[fdo-internals] Serious CentOS 6.x blocker for MapGuide 2.6 final release

Jackie Ng jumpinjackie at gmail.com
Tue Jul 29 20:11:39 PDT 2014

Hi All,

There is a serious defect in the CentOS 6.x build of MapGuide that is
preventing release of 2.6 final for this particular build at least.

It concerns the use of iconv_* family of APIs which fail under MapGuide on
CentOS 6.x. Basically, calls to iconv_open() from within the mgserver
process will almost always return -1 in the charsets we want to convert
to/from. This breaks the macros conv_wide_to_utf8 and conv_utf8_to_wide in
FdoCommonStringUtil.h, that is used in the FdoCommonFile class and by any
FDO provider that needs to do some sort of file operation that would be
using this class.

The most apparent symptom of this defect is that it is not possible to open
any SHP file FDO connection in MapGuide as it will throw back an
FdoException with FDO_1_BADALLOC (Memory allocation failed), which if you
step through the code with gdb will trace back to the above macros that use
the iconv_* APIs.

Now the thing that surprises me is that this API is working properly
outside of MapGuide. A simple application like this (
https://gist.github.com/jumpinjackie/6694c5c0a4e38f1396d0) will have
iconv_open() return a valid iconv_t handle. It's only when this code is
called from within the mgserver process that it will fail.

So currently, I'm currently suspecting that some combination of gcc/g++/ld
flags that have somehow rendered iconv_open() un-usable from within
MapGuide. I suspect this is also the cause of the mysterious "could not
load a transcoding service" errors from xerces during mgserver startup that
has caused me to configure an alternate transcoder for xerces when building
MapGuide for 2.6 beta 1 and newer. Anyone have any idea why iconv_open()
could fail from within MapGuide, but not fail in other applications?

Failing to solve the above issue, the alternative solution would be to
rewrite the conv_wide_to_utf8 and conv_utf8_to_wide macros in
FdoCommonStringUtil.h to use something other than iconv to convert char <->
wchar_t, I'm not sure how feasible/practical this is. Anyone from the FDO
team care to chime in here?

Despite the above wall of text, I'd like to re-iterate that this issue only
affects the CentOS 6.x build of MapGuide. SHP FDO connections work fine on
Ubuntu and Windows. I don't want to put a 2.6 final release that has broken
SHP file support on CentOS 6.x. Any help and/or pointers that would lead us
to solving this problem would be much appreciated.

- Jackie
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