{"id":9276,"date":"2018-07-20T09:00:15","date_gmt":"2018-07-20T13:00:15","guid":{"rendered":"https:\/\/blogs.mathworks.com\/pick\/?p=9276"},"modified":"2018-07-19T14:12:13","modified_gmt":"2018-07-19T18:12:13","slug":"is-net-available","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/pick\/2018\/07\/20\/is-net-available\/","title":{"rendered":"Is Net Available"},"content":{"rendered":"
\n <\/p>\n

Sean<\/a>‘s pick this week is isnetavl<\/a> by Rik Wisselink<\/a>.\n <\/p>\n

<\/introduction><\/p>\n

I was recently writing a function that downloads data from a public location online. I had to call it multiple times to get
\n data for different time ranges but wanted to safe guard against there being no internet connection. If the system failed
\n to download data, I wanted to be able to add the internet connectivity information to the exception<\/a>.\n <\/p>\n

Rik’s isnetavl<\/tt> function, which is an enhancement to another version<\/a> without Unix support, does this.\n <\/p>\n

This is roughly what the code I ended up with looks like. To run this, my computer is in airplane mode.<\/p>\n

try<\/span>\r\n    % Loop over dates, storing output for each one.<\/span>\r\n    for<\/span> ii = numel(dates):-1:1\r\n        data{ii} = string(webread(url, 'date'<\/span>, dates(ii)));\r\n    end<\/span>\r\ncatch<\/span> ME\r\n    % Add information about specific query.<\/span>\r\n    failedquery = MException('DataReader:FailedQuery'<\/span>, 'url: %s\\ndate: %s'<\/span>, url, char(dates(ii)));\r\n    ME = ME.addCause(failedquery);\r\n\r\n    % If the internet is not available, add more information before<\/span>\r\n    % rethrowing the exception.<\/span>\r\n    if<\/span> ~isnetavl\r\n        nointernet = MException('System:NoInternetConnection'<\/span>, 'The system is not connected to the internet.'<\/span>);\r\n        ME = ME.addCause(nointernet);\r\n    end<\/span>\r\n\r\n    % Rethrow the exception with additional causes<\/span>\r\n    rethrow(ME)\r\n\r\nend<\/span><\/pre>\n
Error using webread (line 122)\r\nThe IP address of \"www.mathworks.com\" could not be determined.\r\nError in mainisnetavl (line 28)\r\n        data{ii} = string(webread(url, 'date', dates(ii)));\r\nCaused by:\r\n    url: https:\/\/www.mathworks.com\r\n    date: 04-Jul-2017 13:00:00\r\n    The system is not connected to the internet<\/pre>\n
Caution:<\/b> Though this function tells you the internet connectivity of your computer, it may not reflect the internet connectivity of
\n      MATLAB. MATLAB may have its own proxy settings<\/a> that interfere with its access to the internet.\n   <\/p>\n
Comments<\/a><\/h3>\n
Is connectivity of MATLAB to the internet something you would like to have built-in, perhaps as part of the HTTP Interface<\/a>?  If so, please provide your use case here<\/a>.\n   <\/p>\n
Give it a try and let us know what you think here<\/a> or leave a comment<\/a> for Rik.\n   <\/p>\n