deskflow/src/lib/arch/unix/ArchDaemonUnix.cpp

/*
 * Deskflow -- mouse and keyboard sharing utility
 * SPDX-FileCopyrightText: (C) 2012 - 2016 Symless Ltd.
 * SPDX-FileCopyrightText: (C) 2002 Chris Schoeneman
 * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
 */

#include "arch/unix/ArchDaemonUnix.h"

#include "arch/unix/XArchUnix.h"
#include "base/Log.h"

#include <cstdlib>
#include <errno.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

//
// ArchDaemonUnix
//

ArchDaemonUnix::ArchDaemonUnix()
{
  // do nothing
}

ArchDaemonUnix::~ArchDaemonUnix()
{
  // do nothing
}

#ifdef __APPLE__

// In Mac OS X, fork()'d child processes can't use most APIs (the frameworks
// that Deskflow uses in fact prevent it and make the process just up and die),
// so need to exec a copy of the program that doesn't fork so isn't limited.
int execSelfNonDaemonized()
{
  extern char **NXArgv;
  char **selfArgv = NXArgv;

  setenv("_DESKFLOW_DAEMONIZED", "", 1);

  execvp(selfArgv[0], selfArgv);
  return 0;
}

bool alreadyDaemonized()
{
  return getenv("_DESKFLOW_DAEMONIZED") != NULL;
}

#endif

int ArchDaemonUnix::daemonize(const char *name, DaemonFunc func)
{
#ifdef __APPLE__
  if (alreadyDaemonized())
    return func(1, &name);
#endif

  // fork so shell thinks we're done and so we're not a process
  // group leader
  switch (fork()) {
  case -1:
    // failed
    throw XArchDaemonFailed(new XArchEvalUnix(errno));

  case 0:
    // child
    break;

  default:
    // parent exits
    exit(0);
  }

  // become leader of a new session
  setsid();

#ifndef __APPLE__
  // NB: don't run chdir on apple; causes strange behaviour.
  // chdir to root so we don't keep mounted filesystems points busy
  // TODO: this is a bit of a hack - can we find a better solution?
  int chdirErr = chdir("/");
  if (chdirErr)
    // NB: file logging actually isn't working at this point!
    LOG((CLOG_ERR "chdir error: %i", chdirErr));
#endif

  // mask off permissions for any but owner
  umask(077);

  // close open files.  we only expect stdin, stdout, stderr to be open.
  close(0);
  close(1);
  close(2);

  // attach file descriptors 0, 1, 2 to /dev/null so inadvertent use
  // of standard I/O safely goes in the bit bucket.
  open("/dev/null", O_RDONLY);
  open("/dev/null", O_RDWR);

  int dupErr = dup(1);

  if (dupErr < 0) {
    // NB: file logging actually isn't working at this point!
    LOG((CLOG_ERR "dup error: %i", dupErr));
  }

#ifdef __APPLE__
  return execSelfNonDaemonized();
#endif

  // invoke function
  return func(1, &name);
}