Add WMS DescribeLayer operation support

[ronitjadhav]

Description

Adds support for the WMS DescribeLayer operation to determine the underlying
data type of a WMS layer (e.g. whether it is backed by vector/WFS or raster/WCS data).

Changes

• Add describeLayer(layerName) method to WmsEndpoint
• Add WmsLayerDescription type (layerName, owsType, owsUrl, typeName)
• Add generateDescribeLayerUrl() URL builder in src/wms/url.ts
• Add parseDescribeLayerResponse() XML parser in src/wms/describelayer.ts
• Export WmsLayerDescription from the library entry point

Usage

const endpoint = new WmsEndpoint(url);
await endpoint.isReady();

const description = await endpoint.describeLayer('my_workspace:my_layer');
// { layerName: 'my_workspace:my_layer', owsType: 'WFS', owsUrl: '...', typeName: '...' }

[jahow]

Thank you, a few comments to address!

[jahow]

needs a SLD_VERSION=1.1.0 param here

[jahow]

this can be typed as 'wcs' | 'wfs' as per the spec

[jahow]

I don't think this fixture looks like a real response. For instance this is the response example from the spec:

<DescribeLayerResponse xmlns="http://www.opengis.net/sld" xmlns:ows="http://www.opengis.net/ows"
xmlns:se="http://www.opengis.net/se" xmlns:wfs="http://schemas.opengis.net/wfs"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:myns="http://myserver/somenamespace"
xsi:schemaLocation="http://www.opengis.net/sld DescribeLayer.xsd">
<Version>1.1.0</Version>
<LayerDescription>
 <owsType>wfs</owsType>
 <se:OnlineResource xmlns:xlink="http://www.w3.org/1999/xlink" xlink:type="simple"
xlink:href="http://mywfs/server/ogcwebservice"/>
 <TypeName>
 <se:FeatureTypeName>myns:cloudfeatures</se:FeatureTypeName>
 <TypeName>
</LayerDescription>
</DescribeLayerResponse>

Could you maybe do two different fixtures, one for WCS and one for WFS? Also slightly different, e.g. coming from different services. Thank you!

[jahow]

Make it so that a Promise is always returned, otherwise the API is very awkward

[ronitjadhav]

Thanks for the review. I have addressed the mentioned comments.

[jahow]

Thanks!