Due to the current gap in continued funding from the U.S. National Science Foundation (NSF), the NSF Unidata Program Center has temporarily paused most operations. See NSF Unidata Pause in Most Operations for details.
Due to the current gap in continued funding from the U.S. National Science Foundation (NSF), the NSF Unidata Program Center has temporarily paused most operations. See NSF Unidata Pause in Most Operations for details.
On Oct 11, 2012, at 11:31 AM, Brian Schlining <bschlining@xxxxxxxxx> 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. > I don't think this is exactly correct. In the case that the content-length can be determined, one should call setContentLength(...) on the ServletResponse instance to set the HTTP Response Content-Length header (for Tomcat). The transfer-encoding used to deliver the content should be abstracted by the HTTP Client implementation one is using, you shouldn't have to worry about this. Setting content-length is preferable but it's not always feasible in some implementations where low-latency/high-throughput responses are desired with large responses (i.e. avoid buffering entire response to to calculate content-length before sending any bytes). > 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 > (831) 775-1855 > > http://www.mbari.org/staff/brian > > _______________________________________________ > netcdf-java mailing list > netcdf-java@xxxxxxxxxxxxxxxx > For list information or to unsubscribe, visit: > http://www.unidata.ucar.edu/mailing_lists/ Tom Kunicki Center for Integrated Data Analytics U.S. Geological Survey 8505 Research Way Middleton, WI 53562
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