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

[Duncan Murdoch]

On 23/02/2016 7:06 AM, Mikko Korpela wrote:
> 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

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.)

Duncan Murdoch

> - 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.
>
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