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From Gordon Mohr <goj...@archive.org>
Subject Re: [jira] Resolved: (HTTPCORE-3) HttpParser triggers unfriendly OutOfMemoryError on challenging input
Date Tue, 16 May 2006 22:24:08 GMT
If I understand the HttpCore code properly, there is no direct facility 
for protecting against the OOME in the code -- just a chance to hook in 
a theoretical alternate implementation that would address the problem.

Is that correct?

To use the HttpCore-4.0 facility, it appears I would create my own 
HttpDataReceiver implementation which keeps a count of the bytes it 
shovels & throws an IO or HTTP exception when some count is exceeded; 
create a factory that makes such receivers; install that factory into 
each HttpClientConnection instance before it begins receiving data.

This could work, but seems a roundabout and obscure approach. The really 
valuable feature would be for OOME-resistance -- and friendly, usable 
indicators that extreme content has been encountered -- to be features 
of the library. It's require a switch or paramter to enable, rather than 
patching in custom/third-party code.

Is there a summary of expected dates of Core-4.0/Client-4.0 release 
somewhere, or any assessments of how the 4.0 codebases match up against 
3.0 features? (Is it reasonable for an HttpClient-3.0-using project to 
consider transitioning to the 4.0 codebase(s)?)

- Gordon @ IA

Oleg Kalnichevski (JIRA) wrote:
>      [ http://issues.apache.org/jira/browse/HTTPCORE-3?page=all ]
> Oleg Kalnichevski resolved HTTPCORE-3:
> --------------------------------------
>     Resolution: Invalid
> Feel free to re-open the issue if you think the problem has not been adequately resolved
> Oleg
>> HttpParser triggers unfriendly OutOfMemoryError on challenging input
>> --------------------------------------------------------------------
>>          Key: HTTPCORE-3
>>          URL: http://issues.apache.org/jira/browse/HTTPCORE-3
>>      Project: Jakarta HttpCore
>>         Type: Bug
>>   Components: HttpCore
>>     Reporter: Gordon Mohr
>> Many users of HttpClient use it to connect to servers which generate challenging
HTTP responses, such as responses which include an arbitrarily large number of headers or
headers of arbitrarily large size. (Sometimes such headers are conformant with the spec, in
that they contain legal characters in plausible header formats; other times these are filled
with binary content that is a violation of the relevant specs. Even when technically legal,
often such giant headers are the inadvertent result of server-side bugs.)
>> As a Java execution environment always has a hard cap on the available heap space,
any parsing code which can use an arbitrary amount of memory risks triggering an OutOfMemoryError,
either in its own thread or even another thread that happens to need memory after the parsing
thread has exhausted it all. 
>> Such OutOfMemoryErrors are a particularly unfriendly way to indicate that a practical
limit has been exceeded, compared to other options. They can hide the thread of execution
which is most to blame. It is hard and awkward to set up handlers that catch and recover from
OOMEs wherever they are most likely to occur.  Even with such handlers, the actual allocation
triggering an OOME may occur in another critical thread, even if that thread has minimal and
well-controlled memory needs. 
>> HttpClient ought to provide one or more ways for a user to protect against such OOMEs,
and instead receive a more convenient/recoverable indication of an HTTP response that is impossible
to process with the HttpClient library within the available resources. Many approaches are
possible; the easiest would be to allow a user of HttpClient to set their own optional, pragmatic
limits on header sizes and number. Then, just as a user may already cleanly cancel the stream-reading
of an arbitrarily-long content-body without fouling up their application state, they would
be able to cancel the parsing of oversized response headers. 
>> Similar issues have been discussed before, for example in Bugzilla bug #25468 (http://issues.apache.org/bugzilla/show_bug.cgi?id=25468)
which was to "Provide HttpParser plug-in mechanism." Though that issue is marked resolved/fixed,
there is no such plug-in mechanism allowing an OOME workaround in the 3.x HttpClient, and
it is not clear that a mechanism/work-around exists in whatever 4.0 work has been completed.
>> So my suggestion is that this new issue be used to uniquely track the OOME risk in
HttpParser, and only be considered "fixed" when some version of HttpClient offers an alternative
to throwing OOMEs as a way of dealing with challenging HTTP responses. Alternatively, this
could simply become the issue in the new system for collecting user-contributed workarounds/patches.


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