[Toybox] [PATCH] Support the %N coreutils/busybox extension to date.

[enh]

what's the plan? "half an eye is better than no eye" (especially when
no-one else has this particular missing eye), or "rewrite the test to
use --full-time"?

since i personally have never needed %N except for getting this test
to run, i'm happy to do either.

On Mon, Apr 17, 2017 at 9:42 AM, enh <enh at google.com> wrote:
> take 2 (switches to next_printf, fixes the %%N case):
>
>  tests/date.test   | 14 ++++++++++++++
>  toys/posix/date.c | 50 +++++++++++++++++++++++++++++++++++++++-----------
>  2 files changed, 53 insertions(+), 11 deletions(-)
>
>
> On Sun, Apr 16, 2017 at 4:22 PM, Rob Landley <rob at landley.net> wrote:
>>
>> On 04/16/2017 03:51 PM, enh wrote:
>> > yeah, definitely a mess.
>> >
>> > note that i only did this because (a) existing tests were using it and
>> > (b) busybox has it too. i've been assuming (perhaps incorrectly) that
>> > busybox also tried to avoid needlessly implementing GNU extensions
>> > unless they were actually useful to enough people.
>>
>> As far as I can tell the way people do this is indeed date %N. I've
>> tried to do this before, but adding extra escapes to both input and
>> output via an overlay mechanism turns out to be a hard problem to do
>> right.
>>
>> (Really I want a generic mechanism to wrap arbitrary printf/scanf style
>> things, but the problem space isn't necessarily set up that way. Can I
>> chop strptime parsing into multiple strptime calls that _only_ modify
>> certain fields each time while leaving the others alone? I was reading
>> the posix page and man page stuff about that at one point, something
>> said it only modified specific fields other than the ones you
>> specified... but alas, I got distracted halfway through...)
>
>
> one of the things i liked in Plan 9:
> http://man.cat-v.org/plan_9/2/fmtinstall
>
>>
>> Checking my notes, I was attempting to add %s support to the input path.
>> Except that %s pretty much _replaces_ strptime() because none of the
>> other fields you set make sense in combination with that. (But %s could
>> be in the middle of a context string describing the rest of the input;
>> that I didn't make up, it's in the ubuntu one.) So %s is probably
>> fiddlier than %N. Hmmm...
>>
>> In general I wince at merging half a solution to a larger problem,
>> because it increases the surface area of the problem. (People start
>> using the partial thing, then I break them when I try to fix the rest of
>> it...) That said, if I'm not doing the full fix now and the partial fix
>> is there and we need it... Sigh.
>
>
> plus no-one else supports round trips as far as i can tell, so demand hasn't
> been that great.
>
>>
>> >     Speaking of which, this patch adds %N to output but not to input, so
>> >     date can still only _set_ nanoseconds using the @123456789.123456789
>> >     syntax.
>> >
>> > isn't setting via arbitrary format a toybox extension?
>>
>> Walter Harms added it to busybox in 2006 (back when I maintained it):
>>
>>   http://lists.busybox.net/pipermail/busybox/2006-February/018203.html
>>   https://git.busybox.net/busybox/commit/?id=c5789a6e234c
>>
>> I genericized his original idea a bit because "I want to convert data
>> from one format to another" is awkward to solve otherwise. "This email's
>> datestamp would be what in unix time"... I used to write little C
>> programs to do that.
>>
>> I used to have a button that said "Only XT users know that January 1,
>> 1980 was a tuesday". Toybox says:
>>
>>   $ ./date -D "%m %d %Y" -d "1 1 1980" +%A
>>   Tuesday
>
>
> (given that this question comes up in real life more than "show me the whole
> calendar for 1856" or "show me the calendar for October 1856", i never
> understood why cal will show you a whole year or a whole month but not a
> single day.)
>
>>
>> If you can say %N in + but not in -D I'm doing it wrong. It's a tiny
>> thing, but it bothers me.
>>
>> >     And you're not checking that "%%N is a literal %N". (Sigh. If
>> >     we're going there, may I draw your attention to next_printf() in
>> >     lib/lib.c? Example usage in seq and stat.)
>> >
>> > okay, i'll switch it over (assuming we actually want %N).
>>
>> Eh, we probably want it, I just winced at how expensive it was to
>> implement and it's the wrong place to do it (belongs in libc) and if
>> we're going there I want to do the full fix (get and set, and handling
>> %% and %4N) so it isn't inconsistent...
>>
>> And it needs one of them Focused Review things that have been in short
>> supply recently. (The easter weekend's helped me to dig out a bit. If I
>> got a three day weekend every week, keeping up would be so much easier. :)
>
>
> no extra day off here :-( at the other end of the spectrum, the London
> office have a four-day weekend...
>
>>
>>
>> >     It's kind of sad "ls" can't show nanoseconds. Or "stat". I
>> > understand
>> >     why (nanoseconds were added when makefile dependencies started
>> > breaking
>> >     as computers got faster and multiple build things happened in the
>> > same
>> >     second; nothing else actually _needed_ them in the filesystem) but
>> > it's
>> >     still half-assed.
>> >
>> > ~$ ls -ld --time-style=full-iso /
>>
>> --time-style is a can of worms (I made a design decision _not_ to
>> support more than one output format, now there's a straightforward
>> extension of the existing output format we want to add, but if I use the
>> generic named selection mechanism for it the pressure to support all the
>> rest of 'em will never stop. I lose the ability to draw a clear boundary
>> line.)
>>
>> But --full-time is a synonym, which I can add _and_ make -ll do it too.
>> (Repeat -l and it shows nanoseconds. I like having short options for
>> things, but the letters are all taken here. Still, logically it's a
>> "long long"... :)
>>
>> My concern here is maximizing the surface area of "I can write a script
>> that runs under toybox and under ubuntu as well." Such as the current
>> test suite stuff we're trying to do. I can write one using --full-time
>> it works in both contexts.
>>
>> The problem with using ls for the touch test code is "ls -l" shows
>> ownership information also, varying between systems. You can't output
>> _just_ the info you want without that. We can do the awk/cut trick to
>> filter it and only look at specific fields (todo: can we have spaces or
>> tabs in usernames? You can in the realname field...).
>>
>> tl;dr there's still a call for "date %N".
>>
>> > i'm happy to rewrite the tests instead... i've never used %N personally,
>> > and would just naturally use stat for this kind of thing.
>>
>> How do you get nanoseconds out of stat? (I'm happy to add a toybox
>> extension for it, but relying on that breaks TEST_HOST or "make
>> test_sed" on a non-toybox host.)
>
>
> well, the _text_ form includes nanoseconds. but i guess you meant the
> numeric-only form, in which case, no, i'm not aware of a way to do that.
>
>>
>> > as you say, the asymmetry is ugly, and the divergence from libc is ugly,
>> > so if busybox added this "just because" maybe we shouldn't have it at
>> > all?
>>
>> It was useful, and still is. (Especially the ability to specify
>> different input and output formats so you can convert between them.) And
>> it's already implemented and working. :)
>>
>> Rob
>
>
>
>
> --
> Elliott Hughes - http://who/enh - http://jessies.org/~enh/
> Android native code/tools questions? Mail me/drop by/add me as a reviewer.



-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
Android native code/tools questions? Mail me/drop by/add me as a reviewer.