[jira] [Resolved] (HTTPCLIENT-2033) Connection manager shutdown flushes output buffer without synchronization

["Oleg Kalnichevski (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HTTPCLIENT-2033?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Oleg Kalnichevski resolved HTTPCLIENT-2033.
-------------------------------------------
    Fix Version/s: 4.5.11
       Resolution: Fixed

Merged to the 4.5.x branch.

Oleg

> Connection manager shutdown flushes output buffer without synchronization
> -------------------------------------------------------------------------
>
>                 Key: HTTPCLIENT-2033
>                 URL: https://issues.apache.org/jira/browse/HTTPCLIENT-2033
>             Project: HttpComponents HttpClient
>          Issue Type: Bug
>          Components: HttpClient (classic)
>    Affects Versions: 4.5.10
>         Environment: Linux
>            Reporter: Aapo Laitinen
>            Priority: Major
>             Fix For: 4.5.11
>
>
> We've observed cases of garbled data sent over the wire that seem to correlate with calling {{HttpClientConnectionManager#shutdown()}} while requests are in progress. For example, a PUT request with entity {{ABCD}} (each letter corresponding to 4 kilobytes of data) may be received as {{ABC{color:#172b4d}B{color}}} (the last block replaced with the second block).
> Omitting some intermediate layers, {{HttpClientConnectionManager#shutdown()}} proceeds to call {{AbstractConnPool#shutdown()}}, {{BHttpConnectionBase#close()}}, {{SessionOutputBufferImpl#flush()}} and finally {{SessionOutputBufferImpl#flushBuffer()}}. As far as I can tell, there is nothing to stop the thread that is performing the shutdown from invoking {{flushBuffer()}} while another thread is writing data to the buffer and/or flushing it.
> *How to reproduce*
> I haven't been able to reliably reproduce the garbled data, but I confirmed the lack of synchronization as follows:
> 1. Modified {{flushBuffer()}} so that it will try to a acquire and release a shared lock before proceeding and will report any cases of two threads attempting to flush the same buffer at the same time.
>  2. Acquired the lock while another thread was making requests, making the other thread block inside {{flushBuffer()}}.
>  3. Called {{HttpClientConnectionManager#shutdown()}}
>  4. Observed that the thread doing the shutdown entered {{flushBuffer()}} while the thread that was making requests hadn't exited it yet.
> *What I was expecting to happen*
> I'm not sure what the expected behavior of calling {{HttpClientConnectionManager#shutdown()}} is, but either of flushing the buffer with proper synchronization or abruptly closing the connection ({{BHttpConnectionBase#shutdown()}} instead of {{close()}}) strike me as acceptable. Basically, I'd expect that the received data might be truncated (e.g. {{AB}} or {{ABC}} instead of {{ABCD}}) but never garbled (e.g. {{ABCB}} or {{ABCC}} instead of {{ABCD}}).



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