Adding upstream version 252.22.upstream/252.22

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1445 insertions, 0 deletions

diff --git a/src/shared/calendarspec.c b/src/shared/calendarspec.c
new file mode 100644
index 0000000..86a6d3f
--- /dev/null
+++ b/src/shared/calendarspec.c
@@ -0,0 +1,1445 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <ctype.h>
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "calendarspec.h"
+#include "errno-util.h"
+#include "fileio.h"
+#include "macro.h"
+#include "parse-util.h"
+#include "process-util.h"
+#include "sort-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "time-util.h"
+
+#define BITS_WEEKDAYS 127
+#define MIN_YEAR 1970
+#define MAX_YEAR 2199
+
+/* An arbitrary limit on the length of the chains of components. We don't want to
+ * build a very long linked list, which would be slow to iterate over and might cause
+ * our stack to overflow. It's unlikely that legitimate uses require more than a few
+ * linked components anyway. */
+#define CALENDARSPEC_COMPONENTS_MAX 240
+
+/* Let's make sure that the microsecond component is safe to be stored in an 'int' */
+assert_cc(INT_MAX >= USEC_PER_SEC);
+
+static CalendarComponent* chain_free(CalendarComponent *c) {
+        while (c) {
+                CalendarComponent *n = c->next;
+                free(c);
+                c = n;
+        }
+        return NULL;
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(CalendarComponent*, chain_free);
+
+CalendarSpec* calendar_spec_free(CalendarSpec *c) {
+
+        if (!c)
+                return NULL;
+
+        chain_free(c->year);
+        chain_free(c->month);
+        chain_free(c->day);
+        chain_free(c->hour);
+        chain_free(c->minute);
+        chain_free(c->microsecond);
+        free(c->timezone);
+
+        return mfree(c);
+}
+
+static int component_compare(CalendarComponent * const *a, CalendarComponent * const *b) {
+        int r;
+
+        r = CMP((*a)->start, (*b)->start);
+        if (r != 0)
+                return r;
+
+        r = CMP((*a)->stop, (*b)->stop);
+        if (r != 0)
+                return r;
+
+        return CMP((*a)->repeat, (*b)->repeat);
+}
+
+static void normalize_chain(CalendarComponent **c) {
+        assert(c);
+
+        size_t n = 0;
+        for (CalendarComponent *i = *c; i; i = i->next) {
+                n++;
+
+                /* While we're counting the chain, also normalize 'stop'
+                 * so the length of the range is a multiple of 'repeat'. */
+                if (i->stop > i->start && i->repeat > 0)
+                        i->stop -= (i->stop - i->start) % i->repeat;
+
+                /* If a repeat value is specified, but it cannot even be triggered once, let's suppress it.
+                 *
+                 * Similarly, if the stop value is the same as the start value, then let's just make this a
+                 * non-repeating chain element. */
+                if ((i->stop > i->start && i->repeat > 0 && i->start + i->repeat > i->stop) ||
+                    i->start == i->stop) {
+                        i->repeat = 0;
+                        i->stop = -1;
+                }
+        }
+
+        if (n <= 1)
+                return;
+
+        CalendarComponent **b, **j;
+        b = j = newa(CalendarComponent*, n);
+        for (CalendarComponent *i = *c; i; i = i->next)
+                *(j++) = i;
+
+        typesafe_qsort(b, n, component_compare);
+
+        b[n-1]->next = NULL;
+        CalendarComponent *next = b[n-1];
+
+        /* Drop non-unique entries */
+        for (size_t k = n-1; k > 0; k--) {
+                if (component_compare(&b[k-1], &next) == 0) {
+                        free(b[k-1]);
+                        continue;
+                }
+
+                b[k-1]->next = next;
+                next = b[k-1];
+        }
+
+        *c = next;
+}
+
+static void fix_year(CalendarComponent *c) {
+        /* Turns 12 → 2012, 89 → 1989 */
+
+        while (c) {
+                if (c->start >= 0 && c->start < 70)
+                        c->start += 2000;
+
+                if (c->stop >= 0 && c->stop < 70)
+                        c->stop += 2000;
+
+                if (c->start >= 70 && c->start < 100)
+                        c->start += 1900;
+
+                if (c->stop >= 70 && c->stop < 100)
+                        c->stop += 1900;
+
+                c = c->next;
+        }
+}
+
+static void calendar_spec_normalize(CalendarSpec *c) {
+        assert(c);
+
+        if (streq_ptr(c->timezone, "UTC")) {
+                c->utc = true;
+                c->timezone = mfree(c->timezone);
+        }
+
+        if (c->weekdays_bits <= 0 || c->weekdays_bits >= BITS_WEEKDAYS)
+                c->weekdays_bits = -1;
+
+        if (c->end_of_month && !c->day)
+                c->end_of_month = false;
+
+        fix_year(c->year);
+
+        normalize_chain(&c->year);
+        normalize_chain(&c->month);
+        normalize_chain(&c->day);
+        normalize_chain(&c->hour);
+        normalize_chain(&c->minute);
+        normalize_chain(&c->microsecond);
+}
+
+static bool chain_valid(CalendarComponent *c, int from, int to, bool end_of_month) {
+        assert(to >= from);
+
+        if (!c)
+                return true;
+
+        /* Forbid dates more than 28 days from the end of the month */
+        if (end_of_month)
+                to -= 3;
+
+        if (c->start < from || c->start > to)
+                return false;
+
+        /* Avoid overly large values that could cause overflow */
+        if (c->repeat > to - from)
+                return false;
+
+        /*
+         * c->repeat must be short enough so at least one repetition may
+         * occur before the end of the interval.  For dates scheduled
+         * relative to the end of the month, c->start and c->stop
+         * correspond to the Nth last day of the month.
+         */
+        if (c->stop >= 0) {
+                if (c->stop < from || c ->stop > to)
+                        return false;
+
+                if (c->start + c->repeat > c->stop)
+                        return false;
+        } else {
+                if (end_of_month && c->start - c->repeat < from)
+                        return false;
+
+                if (!end_of_month && c->start + c->repeat > to)
+                        return false;
+        }
+
+        if (c->next)
+                return chain_valid(c->next, from, to, end_of_month);
+
+        return true;
+}
+
+_pure_ bool calendar_spec_valid(CalendarSpec *c) {
+        assert(c);
+
+        if (c->weekdays_bits > BITS_WEEKDAYS)
+                return false;
+
+        if (!chain_valid(c->year, MIN_YEAR, MAX_YEAR, false))
+                return false;
+
+        if (!chain_valid(c->month, 1, 12, false))
+                return false;
+
+        if (!chain_valid(c->day, 1, 31, c->end_of_month))
+                return false;
+
+        if (!chain_valid(c->hour, 0, 23, false))
+                return false;
+
+        if (!chain_valid(c->minute, 0, 59, false))
+                return false;
+
+        if (!chain_valid(c->microsecond, 0, 60*USEC_PER_SEC-1, false))
+                return false;
+
+        return true;
+}
+
+static void format_weekdays(FILE *f, const CalendarSpec *c) {
+        static const char *const days[] = {
+                "Mon",
+                "Tue",
+                "Wed",
+                "Thu",
+                "Fri",
+                "Sat",
+                "Sun",
+        };
+
+        int l, x;
+        bool need_comma = false;
+
+        assert(f);
+        assert(c);
+        assert(c->weekdays_bits > 0 && c->weekdays_bits <= BITS_WEEKDAYS);
+
+        for (x = 0, l = -1; x < (int) ELEMENTSOF(days); x++) {
+
+                if (c->weekdays_bits & (1 << x)) {
+
+                        if (l < 0) {
+                                if (need_comma)
+                                        fputc(',', f);
+                                else
+                                        need_comma = true;
+
+                                fputs(days[x], f);
+                                l = x;
+                        }
+
+                } else if (l >= 0) {
+
+                        if (x > l + 1) {
+                                fputs(x > l + 2 ? ".." : ",", f);
+                                fputs(days[x-1], f);
+                        }
+
+                        l = -1;
+                }
+        }
+
+        if (l >= 0 && x > l + 1) {
+                fputs(x > l + 2 ? ".." : ",", f);
+                fputs(days[x-1], f);
+        }
+}
+
+static bool chain_is_star(const CalendarComponent *c, bool usec) {
+        /* Return true if the whole chain can be replaced by '*'.
+         * This happens when the chain is empty or one of the components covers all. */
+        if (!c)
+                return true;
+        if (usec)
+                for (; c; c = c->next)
+                        if (c->start == 0 && c->stop < 0 && c->repeat == USEC_PER_SEC)
+                                return true;
+        return false;
+}
+
+static void _format_chain(FILE *f, int space, const CalendarComponent *c, bool start, bool usec) {
+        int d = usec ? (int) USEC_PER_SEC : 1;
+
+        assert(f);
+
+        if (start && chain_is_star(c, usec)) {
+                fputc('*', f);
+                return;
+        }
+
+        assert(c->start >= 0);
+
+        fprintf(f, "%0*i", space, c->start / d);
+        if (c->start % d > 0)
+                fprintf(f, ".%06i", c->start % d);
+
+        if (c->stop > 0)
+                fprintf(f, "..%0*i", space, c->stop / d);
+        if (c->stop % d > 0)
+                fprintf(f, ".%06i", c->stop % d);
+
+        if (c->repeat > 0 && !(c->stop > 0 && c->repeat == d))
+                fprintf(f, "/%i", c->repeat / d);
+        if (c->repeat % d > 0)
+                fprintf(f, ".%06i", c->repeat % d);
+
+        if (c->next) {
+                fputc(',', f);
+                _format_chain(f, space, c->next, false, usec);
+        }
+}
+
+static void format_chain(FILE *f, int space, const CalendarComponent *c, bool usec) {
+        _format_chain(f, space, c, /* start = */ true, usec);
+}
+
+int calendar_spec_to_string(const CalendarSpec *c, char **p) {
+        char *buf = NULL;
+        size_t sz = 0;
+        FILE *f;
+        int r;
+
+        assert(c);
+        assert(p);
+
+        f = open_memstream_unlocked(&buf, &sz);
+        if (!f)
+                return -ENOMEM;
+
+        if (c->weekdays_bits > 0 && c->weekdays_bits <= BITS_WEEKDAYS) {
+                format_weekdays(f, c);
+                fputc(' ', f);
+        }
+
+        format_chain(f, 4, c->year, false);
+        fputc('-', f);
+        format_chain(f, 2, c->month, false);
+        fputc(c->end_of_month ? '~' : '-', f);
+        format_chain(f, 2, c->day, false);
+        fputc(' ', f);
+        format_chain(f, 2, c->hour, false);
+        fputc(':', f);
+        format_chain(f, 2, c->minute, false);
+        fputc(':', f);
+        format_chain(f, 2, c->microsecond, true);
+
+        if (c->utc)
+                fputs(" UTC", f);
+        else if (c->timezone) {
+                fputc(' ', f);
+                fputs(c->timezone, f);
+        } else if (IN_SET(c->dst, 0, 1)) {
+
+                /* If daylight saving is explicitly on or off, let's show the used timezone. */
+
+                tzset();
+
+                if (!isempty(tzname[c->dst])) {
+                        fputc(' ', f);
+                        fputs(tzname[c->dst], f);
+                }
+        }
+
+        r = fflush_and_check(f);
+        fclose(f);
+
+        if (r < 0) {
+                free(buf);
+                return r;
+        }
+
+        *p = buf;
+        return 0;
+}
+
+static int parse_weekdays(const char **p, CalendarSpec *c) {
+        static const struct {
+                const char *name;
+                const int nr;
+        } day_nr[] = {
+                { "Monday",    0 },
+                { "Mon",       0 },
+                { "Tuesday",   1 },
+                { "Tue",       1 },
+                { "Wednesday", 2 },
+                { "Wed",       2 },
+                { "Thursday",  3 },
+                { "Thu",       3 },
+                { "Friday",    4 },
+                { "Fri",       4 },
+                { "Saturday",  5 },
+                { "Sat",       5 },
+                { "Sunday",    6 },
+                { "Sun",       6 },
+        };
+
+        int l = -1;
+        bool first = true;
+
+        assert(p);
+        assert(*p);
+        assert(c);
+
+        for (;;) {
+                size_t i;
+
+                for (i = 0; i < ELEMENTSOF(day_nr); i++) {
+                        size_t skip;
+
+                        if (!startswith_no_case(*p, day_nr[i].name))
+                                continue;
+
+                        skip = strlen(day_nr[i].name);
+
+                        if (!IN_SET((*p)[skip], 0, '-', '.', ',', ' '))
+                                return -EINVAL;
+
+                        c->weekdays_bits |= 1 << day_nr[i].nr;
+
+                        if (l >= 0) {
+                                if (l > day_nr[i].nr)
+                                        return -EINVAL;
+
+                                for (int j = l + 1; j < day_nr[i].nr; j++)
+                                        c->weekdays_bits |= 1 << j;
+                        }
+
+                        *p += skip;
+                        break;
+                }
+
+                /* Couldn't find this prefix, so let's assume the
+                   weekday was not specified and let's continue with
+                   the date */
+                if (i >= ELEMENTSOF(day_nr))
+                        return first ? 0 : -EINVAL;
+
+                /* We reached the end of the string */
+                if (**p == 0)
+                        return 0;
+
+                /* We reached the end of the weekday spec part */
+                if (**p == ' ') {
+                        *p += strspn(*p, " ");
+                        return 0;
+                }
+
+                if (**p == '.') {
+                        if (l >= 0)
+                                return -EINVAL;
+
+                        if ((*p)[1] != '.')
+                                return -EINVAL;
+
+                        l = day_nr[i].nr;
+                        *p += 2;
+
+                /* Support ranges with "-" for backwards compatibility */
+                } else if (**p == '-') {
+                        if (l >= 0)
+                                return -EINVAL;
+
+                        l = day_nr[i].nr;
+                        *p += 1;
+
+                } else if (**p == ',') {
+                        l = -1;
+                        *p += 1;
+                }
+
+                /* Allow a trailing comma but not an open range */
+                if (IN_SET(**p, 0, ' ')) {
+                        *p += strspn(*p, " ");
+                        return l < 0 ? 0 : -EINVAL;
+                }
+
+                first = false;
+        }
+}
+
+static int parse_one_number(const char *p, const char **e, unsigned long *ret) {
+        char *ee = NULL;
+        unsigned long value;
+
+        errno = 0;
+        value = strtoul(p, &ee, 10);
+        if (errno > 0)
+                return -errno;
+        if (ee == p)
+                return -EINVAL;
+
+        *ret = value;
+        *e = ee;
+        return 0;
+}
+
+static int parse_component_decimal(const char **p, bool usec, int *res) {
+        unsigned long value;
+        const char *e = NULL;
+        int r;
+
+        if (!ascii_isdigit(**p))
+                return -EINVAL;
+
+        r = parse_one_number(*p, &e, &value);
+        if (r < 0)
+                return r;
+
+        if (usec) {
+                if (value * USEC_PER_SEC / USEC_PER_SEC != value)
+                        return -ERANGE;
+
+                value *= USEC_PER_SEC;
+
+                /* One "." is a decimal point, but ".." is a range separator */
+                if (e[0] == '.' && e[1] != '.') {
+                        unsigned add;
+
+                        e++;
+                        r = parse_fractional_part_u(&e, 6, &add);
+                        if (r < 0)
+                                return r;
+
+                        if (add + value < value)
+                                return -ERANGE;
+                        value += add;
+                }
+        }
+
+        if (value > INT_MAX)
+                return -ERANGE;
+
+        *p = e;
+        *res = value;
+
+        return 0;
+}
+
+static int const_chain(int value, CalendarComponent **c) {
+        CalendarComponent *cc = NULL;
+
+        assert(c);
+
+        cc = new(CalendarComponent, 1);
+        if (!cc)
+                return -ENOMEM;
+
+        *cc = (CalendarComponent) {
+                .start = value,
+                .stop = -1,
+                .repeat = 0,
+                .next = *c,
+        };
+
+        *c = cc;
+
+        return 0;
+}
+
+static int calendarspec_from_time_t(CalendarSpec *c, time_t time) {
+        _cleanup_(chain_freep) CalendarComponent
+                *year = NULL, *month = NULL, *day = NULL,
+                *hour = NULL, *minute = NULL, *us = NULL;
+        struct tm tm;
+        int r;
+
+        if (!gmtime_r(&time, &tm))
+                return -ERANGE;
+
+        if (tm.tm_year > INT_MAX - 1900)
+                return -ERANGE;
+
+        r = const_chain(tm.tm_year + 1900, &year);
+        if (r < 0)
+                return r;
+
+        r = const_chain(tm.tm_mon + 1, &month);
+        if (r < 0)
+                return r;
+
+        r = const_chain(tm.tm_mday, &day);
+        if (r < 0)
+                return r;
+
+        r = const_chain(tm.tm_hour, &hour);
+        if (r < 0)
+                return r;
+
+        r = const_chain(tm.tm_min, &minute);
+        if (r < 0)
+                return r;
+
+        r = const_chain(tm.tm_sec * USEC_PER_SEC, &us);
+        if (r < 0)
+                return r;
+
+        c->utc = true;
+        c->year = TAKE_PTR(year);
+        c->month = TAKE_PTR(month);
+        c->day = TAKE_PTR(day);
+        c->hour = TAKE_PTR(hour);
+        c->minute = TAKE_PTR(minute);
+        c->microsecond = TAKE_PTR(us);
+        return 0;
+}
+
+static int prepend_component(const char **p, bool usec, unsigned nesting, CalendarComponent **c) {
+        int r, start, stop = -1, repeat = 0;
+        CalendarComponent *cc;
+        const char *e = *p;
+
+        assert(p);
+        assert(c);
+
+        if (nesting > CALENDARSPEC_COMPONENTS_MAX)
+                return -ENOBUFS;
+
+        r = parse_component_decimal(&e, usec, &start);
+        if (r < 0)
+                return r;
+
+        if (e[0] == '.' && e[1] == '.') {
+                e += 2;
+                r = parse_component_decimal(&e, usec, &stop);
+                if (r < 0)
+                        return r;
+
+                repeat = usec ? USEC_PER_SEC : 1;
+        }
+
+        if (*e == '/') {
+                e++;
+                r = parse_component_decimal(&e, usec, &repeat);
+                if (r < 0)
+                        return r;
+
+                if (repeat == 0)
+                        return -ERANGE;
+        } else {
+                /* If no repeat value is specified for the µs component, then let's explicitly refuse ranges
+                 * below 1s because our default repeat granularity is beyond that. */
+
+                /* Overflow check */
+                if (start > INT_MAX - repeat)
+                        return -ERANGE;
+
+                if (usec && stop >= 0 && start + repeat > stop)
+                        return -EINVAL;
+        }
+
+        if (!IN_SET(*e, 0, ' ', ',', '-', '~', ':'))
+                return -EINVAL;
+
+        cc = new(CalendarComponent, 1);
+        if (!cc)
+                return -ENOMEM;
+
+        *cc = (CalendarComponent) {
+                .start = start,
+                .stop = stop,
+                .repeat = repeat,
+                .next = *c,
+        };
+
+        *p = e;
+        *c = cc;
+
+        if (*e ==',') {
+                *p += 1;
+                return prepend_component(p, usec, nesting + 1, c);
+        }
+
+        return 0;
+}
+
+static int parse_chain(const char **p, bool usec, CalendarComponent **c) {
+        _cleanup_(chain_freep) CalendarComponent *cc = NULL;
+        const char *t;
+        int r;
+
+        assert(p);
+        assert(c);
+
+        t = *p;
+
+        if (t[0] == '*') {
+                if (usec) {
+                        r = const_chain(0, c);
+                        if (r < 0)
+                                return r;
+                        (*c)->repeat = USEC_PER_SEC;
+                } else
+                        *c = NULL;
+
+                *p = t + 1;
+                return 0;
+        }
+
+        r = prepend_component(&t, usec, 0, &cc);
+        if (r < 0)
+                return r;
+
+        *p = t;
+        *c = TAKE_PTR(cc);
+        return 0;
+}
+
+static int parse_date(const char **p, CalendarSpec *c) {
+        _cleanup_(chain_freep) CalendarComponent *first = NULL, *second = NULL, *third = NULL;
+        const char *t;
+        int r;
+
+        assert(p);
+        assert(*p);
+        assert(c);
+
+        t = *p;
+
+        if (*t == 0)
+                return 0;
+
+        /* @TIMESTAMP — UNIX time in seconds since the epoch */
+        if (*t == '@') {
+                unsigned long value;
+                time_t time;
+
+                r = parse_one_number(t + 1, &t, &value);
+                if (r < 0)
+                        return r;
+
+                time = value;
+                if ((unsigned long) time != value)
+                        return -ERANGE;
+
+                r = calendarspec_from_time_t(c, time);
+                if (r < 0)
+                        return r;
+
+                *p = t;
+                return 1; /* finito, don't parse H:M:S after that */
+        }
+
+        r = parse_chain(&t, false, &first);
+        if (r < 0)
+                return r;
+
+        /* Already the end? A ':' as separator? In that case this was a time, not a date */
+        if (IN_SET(*t, 0, ':'))
+                return 0;
+
+        if (*t == '~')
+                c->end_of_month = true;
+        else if (*t != '-')
+                return -EINVAL;
+
+        t++;
+        r = parse_chain(&t, false, &second);
+        if (r < 0)
+                return r;
+
+        /* Got two parts, hence it's month and day */
+        if (IN_SET(*t, 0, ' ')) {
+                *p = t + strspn(t, " ");
+                c->month = TAKE_PTR(first);
+                c->day = TAKE_PTR(second);
+                return 0;
+        } else if (c->end_of_month)
+                return -EINVAL;
+
+        if (*t == '~')
+                c->end_of_month = true;
+        else if (*t != '-')
+                return -EINVAL;
+
+        t++;
+        r = parse_chain(&t, false, &third);
+        if (r < 0)
+                return r;
+
+        if (!IN_SET(*t, 0, ' '))
+                return -EINVAL;
+
+        /* Got three parts, hence it is year, month and day */
+        *p = t + strspn(t, " ");
+        c->year = TAKE_PTR(first);
+        c->month = TAKE_PTR(second);
+        c->day = TAKE_PTR(third);
+        return 0;
+}
+
+static int parse_calendar_time(const char **p, CalendarSpec *c) {
+        _cleanup_(chain_freep) CalendarComponent *h = NULL, *m = NULL, *s = NULL;
+        const char *t;
+        int r;
+
+        assert(p);
+        assert(*p);
+        assert(c);
+
+        t = *p;
+
+        /* If no time is specified at all, then this means 00:00:00 */
+        if (*t == 0)
+                goto null_hour;
+
+        r = parse_chain(&t, false, &h);
+        if (r < 0)
+                return r;
+
+        if (*t != ':')
+                return -EINVAL;
+
+        t++;
+        r = parse_chain(&t, false, &m);
+        if (r < 0)
+                return r;
+
+        /* Already at the end? Then it's hours and minutes, and seconds are 0 */
+        if (*t == 0)
+                goto null_second;
+
+        if (*t != ':')
+                return -EINVAL;
+
+        t++;
+        r = parse_chain(&t, true, &s);
+        if (r < 0)
+                return r;
+
+        /* At the end? Then it's hours, minutes and seconds */
+        if (*t == 0)
+                goto finish;
+
+        return -EINVAL;
+
+null_hour:
+        r = const_chain(0, &h);
+        if (r < 0)
+                return r;
+
+        r = const_chain(0, &m);
+        if (r < 0)
+                return r;
+
+null_second:
+        r = const_chain(0, &s);
+        if (r < 0)
+                return r;
+
+finish:
+        *p = t;
+        c->hour = TAKE_PTR(h);
+        c->minute = TAKE_PTR(m);
+        c->microsecond = TAKE_PTR(s);
+
+        return 0;
+}
+
+int calendar_spec_from_string(const char *p, CalendarSpec **spec) {
+        const char *utc;
+        _cleanup_(calendar_spec_freep) CalendarSpec *c = NULL;
+        _cleanup_free_ char *p_tmp = NULL;
+        int r;
+
+        assert(p);
+
+        c = new(CalendarSpec, 1);
+        if (!c)
+                return -ENOMEM;
+
+        *c = (CalendarSpec) {
+                .dst = -1,
+                .timezone = NULL,
+        };
+
+        utc = endswith_no_case(p, " UTC");
+        if (utc) {
+                c->utc = true;
+                p = p_tmp = strndup(p, utc - p);
+                if (!p)
+                        return -ENOMEM;
+        } else {
+                const char *e = NULL;
+                int j;
+
+                tzset();
+
+                /* Check if the local timezone was specified? */
+                for (j = 0; j <= 1; j++) {
+                        if (isempty(tzname[j]))
+                                continue;
+
+                        e = endswith_no_case(p, tzname[j]);
+                        if (!e)
+                                continue;
+                        if (e == p)
+                                continue;
+                        if (e[-1] != ' ')
+                                continue;
+
+                        break;
+                }
+
+                /* Found one of the two timezones specified? */
+                if (IN_SET(j, 0, 1)) {
+                        p = p_tmp = strndup(p, e - p - 1);
+                        if (!p)
+                                return -ENOMEM;
+
+                        c->dst = j;
+                } else {
+                        const char *last_space;
+
+                        last_space = strrchr(p, ' ');
+                        if (last_space != NULL && timezone_is_valid(last_space + 1, LOG_DEBUG)) {
+                                c->timezone = strdup(last_space + 1);
+                                if (!c->timezone)
+                                        return -ENOMEM;
+
+                                p = p_tmp = strndup(p, last_space - p);
+                                if (!p)
+                                        return -ENOMEM;
+                        }
+                }
+        }
+
+        if (isempty(p))
+                return -EINVAL;
+
+        if (strcaseeq(p, "minutely")) {
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else if (strcaseeq(p, "hourly")) {
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else if (strcaseeq(p, "daily")) {
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else if (strcaseeq(p, "monthly")) {
+                r = const_chain(1, &c->day);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else if (STRCASE_IN_SET(p,
+                                  "annually",
+                                  "yearly",
+                                  "anually") /* backwards compatibility */ ) {
+
+                r = const_chain(1, &c->month);
+                if (r < 0)
+                        return r;
+                r = const_chain(1, &c->day);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else if (strcaseeq(p, "weekly")) {
+
+                c->weekdays_bits = 1;
+
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else if (strcaseeq(p, "quarterly")) {
+
+                r = const_chain(1, &c->month);
+                if (r < 0)
+                        return r;
+                r = const_chain(4, &c->month);
+                if (r < 0)
+                        return r;
+                r = const_chain(7, &c->month);
+                if (r < 0)
+                        return r;
+                r = const_chain(10, &c->month);
+                if (r < 0)
+                        return r;
+                r = const_chain(1, &c->day);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else if (STRCASE_IN_SET(p,
+                                  "biannually",
+                                  "bi-annually",
+                                  "semiannually",
+                                  "semi-annually")) {
+
+                r = const_chain(1, &c->month);
+                if (r < 0)
+                        return r;
+                r = const_chain(7, &c->month);
+                if (r < 0)
+                        return r;
+                r = const_chain(1, &c->day);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        return r;
+                r = const_chain(0, &c->microsecond);
+                if (r < 0)
+                        return r;
+
+        } else {
+                r = parse_weekdays(&p, c);
+                if (r < 0)
+                        return r;
+
+                r = parse_date(&p, c);
+                if (r < 0)
+                        return r;
+
+                if (r == 0) {
+                        r = parse_calendar_time(&p, c);
+                        if (r < 0)
+                                return r;
+                }
+
+                if (*p != 0)
+                        return -EINVAL;
+        }
+
+        calendar_spec_normalize(c);
+
+        if (!calendar_spec_valid(c))
+                return -EINVAL;
+
+        if (spec)
+                *spec = TAKE_PTR(c);
+        return 0;
+}
+
+static int find_end_of_month(const struct tm *tm, bool utc, int day) {
+        struct tm t = *tm;
+
+        t.tm_mon++;
+        t.tm_mday = 1 - day;
+
+        if (mktime_or_timegm(&t, utc) < 0 ||
+            t.tm_mon != tm->tm_mon)
+                return -1;
+
+        return t.tm_mday;
+}
+
+static int find_matching_component(
+                const CalendarSpec *spec,
+                const CalendarComponent *c,
+                const struct tm *tm,           /* tm is only used for end-of-month calculations */
+                int *val) {
+
+        int d = -1, r;
+        bool d_set = false;
+
+        assert(val);
+
+        /* Finds the *earliest* matching time specified by one of the CalendarCompoment items in chain c.
+         * If no matches can be found, returns -ENOENT.
+         * Otherwise, updates *val to the matching time. 1 is returned if *val was changed, 0 otherwise.
+         */
+
+        if (!c)
+                return 0;
+
+        bool end_of_month = spec->end_of_month && c == spec->day;
+
+        while (c) {
+                int start, stop;
+
+                if (end_of_month) {
+                        start = find_end_of_month(tm, spec->utc, c->start);
+                        stop = find_end_of_month(tm, spec->utc, c->stop);
+
+                        if (stop > 0)
+                                SWAP_TWO(start, stop);
+                } else {
+                        start = c->start;
+                        stop = c->stop;
+                }
+
+                if (start >= *val) {
+
+                        if (!d_set || start < d) {
+                                d = start;
+                                d_set = true;
+                        }
+
+                } else if (c->repeat > 0) {
+                        int k;
+
+                        k = start + c->repeat * DIV_ROUND_UP(*val - start, c->repeat);
+
+                        if ((!d_set || k < d) && (stop < 0 || k <= stop)) {
+                                d = k;
+                                d_set = true;
+                        }
+                }
+
+                c = c->next;
+        }
+
+        if (!d_set)
+                return -ENOENT;
+
+        r = *val != d;
+        *val = d;
+        return r;
+}
+
+static int tm_within_bounds(struct tm *tm, bool utc) {
+        struct tm t;
+        int cmp;
+        assert(tm);
+
+        /*
+         * Set an upper bound on the year so impossible dates like "*-02-31"
+         * don't cause find_next() to loop forever. tm_year contains years
+         * since 1900, so adjust it accordingly.
+         */
+        if (tm->tm_year + 1900 > MAX_YEAR)
+                return -ERANGE;
+
+        t = *tm;
+        if (mktime_or_timegm(&t, utc) < 0)
+                return negative_errno();
+
+        /*
+         * Did any normalization take place? If so, it was out of bounds before.
+         * Normalization could skip next elapse, e.g. result of normalizing 3-33
+         * is 4-2. This skips 4-1. So reset the sub time unit if upper unit was
+         * out of bounds. Normalization has occurred implies find_matching_component() > 0,
+         * other sub time units are already reset in find_next().
+         */
+        if ((cmp = CMP(t.tm_year, tm->tm_year)) != 0)
+                t.tm_mon = 0;
+        else if ((cmp = CMP(t.tm_mon, tm->tm_mon)) != 0)
+                t.tm_mday = 1;
+        else if ((cmp = CMP(t.tm_mday, tm->tm_mday)) != 0)
+                t.tm_hour = 0;
+        else if ((cmp = CMP(t.tm_hour, tm->tm_hour)) != 0)
+                t.tm_min = 0;
+        else if ((cmp = CMP(t.tm_min, tm->tm_min)) != 0)
+                t.tm_sec = 0;
+        else
+                cmp = CMP(t.tm_sec, tm->tm_sec);
+
+        if (cmp < 0)
+                return -EDEADLK; /* Refuse to go backward */
+        if (cmp > 0)
+                *tm = t;
+        return cmp == 0;
+}
+
+static bool matches_weekday(int weekdays_bits, const struct tm *tm, bool utc) {
+        struct tm t;
+        int k;
+
+        if (weekdays_bits < 0 || weekdays_bits >= BITS_WEEKDAYS)
+                return true;
+
+        t = *tm;
+        if (mktime_or_timegm(&t, utc) < 0)
+                return false;
+
+        k = t.tm_wday == 0 ? 6 : t.tm_wday - 1;
+        return (weekdays_bits & (1 << k));
+}
+
+/* A safety valve: if we get stuck in the calculation, return an error.
+ * C.f. https://bugzilla.redhat.com/show_bug.cgi?id=1941335. */
+#define MAX_CALENDAR_ITERATIONS 1000
+
+static int find_next(const CalendarSpec *spec, struct tm *tm, usec_t *usec) {
+        struct tm c;
+        int tm_usec;
+        int r;
+
+        /* Returns -ENOENT if the expression is not going to elapse anymore */
+
+        assert(spec);
+        assert(tm);
+
+        c = *tm;
+        tm_usec = *usec;
+
+        for (unsigned iteration = 0; iteration < MAX_CALENDAR_ITERATIONS; iteration++) {
+                /* Normalize the current date */
+                (void) mktime_or_timegm(&c, spec->utc);
+                c.tm_isdst = spec->dst;
+
+                c.tm_year += 1900;
+                r = find_matching_component(spec, spec->year, &c, &c.tm_year);
+                c.tm_year -= 1900;
+
+                if (r > 0) {
+                        c.tm_mon = 0;
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = tm_usec = 0;
+                }
+                if (r < 0)
+                        return r;
+                if (tm_within_bounds(&c, spec->utc) <= 0)
+                        return -ENOENT;
+
+                c.tm_mon += 1;
+                r = find_matching_component(spec, spec->month, &c, &c.tm_mon);
+                c.tm_mon -= 1;
+
+                if (r > 0) {
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = tm_usec = 0;
+                }
+                if (r < 0 || (r = tm_within_bounds(&c, spec->utc)) < 0) {
+                        c.tm_year++;
+                        c.tm_mon = 0;
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = tm_usec = 0;
+                        continue;
+                }
+                if (r == 0)
+                        continue;
+
+                r = find_matching_component(spec, spec->day, &c, &c.tm_mday);
+                if (r > 0)
+                        c.tm_hour = c.tm_min = c.tm_sec = tm_usec = 0;
+                if (r < 0 || (r = tm_within_bounds(&c, spec->utc)) < 0) {
+                        c.tm_mon++;
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = tm_usec = 0;
+                        continue;
+                }
+                if (r == 0)
+                        continue;
+
+                if (!matches_weekday(spec->weekdays_bits, &c, spec->utc)) {
+                        c.tm_mday++;
+                        c.tm_hour = c.tm_min = c.tm_sec = tm_usec = 0;
+                        continue;
+                }
+
+                r = find_matching_component(spec, spec->hour, &c, &c.tm_hour);
+                if (r > 0)
+                        c.tm_min = c.tm_sec = tm_usec = 0;
+                if (r < 0 || (r = tm_within_bounds(&c, spec->utc)) < 0) {
+                        c.tm_mday++;
+                        c.tm_hour = c.tm_min = c.tm_sec = tm_usec = 0;
+                        continue;
+                }
+                if (r == 0)
+                        /* The next hour we set might be missing if there
+                         * are time zone changes. Let's try again starting at
+                         * normalized time. */
+                        continue;
+
+                r = find_matching_component(spec, spec->minute, &c, &c.tm_min);
+                if (r > 0)
+                        c.tm_sec = tm_usec = 0;
+                if (r < 0 || (r = tm_within_bounds(&c, spec->utc)) < 0) {
+                        c.tm_hour++;
+                        c.tm_min = c.tm_sec = tm_usec = 0;
+                        continue;
+                }
+                if (r == 0)
+                        continue;
+
+                c.tm_sec = c.tm_sec * USEC_PER_SEC + tm_usec;
+                r = find_matching_component(spec, spec->microsecond, &c, &c.tm_sec);
+                tm_usec = c.tm_sec % USEC_PER_SEC;
+                c.tm_sec /= USEC_PER_SEC;
+
+                if (r < 0 || (r = tm_within_bounds(&c, spec->utc)) < 0) {
+                        c.tm_min++;
+                        c.tm_sec = tm_usec = 0;
+                        continue;
+                }
+                if (r == 0)
+                        continue;
+
+                *tm = c;
+                *usec = tm_usec;
+                return 0;
+        }
+
+        /* It seems we entered an infinite loop. Let's gracefully return an error instead of hanging or
+         * aborting. This code is also exercised when timers.target is brought up during early boot, so
+         * aborting here is problematic and hard to diagnose for users. */
+        _cleanup_free_ char *s = NULL;
+        (void) calendar_spec_to_string(spec, &s);
+        return log_warning_errno(SYNTHETIC_ERRNO(EDEADLK),
+                                 "Infinite loop in calendar calculation: %s", strna(s));
+}
+
+static int calendar_spec_next_usec_impl(const CalendarSpec *spec, usec_t usec, usec_t *ret_next) {
+        struct tm tm;
+        time_t t;
+        int r;
+        usec_t tm_usec;
+
+        assert(spec);
+
+        if (usec > USEC_TIMESTAMP_FORMATTABLE_MAX)
+                return -EINVAL;
+
+        usec++;
+        t = (time_t) (usec / USEC_PER_SEC);
+        assert_se(localtime_or_gmtime_r(&t, &tm, spec->utc));
+        tm_usec = usec % USEC_PER_SEC;
+
+        r = find_next(spec, &tm, &tm_usec);
+        if (r < 0)
+                return r;
+
+        t = mktime_or_timegm(&tm, spec->utc);
+        if (t < 0)
+                return -EINVAL;
+
+        if (ret_next)
+                *ret_next = (usec_t) t * USEC_PER_SEC + tm_usec;
+
+        return 0;
+}
+
+typedef struct SpecNextResult {
+        usec_t next;
+        int return_value;
+} SpecNextResult;
+
+int calendar_spec_next_usec(const CalendarSpec *spec, usec_t usec, usec_t *ret_next) {
+        SpecNextResult *shared, tmp;
+        int r;
+
+        assert(spec);
+
+        if (isempty(spec->timezone))
+                return calendar_spec_next_usec_impl(spec, usec, ret_next);
+
+        shared = mmap(NULL, sizeof *shared, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
+        if (shared == MAP_FAILED)
+                return negative_errno();
+
+        r = safe_fork("(sd-calendar)", FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_DEATHSIG|FORK_WAIT, NULL);
+        if (r < 0) {
+                (void) munmap(shared, sizeof *shared);
+                return r;
+        }
+        if (r == 0) {
+                char *colon_tz;
+
+                /* tzset(3) says $TZ should be prefixed with ":" if we reference timezone files */
+                colon_tz = strjoina(":", spec->timezone);
+
+                if (setenv("TZ", colon_tz, 1) != 0) {
+                        shared->return_value = negative_errno();
+                        _exit(EXIT_FAILURE);
+                }
+
+                tzset();
+
+                shared->return_value = calendar_spec_next_usec_impl(spec, usec, &shared->next);
+
+                _exit(EXIT_SUCCESS);
+        }
+
+        tmp = *shared;
+        if (munmap(shared, sizeof *shared) < 0)
+                return negative_errno();
+
+        if (tmp.return_value == 0 && ret_next)
+                *ret_next = tmp.next;
+
+        return tmp.return_value;
+}