patch, 2 partsfsck_commit_buffer(): do not special case the last validation

> Even though a Git commit object is designed to be capable of storing
> any binary data as its payload, in practice people use it to describe
> the changes in textual form, and tools like "git log" are designed to
> treat the payload as text.
> 
> Detect and warn when we see any commit object with a NUL byte in
> it.
> 
> Note that a NUL byte in the header part is already detected as a
> grave error.  This change is purely about the message part.
> 
> Signed-off-by: Junio C Hamano <gitster@pobox.com>

> @@ -610,6 +611,7 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
>  	struct commit_graft *graft;
>  	unsigned parent_count, parent_line_count = 0, author_count;
>  	int err;
> +	const char *buffer_begin = buffer;
>  
>  	if (verify_headers(buffer, size, &commit->object, options))
>  		return -1;

> @@ -671,6 +673,12 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
>  		if (err)
>  			return err;
>  	}
> +	if (memchr(buffer_begin, '\0', size)) {
> +		err = report(options, &commit->object, FSCK_MSG_NUL_IN_COMMIT,
> +			     "NUL byte in the commit object body");
> +		if (err)
> +			return err;
> +	}

>> +	const char *buffer_begin = buffer;
>>  
>>  	if (verify_headers(buffer, size, &commit->object, options))
>>  		return -1;
>
> You need this "buffer_begin" because we move the "buffer" pointer
> forward as we parse. But perhaps whole-buffer checks should simply go at
> the top (next to verify_headers) before we start advancing the pointer.
> To me, that makes the function's flow more natural.

> But alternatively...
>
>> @@ -671,6 +673,12 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
>>  		if (err)
>>  			return err;
>>  	}
>> +	if (memchr(buffer_begin, '\0', size)) {
>> +		err = report(options, &commit->object, FSCK_MSG_NUL_IN_COMMIT,
>> +			     "NUL byte in the commit object body");
>> +		if (err)
>> +			return err;
>> +	}
>
> Here we've parsed to the end of the headers we know about. We know
> there's no NUL there, because verify_headers() would have complained.
> And because the individual header parsers would have complained. So I
> actually think we could check from "buffer" (of course we do still need
> to record the beginning of the buffer to adjust "size" appropriately).

> It's a little more efficient (we don't have to memchr over the same
> bytes again). But I'd worry a little that doing it that way would
> introduce coupling between this check and verify_headers(), though (so
> that if the latter ever changes, our check may start missing cases).
>
> So yet another alternative would be to include this check in
> verify_headers(). It would parse to the end of the headers as now, and
> then from there additionally look for a NUL in the body.
>
> Of the three approaches, I think I like that third one. It's the most
> efficient, and I think the flow is pretty clear. We'd probably want to
> rename verify_headers(), though. :)

> > You need this "buffer_begin" because we move the "buffer" pointer
> > forward as we parse. But perhaps whole-buffer checks should simply go at
> > the top (next to verify_headers) before we start advancing the pointer.
> > To me, that makes the function's flow more natural.
> 
> That was my second iteration.  I didn't want the function return
> with warning without checking more serious errors that may be in the
> object.

> On Thu, Apr 14, 2016 at 02:21:03PM -0400, Jeff King wrote:
>
>> So yet another alternative would be to include this check in
>> verify_headers(). It would parse to the end of the headers as now, and
>> then from there additionally look for a NUL in the body.
>
> Hmm. Looking at verify_headers(), I think it has another bug.
>
> It wants to "return report(...)" as soon as it sees a problem, and stops
> looking for other ones. But the new model for reporting errors is that
> report() might ignore a problem if configured to do so.

> Even though a Git commit object is designed to be capable of storing
> any binary data as its payload, in practice people use it to describe
> the changes in textual form, and tools like "git log" are designed to
> treat the payload as text.
> 
> Detect and warn when we see any commit object with a NUL byte in
> it.
> 
> Note that a NUL byte in the header part is already detected as a
> grave error.  This change is purely about the message part.

> The pattern taken by all the validations in this function is:
> 
> 	if (notice a violation exists) {
> 		err = report(... VIOLATION_KIND ...);
> 		if (err)
> 			return err;
> 	}
> 
> where report() returns zero if specified kind of violation is set to
> be ignored, and otherwise shows an error message and returns non-zero.
> 
> The last validation in the function immediately after the function
> returns 0 to declare "all good" can cheat and directly return the
> return value from report(), and the current code does so, i.e.
> 
> 	if (notice a violation exists)
> 		return report(... VIOLATION_KIND ...);
> 	return 0;
> 
> But that is a selfish code that declares it is the ultimate and
> final form of the function, never to be enhanced later.  To allow
> and invite future enhancements, make the last test follow the same
> pattern.
> 
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  fsck.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

> On Thu, Apr 14, 2016 at 11:07:08AM -0700, Junio C Hamano wrote:
>
>> The pattern taken by all the validations in this function is:
>> 
>> 	if (notice a violation exists) {
>> 		err = report(... VIOLATION_KIND ...);
>> 		if (err)
>> 			return err;
>> 	}
>> 
>> where report() returns zero if specified kind of violation is set to
>> be ignored, and otherwise shows an error message and returns non-zero.
>> 
>> The last validation in the function immediately after the function

>> returns 0 to declare "all good" can cheat and directly return the
>> return value from report(), and the current code does so, i.e.
>> 
>> 	if (notice a violation exists)
>> 		return report(... VIOLATION_KIND ...);
>> 	return 0;
>> 
>> But that is a selfish code that declares it is the ultimate and
>> final form of the function, never to be enhanced later.  To allow
>> and invite future enhancements, make the last test follow the same
>> pattern.
>> 
>> Signed-off-by: Junio C Hamano <gitster@pobox.com>
>> ---
>>  fsck.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> Patch looks good, and nicely explained.
>
> -Peff

> The pattern taken by all the validations in this function is:
> 
> 	if (notice a violation exists) {
> 		err = report(... VIOLATION_KIND ...);
> 		if (err)
> 			return err;
> 	}
> 
> where report() returns zero if specified kind of violation is set to
> be ignored, and otherwise shows an error message and returns non-zero.
> 
> The last validation in the function immediately after the function
> returns 0 to declare "all good" can cheat and directly return the
> return value from report(), and the current code does so, i.e.
> 
> 	if (notice a violation exists)
> 		return report(... VIOLATION_KIND ...);
> 	return 0;
> 
> But that is a selfish code that declares it is the ultimate and
> final form of the function, never to be enhanced later.  To allow
> and invite future enhancements, make the last test follow the same
> pattern.

>> But that is a selfish code that declares it is the ultimate and
>> final form of the function, never to be enhanced later.  To allow
>> and invite future enhancements, make the last test follow the same
>> pattern.
>
> FWIW I agree with this reasoning. Sorry for leaving this to you to clean
> up.