Re: [Patch] Fix newlib/libc/stdio/fgetws.c issue

[Corinna Vinschen <vinschen at redhat dot com>]

On May 30 13:22, Yvan ROUX wrote:
> Hi,
> 
> The actual behaviour of the fgetws function doesn't match with its specs as it
> doesn't read *at most* n-1 wide characters until a newline, but *every* wide
> character until a newline or in buffers if no newline are found. This patch 
> fixes this issue.

Thanks for the patch, but I think the bug in fgetws is a bit more
convoluted.  The expressions:

  nl = memchr (fp->_p, '\n', fp->_r);

and

  nl != NULL ? (nl - fp->_p + 1) : fp->_r

determine the number of bytes to read from the input stream, but `n'
determines the number of maximum wide chars to produce.  So using
the result of the `nl' expressions to compute the number of wide chars
is plain wrong.

So, what about this instead?  It uses the `nl' expressions to compute
the maximum number of input bytes and n to determine the maximum number
of wide chars in a call to mbsnrtowcs:

Index: libc/stdio/fgetws.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio/fgetws.c,v
retrieving revision 1.5
diff -u -p -r1.5 fgetws.c
--- libc/stdio/fgetws.c	30 May 2012 08:58:42 -0000	1.5
+++ libc/stdio/fgetws.c	30 May 2012 12:33:08 -0000
@@ -110,9 +110,13 @@ _DEFUN(_fgetws_r, (ptr, ws, n, fp),
     {
       src = (char *) fp->_p;
       nl = memchr (fp->_p, '\n', fp->_r);
-      nconv = _mbsrtowcs_r (ptr, wsp, &src,
-			    nl != NULL ? (nl - fp->_p + 1) : fp->_r,
-			    &fp->_mbstate);
+      nconv = _mbsnrtowcs_r (ptr, wsp, &src,
+			     /* Read all bytes up to the next NL, or up to the
+				end of the buffer if there is no NL. */
+			     nl != NULL ? (nl - fp->_p + 1) : fp->_r,
+			     /* But never more than n - 1 wide chars. */
+			     n - 1,
+			     &fp->_mbstate);
       if (nconv == (size_t) -1)
 	/* Conversion error */
 	goto error;


Corinna

-- 
Corinna Vinschen
Cygwin Project Co-Leader
Red Hat