Hi,
I’m looking into having GWC own WMS reply to GetLegendGraphics, which is something
the stand-alone version can do, but the embedded one can not.
Now, stand alone GWC has the following setup:
- GetFeatureInfo gets a special treatment, any GWC layer implementation is supposed to provide
support for it via a dedicated method (which might be throwing an exception, but an implementation
of the method has to be there) - For all other WMS requests, there is a special arrangement in the WMS service that check if the
layer is a WMSLayer, and in that case, cascades the request
Now, GeoServer integrated layers are GeoServerTileLayer instances, which are not subclasses
of WMSLayer, so neither arrangement works.
One approach could be to ask all GWC layers to support a custom getLegendGraphics method,
mimicking GetFeatureInfo, but seems a bit heavy handed, and what we do when someone
wants GetStyles support too? Or DescribeLayer?
Another approach could be to roll out a ProxyLayer interface, with a method dedicated to proxying:
ProxyResponse proxy(HttpServletRequest request);
where ProxyResponse would provide a status, a content type, a list of headers and their values, and
an input stream for the response to be sent back.
Then WMSLayer in GWC could implement that, and GeoServerTileLayer implement it as well,
keeping the proxying generic.
Yet another approach would be to tap into the GWC integration at the GwcServiceProxy.dispatch
level, see if the response is one of those that GWC can handle natively, if not, check if the
layer is known to GeoServer, and redirect the request to the internal WMS instead.
Opinions? What if I wanted to backport to the stable series, 2.4.x, would that change your opinion
on which approach is best?
Personally I like the second one (ProxyLayer interface) better, it allows for future extension and
custom layers to try and do some cascading, and the interface is new, so it would not break
existing implementations.
Cheers
Andrea
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