DirectDownload is a new operation (since GeoServer 2.9.x) supported by the CSW service.
In the Meteorology, Oceanography and Earth Observation domains, layers are usually based on complex NetCDF/GRIB files. Protocols such as WCS are set up to allow slice, rescale and reprojection of data, but not to preserve the original data as is.
This new operation allows direct download of the raw data for that layer. If the DirectDownload capability is enabled for a Coverage layer, the CSW record will be updated to contain links pointing back to the CSW service, using the DirectDownload vendor operation that will assemble the files for the requested resource, zip them, and send the result back to the requester.
The download links (one for each data file composing the layer plus a link to get all the files composing the layer) are added as new entries in CSW records:
as additional term-references element for a Dublin Core schema
as additional OnlineResource for ISO Metadata
Those links also contain the validity domain for the file such as envelope/time/elevation/custom dimensions (when present) for multidimensional layers.
DirectDownload capability can be activated as default for all layers, as global CSW configuration. Go into the CSW service panel and click on the enable DirectDownload checkbox if you want it enabled for all layers:
From this section you can also set a download size limit value (0 means no limit). The specified value represents the maximum size (in kilobytes) of the sum of the sizes of the raw data referred to by a single download link. (You can think about the case of a download link referring to the whole layer data which may contain a wide set of files).
Note that the size check is performed on the raw data files prior to any compression.
Per Layer configuration¶
DirectDownload capability can also be enabled/disabled for a specific layer, which will override the global CSW configuration.
Go to the publishing tab of the layer.
Look for the DirectDownload settings section.
The configuration of this parameter follows the same rules as shown for the CSW configuration panel.
A GetRecords response containing a layer with DirectDownload enabled, may result having a piece like this (using ISO Metadata output schema):
... <gmd:CI_OnlineResource> <gmd:linkage> <gmd:URL> http://localhost:8080/geoserver/ows?service=CSW&version=2.0.2&request=DirectDownload&resourceId=geosolutions:Reflectivity_height_above_ground&file=82643c5bf682f67ef8b7de737b90ada759965cd8-samplefile.grib2&ENVELOPE=-2699073.2421875,-1588806.0302734375,2697926.7578125,1588193.9697265625&TIME=2015-06-23T00:00:00.000Z/2015-06-23T00:00:00.000Z&HEIGHT_ABOVE_GROUND=1000.0/4000.0 </gmd:URL> </gmd:linkage> </gmd:CI_OnlineResource> ...
That URL allows the direct download of the indicated file. Note that the filename has a SHA-1 header to avoid publishing the underlying file system structure paths.