Re: [Rd] iconv to UTF-16 encoding produces error due to embedded nulls (write.table with fileEncoding param)

[Duncan Murdoch]

On 24/02/2016 11:16 AM, Duncan Murdoch wrote:
On 24/02/2016 9:55 AM, Mikko Korpela wrote:
On 24.02.2016 15:47, Duncan Murdoch wrote:
On 23/02/2016 7:06 AM, Mikko Korpela wrote:
On 23.02.2016 11:37, Martin Maechler wrote:
nospam@altfeld-im de <nos...@altfeld-im.de>
       on Mon, 22 Feb 2016 18:45:59 +0100 writes:

       > Dear R developers
       > I think I have found a bug that can be reproduced with two
lines of code
       > and I am very thankful to get your first assessment or
feed-back on my
       > report.

       > If this is the wrong mailing list or I did something wrong
       > (e. g. semi "anonymous" email address to protect my privacy
and defend
       > unwanted spam) please let me know since I am new here.

       > Thank you very much :-)

       > J. Altfeld

Dear J.,
(yes, a bit less anonymity would be very welcomed here!),

You are right, this is a bug, at least in the documentation, but
probably "all real", indeed,

but read on.

       > On Tue, 2016-02-16 at 18:25 +0100, nos...@altfeld-im.de wrote:
       >>
       >>
       >> If I execute the code from the "?write.table" examples section
       >>
       >> x <- data.frame(a = I("a \" quote"), b = pi)
       >> # (ommited code)
       >> write.csv(x, file = "foo.csv", fileEncoding = "UTF-16LE")
       >>
       >> the resulting CSV file has a size of 6 bytes which is too short
       >> (truncated):
       >>
       >> """,3

reproducibly, yes.
If you look at what write.csv does
and then simplify, you can get a similar wrong result by

     write.table(x, file = "foo.tab", fileEncoding = "UTF-16LE")

which results in a file with one line

""" 3

and if you debug  write.table() you see that its building blocks
here are
       file <- file(........, encoding = fileEncoding)

a      writeLines(*, file=file)  for the column headers,

and then "deeper down" C code which I did not investigate.

I took a look at connections.c. There is a call to strlen() that gets
confused by null characters. I think the obvious fix is to avoid the
call to strlen() as the size is already known:

Index: src/main/connections.c
===================================================================
--- src/main/connections.c    (revision 70213)
+++ src/main/connections.c    (working copy)
@@ -369,7 +369,7 @@
            /* is this safe? */
            warning(_("invalid char string in output conversion"));
            *ob = '\0';
-        con->write(outbuf, 1, strlen(outbuf), con);
+        con->write(outbuf, 1, ob - outbuf, con);
        } while(again && inb > 0);  /* it seems some iconv signal -1 on
                           zero-length input */
        } else



But just looking a bit at such a file() object with writeLines()
seems slightly revealing, as e.g., 'eol' does not seem to
"work" for this encoding:

       > fn <- tempfile("ffoo"); ff <- file(fn, open="w", encoding =
"UTF-16LE")
       > writeLines(LETTERS[3:1], ff); writeLines("|", ff);
writeLines(">a", ff)
       > close(ff)
       > file.show(fn)
       CBA|>
       > file.size(fn)
       [1] 5
       >

With the patch applied:

       > readLines(fn, encoding="UTF-16LE", skipNul=TRUE)
       [1] "C"  "B"  "A"  "|"  ">a"
       > file.size(fn)
       [1] 22

That may be okay on Unix, but it's not enough on Windows.  There the \n
that writeLines adds at the end of each line isn't translated to
UTF-16LE properly, so things get messed up.  (I think the \n is
translated, but the \r that Windows wants is not, so you get a mix of 8
bit and 16 bit characters.)

That's unfortunate. I tested my tiny patch on Linux. I don't know what
kind of additional changes would be needed to make this work on Windows.


It looks like a big change is needed for a perfect solution:

   - Windows does the translation of \n to \r\n.  In the R code, Windows
is never told that the output is UTF-16LE, so it does an 8 bit translation.

   - Telling Windows that output is UTF-16LE looks hard:  we'd need to
convert the string to wide chars in R, then write it in wide chars.
This seems like a lot of work for a rare case.

   - It might be easier to do a hack:  if the user asks for "UTF-16LE",
then treat it internally as a text file but tell Windows it's a binary
file.  This means no \n to \r\n translation will be done by Windows.  If
the desired output file needs Windows line endings, the user would have
to specify sep="\r\n" in writeLines.

A third possibility is to handle the insertion of the \r completely 
within R.  This will have the advantage of making it optional, so it 
would be a lot easier to write a Unix-style file on Windows.

I think either the first or third possibilities will take too much time 
for me to attempt them before 3.3.0.  I'm not sure about the second one yet.

Duncan Murdoch

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