[OpenJDK 2D-Dev] [15] RFR JDK-8242557: Add length limit for strings in PNGImageWriter

[Prasanta Sadhukhan]

Hi Jay,

But why reader will read more than 79 bytes from the chunk..It should 
also limit it's reading to 1st 79 bytes (if the chunks we get from 
non-oracle non-standard PNG writer is more than 79bytes) as per spec, no?

Regards
Prasanta
On 30-Apr-20 2:01 PM, Jayathirth D v wrote:
> Hi Prasanta,
>
> Thanks for the review.
> If we consume only 79 bytes and continue writing the image, it will 
> lead to unexpected behaviour when user tries to read the image 
> expecting longer than 79 string data. Our reader is also tightly spec 
> compliant for null terminated strings after JDK-8195841 
> <https://bugs.openjdk.java.net/browse/JDK-8195841> and JDK-8191023 
> <https://bugs.openjdk.java.net/browse/JDK-8191023>. Its better to be 
> spec compliant than leaving things open for interpretation.
>
> Regards,
> Jay
>
>
>> On 29-Apr-2020, at 1:22 PM, Prasanta Sadhukhan 
>> <prasanta.sadhukhan at oracle.com 
>> <mailto:prasanta.sadhukhan at oracle.com>> wrote:
>>
>> Hi Jay,
>>
>> Looks good to me . Although I have a question which is, instead of 
>> throwing Exception, can we proceed with 1st 79 bytes of these chunks 
>> and continue?
>>
>> Regards
>> Prasanta
>> On 27-Apr-20 10:51 PM, Philip Race wrote:
>>> I reviewed http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html
>>> and I think you covered all the cases.
>>>
>>> I also reviewed the reader and it seems we already check only up to 
>>> 80 chars there.
>>>
>>> I note we assume the same max length of 80 for the language tag for 
>>> iTxt.
>>> The spec. doesn't specify a limit but I think 80 is more than 
>>> generous here.
>>>
>>> +1
>>>
>>> -phil.
>>>
>>> On 4/27/20, 9:59 AM, Jayathirth D v wrote:
>>>> Hello All,
>>>>
>>>> Please review the following fix for JDK 15:
>>>>
>>>> Bug : https://bugs.openjdk.java.net/browse/JDK-8242557
>>>> Webrev : http://cr.openjdk.java.net/~jdv/8242557/webrev.00/ 
>>>> <http://cr.openjdk.java.net/%7Ejdv/8242557/webrev.00/>
>>>>
>>>> Issue : PNG specification restricts length of strings in some 
>>>> chunks to 79(http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html 
>>>> ) excluding null termination. But our writer implementation has no 
>>>> such check.
>>>> Solution : Add checks in different chunks where there must be 
>>>> restrictions.
>>>>
>>>> Thanks,
>>>> Jay
>
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