[jira] [Commented] (THRIFT-5093) TMemoryBuffer fix wpos for policy == OBSERVER

["Christopher Friedt (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/THRIFT-5093?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17140917#comment-17140917 ] 

Christopher Friedt commented on THRIFT-5093:
--------------------------------------------

Is anyone able to do this review on GH now?

> TMemoryBuffer fix wpos for policy == OBSERVER 
> ----------------------------------------------
>
>                 Key: THRIFT-5093
>                 URL: https://issues.apache.org/jira/browse/THRIFT-5093
>             Project: Thrift
>          Issue Type: Bug
>          Components: C++ - Library
>    Affects Versions: 0.10.0, 0.11.0, 0.12.0, 0.13.0
>            Reporter: Christopher Friedt
>            Priority: Major
>          Time Spent: 2h
>  Remaining Estimate: 0h
>
> The TMemoryBuffer policy is "OBSERVER" by default in a constructor where an external pointer to memory, and the size of that memory, are passed in. That scenario is for externally managed buffers.
> As an observer of a buffer, Thrift should only be able to read. However, previously, `buf.available_read()` would return 0 (and subsequently, `buf.read()` would fail). 
> I've added a test as a separate commit, so it's easy to observe the failure and fix. The current behaviour produces the following failure.
> {noformat}
> TMemoryBufferTest.cpp(141): error: in "TMemoryBufferTest/test_observer": check N == buf.available_read() has failed [1024 != 0]
> {noformat}
> With this change, Thrift applications that use Memory as a transport are able to read `OBSERVER` buffers as well (as one would expect) and the error above is mitigated.



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