Hi Joe,
HTTP 1.1 can support requests for byte-range [a] subsets of a resource.
This capability is optional so not all servers (or resources on a
server) need support it. If you look at the HTTP response headers you
get back from your [1] and [2] URLs you will see that [2] includes an
"Accept-Ranges: bytes" header whereas [1] does not.
The netCDF-Java library can open remote datasets available over HTTP,
without downloading the entire file, if the server supports byte range
requests for that dataset. [However, depending on the access pattern,
this can be very inefficient as the client is doing the subsetting which
may require multiple HTTP requests. For OPeNDAP access, the subsetting
is done on the server and generally only requires one HTTP request.]
Hope that helps,
Ethan
[a] https://en.wikipedia.org/wiki/Byte_serving
On 6/10/2013 8:04 AM, H. Joe Lee wrote:
> Hi, John & Ethan!
>
> Thanks for the help!
>
> Now I figured it out that the "location" tag of NcML does not work
> with the on-demand NetCDF-3 file that is automatically generated by
> "fileout_netcdf" module by OPeNDAP server like [1]. If I save the
> NetCDF-3 file from [1] and put it in a regular HTTP server like [2],
> the NcML works fine.
>
> For comparison, the URL [3] is the DAP response that NCDump in
> ToolsUI can also recognize. Thus, I could make my NcML work by
> dropping .nc as Ethan suggested. Since [3] works fine with NcML, I
> have no reason to save and put it in a separate web server like [2].
>
> However, I still don't know why OPeNDP fileout_netcdf module doesn't
> work with NcML "location". What's the key difference between [1] and
> [2]? It seems like an OPeNDAP sever configuration issue. I'm asking
> opendap-tech mailing list to get some help.
>
> Regards,
>
>
> [1] http://eosdap.hdfgroup.uiuc.edu:8080/opendap/data/hdf4/foo2.hdf.gz.nc
> [2] http://hdfeos.org/foo2.hdf.gz.nc
> [3] dods://eosdap.hdfgroup.uiuc.edu:8080/opendap/data/hdf4/foo2.hdf.gz
>
> --
> HDF: Software that Powers Science
============================
http://eosdap.hdfgroup.uiuc.edu:8080/opendap/data/hdf4/foo2.hdf.gz.nc
GET /opendap/data/hdf4/foo2.hdf.gz.nc HTTP/1.1
Host: eosdap.hdfgroup.uiuc.edu:8080
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:21.0) Gecko/20100101
Firefox/21.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Connection: keep-alive
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Last-Modified: Tue, 02 Oct 2012 02:58:53 GMT
Content-Disposition: attachment; filename="foo2.hdf.gz.nc"
XDODS-Server: dods/3.2
XOPeNDAP-Server: bes/3.11.0, libdap/3.11.7, dap-server/ascii/4.1.2,
fileout_netcdf/1.1.3, hdf4_handler/3.10.1, hdf5_handler/2.1.2,
netcdf_handler/3.10.2, ncml_module/1.2.2, dap-server/usage/4.1.2,
dap-server/www/4.1.2
XDAP: 3.2
Content-Type: application/x-netcdf
Transfer-Encoding: chunked
Date: Mon, 10 Jun 2013 18:55:04 GMT
============================
http://hdfeos.org/foo2.hdf.gz.nc
GET /foo2.hdf.gz.nc HTTP/1.1
Host: hdfeos.org
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:21.0) Gecko/20100101
Firefox/21.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Connection: keep-alive
HTTP/1.1 200 OK
Date: Mon, 10 Jun 2013 18:53:42 GMT
Server: Apache
Last-Modified: Mon, 10 Jun 2013 13:56:13 GMT
Etag: "a20b75-f0-4decd24c9da96"
Accept-Ranges: bytes
Content-Length: 240
Keep-Alive: timeout=2, max=200
Connection: Keep-Alive
Content-Type: application/x-netcdf
Content-Encoding: gzip
--
Ethan Davis UCAR Unidata Program
edavis@xxxxxxxxxxxxxxxx http://www.unidata.ucar.edu
