Bob's response is below.
--
Brian Schlining
Forwarded message:
> From: Bob Simons <bob.simons@xxxxxxxx>
> To: Brian Schlining <bschlining@xxxxxxxxx>
> Date: Thursday, October 11, 2012 10:05:47 AM
> Subject: Re: ERDDAP bug
>
> I understand the issue that you are talking about. I would instead urge
> you not to use this approach. This approach has the implicit assumption
> that there is a static .nc file with the requested subset of the larger
> dataset and that NetCDF-Java can read specific bytes from that file. See
> http://www.unidata.ucar.edu/software/netcdf-java/reference/HTTPservice.html
> That is just not a good way to think about that file. Please request a
> .nc file from ERDDAP only if you want to download that .nc file.
>
> For your purposes, please use NetCDF-Java to access an ERDDAP dataset as
> an OPeNDAP dataset. This is what OPeNDAP was designed for and
> NetCDF-Java supports this *very* well. This approach will work *much*
> better, for a variety of reasons. Here is a code snippet:
>
> NetcdfFile ncFile =
> NetcdfDataset.openFile("http://beach.mbari.org:8180/erddap/griddap/erdRyanSST";,
>
> null);
> //note that there is no file extension at the end of the dataset's name
> //Then you can do what you want with the ncFile object.
>
> I will improve the documentation related to this. Thanks for pointing
> out this weakness in the documentation.
>
> I hope that clarifies the situation. If not, or if you have other
> questions about ERDDAP, please let me know.
>
> P.S. I am not on netcdf-java mailing list. Can you please post this
> response on the netcdf-java mailing list? Thank you.
>
>
> On 10/11/2012 9:31 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
>
> --
> Sincerely,
>
> Bob Simons
> IT Specialist
> Environmental Research Division
> NOAA Southwest Fisheries Science Center
> 1352 Lighthouse Ave
> Pacific Grove, CA 93950-2079
> Phone: (831)658-3205
> Fax: (831)648-8440
> Email: bob.simons@xxxxxxxx (mailto:bob.simons@xxxxxxxx)
>
> The contents of this message are mine personally and
> do not necessarily reflect any position of the
> Government or the National Oceanic and Atmospheric
> Administration.
> <>< <>< <>< <>< <>< <>< <>< <>< <><
>
>
>
