snapcast/common/daemon.cpp

/***
    This file is part of snapcast
    Copyright (C) 2014-2024  Johannes Pohl

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    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, see <http://www.gnu.org/licenses/>.
***/

// prototype/interface header file
#include "daemon.hpp"

// local headers
#include "common/snap_exception.hpp"
#include "common/str_compat.hpp"
#include "common/utils/file_utils.hpp"

// standard headers
#include <cstdlib>
#include <cstring>
#include <fcntl.h>
#include <grp.h>
#include <pwd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <syslog.h>
#include <unistd.h>


Daemon::Daemon(const std::string& user, const std::string& group, const std::string& pidfile)
    : pidFilehandle_(-1), user_(user), group_(group), pidfile_(pidfile)
{
    if (pidfile.empty() || pidfile.find('/') == std::string::npos)
        throw SnapException("invalid pid file \"" + pidfile + "\"");
}


Daemon::~Daemon()
{
    if (pidFilehandle_ != -1)
        close(pidFilehandle_);
}


void Daemon::daemonize()
{
    std::string pidfileDir(pidfile_.substr(0, pidfile_.find_last_of('/')));
    utils::file::mkdirRecursive(pidfileDir.c_str(), S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);

    /// Ensure only one copy
    pidFilehandle_ = open(pidfile_.c_str(), O_RDWR | O_CREAT, 0644);
    if (pidFilehandle_ == -1)
    {
        /// Couldn't open lock file
        throw SnapException("Could not open PID lock file \"" + pidfile_ + "\"");
    }

    auto user_uid = static_cast<uid_t>(-1);
    auto user_gid = static_cast<gid_t>(-1);
    // std::string user_name;
    // #ifdef FREEBSD
    //     bool had_group = false;
    // #endif

    if (!user_.empty())
    {
        struct passwd* pwd = getpwnam(user_.c_str());
        if (pwd == nullptr)
            throw SnapException("no such user \"" + user_ + "\"");
        user_uid = pwd->pw_uid;
        user_gid = pwd->pw_gid;
        // user_name = strdup(user_.c_str());
        /// this is needed by libs such as arts
        setenv("HOME", pwd->pw_dir, 1);
    }

    if (!group_.empty())
    {
        const struct group* grp = getgrnam(group_.c_str());
        if (grp == nullptr)
            throw SnapException("no such group \"" + group_ + "\"");
        user_gid = grp->gr_gid;
        // #ifdef FREEBSD
        //         had_group = true;
        // #endif
    }

    if (chown(pidfile_.c_str(), user_uid, user_gid) == -1)
    {
        /// Couldn't open lock file
        throw SnapException("Could not chown PID lock file \"" + pidfile_ + "\"");
    }

    /// set gid
    if (user_gid != static_cast<gid_t>(-1) && user_gid != getgid() && setgid(user_gid) == -1)
        throw SnapException("Failed to set group " + cpt::to_string(static_cast<int>(user_gid)));

    // #if defined(FREEBSD) && !defined(MACOS)
    // #ifdef FREEBSD
    /// init supplementary groups
    /// (must be done before we change our uid)
    /// no need to set the new user's supplementary groups if we are already this user
    //	if (!had_group && user_uid != getuid() && initgroups(user_name, user_gid) == -1)
    //		throw SnapException("Failed to set supplementary groups of user \"" + user + "\"");
    // #endif
    /// set uid
    if (user_uid != static_cast<uid_t>(-1) && user_uid != getuid() && setuid(user_uid) == -1)
        throw SnapException("Failed to set user " + user_);

    /// Our process ID and Session ID
    pid_t pid, sid;

    /// Fork off the parent process
    pid = fork();
    if (pid < 0)
        exit(EXIT_FAILURE);

    /// If we got a good PID, then we can exit the parent process.
    if (pid > 0)
        exit(EXIT_SUCCESS);

    /// Change the file mode mask
    umask(0);

    /// Open any logs here

    /// Create a new SID for the child process
    sid = setsid();
    if (sid < 0)
    {
        /// Log the failure
        exit(EXIT_FAILURE);
    }

    /// Change the current working directory
    if ((chdir("/")) < 0)
    {
        /// Log the failure
        exit(EXIT_FAILURE);
    }

    /// Try to lock file
    if (lockf(pidFilehandle_, F_TLOCK, 0) == -1)
        throw SnapException("Could not lock PID lock file \"" + pidfile_ + "\". Is the daemon already running?");

    char str[10];
    /// Get and format PID
    sprintf(str, "%d\n", getpid());

    /// write pid to lockfile
    if (write(pidFilehandle_, str, strlen(str)) != static_cast<int>(strlen(str)))
        throw SnapException("Could not write PID to lock file \"" + pidfile_ + "\"");

    /// Close out the standard file descriptors
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);
}