On 10/1/24 15:31, Jeff Newmiller wrote:
This is a problem in macOS libiconv. When converting from "UTF-16" with a BOM,
it correctly learns the byte-order from the BOM, but later forgets it in some cases.
This is not a problem in R, but could be worked-around in R.
So, buggy system code on one system...
As Simon wrote, to avoid running into these problems (in released versions of R), one
should use "UTF-16LE", so explicitly specify the byte-order in the encoding
name.
... leads to institutionalized non-complince.
This is useful also because it is not clear what should be the default when no
BOM is present and different systems have different defaults.
This is nonsense, for reasons previously provided. You are calling a bug a
feature. The BOM is supposed to prevent you from having to know this detail,
and what you do when no BOM is present should have no bearing on this case.
I will try to explain this differently. The handling of BOMs in existing
iconv implementations is unreliable (one issue is documented in R
documentation, one issue is the one we have ran into now). Because it is
unreliable, people who want to be defensive and avoid problems are
advised to use *LE (or *BE) specifications. What is the default
byte-order when no BOM is specified is not reliable, either (defaults
differ between systems and the standard is open to interpretation - e.g.
my Linux and Windows builds of R default to little-endian, while my
macOS build defaults to big-endian). It is thus not advisable to depend
on the default order, either, and a defensive solution is again to use
*LE or *BE specifications. So, in principle, simply always use *LE or *BE.
This advice is not a feature, it is a work-around that works for two
problems: that the byte order for specifications like "UTF-16" is
unknown (bug in the standard) and that specifying the byte-order by a
BOM is unreliable (bugs in implementations of iconv).
If Apple is intransigent (which would not be out of character) you could avoid
institutionalized non-compliance at the user level by recognizing the buggy
system and replacing the generic specification with this inappropriate LE or BE
specification as directed by the BOM in the Mac-specific R code.
Yes, indeed, the work-around for the libiconv bug can be implemented in
future versions of R and an experimental version is already in R-devel
(still subject to change), so that at user level, specifying say
"UTF-16" on an input with BOM will correctly use the byte-order of the BOM.
I don't find anything inappropriate about the *LE/*BE specifications.
Best
Tomas
On October 1, 2024 4:34:41 AM MST, Tomas Kalibera <tomas.kalib...@gmail.com>
wrote:
On 9/9/24 12:53, Tomas Kalibera wrote:
On 9/9/24 10:53, peter dalgaard wrote:
I am confused, and maybe I should just butt out of this, but:
(a) BOM are designed to, um, mark the byte order...
(b) in connections.c we have
if(checkBOM && con->inavail >= 2 &&
((int)con->iconvbuff[0] & 0xff) == 255 &&
((int)con->iconvbuff[1] & 0xff) == 254) {
con->inavail -= (short) 2;
memmove(con->iconvbuff, con->iconvbuff+2, con->inavail);
}
which checks for the two first bytes being FF, FE. However, a big-endian BOM
would be FE, FF and I see no check for that.
I think this is correct, it is executed only for encodings declared
little-endian (UTF-16LE, UCS2-LE) - so, iconv will still know what is the
byte-order from the name of the encoding, it will just not see the same
information in the BOM.
Duncan's file starts
readBin('https://online.stat.psu.edu/onlinecourses/sites/stat501/files/ch15/employee.txt',
what="raw", n=10)
[1] ff fe 74 00 69 00 6d 00 65 00
so the BOM does indeed indicate little-endian, but apparently we proceed to
discard it and read the file with system (big-)endianness, which strikes me as
just plain wrong...
I've tested we are not discarding it by the code above and that iconv gets to
see the BOM bytes.
I see no Mac-specific code for this, only win_iconv.c, so presumably we have
potential issues on everything non-Windows?
I can reproduce the problem and will have a closer look, it may still be there
is a bug in R. We have some work-arounds for recent iconv issues on macOS in
sysutils.c.
This is a problem in macOS libiconv. When converting from "UTF-16" with a BOM,
it correctly learns the byte-order from the BOM, but later forgets it in some cases.
This is not a problem in R, but could be worked-around in R.
As Simon wrote, to avoid running into these problems (in released versions of R), one
should use "UTF-16LE", so explicitly specify the byte-order in the encoding
name. This is useful also because it is not clear what should be the default when no BOM
is present and different systems have different defaults.
Best
Tomas
Tomas
-pd
On 9 Sep 2024, at 01:11 , Simon Urbanek <simon.urba...@r-project.org> wrote:
From the help page:
The encodings ‘"UCS-2LE"’ and ‘"UTF-16LE"’ are treated specially,
as they are appropriate values for Windows ‘Unicode’ text files.
If the first two bytes are the Byte Order Mark ‘0xFEFF’ then these
are removed as some implementations of ‘iconv’ do not accept BOMs.
so "UTF-16LE" is the documented way to reliably read such files.
Cheers,
Simon
On 8 Sep 2024, at 21:23, Duncan Murdoch <murdoch.dun...@gmail.com> wrote:
To R-SIG-Mac, with a copy to Jeff Newmiller:
On R-help there's a thread about reading a remote file that is coded in UTF-16LE with a
byte-order mark. Jeff Newmiller pointed out
(https://stat.ethz.ch/pipermail/r-help/2024-September/479933.html) that it would be
better to declare the encoding as "UTF-16", because the BOM will indicate
little endian.
I tried this on my Mac running R 4.4.1, and it didn't work. I get the same
incorrect result from all of these commands:
# Automatically recognizing a URL and using fileEncoding:
read.delim(
'https://online.stat.psu.edu/onlinecourses/sites/stat501/files/ch15/employee.txt',
fileEncoding = "UTF-16"
)
# Using explicit url() with encoding:
read.delim(
url('https://online.stat.psu.edu/onlinecourses/sites/stat501/files/ch15/employee.txt',
encoding = "UTF-16")
)
# Specifying the endianness incorrectly:
read.delim(
url('https://online.stat.psu.edu/onlinecourses/sites/stat501/files/ch15/employee.txt',
encoding = "UTF-16BE")
)
The only way I get the correct result is if I specify "UTF-16LE" explicitly, whereas Jeff
got correct results on several different systems using "UTF-16".
Is this a MacOS bug or an R for MacOS bug?
Duncan Murdoch
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