PDNSException(reason);
    }
  }
  return true;
}