[musl] strptime("UTC", "%Z", &tm) in musl

[musl] strptime("UTC", "%Z", &tm) in musl

[Alejandro Colomar]

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Hi Rich,

I was trying to develop a function that parses a UTC date in the shadow
project, and I came up with this:
<https://github.com/shadow-maint/shadow/pull/1217/>

	$ grepc -htfd get_date .
	static long
	get_date(const char *s)
	{
		struct tm   tm;
		const char  *p;

		bzero(&tm, sizeof(tm));

		p = strptime("UTC", "%Z", &tm);
		if (p == NULL || !streq(p, ""))
			return -1;

		p = strptime(s, "%F", &tm);
		if (p == NULL || !streq(p, ""))
			return -1;

		return dategm(&tm);
	}

Which works fine in glibc, but fails in musl.

	$ grepc -tfd strptime . | sed -n '/case .Z.:/,/break/p'
		case 'Z':
			if (!strncmp(s, tzname[0], len = strlen(tzname[0]))) {
				tm->tm_isdst = 0;
				s += len;
			} else if (!strncmp(s, tzname[1], len=strlen(tzname[1]))) {
				tm->tm_isdst = 1;
				s += len;
			} else {
				/* FIXME: is this supposed to be an error? */
				while ((*s|32)-'a' <= 'z'-'a') s++;
			}
			break;

It seems "%Z" only accepts the timezone specified in the current locale
(via tzname), but doesn't accept parsing a different timezone (in this
case, I want specifically UTC, regardless of the locale).  I'd say this
is a bug, and an important limitation, BTW.

Is there any way I can workaround this for musl?


Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es/>
<https://www.alejandro-colomar.es:8443/>
<http://www.alejandro-colomar.es:8080/>

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[musl] Re: strptime("UTC", "%Z", &tm) in musl

[Alejandro Colomar]

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[Add libc-alpha@]

On Sun, Apr 06, 2025 at 09:57:39PM +0200, Alejandro Colomar wrote:
> Hi Rich,
> 
> I was trying to develop a function that parses a UTC date in the shadow
> project, and I came up with this:
> <https://github.com/shadow-maint/shadow/pull/1217/>
> 
> 	$ grepc -htfd get_date .
> 	static long
> 	get_date(const char *s)
> 	{
> 		struct tm   tm;
> 		const char  *p;
> 
> 		bzero(&tm, sizeof(tm));
> 
> 		p = strptime("UTC", "%Z", &tm);
> 		if (p == NULL || !streq(p, ""))
> 			return -1;
> 
> 		p = strptime(s, "%F", &tm);
> 		if (p == NULL || !streq(p, ""))
> 			return -1;
> 
> 		return dategm(&tm);
> 	}
> 
> Which works fine in glibc, but fails in musl.

Actually, I've now read the glibc sources, and it seems even worse in
glibc.  glibc ignores the parsed timezone at all.
So, both glibc and musl have a bug here, I think.

Is there any way to parse a UTC date?  That is, parse a "YYYY-MM-DD"
date that is not in local time, but in UTC time.

Have a lovely night!
Alex

> 
> 	$ grepc -tfd strptime . | sed -n '/case .Z.:/,/break/p'
> 		case 'Z':
> 			if (!strncmp(s, tzname[0], len = strlen(tzname[0]))) {
> 				tm->tm_isdst = 0;
> 				s += len;
> 			} else if (!strncmp(s, tzname[1], len=strlen(tzname[1]))) {
> 				tm->tm_isdst = 1;
> 				s += len;
> 			} else {
> 				/* FIXME: is this supposed to be an error? */
> 				while ((*s|32)-'a' <= 'z'-'a') s++;
> 			}
> 			break;
> 
> It seems "%Z" only accepts the timezone specified in the current locale
> (via tzname), but doesn't accept parsing a different timezone (in this
> case, I want specifically UTC, regardless of the locale).  I'd say this
> is a bug, and an important limitation, BTW.
> 
> Is there any way I can workaround this for musl?
> 
> 
> Have a lovely day!
> Alex
> 
> -- 
> <https://www.alejandro-colomar.es/>
> <https://www.alejandro-colomar.es:8443/>
> <http://www.alejandro-colomar.es:8080/>



-- 
<https://www.alejandro-colomar.es/>
<https://www.alejandro-colomar.es:8443/>
<http://www.alejandro-colomar.es:8080/>

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Re: [musl] strptime("UTC", "%Z", &tm) in musl

[Haelwenn (lanodan) Monnier]

[2025-04-06 21:57:35+0200] Alejandro Colomar:
>I was trying to develop a function that parses a UTC date in the shadow
>project, and I came up with this:
><https://github.com/shadow-maint/shadow/pull/1217/>
>
>	$ grepc -htfd get_date .
>	static long
>	get_date(const char *s)
>	{
>		struct tm   tm;
>		const char  *p;
>
>		bzero(&tm, sizeof(tm));
>
>		p = strptime("UTC", "%Z", &tm);
>		if (p == NULL || !streq(p, ""))
>			return -1;

That bzero seems like a bit of a bad idea, `struct tm` can have some extra
fields where 0 isn't the correct value.
Quite like how `tm_isdst` uses -1 for unknown state, 0 for no-DST, 1 for DST.

Could probably use `if(!gmtime_r(0, &tm)) { /* handle err */ }` instead
which also has the nice effect of initializing tm for UTC,
allowing to skip the problematic strptime %Z.

Best regards

Re: [musl] strptime("UTC", "%Z", &tm) in musl

[Alejandro Colomar]

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Hi Haelwenn,

On Sun, Apr 06, 2025 at 10:55:46PM +0200, Haelwenn (lanodan) Monnier wrote:
> [2025-04-06 21:57:35+0200] Alejandro Colomar:
> > I was trying to develop a function that parses a UTC date in the shadow
> > project, and I came up with this:
> > <https://github.com/shadow-maint/shadow/pull/1217/>
> > 
> > 	$ grepc -htfd get_date .
> > 	static long
> > 	get_date(const char *s)
> > 	{
> > 		struct tm   tm;
> > 		const char  *p;
> > 
> > 		bzero(&tm, sizeof(tm));
> > 
> > 		p = strptime("UTC", "%Z", &tm);
> > 		if (p == NULL || !streq(p, ""))
> > 			return -1;
> 
> That bzero seems like a bit of a bad idea, `struct tm` can have some extra
> fields where 0 isn't the correct value.
> Quite like how `tm_isdst` uses -1 for unknown state, 0 for no-DST, 1 for DST.
> 
> Could probably use `if(!gmtime_r(0, &tm)) { /* handle err */ }` instead
> which also has the nice effect of initializing tm for UTC,
> allowing to skip the problematic strptime %Z.

Thanks!  This is quite clever.  I've changed this to my patch:

	diff --git i/lib/strtoday.c w/lib/strtoday.c
	index 2d88e8b6..ab03b921 100644
	--- i/lib/strtoday.c
	+++ w/lib/strtoday.c
	@@ -47,13 +47,13 @@ strtoday(const char *str)
	 static long
	 get_date(const char *s)
	 {
	+       time_t      t;
		struct tm   tm;
		const char  *p;
	 
	-       bzero(&tm, sizeof(tm));
	-
	-       p = strptime("UTC", "%Z", &tm);
	-       if (p == NULL || !streq(p, ""))
	+       // Set timezone to UTC
	+       t = 0;
	+       if (gmtime_r(&t, &tm) == NULL)
			return -1;
	 
		p = strptime(s, "%F", &tm);

If you don't mind, I'd like to add you as a co-author of the patch, and
assign you copyright in that file.  Please sign the following commit, if
you approve it.


Have a lovely night!
Alex


---

<https://github.com/shadow-maint/shadow/pull/1217>

Author: Alejandro Colomar <alx@kernel.org>
Date:   Tue Feb 18 23:25:29 2025 +0100

    lib/getdate.c: Use strptime(3) to simplify
    
    The following trick:
    
            t = 0;
            gmtime_r(&t, &tm);
    
    is a clever way to clear the tm(3type) structure, and set it to use UTC.
    
    We need to set it to set UTC with this trick, because strptime(3)
    doesn't set the timezone.  I (Alex) tried previously using
    
            bzero(&tm, sizeof(tm));
            strptime("UTC", "%Z", &tm);
    
    but glibc ignores the timezone, and musl (at least I tried in an Alpine
    container) seems to report an error.
    
    The idea to use gmtime_r(3) was from lanodan.
    
    Link: <https://inbox.sourceware.org/libc-alpha/Z_LqUgildoq33vI-@cloudsdale.the-delta.net.eu.org/T/#u>
    Cc: Iker Pedrosa <ipedrosa@redhat.com>
    Cc: Serge Hallyn <serge@hallyn.com>
    Cc: Rich Felker <dalias@libc.org>
    Co-authored-by: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
    Signed-off-by: Alejandro Colomar <alx@kernel.org>

diff --git a/lib/getdate.c b/lib/getdate.c
index 31a5c25b..fa2df83e 100644
--- a/lib/getdate.c
+++ b/lib/getdate.c
@@ -1,81 +1,31 @@
 // SPDX-FileCopyrightText: 2025, Alejandro Colomar <alx@kernel.org>
+// SPDX-FileCopyrightText: 2025, "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
 // SPDX-License-Identifier: BSD-3-Clause
 
 
 #include <config.h>
 
-#include <errno.h>
-#include <limits.h>
 #include <stddef.h>
-#include <string.h>
 #include <time.h>
 
-#include "atoi/a2i/a2s.h"
 #include "getdate.h"
-#include "string/strchr/strchrcnt.h"
 #include "string/strcmp/streq.h"
-#include "string/strcmp/strprefix.h"
-#include "string/strcmp/strsuffix.h"
-#include "string/strspn/stpspn.h"
-
-
-#define TM_YEAR_ORIGIN 1900
-
-
-static long  yyDay;
-static long  yyMonth;
-static long  yyYear;
-
-
-static int parse_date(const char *s);
 
 
 time_t
-get_date(const char *s);
+get_date(const char *s)
 {
-       struct tm  tm;
+       time_t      t;
+       struct tm   tm;
+       const char  *p;
 
-       if (parse_date(p) == -1)
+       t = 0;
+       if (gmtime_r(&t, &tm) == NULL)
                return -1;
 
-       tm.tm_year = yyYear - TM_YEAR_ORIGIN;
-       tm.tm_mon = yyMonth - 1;
-       tm.tm_mday = yyDay;
-       tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
-       tm.tm_isdst = 0;
+       p = strptime(s, "%F", &tm);
+       if (p == NULL || !streq(p, ""))
+               return -1;
 
        return timegm(&tm);
 }
-
-
-static int
-parse_date(const char *s)
-{
-       long  n;
-
-       if (!streq(stpspn(s, "0123456789-"), "")
-        || strchrcnt(s, '-') != 2
-        || strprefix(s, "-")
-        || strsuffix(s, "-")
-        || strstr(s, "--"))
-       {
-               return -1;
-       }
-
-       if (a2sl(&yyYear, s, &s, 10, LONG_MIN, LONG_MAX) == -1 && errno != ENOTSUP)
-               return -1;
-
-       if (!strprefix(s++, "-"))
-               return -1;
-
-       if (a2sl(&yyMonth, s, &s, 10, LONG_MIN, LONG_MAX) == -1 && errno != ENOTSUP)
-               return -1;
-
-       if (!strprefix(s++, "-"))
-               return -1;
-
-       if (a2sl(&yyDay, s, NULL, 10, LONG_MIN, LONG_MAX) == -1)
-               return -1;
-
-       return 0;
-}

-- 
<https://www.alejandro-colomar.es/>
<https://www.alejandro-colomar.es:8443/>
<http://www.alejandro-colomar.es:8080/>

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Re: [musl] strptime("UTC", "%Z", &tm) in musl

[Rich Felker]

On Sun, Apr 06, 2025 at 09:57:35PM +0200, Alejandro Colomar wrote:
> Hi Rich,
> 
> I was trying to develop a function that parses a UTC date in the shadow
> project, and I came up with this:
> <https://github.com/shadow-maint/shadow/pull/1217/>
> 
> 	$ grepc -htfd get_date .
> 	static long
> 	get_date(const char *s)
> 	{
> 		struct tm   tm;
> 		const char  *p;
> 
> 		bzero(&tm, sizeof(tm));
> 
> 		p = strptime("UTC", "%Z", &tm);
> 		if (p == NULL || !streq(p, ""))
> 			return -1;
> 
> 		p = strptime(s, "%F", &tm);
> 		if (p == NULL || !streq(p, ""))
> 			return -1;
> 
> 		return dategm(&tm);
> 	}
> 
> Which works fine in glibc, but fails in musl.
> 
> 	$ grepc -tfd strptime . | sed -n '/case .Z.:/,/break/p'
> 		case 'Z':
> 			if (!strncmp(s, tzname[0], len = strlen(tzname[0]))) {
> 				tm->tm_isdst = 0;
> 				s += len;
> 			} else if (!strncmp(s, tzname[1], len=strlen(tzname[1]))) {
> 				tm->tm_isdst = 1;
> 				s += len;
> 			} else {
> 				/* FIXME: is this supposed to be an error? */
> 				while ((*s|32)-'a' <= 'z'-'a') s++;
> 			}
> 			break;
> 
> It seems "%Z" only accepts the timezone specified in the current locale
> (via tzname), but doesn't accept parsing a different timezone (in this
> case, I want specifically UTC, regardless of the locale).  I'd say this
> is a bug, and an important limitation, BTW.
> 
> Is there any way I can workaround this for musl?

See commit fced99e93daeefb0192fd16304f978d4401d1d77. The newly added
specifiers were added only with their POSIX-specified behavior, not
anything else. I don't think the POSIX-specified behavior is terribly
useful, but it's indicative that there's not consensus on any behavior
beyond that, and that programs that depend on any particular
implementation behavior beyond what's specified are likely not
portable.

I'm not sure what you're trying to achieve so I don't know what
alternative I'd recommend.

Rich

Re: [musl] strptime("UTC", "%Z", &tm) in musl

[Haelwenn (lanodan) Monnier]

[2025-04-07 01:54:14+0200] Alejandro Colomar:
>Hi Haelwenn,
>
>On Sun, Apr 06, 2025 at 10:55:46PM +0200, Haelwenn (lanodan) Monnier wrote:
>> [2025-04-06 21:57:35+0200] Alejandro Colomar:
>> > I was trying to develop a function that parses a UTC date in the shadow
>> > project, and I came up with this:
>> > <https://github.com/shadow-maint/shadow/pull/1217/>
>> >
>> > 	$ grepc -htfd get_date .
>> > 	static long
>> > 	get_date(const char *s)
>> > 	{
>> > 		struct tm   tm;
>> > 		const char  *p;
>> >
>> > 		bzero(&tm, sizeof(tm));
>> >
>> > 		p = strptime("UTC", "%Z", &tm);
>> > 		if (p == NULL || !streq(p, ""))
>> > 			return -1;
>>
>> That bzero seems like a bit of a bad idea, `struct tm` can have some extra
>> fields where 0 isn't the correct value.
>> Quite like how `tm_isdst` uses -1 for unknown state, 0 for no-DST, 1 for DST.
>>
>> Could probably use `if(!gmtime_r(0, &tm)) { /* handle err */ }` instead
>> which also has the nice effect of initializing tm for UTC,
>> allowing to skip the problematic strptime %Z.
>
>Thanks!  This is quite clever.  I've changed this to my patch:
>
>	diff --git i/lib/strtoday.c w/lib/strtoday.c
>	index 2d88e8b6..ab03b921 100644
>	--- i/lib/strtoday.c
>	+++ w/lib/strtoday.c
>	@@ -47,13 +47,13 @@ strtoday(const char *str)
>	 static long
>	 get_date(const char *s)
>	 {
>	+       time_t      t;
>		struct tm   tm;
>		const char  *p;
>	
>	-       bzero(&tm, sizeof(tm));
>	-
>	-       p = strptime("UTC", "%Z", &tm);
>	-       if (p == NULL || !streq(p, ""))
>	+       // Set timezone to UTC
>	+       t = 0;
>	+       if (gmtime_r(&t, &tm) == NULL)
>			return -1;
>	
>		p = strptime(s, "%F", &tm);
>
>If you don't mind, I'd like to add you as a co-author of the patch, and
>assign you copyright in that file.  Please sign the following commit, if
>you approve it.

Yeah, looks good to me. And I guess Signed-off-by is the correct field for this.

Signed-off-by: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>

Best regards

>Have a lovely night!
>Alex
>
>
>---
>
><https://github.com/shadow-maint/shadow/pull/1217>
>
>Author: Alejandro Colomar <alx@kernel.org>
>Date:   Tue Feb 18 23:25:29 2025 +0100
>
>    lib/getdate.c: Use strptime(3) to simplify
>
>    The following trick:
>
>            t = 0;
>            gmtime_r(&t, &tm);
>
>    is a clever way to clear the tm(3type) structure, and set it to use UTC.
>
>    We need to set it to set UTC with this trick, because strptime(3)
>    doesn't set the timezone.  I (Alex) tried previously using
>
>            bzero(&tm, sizeof(tm));
>            strptime("UTC", "%Z", &tm);
>
>    but glibc ignores the timezone, and musl (at least I tried in an Alpine
>    container) seems to report an error.
>
>    The idea to use gmtime_r(3) was from lanodan.
>
>    Link: <https://inbox.sourceware.org/libc-alpha/Z_LqUgildoq33vI-@cloudsdale.the-delta.net.eu.org/T/#u>
>    Cc: Iker Pedrosa <ipedrosa@redhat.com>
>    Cc: Serge Hallyn <serge@hallyn.com>
>    Cc: Rich Felker <dalias@libc.org>
>    Co-authored-by: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
>    Signed-off-by: Alejandro Colomar <alx@kernel.org>
>
>diff --git a/lib/getdate.c b/lib/getdate.c
>index 31a5c25b..fa2df83e 100644
>--- a/lib/getdate.c
>+++ b/lib/getdate.c
>@@ -1,81 +1,31 @@
> // SPDX-FileCopyrightText: 2025, Alejandro Colomar <alx@kernel.org>
>+// SPDX-FileCopyrightText: 2025, "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
> // SPDX-License-Identifier: BSD-3-Clause
>
>
> #include <config.h>
>
>-#include <errno.h>
>-#include <limits.h>
> #include <stddef.h>
>-#include <string.h>
> #include <time.h>
>
>-#include "atoi/a2i/a2s.h"
> #include "getdate.h"
>-#include "string/strchr/strchrcnt.h"
> #include "string/strcmp/streq.h"
>-#include "string/strcmp/strprefix.h"
>-#include "string/strcmp/strsuffix.h"
>-#include "string/strspn/stpspn.h"
>-
>-
>-#define TM_YEAR_ORIGIN 1900
>-
>-
>-static long  yyDay;
>-static long  yyMonth;
>-static long  yyYear;
>-
>-
>-static int parse_date(const char *s);
>
>
> time_t
>-get_date(const char *s);
>+get_date(const char *s)
> {
>-       struct tm  tm;
>+       time_t      t;
>+       struct tm   tm;
>+       const char  *p;
>
>-       if (parse_date(p) == -1)
>+       t = 0;
>+       if (gmtime_r(&t, &tm) == NULL)
>                return -1;
>
>-       tm.tm_year = yyYear - TM_YEAR_ORIGIN;
>-       tm.tm_mon = yyMonth - 1;
>-       tm.tm_mday = yyDay;
>-       tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
>-       tm.tm_isdst = 0;
>+       p = strptime(s, "%F", &tm);
>+       if (p == NULL || !streq(p, ""))
>+               return -1;
>
>        return timegm(&tm);
> }
>-
>-
>-static int
>-parse_date(const char *s)
>-{
>-       long  n;
>-
>-       if (!streq(stpspn(s, "0123456789-"), "")
>-        || strchrcnt(s, '-') != 2
>-        || strprefix(s, "-")
>-        || strsuffix(s, "-")
>-        || strstr(s, "--"))
>-       {
>-               return -1;
>-       }
>-
>-       if (a2sl(&yyYear, s, &s, 10, LONG_MIN, LONG_MAX) == -1 && errno != ENOTSUP)
>-               return -1;
>-
>-       if (!strprefix(s++, "-"))
>-               return -1;
>-
>-       if (a2sl(&yyMonth, s, &s, 10, LONG_MIN, LONG_MAX) == -1 && errno != ENOTSUP)
>-               return -1;
>-
>-       if (!strprefix(s++, "-"))
>-               return -1;
>-
>-       if (a2sl(&yyDay, s, NULL, 10, LONG_MIN, LONG_MAX) == -1)
>-               return -1;
>-
>-       return 0;
>-}
>
>-- 
><https://www.alejandro-colomar.es/>
><https://www.alejandro-colomar.es:8443/>
><http://www.alejandro-colomar.es:8080/>

Re: [musl] strptime("UTC", "%Z", &tm) in musl

[Alejandro Colomar]

[-- Attachment #1: Type: text/plain, Size: 345 bytes --]

Hi,

On Mon, Apr 07, 2025 at 07:01:35PM +0200, Haelwenn (lanodan) Monnier wrote:
> Yeah, looks good to me. And I guess Signed-off-by is the correct field for this.
> 
> Signed-off-by: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
> 
> Best regards

Thanks!  Have a lovely night!
Alex

-- 
<https://www.alejandro-colomar.es/>

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