[gdal-dev] Resquest for comments (RFC 36)

[Frank Warmerdam]

On Mon, Oct 3, 2011 at 6:14 PM, Daniel Morissette
<dmorissette at mapgears.com> wrote:
> I like the idea, especially since it can increase performance in some cases.
> However unless I'm mistaken the proposed patch seems to fall back on the
> regular test-open loop when the GDALOpenInternal() call with the explicit
> driver name failed, no matter why it failed. e.g. I specify the invalid
> "hfa:test.tif" open string, then I should get a NULL return value and not a
> handle to a TIFF file.

Daniel,

I believe that is because it is hard to know if HFA:test.tif was really
something other than a request for the HFA driver.  It could actually
be a file named "HFA:test.tif" or it could be that another driver happens
to use the HFA: prefix to mean something.   I believe this is an
effort to avoid failure in these cases.

> The patch would need to be reworked for this, but I think that if the
> GetDriverByName() call succeeds (i.e. the driver name prefix is recognized
> by GDAL) and the call to poDriver->pfnOpen() fails then we should return
> NULL to the application code (and not fall back on the test-open loop).
> OTOH, if the GetDriverByName() lookup failed, then we should fall back on
> the test-open loop.
>
> Also, if we implement this mechanism in GDAL, then we'd have to provide it
> in OGR as well to be consistent.

I'm not convinced that this is necessary.  I have had a hope for
some time to provide a standard way of binding up open options,
including the driver name, for OGR as demonstrated by a
request like:

  @driver=ingres,dbname=test

One objection I had previously to Ivan's proposal is that I'm
interested in pursuing this general purpose mechanism for
many open options in OGR and in GDAL.  But since I haven't
gotten to it for so long there is no point in holding up Ivan's
fairly straight forward change.  Nevertheless, I'm hesitant to
push his change to OGR unnecessarily.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Software Developer