libc: common: implement multiple time functions

Implemented the following:
- `asctime_r()`
- `asctime()`
- `localtime()`
- `localtime_r()`
- `ctime()`
- `ctime_r()`

Specifically:
- the implementation of `localtime()` & `localtime_r()` simply
  wraps around the gmtime() & gmtime_r() functions, the
  results are always expressed as UTC.
- `ctime()` is equivalent to `asctime(localtime(clock))`, it
  inherits the limitation of `localtime()` as well, which only
  supports UTC results currently.

Added tests for these newly implemented functions.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>

doc/services/portability/posix/option_groups/index.rst

@@ -981,8 +981,8 @@ Enable this option with :kconfig:option:`CONFIG_POSIX_THREAD_SAFE_FUNCTIONS`.
     :header: API, Supported
     :widths: 50,10
 
-    asctime_r(),
-    ctime_r(),
+    asctime_r(), yes
+    ctime_r(), yes (UTC timezone only)
     flockfile(),
     ftrylockfile(),
     funlockfile(),
@@ -993,7 +993,7 @@ Enable this option with :kconfig:option:`CONFIG_POSIX_THREAD_SAFE_FUNCTIONS`.
     getpwnam_r(),yes :ref:`†<posix_undefined_behaviour>`
     getpwuid_r(),yes :ref:`†<posix_undefined_behaviour>`
     gmtime_r(), yes
-    localtime_r(),
+    localtime_r(), yes (UTC timezone only)
     putc_unlocked(),
     putchar_unlocked(),
     rand_r(), yes

lib/libc/common/CMakeLists.txt

@@ -5,7 +5,10 @@ zephyr_system_include_directories(include)
 zephyr_library()
 zephyr_library_property(ALLOW_EMPTY TRUE)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_ABORT source/stdlib/abort.c)
+zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_ASCTIME source/time/asctime.c)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_GMTIME_R source/time/gmtime_r.c)
+zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_LOCALTIME_R_UTC source/time/localtime_r_utc.c)
+zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_CTIME source/time/ctime.c)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_TIME source/time/time.c)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_MALLOC source/stdlib/malloc.c)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_STRNLEN source/string/strnlen.c)

lib/libc/common/Kconfig

@@ -6,11 +6,44 @@ config COMMON_LIBC_ABORT
 	help
 	  common implementation of abort().
 
+config COMMON_LIBC_ASCTIME
+	bool
+	help
+	  common implementation of asctime().
+
+config COMMON_LIBC_ASCTIME_R
+	bool "Thread-safe version of asctime()"
+	default y if POSIX_THREAD_SAFE_FUNCTIONS
+	select COMMON_LIBC_ASCTIME
+	help
+	  common implementation of asctime_r().
+
+config COMMON_LIBC_CTIME
+	bool
+	select COMMON_LIBC_LOCALTIME_R_UTC
+	help
+	  common implementation of ctime().
+
+config COMMON_LIBC_CTIME_R
+	bool "Thread-safe version of ctime()"
+	default y if POSIX_THREAD_SAFE_FUNCTIONS
+	select COMMON_LIBC_CTIME
+	help
+	  common implementation of ctime_r().
+
 config COMMON_LIBC_GMTIME_R
 	bool
 	help
 	  common implementation of gmtime_r().
 
+config COMMON_LIBC_LOCALTIME_R_UTC
+	bool
+	select COMMON_LIBC_GMTIME_R
+	help
+	  Simple implementation of localtime() & localtime_r().
+	  This option just wraps around the gmtime(), the result is always expressed as
+	  Coordinated Universal Time (UTC).
+
 config COMMON_LIBC_TIME
 	bool
 	help

lib/libc/common/source/time/asctime.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2024 Meta Platforms
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+
+#include <zephyr/sys/util.h>
+
+#define DATE_STRING_BUF_SZ  26U
+#define DATE_WDAY_STRING_SZ 7U
+#define DATE_MON_STRING_SZ  12U
+#define DATE_TM_YEAR_BASE   1900
+
+static char *asctime_impl(const struct tm *tp, char *buf)
+{
+	static const char wday_str[DATE_WDAY_STRING_SZ][3] = {
+		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
+	};
+	static const char mon_str[DATE_MON_STRING_SZ][3] = {
+		"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
+	};
+
+	if ((buf == NULL) || (tp == NULL) || ((unsigned int)tp->tm_wday >= DATE_WDAY_STRING_SZ) ||
+	    ((unsigned int)tp->tm_mon >= DATE_MON_STRING_SZ)) {
+		return NULL;
+	}
+
+	unsigned int n = (unsigned int)snprintf(
+		buf, DATE_STRING_BUF_SZ, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n", wday_str[tp->tm_wday],
+		mon_str[tp->tm_mon], tp->tm_mday, tp->tm_hour, tp->tm_min, tp->tm_sec,
+		DATE_TM_YEAR_BASE + tp->tm_year);
+
+	if (n >= DATE_STRING_BUF_SZ) {
+		return NULL;
+	}
+
+	return buf;
+}
+
+char *asctime(const struct tm *tp)
+{
+	static char buf[DATE_STRING_BUF_SZ];
+
+	return asctime_impl(tp, buf);
+}
+
+#if defined(CONFIG_COMMON_LIBC_ASCTIME_R)
+char *asctime_r(const struct tm *tp, char *buf)
+{
+	return asctime_impl(tp, buf);
+}
+#endif /* CONFIG_COMMON_LIBC_ASCTIME_R */

lib/libc/common/source/time/ctime.c

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2024 Meta Platforms
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <time.h>
+
+/**
+ * `ctime()` is equivalent to `asctime(localtime(clock))`
+ * See: https://pubs.opengroup.org/onlinepubs/009695399/functions/ctime.html
+ */
+
+char *ctime(const time_t *clock)
+{
+	return asctime(localtime(clock));
+}
+
+#if defined(CONFIG_COMMON_LIBC_CTIME_R)
+char *ctime_r(const time_t *clock, char *buf)
+{
+	struct tm tmp;
+
+	return asctime_r(localtime_r(clock, &tmp), buf);
+}
+#endif /* CONFIG_COMMON_LIBC_CTIME_R */

lib/libc/common/source/time/localtime_r_utc.c

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2024 Meta Platforms
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <time.h>
+
+struct tm *localtime_r(const time_t *timer, struct tm *result)
+{
+	return gmtime_r(timer, result);
+}
+
+struct tm *localtime(const time_t *timer)
+{
+	return gmtime(timer);
+}

lib/libc/minimal/Kconfig

@@ -39,6 +39,9 @@ config MINIMAL_LIBC_TIME
 	bool "Time functions"
 	select COMMON_LIBC_TIME if POSIX_TIMERS
 	select COMMON_LIBC_GMTIME_R
+	select COMMON_LIBC_ASCTIME
+	select COMMON_LIBC_LOCALTIME_R_UTC
+	select COMMON_LIBC_CTIME
 	default y
 	help
 	  Enable time() and gmtime_r() for the minimal libc.

lib/libc/minimal/include/time.h

@@ -45,12 +45,22 @@ typedef _SUSECONDS_T_ suseconds_t;
 
 /*
  * Conversion between civil time and UNIX time.  The companion
- * localtime() and inverse mktime() are not provided here since they
+ * mktime() is not provided here since it
  * require access to time zone information.
+ *
+ * The localtime() & localtime_r() simply
+ * wraps around the gmtime() & gmtime_r() functions, the
+ * results are always expressed as UTC.
  */
 struct tm *gmtime(const time_t *timep);
 struct tm *gmtime_r(const time_t *ZRESTRICT timep,
 		    struct tm *ZRESTRICT result);
+char *asctime(const struct tm *timeptr);
+struct tm *localtime(const time_t *timer);
+char *ctime(const time_t *clock);
+char *asctime_r(const struct tm *ZRESTRICT tp, char *ZRESTRICT buf);
+char *ctime_r(const time_t *clock, char *buf);
+struct tm *localtime_r(const time_t *ZRESTRICT timer, struct tm *ZRESTRICT result);
 
 time_t time(time_t *tloc);
 

lib/posix/options/Kconfig

@@ -10,6 +10,7 @@ rsource "Kconfig.profile"
 
 rsource "Kconfig.aio"
 rsource "Kconfig.barrier"
+rsource "Kconfig.c_lang_r"
 rsource "Kconfig.c_lib_ext"
 rsource "Kconfig.device_io"
 rsource "Kconfig.fd_mgmt"

lib/posix/options/Kconfig.c_lang_r

@@ -0,0 +1,18 @@
+# Copyright (c) 2024 Tenstorrent AI ULC
+# Copyright (c) 2024 Meta Platforms
+#
+# SPDX-License-Identifier: Apache-2.0
+
+config POSIX_C_LANG_SUPPORT_R
+	bool "Thread-Safe General ISO C Library"
+	select COMMON_LIBC_ASCTIME_R
+	select COMMON_LIBC_CTIME_R
+	select COMMON_LIBC_GMTIME_R
+	select COMMON_LIBC_LOCALTIME_R_UTC
+	help
+	  Select 'y' here and Zephyr will provide an implementation of the POSIX_C_LANG_SUPPORT_R
+	  Option Group, consisting of asctime_r(), ctime_r(), gmtime_r(), localtime_r(), rand_r(),
+	  strerror_r(), and strtok_r()
+
+	  For more informnation, please see
+	  https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_subprofiles.html

lib/posix/options/Kconfig.pthread

@@ -157,6 +157,7 @@ config POSIX_THREAD_PRIO_PROTECT
 config POSIX_THREAD_SAFE_FUNCTIONS
 	bool "POSIX thread-safe functions"
 	select POSIX_FILE_SYSTEM_R if POSIX_FILE_SYSTEM
+	select POSIX_C_LANG_SUPPORT_R
 	help
 	  Select 'y' here to enable POSIX thread-safe functions including asctime_r(), ctime_r(),
 	  flockfile(), ftrylockfile(), funlockfile(), getc_unlocked(), getchar_unlocked(),

tests/lib/c_lib/common/src/main.c

@@ -22,6 +22,7 @@
 
 #include <zephyr/kernel.h>
 #include <zephyr/sys/__assert.h>
+#include <zephyr/sys/util.h>
 #include <zephyr/ztest.h>
 
 #include <limits.h>
@@ -1075,7 +1076,7 @@ ZTEST(libc_common, test_strtok_r)
  *
  * @see gmtime(),gmtime_r().
  */
-ZTEST(libc_common, test_time)
+ZTEST(libc_common, test_time_gmtime)
 {
 	time_t tests1 = 0;
 	time_t tests2 = -5;
@@ -1092,6 +1093,86 @@ ZTEST(libc_common, test_time)
 	zassert_not_null(gmtime_r(&tests4, &tp), "gmtime_r failed");
 }
 
+/**
+ * @brief Test time function
+ *
+ * @see asctime(), asctime_r().
+ */
+ZTEST(libc_common, test_time_asctime)
+{
+	char buf[26] = {0};
+	struct tm tp = {
+		.tm_sec = 10,   /* Seconds */
+		.tm_min = 30,   /* Minutes */
+		.tm_hour = 14,  /* Hour (24-hour format) */
+		.tm_wday = 5,   /* Day of the week (0-6, 0 = Sun) */
+		.tm_mday = 1,   /* Day of the month */
+		.tm_mon = 5,    /* Month (0-11, January = 0) */
+		.tm_year = 124, /* Year (current year - 1900) */
+	};
+
+	zassert_not_null(asctime_r(&tp, buf));
+	zassert_equal(strncmp("Fri Jun  1 14:30:10 2024\n", buf, sizeof(buf)), 0);
+
+	zassert_not_null(asctime(&tp));
+	zassert_equal(strncmp("Fri Jun  1 14:30:10 2024\n", asctime(&tp), sizeof(buf)), 0);
+
+	if (IS_ENABLED(CONFIG_COMMON_LIBC_ASCTIME_R)) {
+		zassert_is_null(asctime_r(NULL, buf));
+		zassert_is_null(asctime(NULL));
+
+		zassert_is_null(asctime_r(&tp, NULL));
+
+		tp.tm_wday = 8;
+		zassert_is_null(asctime_r(&tp, buf));
+		zassert_is_null(asctime(&tp));
+
+		tp.tm_wday = 5;
+		tp.tm_mon = 12;
+		zassert_is_null(asctime_r(&tp, buf));
+		zassert_is_null(asctime(&tp));
+	}
+}
+
+/**
+ * @brief Test time function
+ *
+ * @see localtime(), localtime_r().
+ */
+ZTEST(libc_common, test_time_localtime)
+{
+	time_t tests1 = 0;
+	time_t tests2 = -5;
+	time_t tests3 = (time_t) -214748364800;
+	time_t tests4 = 951868800;
+
+	struct tm tp;
+
+	zassert_not_null(localtime(&tests1), "localtime failed");
+	zassert_not_null(localtime(&tests2), "localtime failed");
+
+	tp.tm_wday = -5;
+	zassert_not_null(localtime_r(&tests3, &tp), "localtime_r failed");
+	zassert_not_null(localtime_r(&tests4, &tp), "localtime_r failed");
+}
+
+/**
+ * @brief Test time function
+ *
+ * @see ctime(), ctime_r().
+ */
+ZTEST(libc_common, test_time_ctime)
+{
+	char buf[26] = {0};
+	time_t time = 1718260000;
+
+	zassert_not_null(ctime_r(&time, buf));
+	zassert_equal(strncmp("Thu Jun 13 06:26:40 2024\n", buf, sizeof(buf)), 0);
+
+	zassert_not_null(ctime(&time));
+	zassert_equal(strncmp("Thu Jun 13 06:26:40 2024\n", ctime(&time), sizeof(buf)), 0);
+}
+
 /**
  *
  * @brief Test rand function

tests/lib/c_lib/common/testcase.yaml

@@ -13,6 +13,8 @@ tests:
       - CONFIG_MINIMAL_LIBC=y
       - CONFIG_MINIMAL_LIBC_NON_REENTRANT_FUNCTIONS=y
       - CONFIG_MINIMAL_LIBC_RAND=y
+      - CONFIG_COMMON_LIBC_ASCTIME_R=y
+      - CONFIG_COMMON_LIBC_CTIME_R=y
   libraries.libc.common.newlib:
     filter: CONFIG_NEWLIB_LIBC_SUPPORTED
     min_ram: 32