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

[Jayathirth D v]

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> 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 <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 <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 <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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