Also, the "Accept_Ranges" header is needed, details here:
http://www.unidata.ucar.edu/software/netcdf-java/reference/HTTPservice.html
On 10/11/2012 10:31 AM, Brian Schlining wrote:
Hi Bob,
We're doing some work with ERDDAP and running into an issue using
NetCDF-Java to access files served by ERDDAP. I think I understand the
issue and know how to address it, so I'm passing the info onto you all
so it can be addressed. So here goes:
1) ERDDAP allows one to download a NetCDF file by building a link
appended with '.nc'. The link URL for the netcdf file would be something
like http://beach.mbari.org:8180/erddap/griddap/erdRyanSST.nc. This
works great for downloading the files. However, it does NOT work with
the NetCDF-Java API; NetCDF-Java can normally read NetCDF files from
arbitrary non-opendap http urls.
2) The reason it fails is because NetCDF-Java needs to know the size of
the file being served. This requires that the HTTP response for a URL
like http://beach.mbari.org:8180/erddap/griddap/erdRyanSST.nc to contain
a 'Content-Length' field. ERDDAP is not sending that … here's a response
header from ERDDAP (notice there's no 'Content-Length':
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Date: Thu, 11 Oct 2012 15:44:19 GMT
Last-Modified: Thu, 11 Oct 2012 15:44:19 GMT
xdods-server: dods/3.7
erddap-server: 1.38
Content-Disposition: attachment;filename=erdRyanSST_8571_f367_229e.nc
Content-Encoding:
Content-Type: application/x-download
Transfer-Encoding: chunked
3) Since ERDDAP is running on Tomcat, the only way I know of to set the
'Content-Length' is to explicitly call 'response.setBufferSize()' in the
servlet that returns the NetCDF file. Note that once the response size
goes beyond the bufferSize, Tomcat will fallback to 'Transfer-Encoding:
Chunked' (which we don't want). So make sure you're setting the buffer
size to the correct value.
Hope that helps!
p.s. I cc'd this to the netcdf-java mailing list in case I got something
wrong. Hopefully someone will correct me.
Cheers
-- B
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Brian Schlining
MBARI
Software Engineer, Research and Development
brian@xxxxxxxxx <mailto:brian@xxxxxxxxx>
(831) 775-1855
http://www.mbari.org/staff/brian
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