pEpJSONServerAdapter/server/daemonize.cc

#include "daemonize.hh"

#ifdef _WIN32

#include <windows.h>
#include <tchar.h>
#include <stdio.h>
#include <strsafe.h>
#include <inttypes.h>

#include <thread>
#include <iostream>
#include <stdexcept>
#include <system_error>

HANDLE gPipeRd = NULL;
HANDLE gPipeWr = NULL;

void daemonize (const bool daemonize, const uintptr_t status_handle)
{
    TCHAR * szWinFrontCmdline, * szWinSrvCmdline;
    DWORD dwWinFrontCmdlineLen;
    SECURITY_ATTRIBUTES saAttr;
    PROCESS_INFORMATION piProcInfo;
    STARTUPINFO siStartInfo;
    BOOL bStatusReceived = FALSE;
    DWORD dwRead = 0, dwTotRead = 0;
    DWORD dwRetVal = 1, dwNewRetVal = 0;
    BOOL bSuccess = FALSE;

    /*
     * On Windows there is no need and possibility for a daemonization fork-dance.
     * Instead we launch the same binary ("image") again, passing it
     * additional open file handles. But the new process must learn about the
     * value of the filehandles somehow; only handles dedicated to stderr/stdout/stdin
     * redirection can be passed "internally" via system call. So we simply pass the
     * handle as a string over the command line; #defined STATUS_HANDLE "status-handle".
     * See CreateProcess documentation for more information.
     */

    gPipeWr = (HANDLE) status_handle;

    if (gPipeWr == NULL)
    {
        ZeroMemory(&saAttr, sizeof(SECURITY_ATTRIBUTES));
        saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
        saAttr.bInheritHandle = TRUE;
        saAttr.lpSecurityDescriptor = NULL;

        if (!CreatePipe(&gPipeRd, &gPipeWr, &saAttr, 0))
            throw std::runtime_error("Cannot create pipe!");

        if (!SetHandleInformation(gPipeRd, HANDLE_FLAG_INHERIT, 0))
            throw std::runtime_error("Cannot configure pipe read handle!");

        /*
         * Create new command line with appended " --status-handle <handle>"
         */
        szWinFrontCmdline = GetCommandLine();           // FIXME: Unicode GetCommandLineW, and wmain()
        dwWinFrontCmdlineLen = _tcslen(szWinFrontCmdline) + _tcslen(_T(" -- ")) + _tcslen(_T(STATUS_HANDLE));
        if (dwWinFrontCmdlineLen + 40 >= MAX_PATH)      // + 40 to accommodate PRIuPRT
            throw std::runtime_error("Command line too long to be extend!");

        if (!(szWinSrvCmdline = (TCHAR *)calloc(dwWinFrontCmdlineLen + 40 + 1, sizeof(TCHAR))))
            throw std::runtime_error("Memory allocation for background process command line failed!");

        _stprintf_s(szWinSrvCmdline, dwWinFrontCmdlineLen + 40 + 0,
                    _T("%s --" STATUS_HANDLE " %") PRIuPTR, szWinFrontCmdline,
                                                            ((uintptr_t)gPipeWr));

        ZeroMemory(&piProcInfo, sizeof(PROCESS_INFORMATION));

        ZeroMemory(&siStartInfo, sizeof(STARTUPINFO));
        siStartInfo.cb = sizeof(STARTUPINFO);
        siStartInfo.hStdError = GetStdHandle(STD_ERROR_HANDLE);
        siStartInfo.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
        siStartInfo.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
        siStartInfo.dwFlags |= /* STARTF_USESTDHANDLES | */ STARTF_USESHOWWINDOW;
        siStartInfo.wShowWindow = SW_HIDE;

        bSuccess = CreateProcess(
            NULL,               // application name
            szWinSrvCmdline,    // command line (len+NULL <= MAX_PATH | if appl. name == NULL)
            &saAttr,            // process security attributes
            NULL,               // primary thread security attributes
            TRUE,               // handles are inherited
            0,                  // creation flags, e.g. CREATE_UNICODE_ENVIRONMENT (FIXME: wmain)
            NULL,               // use parent's environment
            NULL,               // use parent's current directory
            &siStartInfo,       // STARTUPINFO pointer
            &piProcInfo         // receives PROCESS_INFORMATION
        );

        free(szWinSrvCmdline);

        if (!bSuccess)
            throw std::runtime_error("Failed to start background process!");

        /*
         * Now wait for the background process to give status feedback
         * via the pipe or for the process to exit (unexpectendly).
         *
         * Close the writing side in the foreground process so that we get EOF when
         * the background process crashes.
         */
        if (!CloseHandle(gPipeWr))
            throw std::runtime_error("Foreground process could not close pipe's write end!");

        do
        {
            bSuccess = ReadFile(gPipeRd, &dwNewRetVal + dwTotRead, sizeof(DWORD) - dwTotRead, &dwRead, NULL);
            dwTotRead += dwRead;
            if (bSuccess == FALSE) {
                if (GetLastError() == ERROR_BROKEN_PIPE)
                    break;

                throw std::runtime_error("Error in foreground process while reading pipe!");
            }

            if (dwTotRead < sizeof(DWORD)) continue;

            dwRetVal = dwNewRetVal;
            bStatusReceived = TRUE;
        } while (1);

        /*
         * If status reporting was not complete, wait for the process to exit,
         * and proxy the return value.
         */
        if (bStatusReceived == FALSE)
        {
            dwNewRetVal = STILL_ACTIVE;   /* STILL_ACTIVE = 259 */
            while (dwNewRetVal == STILL_ACTIVE)
            {
                if (!(bSuccess = GetExitCodeProcess(piProcInfo.hProcess, &dwNewRetVal)))
                    throw std::runtime_error("Can not read exit code from background process!");

                if (dwNewRetVal == STILL_ACTIVE)
                    std::this_thread::sleep_for(std::chrono::milliseconds(250));
            }
            dwRetVal = dwNewRetVal;
        }

        exit(dwRetVal);
    }

}

void daemonize_commit (int retval)
{
    DWORD dwWritten = 0;
    DWORD dwRetVal;
    BOOL bSuccess = FALSE;

    dwRetVal = (DWORD) retval;

    if (gPipeWr == NULL)
        return;

    bSuccess = WriteFile(gPipeWr, &dwRetVal, sizeof(DWORD), &dwWritten, NULL);

    if (bSuccess == FALSE && GetLastError() != ERROR_BROKEN_PIPE)
        throw std::runtime_error("Can not write to pipe's write end in background process!");

    if (!(bSuccess = FreeConsole()))
        throw std::runtime_error("Can not detach from console in background process!");

    if (!CloseHandle(gPipeWr))
        throw std::runtime_error("Can not close pipe's write end in background process!");
}

#else

// Unix/Linux implementation
#include <cstdlib>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/wait.h>

#include <thread>
#include <iostream>
#include <stdexcept>
#include <system_error>


volatile sig_atomic_t sig_term_recv = 0;
int retval_pipefd[2];   /* read fd, write fd */
pid_t fpid = 1;         /* frontend process PID */

void handle_sig_term (int signal)
{
    sig_term_recv = 1;
}

void daemonize (const bool daemonize, const uintptr_t status_handle)
{
    int retval = EXIT_FAILURE;
    pid_t pid, sid, daemon_pid;

    struct sigaction sig_action = {};
    sig_action.sa_handler = handle_sig_term;
    bool this_process_should_term = 0;
    int child_status = 0;

    FILE * ipipe;
    int c;

    pid = getpid();
    if ( daemonize == true && fpid == 1 ) fpid = pid;

    /* only the frontend process shall continue */
    if ( fpid == 1 || fpid != pid ) return;

    if (pipe (retval_pipefd))
        throw std::runtime_error ("Cannot create return-value pipe!");

    /* now fork the intermediate process */
    pid = fork ();
    if (pid < 0)
        throw std::runtime_error ("Cannot fork child process!");

    if (pid > 0)
    {
        /*
         * This is the foreground process which needs to stick around until the
         * background process has comminicated success or failure or has crashed.
         * As soon as a feedback is obtained from the background process, inform
         * the intermediate process to exit (kill TERM) and eventually "copy up"
         * the exit value of the background process.
         */

        /* close the write end of the return value pipe */
        close (retval_pipefd[1]);

        /* read pipe until closed or crashed on writing side */
        ipipe = fdopen (retval_pipefd[0], "r");
        while ((c = getw (ipipe)) != EOF)
        {
            retval = c;
            this_process_should_term = 1;
        }
        fclose (ipipe);
        if (c == EOF)
            this_process_should_term = 1;

        do
        {
            kill (pid, SIGTERM);
            if (!this_process_should_term && (waitpid (pid, &child_status, WUNTRACED) > 0))
            {
                if (WIFEXITED(child_status) || WIFSIGNALED(child_status))
                {
                    retval = WEXITSTATUS(child_status);
                    this_process_should_term = 1;
                }
            }
        } while (!this_process_should_term);

        exit (retval); /* exit the foreground process */
    }

    /*
     * At this point we are the intermediate child process,
     * which now needs to fork the daemon process.
     */

    /* close the read end of the pipe, belonging to the foreground process */
    close (retval_pipefd[0]);

    /* create a new SID for the child process */
    sid = setsid();
    if (sid < 0)
        throw std::runtime_error ("Cannot call setsid()");

    daemon_pid = fork();
    if (daemon_pid < 0)
        throw std::runtime_error ("Cannot fork again!");

    if (daemon_pid > 0)
    {
        /*
         * This now sticks around until it gets the TERM signal from the
         * foreground process. At that point, it will see if the daemon
         * process is still running, and if not, proxy it's retval (which
         * will be again proxied by the frontend process).
         */

        close (retval_pipefd[1]);

        do {
            if (!this_process_should_term && (waitpid (daemon_pid, &child_status, WUNTRACED) > 0))
            {
                if ((WIFEXITED(child_status) || WIFSIGNALED(child_status)))
                {
                    retval = WEXITSTATUS(child_status);
                    this_process_should_term = 1;
                }
            }
        }
        while (!(sig_term_recv || this_process_should_term));

        _exit (retval);
    }

    /* At this point we are a daemon process */

    sig_action.sa_handler = SIG_DFL;
    sigaction (SIGTERM, &sig_action, NULL);

    umask (0007);

    /* daemons normally chdir("/"), we don't do this until our code has evolved */
    /* chdir("/"); */

    /* We delay closing the terminal to daemonize_commit(). */

    const int fd = open ("/dev/null", O_RDONLY, 0);
    if (fd == -1)
        throw std::runtime_error ("Cannot open /dev/null!");
    
    dup2 (fd, STDIN_FILENO);
}


void daemonize_commit (const int retval)
{
    static int commited = 0;
    FILE * retvalfd;
    pid_t pid;

    pid = getpid();

    /* nothing to do if not the daemon process */
    if ( fpid == 1 || fpid == pid )
        return;

    if (commited) return;
    commited = 1;

    const int fd = open ("/dev/null", O_WRONLY, 0);
    if (fd == -1)
        throw std::runtime_error ("Cannot open /dev/null!");

    retvalfd = fdopen (retval_pipefd[1], "a");
    putw (retval, retvalfd);
    fclose (retvalfd);
    close (retval_pipefd[1]);

    dup2 (fd, STDOUT_FILENO);
    dup2 (fd, STDERR_FILENO);
}

#endif // ! _WIN32