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

[Mikko Korpela]

On 23.02.2016 11:37, Martin Maechler wrote:
>>>>>> nospam at altfeld-im de <nospam at 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, nospam at 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

- Mikko Korpela

>     >> The problem seems to be the iconv function:
>     >> 
>     >> iconv("foo", to="UTF-16")
>     >> 
>     >> produces
>     >> 
>     >> Error in iconv("foo", to = "UTF-16"):
>     >> embedded nul in string: '\xff\xfef\0o\0o\0'
> 
> but this works
> 
>     > iconv("foo", to="UTF-16", toRaw=TRUE)
>     [[1]]
>     [1] ff fe 66 00 6f 00 6f 00
> 
> (indeed showing the embedded '\0's)
> 
>     >> In 2010 a (partial) patch for this problem was submitted:
>     >> http://tolstoy.newcastle.edu.au/R/e10/devel/10/06/0648.html
> 
> the patch only related to the iconv() problem not allowing 'raw'
> (instead of character) argument x.
> 
> ... and it is > 5.5 years old, for an iconv() version that was less
> featureful than today.
> Rather, current iconv(x) allows x to be a list of raw entries.
> 
> 
>     >> Are there chances to fix this problem since it prevents writing Windows
>     >> UTF-16LE text files?
> 
>     >> 
>     >> PS: This problem can be reproduced on Windows and Linux.
> 
> indeed.... also on "R devel of today".
> 
> I agree it should be fixed... but as I said not by the patch you
> mentioned.
> 
> Tested patches to fix this are welcome, indeed.