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https://issues.apache.org/jira/browse/XERCESC-1756?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alberto Massari resolved XERCESC-1756.
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Resolution: Fixed
Fix Version/s: 3.0.0
Assignee: Alberto Massari
I have aligned the code with the fopen.c sample that ships with libcurl
(including the maxfd+1 expression in the call to select)
> CurlURLInputStream misusing fd_set structure in libcurl and select calls
> ------------------------------------------------------------------------
>
> Key: XERCESC-1756
> URL: https://issues.apache.org/jira/browse/XERCESC-1756
> Project: Xerces-C++
> Issue Type: Bug
> Components: Miscellaneous
> Affects Versions: 3.0.0
> Environment: Windows XP, Visual Studio 2005, libcurl 7.17.1
> Reporter: Scott Cantor
> Assignee: Alberto Massari
> Fix For: 3.0.0
>
>
> I did some work to backport the new libcurl NetAccessor to plugin to Xerces
> 2.8.0, and found some bugs in the process that are also broken for 3.0. The
> use of fd_set seems to be broken. Arrays of fd_sets (which are themselves
> length-prefixed arrays of sockets) are being passed into curl_multi_fdset
> without being zeroed out with FD_ZERO first, which causes a crash because the
> socket count on input is wrong.
> I believe the correct code should be to declare only a single set of fd_set
> variables, not arrays, and call FD_ZERO first, then pass the address of the
> variables into curl_multi_fdset and the select call below.
> This seems to work for me under simple test cases.
> Specifically the loop at the end looks like:
> // If there is no further data to read, and we haven't
> // read any yet on this invocation, call select to wait for data
> if (!tryAgain && fBytesRead == 0)
> {
> fd_set readSet;
> fd_set writeSet;
> fd_set exceptSet;
> int fdcnt=0;
>
> // Ask curl for the file descriptors to wait on
> FD_ZERO(&readSet);
> FD_ZERO(&writeSet);
> FD_ZERO(&exceptSet);
> (void) curl_multi_fdset(fMulti, &readSet, &writeSet,
> &exceptSet, &fdcnt);
>
> // Wait on the file descriptors
> timeval tv;
> tv.tv_sec = 2;
> tv.tv_usec = 0;
> (void) select(fdcnt, &readSet, &writeSet, &exceptSet,
> &tv);
> }
> A better implementation of this would be to dump the multi libcurl API, which
> is far more complicated than this use case requires, but I didn't have time
> to try that for now.
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