Bug in reading UTF-16LE file?

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.

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 see no Mac-specific code for this, only win_iconv.c, so presumably we have potential issues on everything non-Windows?

-pd

On 9 Sep 2024, at 01:11 , Simon Urbanek <simon.urbanek at 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.duncan at 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