[Rd] Another issue with Sys.timezone
Stephen Berman
stephen.berman at gmx.net
Thu Oct 19 17:12:50 CEST 2017
On Wed, 18 Oct 2017 18:09:41 +0200 Martin Maechler <maechler at stat.math.ethz.ch> wrote:
>>>>>> Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>> on Mon, 16 Oct 2017 19:13:31 +0200 writes:
(I also included a reply to part of this response of yours below.)
>>>>>> Stephen Berman <stephen.berman at gmx.net>
>>>>>> on Sun, 15 Oct 2017 01:53:12 +0200 writes:
>
>> > (I reported the test failure mentioned below to R-help but was advised
>> > that this list is the right one to address the issue; in the meantime I
>> > investigated the matter somewhat more closely, including searching
>> > recent R-devel postings, since I haven't been following this list.)
>>
>> > Last May there were two reports here of problems with Sys.timezone, one
>> > where the zoneinfo directory is in a nonstandard location
>> > (https://stat.ethz.ch/pipermail/r-devel/2017-May/074267.html) and the
>> > other where the system lacks the file /etc/localtime
>> > (https://stat.ethz.ch/pipermail/r-devel/2017-May/074275.html). My
>> > system exhibits a third case: it lacks /etc/timezone and does not set TZ
>> > systemwide, but it does have /etc/localtime, which is a copy of, rather
>> > than a symlink to, a file under zoneinfo. On this system Sys.timezone()
>> > returns NA and the Sys.timezone test in reg-tests-1d fails. However, on
>> > my system I can get the (abbreviated) timezone in R by using as.POSIXlt,
>> > e.g. as.POSIXlt(Sys.time())$zone. If Sys.timezone took advantage of
>> > this, e.g. as below, it would be useful on such systems as mine and the
>> > regression test would pass.
>>
>> > my.Sys.timezone <-
>> > function (location = TRUE)
>> > {
>> > tz <- Sys.getenv("TZ", names = FALSE)
>> > if (!location || nzchar(tz))
>> > return(Sys.getenv("TZ", unset = NA_character_))
>> > lt <- normalizePath("/etc/localtime")
>> > if (grepl(pat <- "^/usr/share/zoneinfo/", lt) ||
>> > grepl(pat <- "^/usr/share/zoneinfo.default/", lt))
>> > sub(pat, "", lt)
>> > else if (lt == "/etc/localtime")
>> > if (!file.exists("/etc/timezone"))
>> > return(as.POSIXlt(Sys.time())$zone)
>> > else if (dir.exists("/usr/share/zoneinfo") && {
>> > info <- file.info(normalizePath("/etc/timezone"), extra_cols = FALSE)
>> > (!info$isdir && info$size <= 200L)
>> > } && {
>> > tz1 <- tryCatch(readBin("/etc/timezone", "raw", 200L),
>> > error = function(e) raw(0L))
>> > length(tz1) > 0L && all(tz1 %in% as.raw(c(9:10, 13L, 32:126)))
>> > } && {
>> > tz2 <- gsub("^[[:space:]]+|[[:space:]]+$", "", rawToChar(tz1))
>> > tzp <- file.path("/usr/share/zoneinfo", tz2)
>> > file.exists(tzp) && !dir.exists(tzp) &&
>> > identical(file.size(normalizePath(tzp)), file.size(lt))
>> > })
>> > tz2
>> > else NA_character_
>> > }
>>
>> > One problem with this is that the zone component of as.POSIXlt only
>> > holds the abbreviated timezone, not the Olson name.
>>
>> Yes, indeed. So, really only for Sys.timezone(location = FALSE) this
>> should be given, for the default location = TRUE it should
>> still give NA (i.e. NA_character_) in your setup.
>>
>> Interestingly, the Windows versions of Sys.timezone(location =
>> FALSE) uses something like your proposal, and I tend to think that
>> -- again only for location=FALSE -- this should be used on
>> on-Windows as well, at least instead of returning NA then.
>>
>> Also for me on 3 different Linuxen (Fedora 24, F. 26, and ubuntu
>> 14.04 LTS), I get
>>
>> > Sys.timezone()
>> [1] "Europe/Zurich"
>> > Sys.timezone(FALSE)
>> [1] NA
>> >
>>
>> whereas on Windows I get Europe/Berlin for the first (why on
>> earth - I'm really in Zurich) and get "CEST" ("Central European Summer Time")
>> for the 2nd one instead of NA ... simply using a smarter version
>> of your proposal. The windows source is
>> in R's source at src/library/base/R/windows/system.R :
>>
>> Sys.timezone <- function(location = TRUE)
>> {
>> tz <- Sys.getenv("TZ", names = FALSE)
>> if(nzchar(tz)) return(tz)
>> if(location) return(.Internal(tzone_name()))
>> z <- as.POSIXlt(Sys.time())
>> zz <- attr(z, "tzone")
>> if(length(zz) == 3L) zz[2L + z$isdst] else zz[1L]
>> }
>>
>> >From what I read, the last three lines also work in your setup
>> where it seems zz would be of length 1, right ?
Those line do indeed work here, but zz has three elements:
> attributes(as.POSIXlt(Sys.time()))$tzone
[1] "" "CET" "CEST"
>> I'd really propose to use these 3 lines in the non-Windows
>> version of Sys.timezone .. at the end *instead* of NA_character_
>> (or a slightly safer version which gives NA_character_ if zz is
>> of length 0 {e.g. if there is no "tzone" attribute}.
>>
>> > i don't know how to
>> > get the Olson name using only R functions, but maybe it would be good
>> > enough to return the abbreviated timezone where possible, e.g. as above.
>> > (On my system I can get the Olson name of the timezone in R with a shell
>> > pipeline, e.g.: system("find /usr/share/zoneinfo/ -type f | xargs md5sum
>> > | grep $(md5sum /etc/localtime | cut -d ' ' -f 1) | head -n 1 | cut -d
>> > '/' -f 5,6"), but the last part of this is tailored to my configuration
>> > and the whole thing is not OS-neutral, so it isn't suitable for
>> > Sys.timezone.)
>>
>> > Steve Berman
>>
>> Definitely not. I still recommend you think of a more portable
>> solution for the `location = TRUE` (default) case in Sys.timezone().
>> Returning the non-location form (e.g "CEST") when something like
>> "Europe/Zurich" is expected is really not a good idea,
>> and you are lucky that the regression test passes "accidentally" ...
>>
>> Martin
>
> In the mean time, I have committed a common version (Windows and
> non-Windows) of Sys.timezone() to the R development sources
> (aka "R-devel").
>
> That now uses as.POSIXlt(Sys.time()) very similarly to the
> above "Windows only" case, but __only__ for 'location=FALSE'
> which is not the default.
Thanks, I think that's definitely better than returning NA when
`location' is false...
> The most current development source is always available (via
> 'svn' or alternatively for browsing via your web browser) from
>
> https://svn.r-project.org/R/trunk/src/library/base/R/datetime.R
...however, I tried the test that failed for me during `make check' now
with this new definition of Sys.timezone() by pasting the definition (as
new.Sys.timezone()) and the two lines of the test code into the R console,
and this is what happened:
> new.Sys.timezone()
> new.Sys.timezone(FALSE)
[1] "CEST"
> (S.t <- new.Sys.timezone())
NULL
> if(is.na(S.t) || !nzchar(S.t)) stop("could not get timezone")
Error in if (is.na(S.t) || !nzchar(S.t)) stop("could not get timezone") :
missing value where TRUE/FALSE needed
In addition: Warning message:
In is.na(S.t) : is.na() applied to non-(list or vector) of type 'NULL'
This is because `location' is true but all the if-clauses in the body
following `if(location)' are false, so it returns NULL. If you add the
line `else NA_character_' below the line `tz2', then NA is returned and
the test fails as before instead of as above.
> As you say yourself, the above system("... xargs md5sum ...")
> using workaround is really too platform specific but I'd guess
> there should be a less error prone way to get the long timezone
> name on your system ...
If I understand the zic(8) man page, the files in /usr/share/zoneinfo
should contain this information, but I don't know how to extract it,
since these are compiled files. And since on my system /etc/localtime
is a copy of one of these compiled files, I don't know of any other way
to recover the location name without comparing it to those files.
> If that remains "contained" (i.e. small) and works with files
> and R's files tools -- e.g. file.*() ones [but not system()],
> I'd consider a patch to the above source file
> (sent by you to the R-devel mailing list --- or after having
> gotten an account there by asking, via bug report & patch
> attachment at https://bugs.r-project.org/ )
If comparing file size sufficed, that would be easy to do in R;
unfortunately, it is not sufficient, since some files designating
different time zones in /usr/share/zoneinfo do have the same size. So
the only alternative I can think of is to compare bytes, e.g. with
md5sum or with cmp. Is there some way to do this in R without using
system()?
Steve Berman
More information about the R-devel
mailing list