xserver-multidpi/hw/xquartz/mach-startup/bundle-main.c

/* main.c -- X application launcher
 * Copyright (c) 2007 Jeremy Huddleston
 * Copyright (c) 2007-2012 Apple Inc. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE ABOVE LISTED COPYRIGHT
 * HOLDER(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * Except as contained in this notice, the name(s) of the above
 * copyright holders shall not be used in advertising or otherwise to
 * promote the sale, use or other dealings in this Software without
 * prior written authorization.
 */

#include <CoreFoundation/CoreFoundation.h>
#include <AvailabilityMacros.h>

#ifdef HAVE_DIX_CONFIG_H
#include <dix-config.h>
#endif

#include <X11/Xlib.h>
#include <assert.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#include <signal.h>

#ifdef HAVE_LIBDISPATCH
#include <dispatch/dispatch.h>
#else
#include <pthread.h>
#endif

#include <sys/socket.h>
#include <sys/un.h>

#include <fcntl.h>

#include <mach/mach.h>
#include <mach/mach_error.h>
#include <servers/bootstrap.h>
#include "mach_startup.h"
#include "mach_startupServer.h"

#include "console_redirect.h"

/* From darwinEvents.c ... but don't want to pull in all the server cruft */
void
DarwinListenOnOpenFD(int fd);

extern aslclient aslc;

/* Ditto, from os/log.c */
extern void
ErrorF(const char *f, ...) _X_ATTRIBUTE_PRINTF(1, 2);
extern void
FatalError(const char *f, ...) _X_ATTRIBUTE_PRINTF(1, 2) _X_NORETURN;

extern int noPanoramiXExtension;

#define DEFAULT_CLIENT X11BINDIR "/xterm"
#define DEFAULT_STARTX X11BINDIR "/startx"
#define DEFAULT_SHELL  "/bin/sh"

#ifndef BUILD_DATE
#define BUILD_DATE ""
#endif
#ifndef XSERVER_VERSION
#define XSERVER_VERSION "?"
#endif

static char __crashreporter_info_buff__[4096] = { 0 };
static const char *__crashreporter_info__ __attribute__((__used__)) =
    &__crashreporter_info_buff__[0];
#if MAC_OS_X_VERSION_MIN_REQUIRED >= 1050
// This is actually a toolchain requirement, but I'm not sure the correct check,
// but it should be fine to just only include it for Leopard and later.  This line
// just tells the linker to never strip this symbol (such as for space optimization)
asm (".desc ___crashreporter_info__, 0x10");
#endif

static const char *__crashreporter_info__base =
    "X.Org X Server " XSERVER_VERSION " Build Date: " BUILD_DATE;

char *bundle_id_prefix = NULL;
static char *server_bootstrap_name = NULL;

#define DEBUG 1

/* This is in quartzStartup.c */
int
server_main(int argc, char **argv, char **envp);

static int
execute(const char *command);
static char *
command_from_prefs(const char *key, const char *default_value);

static char *pref_app_to_run;
static char *pref_login_shell;
static char *pref_startx_script;

#ifndef HAVE_LIBDISPATCH
/*** Pthread Magics ***/
static pthread_t
create_thread(void *(*func)(void *), void *arg)
{
    pthread_attr_t attr;
    pthread_t tid;

    pthread_attr_init(&attr);
    pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    pthread_create(&tid, &attr, func, arg);
    pthread_attr_destroy(&attr);

    return tid;
}
#endif

/*** Mach-O IPC Stuffs ***/

union MaxMsgSize {
    union __RequestUnion__mach_startup_subsystem req;
    union __ReplyUnion__mach_startup_subsystem rep;
};

static mach_port_t
checkin_or_register(char *bname)
{
    kern_return_t kr;
    mach_port_t mp;

    /* If we're started by launchd or the old mach_init */
    kr = bootstrap_check_in(bootstrap_port, bname, &mp);
    if (kr == KERN_SUCCESS)
        return mp;

    /* We probably were not started by launchd or the old mach_init */
    kr = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &mp);
    if (kr != KERN_SUCCESS) {
        ErrorF("mach_port_allocate(): %s\n", mach_error_string(kr));
        exit(EXIT_FAILURE);
    }

    kr = mach_port_insert_right(
        mach_task_self(), mp, mp, MACH_MSG_TYPE_MAKE_SEND);
    if (kr != KERN_SUCCESS) {
        ErrorF("mach_port_insert_right(): %s\n", mach_error_string(kr));
        exit(EXIT_FAILURE);
    }

#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations" // bootstrap_register
#endif
    kr = bootstrap_register(bootstrap_port, bname, mp);
#ifdef __clang__
#pragma clang diagnostic pop
#endif

    if (kr != KERN_SUCCESS) {
        ErrorF("bootstrap_register(): %s\n", mach_error_string(kr));
        exit(EXIT_FAILURE);
    }

    return mp;
}

/*** $DISPLAY handoff ***/
static int
accept_fd_handoff(int connected_fd)
{
    int launchd_fd;

    char databuf[] = "display";
    struct iovec iov[1];

    union {
        struct cmsghdr hdr;
        char bytes[CMSG_SPACE(sizeof(int))];
    } buf;

    struct msghdr msg;
    struct cmsghdr *cmsg;

    iov[0].iov_base = databuf;
    iov[0].iov_len = sizeof(databuf);

    msg.msg_iov = iov;
    msg.msg_iovlen = 1;
    msg.msg_control = buf.bytes;
    msg.msg_controllen = sizeof(buf);
    msg.msg_name = 0;
    msg.msg_namelen = 0;
    msg.msg_flags = 0;

    cmsg = CMSG_FIRSTHDR(&msg);
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = SCM_RIGHTS;
    cmsg->cmsg_len = CMSG_LEN(sizeof(int));

    msg.msg_controllen = cmsg->cmsg_len;

    *((int *)CMSG_DATA(cmsg)) = -1;

    if (recvmsg(connected_fd, &msg, 0) < 0) {
        ErrorF(
            "X11.app: Error receiving $DISPLAY file descriptor.  recvmsg() error: %s\n",
            strerror(errno));
        return -1;
    }

    launchd_fd = *((int *)CMSG_DATA(cmsg));

    return launchd_fd;
}

typedef struct {
    int fd;
    string_t filename;
} socket_handoff_t;

/* This thread accepts an incoming connection and hands off the file
 * descriptor for the new connection to accept_fd_handoff()
 */
#ifdef HAVE_LIBDISPATCH
static void
socket_handoff(socket_handoff_t *handoff_data)
{
#else
static void *
socket_handoff_thread(void *arg)
{
    socket_handoff_t *handoff_data = (socket_handoff_t *)arg;
#endif

    int launchd_fd = -1;
    int connected_fd;

    /* Now actually get the passed file descriptor from this connection
     * If we encounter an error, keep listening.
     */
    while (launchd_fd == -1) {
        connected_fd = accept(handoff_data->fd, NULL, NULL);
        if (connected_fd == -1) {
            ErrorF(
                "X11.app: Failed to accept incoming connection on socket (fd=%d): %s\n",
                handoff_data->fd, strerror(errno));
            sleep(2);
            continue;
        }

        launchd_fd = accept_fd_handoff(connected_fd);
        if (launchd_fd == -1)
            ErrorF(
                "X11.app: Error receiving $DISPLAY file descriptor, no descriptor received?  Waiting for another connection.\n");

        close(connected_fd);
    }

    close(handoff_data->fd);
    unlink(handoff_data->filename);
    free(handoff_data);

    ErrorF(
        "X11.app Handing off fd to server thread via DarwinListenOnOpenFD(%d)\n",
        launchd_fd);
    DarwinListenOnOpenFD(launchd_fd);

#ifndef HAVE_LIBDISPATCH
    return NULL;
#endif
}

static int
create_socket(char *filename_out)
{
    struct sockaddr_un servaddr_un;
    struct sockaddr *servaddr;
    socklen_t servaddr_len;
    int ret_fd;
    size_t try, try_max;

    for (try = 0, try_max = 5; try < try_max; try++) {
        tmpnam(filename_out);

        /* Setup servaddr_un */
        memset(&servaddr_un, 0, sizeof(struct sockaddr_un));
        servaddr_un.sun_family = AF_UNIX;
        strlcpy(servaddr_un.sun_path, filename_out,
                sizeof(servaddr_un.sun_path));

        servaddr = (struct sockaddr *)&servaddr_un;
        servaddr_len = sizeof(struct sockaddr_un) -
                       sizeof(servaddr_un.sun_path) + strlen(filename_out);

        ret_fd = socket(PF_UNIX, SOCK_STREAM, 0);
        if (ret_fd == -1) {
            ErrorF(
                "X11.app: Failed to create socket (try %d / %d): %s - %s\n",
                (int)try + 1, (int)try_max, filename_out, strerror(errno));
            continue;
        }

        if (bind(ret_fd, servaddr, servaddr_len) != 0) {
            ErrorF("X11.app: Failed to bind socket: %d - %s\n", errno,
                   strerror(
                       errno));
            close(ret_fd);
            return 0;
        }

        if (listen(ret_fd, 10) != 0) {
            ErrorF("X11.app: Failed to listen to socket: %s - %d - %s\n",
                   filename_out, errno, strerror(
                       errno));
            close(ret_fd);
            return 0;
        }

#ifdef DEBUG
        ErrorF("X11.app: Listening on socket for fd handoff:  (%d) %s\n",
               ret_fd,
               filename_out);
#endif

        return ret_fd;
    }

    return 0;
}

static int launchd_socket_handed_off = 0;

kern_return_t
do_request_fd_handoff_socket(mach_port_t port, string_t filename)
{
    socket_handoff_t *handoff_data;

    launchd_socket_handed_off = 1;

    handoff_data = (socket_handoff_t *)calloc(1, sizeof(socket_handoff_t));
    if (!handoff_data) {
        ErrorF("X11.app: Error allocating memory for handoff_data\n");
        return KERN_FAILURE;
    }

    handoff_data->fd = create_socket(handoff_data->filename);
    if (!handoff_data->fd) {
        free(handoff_data);
        return KERN_FAILURE;
    }

    strlcpy(filename, handoff_data->filename, STRING_T_SIZE);

#ifdef HAVE_LIBDISPATCH
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
                                             0), ^ {
                       socket_handoff(handoff_data);
                   });
#else
    create_thread(socket_handoff_thread, handoff_data);
#endif

#ifdef DEBUG
    ErrorF(
        "X11.app: Thread created for handoff.  Returning success to tell caller to connect and push the fd.\n");
#endif

    return KERN_SUCCESS;
}

kern_return_t
do_request_pid(mach_port_t port, int *my_pid)
{
    *my_pid = getpid();
    return KERN_SUCCESS;
}

/*** Server Startup ***/
kern_return_t
do_start_x11_server(mach_port_t port, string_array_t argv,
                    mach_msg_type_number_t argvCnt,
                    string_array_t envp,
                    mach_msg_type_number_t envpCnt)
{
    /* And now back to char ** */
    char **_argv = alloca((argvCnt + 1) * sizeof(char *));
    char **_envp = alloca((envpCnt + 1) * sizeof(char *));
    size_t i;

    /* If we didn't get handed a launchd DISPLAY socket, we should
     * unset DISPLAY or we can run into problems with pbproxy
     */
    if (!launchd_socket_handed_off) {
        ErrorF("X11.app: No launchd socket handed off, unsetting DISPLAY\n");
        unsetenv("DISPLAY");
    }

    if (!_argv || !_envp) {
        return KERN_FAILURE;
    }

    ErrorF("X11.app: do_start_x11_server(): argc=%d\n", argvCnt);
    for (i = 0; i < argvCnt; i++) {
        _argv[i] = argv[i];
        ErrorF("\targv[%u] = %s\n", (unsigned)i, argv[i]);
    }
    _argv[argvCnt] = NULL;

    for (i = 0; i < envpCnt; i++) {
        _envp[i] = envp[i];
    }
    _envp[envpCnt] = NULL;

    if (server_main(argvCnt, _argv, _envp) == 0)
        return KERN_SUCCESS;
    else
        return KERN_FAILURE;
}

static int
startup_trigger(int argc, char **argv, char **envp)
{
    Display *display;
    const char *s;

    /* Take care of the case where we're called like a normal DDX */
    if (argc > 1 && argv[1][0] == ':') {
        size_t i;
        kern_return_t kr;
        mach_port_t mp;
        string_array_t newenvp;
        string_array_t newargv;

        /* We need to count envp */
        int envpc;
        for (envpc = 0; envp[envpc]; envpc++) ;

        /* We have fixed-size string lengths due to limitations in IPC,
         * so we need to copy our argv and envp.
         */
        newargv = (string_array_t)alloca(argc * sizeof(string_t));
        newenvp = (string_array_t)alloca(envpc * sizeof(string_t));

        if (!newargv || !newenvp) {
            ErrorF("Memory allocation failure\n");
            exit(EXIT_FAILURE);
        }

        for (i = 0; i < argc; i++) {
            strlcpy(newargv[i], argv[i], STRING_T_SIZE);
        }
        for (i = 0; i < envpc; i++) {
            strlcpy(newenvp[i], envp[i], STRING_T_SIZE);
        }

        kr = bootstrap_look_up(bootstrap_port, server_bootstrap_name, &mp);
        if (kr != KERN_SUCCESS) {
#if MAC_OS_X_VERSION_MIN_REQUIRED >= 1050
            ErrorF("bootstrap_look_up(%s): %s\n", server_bootstrap_name,
                   bootstrap_strerror(
                       kr));
#else
            ErrorF("bootstrap_look_up(%s): %ul\n", server_bootstrap_name,
                   (unsigned long)kr);
#endif
            exit(EXIT_FAILURE);
        }

        kr = start_x11_server(mp, newargv, argc, newenvp, envpc);
        if (kr != KERN_SUCCESS) {
            ErrorF("start_x11_server: %s\n", mach_error_string(kr));
            exit(EXIT_FAILURE);
        }
        exit(EXIT_SUCCESS);
    }

    /* If we have a process serial number and it's our only arg, act as if
     * the user double clicked the app bundle: launch app_to_run if possible
     */
    if (argc == 1 || (argc == 2 && !strncmp(argv[1], "-psn_", 5))) {
        /* Now, try to open a display, if so, run the launcher */
        display = XOpenDisplay(NULL);
        if (display) {
            /* Could open the display, start the launcher */
            XCloseDisplay(display);

            return execute(pref_app_to_run);
        }
    }

    /* Start the server */
    if ((s = getenv("DISPLAY"))) {
        ErrorF(
            "X11.app: Could not connect to server (DISPLAY=\"%s\", unsetting).  Starting X server.\n",
            s);
        unsetenv("DISPLAY");
    }
    else {
        ErrorF(
            "X11.app: Could not connect to server (DISPLAY is not set).  Starting X server.\n");
    }
    return execute(pref_startx_script);
}

/** Setup the environment we want our child processes to inherit */
static void
ensure_path(const char *dir)
{
    char buf[1024], *temp;

    /* Make sure /usr/X11/bin is in the $PATH */
    temp = getenv("PATH");
    if (temp == NULL || temp[0] == 0) {
        snprintf(buf, sizeof(buf),
                 "/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:%s",
                 dir);
        setenv("PATH", buf, TRUE);
    }
    else if (strnstr(temp, X11BINDIR, sizeof(temp)) == NULL) {
        snprintf(buf, sizeof(buf), "%s:%s", temp, dir);
        setenv("PATH", buf, TRUE);
    }
}

static void
setup_console_redirect(const char *bundle_id)
{
    char *asl_sender;
    char *asl_facility;

    asprintf(&asl_sender, "%s.server", bundle_id);
    assert(asl_sender);

    asl_facility = strdup(bundle_id);
    assert(asl_facility);
    if (strcmp(asl_facility + strlen(asl_facility) - 4, ".X11") == 0)
        asl_facility[strlen(asl_facility) - 4] = '\0';

    assert(aslc = asl_open(asl_sender, asl_facility, ASL_OPT_NO_DELAY));
    free(asl_sender);
    free(asl_facility);

    asl_set_filter(aslc, ASL_FILTER_MASK_UPTO(ASL_LEVEL_WARNING));
    xq_asl_capture_fd(aslc, NULL, ASL_LEVEL_INFO, STDOUT_FILENO);
    xq_asl_capture_fd(aslc, NULL, ASL_LEVEL_NOTICE, STDERR_FILENO);
}

static void
setup_env(void)
{
    char *temp;
    const char *pds = NULL;
    const char *disp = getenv("DISPLAY");
    size_t len;

    /* Pass on our prefs domain to startx and its inheritors (mainly for
     * quartz-wm and the Xquartz stub's MachIPC)
     */
    CFBundleRef bundle = CFBundleGetMainBundle();
    if (bundle) {
        CFStringRef pd = CFBundleGetIdentifier(bundle);
        if (pd) {
            pds = CFStringGetCStringPtr(pd, 0);
        }
    }

    /* fallback to hardcoded value if we can't discover it */
    if (!pds) {
        pds = BUNDLE_ID_PREFIX ".X11";
    }

    setup_console_redirect(pds);

    server_bootstrap_name = strdup(pds);
    if (!server_bootstrap_name) {
        ErrorF("X11.app: Memory allocation error.\n");
        exit(1);
    }
    setenv("X11_PREFS_DOMAIN", server_bootstrap_name, 1);

    len = strlen(server_bootstrap_name);
    bundle_id_prefix = malloc(sizeof(char) * (len - 3));
    if (!bundle_id_prefix) {
        ErrorF("X11.app: Memory allocation error.\n");
        exit(1);
    }
    strlcpy(bundle_id_prefix, server_bootstrap_name, len - 3);

    /* We need to unset DISPLAY if it is not our socket */
    if (disp) {
        /* s = basename(disp) */
        const char *d, *s;
        for (s = NULL, d = disp; *d; d++) {
            if (*d == '/')
                s = d + 1;
        }

        if (s && *s) {
            if (strcmp(bundle_id_prefix,
                       "org.x") == 0 && strcmp(s, ":0") == 0) {
                ErrorF(
                    "X11.app: Detected old style launchd DISPLAY, please update xinit.\n");
            }
            else {
                temp = (char *)malloc(sizeof(char) * len);
                if (!temp) {
                    ErrorF(
                        "X11.app: Memory allocation error creating space for socket name test.\n");
                    exit(1);
                }
                strlcpy(temp, bundle_id_prefix, len);
                strlcat(temp, ":0", len);

                if (strcmp(temp, s) != 0) {
                    /* If we don't have a match, unset it. */
                    ErrorF(
                        "X11.app: DISPLAY (\"%s\") does not match our id (\"%s\"), unsetting.\n",
                        disp, bundle_id_prefix);
                    unsetenv("DISPLAY");
                }
                free(temp);
            }
        }
        else {
            /* The DISPLAY environment variable is not formatted like a launchd socket, so reset. */
            ErrorF(
                "X11.app: DISPLAY does not look like a launchd set variable, unsetting.\n");
            unsetenv("DISPLAY");
        }
    }

    /* Make sure PATH is right */
    ensure_path(X11BINDIR);

    /* cd $HOME */
    temp = getenv("HOME");
    if (temp != NULL && temp[0] != '\0')
        chdir(temp);
}

/*** Main ***/
int
main(int argc, char **argv, char **envp)
{
    Bool listenOnly = FALSE;
    int i;
    mach_msg_size_t mxmsgsz = sizeof(union MaxMsgSize) + MAX_TRAILER_SIZE;
    mach_port_t mp;
    kern_return_t kr;

    /* Setup our environment for our children */
    setup_env();

    /* The server must not run the PanoramiX operations. */
    noPanoramiXExtension = TRUE;

    /* Setup the initial crasherporter info */
    strlcpy(__crashreporter_info_buff__, __crashreporter_info__base,
            sizeof(__crashreporter_info_buff__));

    ErrorF("X11.app: main(): argc=%d\n", argc);
    for (i = 0; i < argc; i++) {
        ErrorF("\targv[%u] = %s\n", (unsigned)i, argv[i]);
        if (!strcmp(argv[i], "--listenonly")) {
            listenOnly = TRUE;
        }
    }

    mp = checkin_or_register(server_bootstrap_name);
    if (mp == MACH_PORT_NULL) {
        ErrorF("NULL mach service: %s", server_bootstrap_name);
        return EXIT_FAILURE;
    }

    /* Check if we need to do something other than listen, and make another
     * thread handle it.
     */
    if (!listenOnly) {
        pid_t child1, child2;
        int status;

        pref_app_to_run = command_from_prefs("app_to_run", DEFAULT_CLIENT);
        assert(pref_app_to_run);

        pref_login_shell = command_from_prefs("login_shell", DEFAULT_SHELL);
        assert(pref_login_shell);

        pref_startx_script = command_from_prefs("startx_script",
                                                DEFAULT_STARTX);
        assert(pref_startx_script);

        /* Do the fork-twice trick to avoid having to reap zombies */
        child1 = fork();
        switch (child1) {
        case -1:                                    /* error */
            FatalError("fork() failed: %s\n", strerror(errno));

        case 0:                                     /* child1 */
            child2 = fork();

            switch (child2) {
                int max_files;

            case -1:                                    /* error */
                FatalError("fork() failed: %s\n", strerror(errno));

            case 0:                                     /* child2 */
                /* close all open files except for standard streams */
                max_files = sysconf(_SC_OPEN_MAX);
                for (i = 3; i < max_files; i++)
                    close(i);

                /* ensure stdin is on /dev/null */
                close(0);
                open("/dev/null", O_RDONLY);

                return startup_trigger(argc, argv, envp);

            default:                                    /* parent (child1) */
                _exit(0);
            }
            break;

        default:                                    /* parent */
            waitpid(child1, &status, 0);
        }

        free(pref_app_to_run);
        free(pref_login_shell);
        free(pref_startx_script);
    }

    /* Main event loop */
    ErrorF("Waiting for startup parameters via Mach IPC.\n");
    kr = mach_msg_server(mach_startup_server, mxmsgsz, mp, 0);
    if (kr != KERN_SUCCESS) {
        ErrorF("%s.X11(mp): %s\n", BUNDLE_ID_PREFIX, mach_error_string(kr));
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

static int
execute(const char *command)
{
    const char *newargv[4];
    const char **p;

    newargv[0] = pref_login_shell;
    newargv[1] = "-c";
    newargv[2] = command;
    newargv[3] = NULL;

    ErrorF("X11.app: Launching %s:\n", command);
    for (p = newargv; *p; p++) {
        ErrorF("\targv[%ld] = %s\n", (long int)(p - newargv), *p);
    }

    execvp(newargv[0], (char *const *)newargv);
    perror("X11.app: Couldn't exec.");
    return 1;
}

static char *
command_from_prefs(const char *key, const char *default_value)
{
    char *command = NULL;

    CFStringRef cfKey;
    CFPropertyListRef PlistRef;

    if (!key)
        return NULL;

    cfKey = CFStringCreateWithCString(NULL, key, kCFStringEncodingASCII);

    if (!cfKey)
        return NULL;

    PlistRef = CFPreferencesCopyAppValue(cfKey,
                                         kCFPreferencesCurrentApplication);

    if ((PlistRef == NULL) ||
        (CFGetTypeID(PlistRef) != CFStringGetTypeID())) {
        CFStringRef cfDefaultValue = CFStringCreateWithCString(
            NULL, default_value, kCFStringEncodingASCII);
        int len = strlen(default_value) + 1;

        if (!cfDefaultValue)
            goto command_from_prefs_out;

        CFPreferencesSetAppValue(cfKey, cfDefaultValue,
                                 kCFPreferencesCurrentApplication);
        CFPreferencesAppSynchronize(kCFPreferencesCurrentApplication);
        CFRelease(cfDefaultValue);

        command = (char *)malloc(len * sizeof(char));
        if (!command)
            goto command_from_prefs_out;
        strcpy(command, default_value);
    }
    else {
        int len = CFStringGetLength((CFStringRef)PlistRef) + 1;
        command = (char *)malloc(len * sizeof(char));
        if (!command)
            goto command_from_prefs_out;
        CFStringGetCString((CFStringRef)PlistRef, command, len,
                           kCFStringEncodingASCII);
    }

command_from_prefs_out:
    if (PlistRef)
        CFRelease(PlistRef);
    if (cfKey)
        CFRelease(cfKey);
    return command;
}