Re: Further wide stdio issues [Was: Re: [PATCH] fix fgetwc when decoding a character that crosses buffer boundary]

[Rich Felker <dalias@libc.org>]

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On Sun, Nov 19, 2017 at 08:48:53PM -0500, Rich Felker wrote:
> On Sat, Nov 18, 2017 at 05:51:48PM +0100, Szabolcs Nagy wrote:
> > Update the buffer position according to the bytes consumed into st when
> > decoding an incomplete character at the end of the buffer.
> 
> Further related problems:
> 
> 1. fgetws is unable to accurately determine whether fgetwc failed due
>    to hitting EOF on a clean stream vs hitting EOF in the middle of a
>    truncated character. The latter is an EILSEQ condition and should
>    cause fgetws to return a null pointer rather than a line not ending
>    in newline.
> 
> 2. fgetwc attempts to leave all but the first byte unread on EILSEQ so
>    that calling fgetwc again will resync, but doesn't do this
>    consistently when it has to call getc_unlocked to get new bytes
>    rather than reading from the buffer.
> 
> I think (1) can be fixed in an ugly way by setting errno to something
> other than EILSEQ before calling fgetwc, then checking if EILSEQ upon
> failure.

Patching this; here's a test case (attached).

Rich

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#include <stdio.h>
#include <poll.h>
#include <locale.h>
#include <wchar.h>
#include <unistd.h>

int main()
{
	setlocale(LC_CTYPE, "");
	int p[2];
	pipe(p);
	write(p[1], "x\340\240xxx", 3);
	close(p[1]);
	dup2(p[0], 0);
	wchar_t buf[100] = {0};
	wchar_t *ws = fgetws(buf, 100, stdin);
	printf("%p [%ls]\n", ws, buf);
}