+ /* Start with the week day */
+ assert((size_t) tm.tm_wday < ELEMENTSOF(weekdays));
+ memcpy(buf, weekdays[tm.tm_wday], 4);
+
+ /* Add the main components */
+ if (strftime(buf + 3, l - 3, " %Y-%m-%d %H:%M:%S", &tm) <= 0)
+ return NULL; /* Doesn't fit */
+
+ /* Append the microseconds part, if that's requested */
+ if (us) {
+ n = strlen(buf);
+ if (n + 8 > l)
+ return NULL; /* Microseconds part doesn't fit. */
+
+ sprintf(buf + n, ".%06llu", (unsigned long long) (t % USEC_PER_SEC));
+ }
+
+ /* Append the timezone */
+ n = strlen(buf);
+ if (utc) {
+ /* If this is UTC then let's explicitly use the "UTC" string here, because gmtime_r() normally uses the
+ * obsolete "GMT" instead. */
+ if (n + 5 > l)
+ return NULL; /* "UTC" doesn't fit. */
+
+ strcpy(buf + n, " UTC");
+
+ } else if (!isempty(tm.tm_zone)) {
+ size_t tn;
+
+ /* An explicit timezone is specified, let's use it, if it fits */
+ tn = strlen(tm.tm_zone);
+ if (n + 1 + tn + 1 > l) {
+ /* The full time zone does not fit in. Yuck. */
+
+ if (n + 1 + _POSIX_TZNAME_MAX + 1 > l)
+ return NULL; /* Not even enough space for the POSIX minimum (of 6)? In that case, complain that it doesn't fit */
+
+ /* So the time zone doesn't fit in fully, but the caller passed enough space for the POSIX
+ * minimum time zone length. In this case suppress the timezone entirely, in order not to dump
+ * an overly long, hard to read string on the user. This should be safe, because the user will
+ * assume the local timezone anyway if none is shown. And so does parse_timestamp(). */
+ } else {
+ buf[n++] = ' ';
+ strcpy(buf + n, tm.tm_zone);
+ }
+ }
+