OpenDAP https behind Proxy

Hello,

I'm using Windows Matlab 2020b. I am attempting to read HTTPS OpenDAP data from matlab behind a proxy.

I can confirm with wget and my web browser that the proxy works for both http and https to the tds.hycom.org domain.

For Matlab, I've set HTTP_PROXY=proxy.mycompany.com:3129 and HTTPS_PROXY=proxy.mycompany.com:3129. I've done this from Windows 10's Settings => Edit Environment Variables for your account. After setting those variables I start a new matlab.

test HTTP, it works:

>> ncinfo('http://tds.hycom.org/thredds/dodsC/GLBy0.08/expt_93.0')

ans = 

  struct with fields:

      Filename: 'http://tds.hycom.org/thredds/dodsC/GLBy0.08/expt_93.0'
          Name: '/'
    Dimensions: [1×4 struct]
     Variables: [1×14 struct]
    Attributes: [1×10 struct]
        Groups: []
        Format: 'classic'

test HTTPS, it fails:

>> ncinfo('https://tds.hycom.org/thredds/dodsC/GLBy0.08/expt_93.0');
Error using netcdflib
The NetCDF library encountered an error during execution of 'open' function - 'I/O failure
(NC_EIO)'. If the data source was an  OPeNDAP URL, see the OPeNDAP Troubleshooting section in the
Users Guide.

Error in netcdf.open (line 67)
        [varargout{:}] = netcdflib ( 'open', filename, varargin{1} );

Error in internal.matlab.imagesci.nc/openToRead (line 1278)
            this.ncRootid = netcdf.open(this.Filename,'NOWRITE');

Error in internal.matlab.imagesci.nc (line 121)
                    this.openToRead();

Error in ncinfo (line 88)
ncObj   = internal.matlab.imagesci.nc(ncFile);

My company's IT has confirmed that Matlab is making the request and getting a response from the server.

Is this a known limitation of the netcdf library matlab is using? Are there additional ways to get debugging information or understand the cause of the failure?

Related posts:

https://www.mathworks.com/matlabcentral/answers/223837-problem-to-access-opendap-data-behind-https-urls notes that no https access was available until ~2017.

https://www.mathworks.com/matlabcentral/answers/658718-problem-to-access-opendap-data-behind-https-urls notes that https didn't work for a particular URL in 2019b but a Mathworks Saff memeber notes that it works in 2020b (my version).

Thank you,

Luke

Answer 1

[daruzi]

>> ncinfo('https://tds.hycom.org/thredds/dodsC/GLBv0.08/expt_53.X/data/2006')

ans =

Filename: 'https://tds.hycom.org/thredds/dodsC/GLBv0.08/expt_53.X/data/2006'

Name: '/'

Dimensions: [1×4 struct]

Variables: [1×14 struct]

Attributes: [1×9 struct]

Groups: []

Format: 'classic'

[Luke Robison]

This does not work behind a proxy. Are you behind a proxy?

[daruzi]

• I was able to download the data using HTTPS