RFR [9] 8139706: JarFile.getBytes could use InputStream.readNBytes

Chris Hegarty chris.hegarty at oracle.com
Fri Oct 16 12:03:21 UTC 2015

On 16/10/15 12:49, Claes Redestad wrote:
> On 2015-10-16 04:09, Xueming Shen wrote:
>> On 10/15/15 3:08 PM, Claes Redestad wrote:
>>> On 2015-10-15 23:21, Chris Hegarty wrote:
>>>>> On 15 Oct 2015, at 21:59, ecki at zusammenkunft.net wrote:
>>>>> Hello,
>>>>> This does change a bit the semantic of the length check. If the
>>>>> stream would return more bytes than the zipentry says the new
>>>>> version would ignore them, the  old version was consuming then and
>>>>> then fail the check. However I am not sure if this is relevant.
>>>> Right, there are certainly some subtle differences resulting from
>>>> the proposed change. When working on JDK-8138978 I thought
>>>> about using readNBytes, but played it safe as IOUtils was growing
>>>> the bye[] lazily too, so no real perf difference.  In fact, I think
>>>> I seen
>>>> a test failure with using readNBytes here. I’ll have to check.
>>> Seeing no jtreg test failures in java/util/zip nor java/util/jar
>>> (apart from 2 ignored tests), but I can see a reason for the current
>>> implementation being conservative: Corrupt/malicious jar files might
>>> lie about the entry length and report very large values, which could
>>> bring a down with OOME.
>>> I believe we could be both safe and faster than baseline by adding a
>>> reasonable limit for when to use readNBytes, e.g., 32k would deal
>>> with the majority of .class files.
>> getBytes should be used to read the meta-inf files only, not the
>> .class files.
> Correct, but this is still enough to cause statistically significant
> increases on our footprint measures.
> With a reasonable trust limit this change should be safe while avoiding
> most temporary byte[] allocations when reading meta-inf files. I've
> verified the startup and footprint numbers and ran it through all
> java/util/jar and /zip tests without error.
> New webrev: http://cr.openjdk.java.net/~redestad/8139706/webrev.02/

This latest webrev looks good to me.


> /Claes
>> -sherman

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