date,touch: allow timezone offsets in dates

Allow ISO 8601 style dates to include a timezone offset.  Like
the '@' format these dates aren't relative to the user's current
timezone and shouldn't be subject to DST adjustment.

- The implementation uses the strptime() '%z' format specifier.
  This an extension which may not be available so the use of
  timezones is a configuration option.

- The 'touch' applet has been updated to respect whether DST
  adjustment is required, matching 'date'.

function                                             old     new   delta
parse_datestr                                        624     730    +106
static.fmt_str                                       106     136     +30
touch_main                                           388     392      +4
date_main                                            818     819      +1
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/0 up/down: 141/0)             Total: 141 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

6 files changed, 83 insertions, 10 deletions

diff --git a/coreutils/date.c b/coreutils/date.c
index 7061f17..abcc37c 100644
--- a/coreutils/date.c
+++ b/coreutils/date.c
@@ -266,6 +266,7 @@ int date_main(int argc UNUSED_PARAM, char **argv)
 
 	/* If date string is given, update tm_time, and maybe set date */
 	if (date_str != NULL) {
+		int check_dst = 1;
 		/* Zero out fields - take her back to midnight! */
 		tm_time.tm_sec = 0;
 		tm_time.tm_min = 0;
@@ -276,12 +277,12 @@ int date_main(int argc UNUSED_PARAM, char **argv)
 			if (strptime(date_str, fmt_str2dt, &tm_time) == NULL)
 				bb_error_msg_and_die(bb_msg_invalid_date, date_str);
 		} else {
-			parse_datestr(date_str, &tm_time);
+			check_dst = parse_datestr(date_str, &tm_time);
 		}
 
 		/* Correct any day of week and day of year etc. fields */
-		/* Be sure to recheck dst (but not if date is time_t format) */
-		if (date_str[0] != '@')
+		/* Be sure to recheck dst (but not if date is UTC) */
+		if (check_dst)
 			tm_time.tm_isdst = -1;
 		ts.tv_sec = validate_tm_time(date_str, &tm_time);
 		ts.tv_nsec = 0;
diff --git a/coreutils/touch.c b/coreutils/touch.c
index 78100ba..7e13a27 100644
--- a/coreutils/touch.c
+++ b/coreutils/touch.c
@@ -140,15 +140,17 @@ int touch_main(int argc UNUSED_PARAM, char **argv)
 	if (opts & (OPT_d|OPT_t)) {
 		struct tm tm_time;
 		time_t t;
+		int check_dst;
 
 		//memset(&tm_time, 0, sizeof(tm_time));
 		/* Better than memset: makes "HH:MM" dates meaningful */
 		time(&t);
 		localtime_r(&t, &tm_time);
-		parse_datestr(date_str, &tm_time);
+		check_dst = parse_datestr(date_str, &tm_time);
 
 		/* Correct any day of week and day of year etc. fields */
-		tm_time.tm_isdst = -1;  /* Be sure to recheck dst */
+		if (check_dst)
+			tm_time.tm_isdst = -1;  /* recheck dst unless date is UTC */
 		t = validate_tm_time(date_str, &tm_time);
 
 		timebuf[1].tv_sec = timebuf[0].tv_sec = t;
diff --git a/include/libbb.h b/include/libbb.h
index 7d6ab4a..1ec8d2d 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -690,7 +690,7 @@ struct BUG_too_small {
 };
 
 
-void parse_datestr(const char *date_str, struct tm *ptm) FAST_FUNC;
+int parse_datestr(const char *date_str, struct tm *ptm) FAST_FUNC;
 time_t validate_tm_time(const char *date_str, struct tm *ptm) FAST_FUNC;
 char *strftime_HHMMSS(char *buf, unsigned len, time_t *tp) FAST_FUNC;
 char *strftime_YYYYMMDDHHMMSS(char *buf, unsigned len, time_t *tp) FAST_FUNC;
diff --git a/libbb/Config.src b/libbb/Config.src
index f97de8e..58c5fad 100644
--- a/libbb/Config.src
+++ b/libbb/Config.src
@@ -395,3 +395,14 @@ config FEATURE_HWIB
 	default y
 	help
 	Support for printing infiniband addresses in network applets.
+
+config FEATURE_TIMEZONE
+	bool "Allow timezone in dates"
+	default y
+	depends on DESKTOP
+	help
+	Permit the use of timezones when parsing user-provided data
+	strings, e.g. '1996-04-09 12:45:00 -0500'.
+
+	This requires support for the '%z' extension to strptime() which
+	may not be available in all implementations.
diff --git a/libbb/time.c b/libbb/time.c
index 365b1df..41a69c7 100644
--- a/libbb/time.c
+++ b/libbb/time.c
@@ -8,7 +8,9 @@
  */
 #include "libbb.h"
 
-void FAST_FUNC parse_datestr(const char *date_str, struct tm *ptm)
+/* Returns 0 if the time structure contains an absolute UTC time which
+ * should not be subject to DST adjustment by the caller. */
+int FAST_FUNC parse_datestr(const char *date_str, struct tm *ptm)
 {
 	char end = '\0';
 #if ENABLE_DESKTOP
@@ -27,6 +29,10 @@ void FAST_FUNC parse_datestr(const char *date_str, struct tm *ptm)
 		"%b %d %T %Y" "\0"      /* month_name d HH:MM:SS YYYY */
 		"%Y-%m-%d %R" "\0"      /* yyyy-mm-dd HH:MM */
 		"%Y-%m-%d %T" "\0"      /* yyyy-mm-dd HH:MM:SS */
+#if ENABLE_FEATURE_TIMEZONE
+		"%Y-%m-%d %R %z" "\0"   /* yyyy-mm-dd HH:MM TZ */
+		"%Y-%m-%d %T %z" "\0"   /* yyyy-mm-dd HH:MM:SS TZ */
+#endif
 		"%Y-%m-%d %H" "\0"      /* yyyy-mm-dd HH */
 		"%Y-%m-%d" "\0"         /* yyyy-mm-dd */
 		/* extra NUL */;
@@ -38,8 +44,28 @@ void FAST_FUNC parse_datestr(const char *date_str, struct tm *ptm)
 	fmt = fmt_str;
 	while (*fmt) {
 		endp = strptime(date_str, fmt, ptm);
-		if (endp && *endp == '\0')
-			return;
+		if (endp && *endp == '\0') {
+#if ENABLE_FEATURE_TIMEZONE
+			if (strchr(fmt, 'z')) {
+				time_t t;
+				struct tm *utm;
+
+				/* we have timezone offset: obtain Unix time_t */
+				ptm->tm_sec -= ptm->tm_gmtoff;
+				ptm->tm_isdst = 0;
+				t = timegm(ptm);
+				if (t == (time_t)-1)
+					break;
+				/* convert Unix time_t to struct tm in user's locale */
+				utm = localtime(&t);
+				if (!utm)
+					break;
+				*ptm = *utm;
+				return 0;
+			}
+#endif
+			return 1;
+		}
 		*ptm = save;
 		while (*++fmt)
 			continue;
@@ -124,7 +150,7 @@ void FAST_FUNC parse_datestr(const char *date_str, struct tm *ptm)
 			struct tm *lt = localtime(&t);
 			if (lt) {
 				*ptm = *lt;
-				return;
+				return 0;
 			}
 		}
 		end = '1';
@@ -241,6 +267,7 @@ void FAST_FUNC parse_datestr(const char *date_str, struct tm *ptm)
 	if (end != '\0') {
 		bb_error_msg_and_die(bb_msg_invalid_date, date_str);
 	}
+	return 1;
 }
 
 time_t FAST_FUNC validate_tm_time(const char *date_str, struct tm *ptm)
diff --git a/testsuite/date/date-timezone b/testsuite/date/date-timezone
new file mode 100644
index 0000000..8628aa1
--- /dev/null
+++ b/testsuite/date/date-timezone
@@ -0,0 +1,32 @@
+# FEATURE: CONFIG_FEATURE_TIMEZONE
+
+# 'Z' is UTC
+dt=$(TZ=UTC0 busybox date -d '1999-1-2 3:4:5Z')
+dt=$(echo "$dt" | cut -b1-19)
+test x"$dt" = x"Sat Jan  2 03:04:05"
+
+# '+0600' is six hours ahead of UTC
+dt=$(TZ=UTC0 busybox date -d '1999-1-2 3:4:5 +0600')
+dt=$(echo "$dt" | cut -b1-19)
+test x"$dt" = x"Fri Jan  1 21:04:05"
+
+# '-0600' is six hours behind UTC
+dt=$(TZ=UTC0 busybox date -d '1999-1-2 3:4:5 -0600')
+dt=$(echo "$dt" | cut -b1-19)
+test x"$dt" = x"Sat Jan  2 09:04:05"
+
+# before dst is switched on
+dt=$(TZ=GMT0BST,M3.5.0/1,M10.5.0/2 busybox date -d '2021-03-28 00:59:59 +0000')
+test x"$dt" = x"Sun Mar 28 00:59:59 GMT 2021"
+
+# after dst is switched on
+dt=$(TZ=GMT0BST,M3.5.0/1,M10.5.0/2 busybox date -d '2021-03-28 01:00:01 +0000')
+test x"$dt" = x"Sun Mar 28 02:00:01 BST 2021"
+
+# before dst is switched off
+dt=$(TZ=GMT0BST,M3.5.0/1,M10.5.0/2 busybox date -d '2021-10-31 00:00:01 +0000')
+test x"$dt" = x"Sun Oct 31 01:00:01 BST 2021"
+
+# after dst is switched off: back to 01:00:01 but with different TZ
+dt=$(TZ=GMT0BST,M3.5.0/1,M10.5.0/2 busybox date -d '2021-10-31 01:00:01 +0000')
+test x"$dt" = x"Sun Oct 31 01:00:01 GMT 2021"