Aapo Laitinen created HTTPCLIENT-2033:
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Summary: 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
We've observed cases of garbled data sent over the wire that seem to correlate
with calling {{HttpClientConnectionManager#shutdown()}} while request 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}+*}}.
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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