[musl] [PATCH] fgetws: fix checking for fgetwc errors

[musl] [PATCH] fgetws: fix checking for fgetwc errors

[Pinghao Wu]

This corrects checking for fgetwc errors by arming dummy errno before
each invocation, and checking errors only if it returns WEOF.
---
 src/stdio/fgetws.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/stdio/fgetws.c b/src/stdio/fgetws.c
index b08b3049..edcd769b 100644
--- a/src/stdio/fgetws.c
+++ b/src/stdio/fgetws.c
@@ -12,18 +12,19 @@ wchar_t *fgetws(wchar_t *restrict s, int n, FILE *restrict f)
 
 	FLOCK(f);
 
-	/* Setup a dummy errno so we can detect EILSEQ. This is
-	 * the only way to catch encoding errors in the form of a
-	 * partial character just before EOF. */
-	errno = EAGAIN;
+	wint_t c;
 	for (; n; n--) {
-		wint_t c = __fgetwc_unlocked(f);
+		/* Setup a dummy errno so we can detect EILSEQ. This is
+		 * the only way to catch encoding errors in the form of a
+		 * partial character just before EOF. */
+		errno = EAGAIN;
+		c = __fgetwc_unlocked(f);
 		if (c == WEOF) break;
 		*p++ = c;
 		if (c == '\n') break;
 	}
 	*p = 0;
-	if (ferror(f) || errno==EILSEQ) p = s;
+	if (c == WEOF && (ferror(f) || errno==EILSEQ)) p = s;
 
 	FUNLOCK(f);
 
-- 
2.35.1

Re: [musl] [PATCH] fgetws: fix checking for fgetwc errors

[Rich Felker]

On Thu, Feb 10, 2022 at 02:47:36AM +0800, Pinghao Wu wrote:
> This corrects checking for fgetwc errors by arming dummy errno before
> each invocation, and checking errors only if it returns WEOF.
> ---
>  src/stdio/fgetws.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/src/stdio/fgetws.c b/src/stdio/fgetws.c
> index b08b3049..edcd769b 100644
> --- a/src/stdio/fgetws.c
> +++ b/src/stdio/fgetws.c
> @@ -12,18 +12,19 @@ wchar_t *fgetws(wchar_t *restrict s, int n, FILE *restrict f)
>  
>  	FLOCK(f);
>  
> -	/* Setup a dummy errno so we can detect EILSEQ. This is
> -	 * the only way to catch encoding errors in the form of a
> -	 * partial character just before EOF. */
> -	errno = EAGAIN;
> +	wint_t c;
>  	for (; n; n--) {
> -		wint_t c = __fgetwc_unlocked(f);
> +		/* Setup a dummy errno so we can detect EILSEQ. This is
> +		 * the only way to catch encoding errors in the form of a
> +		 * partial character just before EOF. */
> +		errno = EAGAIN;
> +		c = __fgetwc_unlocked(f);
>  		if (c == WEOF) break;
>  		*p++ = c;
>  		if (c == '\n') break;
>  	}
>  	*p = 0;
> -	if (ferror(f) || errno==EILSEQ) p = s;
> +	if (c == WEOF && (ferror(f) || errno==EILSEQ)) p = s;
>  
>  	FUNLOCK(f);
>  
> -- 
> 2.35.1

Thanks. I didn't get from your previous patch for fgetwc that there
was a problem in fgetws that you were trying to fix. Now it makes a
lot more sense.

I think the above has at least one bug though: errno and c will both
be uninitialized if n was zero going into the loop (possible if the
initial value of n at function entry was 1). The error handling logic
should probably just be moved inside the loop instead of breaking out
to do it.

Rich