OGR outputs fail in fastcgi mode when STORAGE is set to stream

[tbonfort]

When setting FORMATOPTION "STORAGE=stream" in an OGR outputformat, all fastcgi requests for that format will result in a 0 length response. This seems reasonable as the /vsistdout/ datasource is not connected to the fastcgi msIO.

cc @rouault . is there a workaround to use msIO* functions in OGR? Would there be any reason to not switch to a memory storage if we can detect we are run in an fcgi container?

[rouault]

There's currently no way (that I can imagine of) of using msIO* in OGR. But I can imagine that the CPL library in GDAL could be extended to accept user provided callbacks, that MapServer would set with its msIO functions.

Using memory storage is an alternative if the output fits in RAM. /vsistdout/ has the advantage to be a streaming mode.

[tbonfort]

I suspect the streaming mode will also fail if used through mapscript when the msIO functions have been configured to output to a buffer. I'll try to cook a workaround for this ...

[tbonfort]

@rouault @szekerest could you have a look at the proposed fix ?

[rouault]

Looks good to me. At some point, I should try to find a way for mapserver to plug its msIO functions to be used by the vsistdout virtual file system.

[tbonfort]

applied for 6.4.2 in 3d174b4