mx_util.c

#define _GNU_SOURCE

#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include <stdio.h>
#include <libgen.h>
#include <unistd.h>

#include <ctype.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/vfs.h>
#include <fcntl.h>
#include <sys/wait.h>

#include "mx_log.h"
#include "mx_util.h"

static int _mx_strbeginswith(char *str, const char *start, char **endptr, short ignore_case)
{
    size_t len;
    int res;

    assert(str);
    assert(start);

    len = strlen(start);
    if (ignore_case)
        res = strncasecmp(str, start, len);
    else
        res = strncmp(str, start, len);

    if (res != 0 || !endptr)
        return !res;

    *endptr  = str + len;

    return 1;
}

int mx_strbeginswith(char *str, const char *start, char **endptr)
{
    return _mx_strbeginswith(str, start, endptr, 0);
}

int mx_stribeginswith(char *str, const char *start, char **endptr)
{
    return _mx_strbeginswith(str, start, endptr, 1);
}

static int _mx_strbeginswithany(char *str, char **starts, char **endptr, short ignore_case)
{
    char **s;
    char *end;
    char *longestmatch = NULL;
    int res;

    for (s = starts; *s; s++) {
        res = _mx_strbeginswith(str, *s, &end, ignore_case);
        if (res && (!longestmatch || end > longestmatch))
            longestmatch = end;
    }

    if (longestmatch) {
        *endptr = longestmatch;
        return 1;
    }

    return 0;
}

int mx_strbeginswithany(char *str, char **starts, char **endptr)
{
    return _mx_strbeginswithany(str, starts, endptr, 0);
}

int mx_stribeginswithany(char *str, char **starts, char **endptr)
{
    return _mx_strbeginswithany(str, starts, endptr, 1);
}

int mx_strtobytes(char *str, unsigned long long int *bytes)
{
    unsigned long long int s = 0;
    unsigned long long int t;

    char *end;

    if (!str || !*str)
        return -(errno=EINVAL);

    if (strchr(str, '-'))
        return -(errno=ERANGE);

    do {
        errno = 0;
        t = strtoull(str, &end, 10);

        if (errno)
            return -errno;

        if (str == end)
            return -(errno=EINVAL);

        for (;*end && *end == ' '; end++)
            /* empty */;

        switch (*end) {

            case 'T': /* tebi */
                t *= 1024;
                // fall through
            case 'G': /* gibi */
                t *= 1024;
                // fall through
            case 'M': /* mebi */
                t *= 1024;
                // fall through
            case 'k': /* kibi */
            case 'K':
                t *= 1024;
                // fall through
            case 'B': /* bytes */
                end++;
                break;

            default:
                return -(errno=EINVAL);
        }

        if (s+t < s)
            return -(errno=ERANGE);

        s += t;

        for (;*end && *end == ' '; end++)
            /* empty */;

        str = end;

    } while (*str);

    *bytes = s;

    return 0;
}

int mx_strtoseconds(char *str, unsigned long long int *seconds)
{
    unsigned long long int s = 0;
    unsigned long long int t;

    char *end;

    if (!str || !*str)
        return -(errno=EINVAL);

    if (strchr(str, '-'))
        return -(errno=ERANGE);

    do {
        errno = 0;
        t = strtoull(str, &end, 10);

        if (errno)
            return -errno;

        if (str == end)
            return -(errno=EINVAL);

        for (;*end && *end == ' '; end++)
            /* empty */;

        //if (mx_strtounit(end, &end));

        switch (*end) {

            case 'y': /* years */
                t *= 52;
                // fall through
            case 'w': /* weeks */
                t *= 7;
                // fall through
            case 'd': /* days */
                t *= 24;
                // fall through
            case 'h': /* hours */
                t *= 60;
                // fall through
            case 'm': /* minutes */
                t *= 60;
                // fall through
            case 's': /* seconds */
                end++;
                break;

            default:
                return -(errno=EINVAL);
        }

        if (s+t < s)
            return -(errno=ERANGE);

        s += t;

        for (;*end && *end == ' '; end++)
            /* empty */;

        str = end;

    } while (*str);

    *seconds = s;

    return 0;
}

int mx_strtominutes(char *str, unsigned long long int *minutes)
{
    int res;

    res = mx_strtoseconds(str, minutes);

    if (res >= 0)
        *minutes /= 60;

    return res;
}

char *mx_strskipwhitespaces(char *str)
{
    char *s;

    assert(str);

    for (s = str; *s && *s == ' '; s++)
        /* empty */;

    return s;
}

/* wrapper unsigned */

int mx_strtoul(char *str, unsigned long int *to)
{
    unsigned long int ul;
    char *end;

    assert(str);
    assert(to);

    errno = 0;

    ul = strtoul(str, &end, 0);

    if (errno > 0)
        return -errno;

    end = mx_strskipwhitespaces(end);

    if (!end || str == end || *end)
        return -(errno=EINVAL);

    if (strchr(str, '-'))
        return -(errno=ERANGE);

    *to = ul;

    return 0;
}

int mx_strtoull(char *str, unsigned long long int *to)
{
    unsigned long long int ull;
    char *end;

    assert(str);
    assert(to);

    errno = 0;

    ull = strtoull(str, &end, 0);

    if (errno > 0)
        return -errno;

    end = mx_strskipwhitespaces(end);

    if (!end || str == end || *end)
        return -(errno=EINVAL);

    if (strchr(str, '-'))
        return -(errno=ERANGE);

    *to = ull;

    return 0;
}

/* wrapper signed */

int mx_strtol(char *str, signed long int *to)
{
    long int l;
    char *end;

    assert(str);
    assert(to);

    errno = 0;

    l = strtoul(str, &end, 0);

    if (errno > 0)
        return -errno;

    end = mx_strskipwhitespaces(end);

    if (!end || str == end || *end)
        return -(errno=EINVAL);

    *to = l;

    return 0;
}

int mx_strtoll(char *str, signed long long int *to)
{
    long long int ll;
    char *end;

    assert(str);
    assert(to);

    errno = 0;

    ll = strtoll(str, &end, 0);

    if (errno > 0)
        return -errno;

    end = mx_strskipwhitespaces(end);

    if (!end || str == end || *end)
        return -(errno=EINVAL);

    *to = ll;

    return 0;
}

/* unsigned */

int mx_strtoui(char *str, unsigned int *to)
{
    unsigned long int ul;
    int res;

    assert(str);
    assert(to);

    res = mx_strtoul(str, &ul);
    if (res < 0)
        return res;

    if ((unsigned long int)(unsigned int)ul != ul)
        return -(errno=ERANGE);

    *to = (unsigned int)ul;

    return 0;
}

int mx_strtou8(char *str, uint8_t *to)
{
    unsigned long int ul;
    int res;

    assert(str);
    assert(to);

    res = mx_strtoul(str, &ul);
    if (res < 0)
        return res;

    if ((unsigned long int)(uint8_t)ul != ul)
        return -(errno=ERANGE);

    *to = (uint8_t)ul;

    return 0;
}

int mx_strtou16(char *str, uint16_t *to)
{
    unsigned long int ul;
    int res;

    assert(str);
    assert(to);

    res = mx_strtoul(str, &ul);
    if (res < 0)
        return res;

    if ((unsigned long int)(uint16_t)ul != ul)
        return -(errno=ERANGE);

    *to = (uint16_t)ul;

    return 0;
}

int mx_strtou32(char *str, uint32_t *to)
{
    unsigned long int ul;
    int res;

    assert(str);
    assert(to);

    res = mx_strtoul(str, &ul);
    if (res < 0)
        return res;

    if ((unsigned long int)(uint32_t)ul != ul)
        return -(errno=ERANGE);

    *to = (uint32_t)ul;

    return 0;
}

int mx_strtou64(char *str, uint64_t *to)
{
    unsigned long long int ull;
    int res;

    assert(str);
    assert(to);

    res = mx_strtoull(str, &ull);
    if (res < 0)
        return res;

    if ((unsigned long long int)(uint64_t)ull != ull)
        return -(errno=ERANGE);

    *to = (uint64_t)ull;

    return 0;
}

/* signed */

int mx_strtoi(char *str, signed int *to)
{
    signed long int l;
    int res;

    assert(str);
    assert(to);

    res = mx_strtol(str, &l);
    if (res < 0)
        return res;

    if ((signed long int)(signed int)l != l)
        return -(errno=ERANGE);

    *to = (signed int)l;

    return 0;
}

int mx_strtoi8(char *str, int8_t *to)
{
    signed long int l;
    int res;

    assert(str);
    assert(to);

    res = mx_strtol(str, &l);
    if (res < 0)
        return res;

    if ((signed long int)(int8_t)l != l)
        return -(errno=ERANGE);

    *to = (uint8_t)l;

    return 0;
}

int mx_strtoi16(char *str, int16_t *to)
{
    signed long int l;
    int res;

    assert(str);
    assert(to);

    res = mx_strtol(str, &l);
    if (res < 0)
        return res;

    if ((signed long int)(int16_t)l != l)
        return -(errno=ERANGE);

    *to = (uint16_t)l;

    return 0;
}

int mx_strtoi32(char *str, int32_t *to)
{
    signed long int l;
    int res;

    assert(str);
    assert(to);

    res = mx_strtol(str, &l);
    if (res < 0)
        return res;

    if ((signed long int)(int32_t)l != l)
        return -(errno=ERANGE);

    *to = (int32_t)l;

    return 0;
}

int mx_strtoi64(char *str, int64_t *to)
{
    signed long long int ll;
    int res;

    assert(str);
    assert(to);

    res = mx_strtoll(str, &ll);
    if (res < 0)
        return res;

    if ((signed long long int)(int64_t)ll != ll)
        return -(errno=ERANGE);

    *to = (int64_t)ll;

    return 0;
}

void *mx_malloc_forever(size_t size)
{
    void *ret;

    do {
        ret = malloc(size);
        assert(ret || (!ret && errno == ENOMEM));
    } while (!ret);

    return ret ;
}

char *mx_strdup_forever(char *str)
{
    char *dup;

    do {
        dup = strdup(str);
        assert(dup || (!dup && errno == ENOMEM));
    } while(!dup);

    return dup;
}

char *mx_vasprintf_forever(const char *fmt, va_list ap)
{
    int len;
    char *strp;

    do {
        len = vasprintf(&strp, fmt, ap);
    } while (len < 0);

    return strp;
}


char *mx_asprintf_forever(const char *fmt, ...)
{
    va_list ap;

    va_start(ap, fmt);
    char *strp = mx_vasprintf_forever(fmt, ap);
    va_end(ap);

    return strp;
}

char *mx_hostname(void)
{
    static char hostname[1024] = "";
    int res;

    if (*hostname)
        return hostname;

    res = gethostname(hostname, 1024);
    if (res == -1) {
        if (errno != ENAMETOOLONG)
            assert_perror(errno);
        hostname[1024-1] = 0;
    }

    return hostname;
}

char *mx_dirname(char *path)
{
    char *tmp;
    char *dname;
    char *result;

    assert(path);

    tmp = strdup(path);
    if (!tmp)
        return NULL;

    dname = dirname(tmp);

    assert(dname);

    result = strdup(dname);

    free(tmp);

    return result;
}

char *mx_dirname_forever(char *path)
{
    char *dname;

    assert(path);

    do {
        dname = mx_dirname(path);
    } while (!dname);

    return dname;
}

int mx_dup2_close_new(int oldfd, int newfd)
{
    int res;

    if (oldfd == newfd)
        return 0;

    res = close(newfd);
    if (res == -1 && errno == EBADF)
        return -errno;

    res = dup2(oldfd, newfd);
    if(res == -1)
        return -errno;

    return res;
}

int mx_dup2_close_both(int oldfd, int newfd)
{
    int res;

    if (oldfd == newfd)
        return 0;

    res = mx_dup2_close_new(oldfd, newfd);
    if (res < 0)
        return res;

    assert(res == newfd);

    res = close(oldfd);
    if (res == -1 && errno == EBADF)
        return -errno;

    return newfd;
}

int mx_setenv_forever(const char *name, const char *value)
{
    assert(name);
    assert(*name);

    int res;

    do {
        res = setenv(name, value, 1);
        if (!res)
            return 0;
        assert(errno != EINVAL);
    } while (errno == ENOMEM);

    assert(errno == ENOMEM);
    return -errno;
}

int mx_setenvf_forever(const char *name, char *fmt, ...)
{
    assert(name);
    assert(*name);
    assert(fmt);

    va_list ap;
    int res;

    va_start(ap, fmt);
    char *value = mx_vasprintf_forever(fmt, ap);
    va_end(ap);

    res = mx_setenv_forever(name, value);

    free(value);

    return res;
}

int mx_open_newfile(char *fname)
{
    int fh;
    int res;

    int    flags = 0;
    mode_t mode  = 0;

    flags |= O_CREAT|O_WRONLY|O_TRUNC;
    flags |= O_NOFOLLOW;

    mode |= S_IRUSR|S_IWUSR;
    mode |= S_IRGRP|S_IWGRP;
    mode |= S_IROTH|S_IWOTH;

    if (!fname) {
        fname = "/dev/null";
    } else if (strcmp(fname, "/dev/null") != 0) {
        res = unlink(fname);
        if (res == -1 && errno != ENOENT)
            return -errno;

        flags |= O_EXCL;
    }

    fh = open(fname, flags, mode);
    if (fh == -1)
        return -errno;

    return fh;
}

int mx_read_first_line_from_file(char *fname, char **line)
{
    _mx_cleanup_fclose_ FILE *fp;
    char *buf = NULL;
    size_t n = 0;
    ssize_t res;

    fp = fopen(fname, "r");
    if (!fp)
        return -errno;

    res = getline(&buf, &n, fp);
    if (res == -1)
        return -errno;

    *line = buf;

    if (!res)
        return res;

    res--;

    if (buf[res] == '\n')
        buf[res] = 0;

    return res;
}

int mx_strscan_ull(char **str, unsigned long long int *to)
{
    unsigned long long int l;
    char *s;
    char *p;
    char o = 0;
    int res;

    s = *str;

    p = strchr(s, ' ');
    if (p) {
        o = *p;
        *p = 0;
        p++;
    } else {
        p = s + strlen(s);
    }

    res = mx_strtoull(s, &l);
    if (o)
        *(p-1) = o;

    if (res == 0) {
        *to = l;
        *str = p;
    }

    return res;
}

int mx_strscan_ll(char **str, long long int *to)
{
    long long int l;
    char *s;
    char *p;
    char o = 0;
    int res;

    s = *str;

    p = strchr(s, ' ');
    if (p) {
        o = *p;
        *p = 0;
        p++;
    } else {
        p = s + strlen(s);
    }

    res = mx_strtoll(s, &l);
    if (o)
        *(p-1) = o;

    if (res == 0) {
        *to = l;
        *str = p;
    }

    return res;
}

char *_mx_strconcat_do(char *first, ...)
{
    va_list ap;
    char *join = NULL;
    char *str;
    char *ptr;
    size_t len;

    if (!first) {
        join = strdup("");
        return join;
    }

    len = strlen(first);

    va_start(ap, first);
        do {
            str = va_arg(ap, char *);
            if (!str)
                break;
            len += strlen(str);
        } while(1);
    va_end(ap);

    join = malloc(len+1);
    if (!join)
        return NULL;

    ptr = stpcpy(join, first);
    va_start(ap, first);
        do {
            str = va_arg(ap, char *);
            if (!str)
                break;
            ptr = stpcpy(ptr, str);
        } while(1);
    va_end(ap);

    return join;
}

int mx_sleep(unsigned int seconds)
{
    if (seconds)
        return sleep(seconds);
    return 0;
}

int mx_sleep_nofail(unsigned int seconds)
{
    mx_sleep(seconds);
    return 1;
}

void *mx_calloc_forever_sec(size_t nmemb, size_t size, unsigned int time)
{
    void *ptr;

    while (1) {
        ptr = calloc(nmemb, size);
        if (ptr)
            break;

        mx_log_debug("calloc() failed: %m - retrying (forever) in %d second(s).", time);
        if (time)
            mx_sleep(time);
    }

    return ptr;
}

char **mx_strvec_new(void)
{
    char **strvec;

    strvec = calloc(sizeof(*strvec), 1);
    if (!strvec)
        return NULL;

    return strvec;
}

size_t mx_strvec_length(char ** strvec)
{
    char ** sv;
    size_t len;

    assert(strvec);

    sv = strvec;
    for (; *sv; sv++);

    len = sv-strvec;
    return len;
}

int mx_strvec_push_str(char *** strvecp, char * str)
{
    char ** sv;

    size_t len;

    assert(strvecp);
    assert(*strvecp);
    assert(str);

    len = mx_strvec_length(*strvecp);

    sv = realloc(*strvecp, sizeof(**strvecp) * (len + 2));
    if (!sv) {
       return 0;
    }

    sv[len++] = str;
    sv[len] = NULL;

    *strvecp = sv;

    return 1;
}

int mx_strvec_push_strvec(char ***strvecp, char **strvec)
{
    char **sv;

    size_t len1;
    size_t len2;

    assert(strvecp);
    assert(*strvecp);
    assert(strvec);

    len1 = mx_strvec_length(*strvecp);
    len2 = mx_strvec_length(strvec);

    sv = realloc(*strvecp, sizeof(**strvecp) * (len1 + len2 + 1));
    if (!sv) {
       return 0;
    }

    memcpy(sv+len1, strvec, sizeof(*strvec) * (len2 + 1));

    *strvecp = sv;

    return 1;
}

char *mx_strvec_to_str(char **strvec)
{
    char **sv;
    char*  buf;
    char*  s;
    size_t totallen;
    char*  str;

    assert(strvec);

    totallen = 0;
    for (sv = strvec; *sv; sv++) {
        totallen += strlen(*sv);
    }

    buf = malloc(sizeof(*buf) * (totallen * 2 + 2) + 1);
    if (!buf)
        return NULL;

    str  = buf;
    *str = 0;

    for (sv = strvec; *sv; sv++) {
        for (s=*sv; *s; s++) {
            switch (*s) {
                case '\\':
                    *(str++) = '\\';
                    *(str++) = '\\';
                    break;

                default:
                    *(str++) = *s;
            }
        }
        *(str++) = '\\';
        *(str++) = '0';
    }

    *str = '\0';

    return buf;
}

void mx_strvec_free(char **strvec)
{
    char **sv;

    if (!strvec)
        return;

    for (sv = strvec; *sv; sv++) {
        free(*sv);
    }
    free(strvec);
}

char **mx_strvec_from_str(char *str)
{
    int res;
    char* s;
    char* p;
    char** strvec;

    strvec = mx_strvec_new();
    if (!strvec)
        return NULL;

    for (s=str; *s; s=p+2) {
       p = strstr(s, "\\0");
       if (!p) {
           free(strvec);
           errno = EINVAL;
           return NULL;
       }
       *p = 0;

       res = mx_strvec_push_str(&strvec, s);
       if (!res) {
          free(strvec);
          return NULL;
       }
    }

    return strvec;
}

int mx_str_to_cpuset(cpu_set_t* cpuset_ptr, char *str)
{
    char c;
    int cpu_low;
    int cpu_high;
    char *next;
    int i;

    CPU_ZERO(cpuset_ptr);

    while (1) {
        c = *str;

        if (c == '\0')
            break;

        if (!isdigit(c))
            return -(errno=EINVAL);

        cpu_low = strtol(str, &next, 10);
        str = next;

        if (cpu_low < 0 || cpu_low >= CPU_SETSIZE)
            return -(errno=ERANGE);

        c = *str;

        CPU_SET(cpu_low, cpuset_ptr);

        if (c == '\0') {
            break;
        } else if (c == ',') {
            str++;
            continue;
        } else if (c != '-') {
            return -(errno=EINVAL);
        }

        str++;
        c = *str;

        if (!isdigit(c))
            return -(errno=EINVAL);

        cpu_high = strtol(str, &next, 10);
        str = next;

        if (cpu_high < 0 || cpu_high >= CPU_SETSIZE || cpu_high < cpu_low)
            return -(errno=ERANGE);

        for (i = cpu_low+1; i <= cpu_high; i++)
            CPU_SET(i, cpuset_ptr);

        c = *str;

        if (c == '\0') {
            break;
        } else if (c != ',') {
            return -(errno=EINVAL);
        }

        str++;
    }
    return 0;
}

char *mx_strvec_join(char *sep,char **strvec)
{
    int elements=0;
    int len=0;
    char *out;
    char *in;
    char *p;
    int i;

    assert(sep);
    assert(strvec);

    for (i=0;(in=strvec[i]);i++) {
        elements++;
        len += strlen(in);
    }

    if (elements == 0)
        return mx_strdup_forever("");

    len += strlen(sep)*(elements-1);
    out  = mx_malloc_forever(len+1);
    p    = out;

    for (i=0;i<elements-1;i++) {
        p = stpcpy(p, strvec[i]);
        p = stpcpy(p, sep);
    }
    stpcpy(p, strvec[i]);

    return out;
}

char *mx_cpuset_to_str(cpu_set_t* cpuset_ptr)
{
    char **strvec;
    int cpu;
    int cpu_low;
    int cpu_high;
    char *str;
    int res;
    char *out;

    strvec=mx_strvec_new();
    if (!strvec)
        return NULL;

    cpu=0;
    while(1) {
        if (cpu>=CPU_SETSIZE)
            break;

        if (CPU_ISSET(cpu,cpuset_ptr)) {
            cpu_low=cpu;
            while (1) {
                cpu++;
                if (cpu>=CPU_SETSIZE || !CPU_ISSET(cpu,cpuset_ptr))
                    break;
            }
            cpu_high=cpu-1;
            if (cpu_low==cpu_high) {
                str = mx_asprintf_forever("%d", cpu_low);
            } else {
                str = mx_asprintf_forever("%d-%d", cpu_low, cpu_high);
            }
            res=mx_strvec_push_str(&strvec,str);
            if (!res) {
                mx_strvec_free(strvec);
                return NULL;
            }
        } else {
            cpu++;
        }
    }

    out=mx_strvec_join(",",strvec);
    mx_strvec_free(strvec);
    return out;
}

int mx_mkdir_p(char *path, mode_t mode)
{
    struct stat st;
    int err;
    char *d;
    _mx_cleanup_free_ char *copy = NULL;

    if (stat(path, &st) == 0)
        return 0;

    copy=mx_strdup_forever(path);
    d=copy;

    while (*++d == '/');

    while ((d = strchr(d, '/'))) {
        *d = '\0';
        err = stat(copy, &st) && mkdir(copy, mode);
        *d++ = '/';
        if (err)
           return -errno;
        while (*d == '/')
            ++d;
    }
    return (stat(copy, &st) && mkdir(copy, mode)) ? -errno : 0;
}

int mx_daemon(int nochdir, int noclose)
{
    return daemon(nochdir, noclose);
}

/* guarantee stable sort */
void _mx_sort_linked_list (void **list,  int (*cmp)(void *o1,void *o2), void ** getnextptr(void *o)) {

    void *unsorted=*list;
    void *sorted=NULL;

    while (unsorted) {
        void *o;
        void **s_ptr;
        void *s;

        o=unsorted;
        unsorted=*(getnextptr(o));

        s_ptr=&sorted;
        while(1) {
            s=*s_ptr;
            if (s==NULL || cmp(o,s)<0) {
                break;
            }
            s_ptr=getnextptr(s);
        }
        *(getnextptr(o))=s;
        *s_ptr=o;
    }
    *list=sorted;
}

unsigned long mx_df(const char *path) {
    int res;
    struct statfs s;

    res=statfs(path, &s);
    if (res<0) {
        return 0;
    }
    return s.f_bavail*s.f_frsize;
}

time_t mx_clock_boottime(void) {
    struct timespec ts;
    int res = clock_gettime(CLOCK_BOOTTIME, &ts);
    if (res != 0) {
        mx_log_err("clock_gettime: %m");
    }
    return (ts.tv_sec);
}

int mx_call_external(char *helper, char **argv) {
    pid_t pid = fork();
    if (pid == 0) {
        execv(helper, argv);
        mx_log_err("%s: %m", helper);
        _exit(1);
    }
    if (pid == -1)
        return  -1;
    int wstatus;
    waitpid(pid, &wstatus, 0);
    if (wstatus != 0) {
        errno = EPROTO;
        return -1;
    }
    return 0;
}

static ssize_t readall(int fd, char *buf, size_t buflen) {
    ssize_t len = 0;
    while (buflen) {
        ssize_t l = read(fd, buf, buflen);
        if (l==0)
            return len;
        if (l<0)
            return l;
        len += l;
        buf += l;
        buflen -= l;
    }
    return len;
}

char *mx_pipe_external(char *helper, char **argv) {
    int pipefd[2];
    int err;
    char buf[2048];

    if (pipe(pipefd) < 0) {
        return NULL;
    }
    pid_t pid = fork();
    if (pid == 0) {
        close(pipefd[0]);
        dup2(pipefd[1], 1);
        execv(helper, argv);
        mx_log_err("%s: %m", helper);
        _exit(1);
    }
    if (pid == -1) {
        err = errno;
        close(pipefd[0]);
        close(pipefd[1]);
        errno = err;
        return NULL;
    }
    close(pipefd[1]);
    ssize_t len = readall(pipefd[0], buf, sizeof(buf));
    if (len<0) {
        err = errno;
        goto err_close;
    }
    if (len == sizeof(buf)) {
        err = EPROTO;
        goto err_close;
    }

    close(pipefd[0]);

    int wstatus;
    waitpid(pid, &wstatus, 0);
    if (wstatus != 0) {
        err = EPROTO;
        goto err_err;
    }
    buf[len] = '\0';
    if (len && buf[len-1] == '\n')
            buf[len-1] = 0;
    return mx_strdup_forever(buf);

err_close:
    close(pipefd[0]);
    waitpid(pid, NULL, 0);
err_err:
    errno = err;
    return NULL;
}