Hi Gabriel thanks for your input. I think I might have discovered an issue
with specifying the port number on geowebcache.xml's wmsUrl element -
explained further below.

I am using GeoServer 2.1.3, sorry for not mentioning in my original message
- I knew I would leave something out!

Also I think it's worth explaining exactly what I'm hoping to achieve in
case this points to any obvious issues. I have a version of Oracle that
doesn't support 900913 (aka 3875) so I am having to work around this. I
transformed my original data (in 4326) to 3785 (this is not a typo) with a
'USE_SPHERICAL' argument as described here:
https://forums.oracle.com/forums/thread.jspa?threadID=2228982. The end
result is coordinates that align almost perfectly (sub-millimetre) with the
same locations in 900913.

With the bulid of OpenLayers I am using (2.11 Release) it does not seem
possible to request two layers for the same map with different projections -
though I'm told the trunk might offer this capability - so I can't ask
GeoServer to give me my adjusted 3785 'live' data and GWC to give me the
900913 cached data, even though they should line up just fine. So... what
I'm trying to do here is define a 3785 gridset in GWC which is actually
using 900913 behind the scenes, so that OpenLayers can request both live and
cached layers in 3785.

The gridset in geowebcache.xml looks like this:

  <gridSets>
    <gridSet>
      <name>3785</name>
      <srs>
        <number>900913</number>
      </srs>
      <extent>
        <coords>
          <double>-20037508.0</double>
          <double>-20037508.0</double>
          <double>20037508.0</double>
          <double>20037508.0</double>
        </coords>
      </extent>
      <metersPerUnit>1</metersPerUnit>
      <tileHeight>256</tileHeight>
      <tileWidth>256</tileWidth>
    </gridSet>
  </gridSets>

Trying to preview the layer via GWC gives this in the GeoServer log: ERROR
[geowebcache.GeoWebCacheDispatcher] - All backends (1) failed. Reason:
Unexpected response code from backend: 404 for
http://host_name:8080/geoserver/test/wms?.  Last request:
'http://host_name:8080/geoserver/test/wms?'. 
http://host_name:8080/geoserver/gwc/service/wms

When I look at the Apache access log I see the 404 requests like this:
/geoserver/test/wms?BBOX=-2.0037508E7%2C-2.0037508E7%2C2.0037508E7%2C2.0037508E7&TRANSPARENT=TRUE&EXCEPTIONS=application%2Fvnd.ogc.se_xml&VERSION=1.1.1&FORMAT=image%2Fpng&SERVICE=WMS&HEIGHT=512&LAYERS=highway_line_gwc&REQUEST=GetMap&STYLES=&WIDTH=512&SRS=EPSG%3A900913

If I copy and paste that same URL into a browser, but prefixed with
http://host_name:8080 I get a 200 response and an image. This was mighty
confusing, but then I realised I would get a 404 if the request actually
went to http://host_name:80/... I updated and reloaded geowebcache.xml with
a random port number and I get the same result. Is it possible that GWC is
ignoring the port number in the wmsUrl element?

Also, I'd really like to see how the default gridsets and layers added by
GeoServer are configured - is there an xml config file buried somewhere for
layers which work that I can use as a reference?

Any feedback much appreciated.

--
View this message in context: 
http://osgeo-org.1560.n6.nabble.com/GeoWebCache-geowebcache-xml-bug-custom-GridSet-and-applying-it-to-a-layer-tp4538078p4552096.html
Sent from the GeoServer - User mailing list archive at Nabble.com.

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