load data via HTTP protocol

This tutorial present HTTP network connection via the HTTP javascript library.
HTTP javascript library offers same functionality than XMLHttpRequest.

In fist time, we send a request to Google and we display result in console.

To send request, we use the get method (GET HTTP request).
Get method : void get (String url, Function callback, String encoding)
url is the google URL (http://google.com).
callback is a function to process request result.
encoding is optional (by default UTF-8). We use the default value.

First example code:

Group {
  children [
    Script {
      url "javascript:
      	function initialize() {
      	  Http.get ('http://google.com/', callback);
      	}
        //HTTP request response processing    
        function callback(url, responseCode, responseData, now) {
          Browser.print ( responseData );
        }
      "
    }
  ]
}

In previous example, we send a HTTP request and display the result.
Detail of the callback function:

function callback(url, responseCode, responseData, now)

url: Initial request URL
responseCode: The HTTP response.
Return 200 if result if OK, 40X if result is KO
See the rfc 2616 to know all response code.
responseData: Data of the response (Web page, web service result, ...)
now: current time (MeMo time)

In next example, with callback function, we verify the response:

Group {
  children [
    Script {
      url "javascript:
      	function initialize() {
      	  Http.get ('http://google.com/', callback);
      	}
        //HTTP request response processing    
        function callback(url, responseCode, responseData, now) {
          if ( responseCode == 200 ) {
          	Browser.print ( responseData );
          } else {
            Browser.print ( 'HTTP error: ' + responseCode );
          }
        }
      "
    }
  ]
}

Try to change URL to verify if you catch an error (example, use URL 'http://goolgle.com').

To optimize network access, MeMo offers cache features.
See cache part, in advanced chapter.

Cache example:

Group {
  children [
    Script {
      url "javascript:
      	function initialize() {
      	  //Load page in cache if page is already loaded.
      	  //Else, at first access, load page on the web
      	  Http.get ('cache://cachedpage.html,http://google.com/', callback);
      	}
        //HTTP request response processing    
        function callback(url, responseCode, responseData, now) {
          if ( responseCode == 200 ) {
          	Browser.print ( responseData );
          } else {
            Browser.print ( 'HTTP error: ' + responseCode );
          }
        }
      "
    }
  ]
}

To process XML (web service, ...) or JSON responses, Mobile Widgets offers javascript libraries.
See JSON library documentation for process JSON result.
See XML library documentation for process XML result.

Example: Load JSON data and process JSON result:

Group {
  children [
    Script {
      url "javascript:
      	function initialize() {
      	  Http.get ('http://my_json_service/', parseJson);
      	}
        //HTTP request response processing    
        function parseJson(url, responseCode, responseData, now) {
          // Parse Json response
          var id = JSON.open(responseData , JSON.BUFFER);
          JSON.find(id, '/result');
          Browser.print('Result: '+JSON.getValue(id)); // Prints "Result: myContent"
          JSON.close(id); // Free all resources associated
        }
      "
    }
  ]
}

Example: Load XML data and process XML result:

Group {
  children [
    Script {
      url "javascript:
      	function initialize() {
      	  Http.get ('http://my_xml_service/', parseXml);
      	}
        //HTTP request response processing    
        function parseXml(url, responseCode, responseData, now) {
          // Parse XML response, like JSON response
          var id = XML.open(responseData , XML.BUFFER);
          XML.find(id, '/result');
          Browser.print('Result: '+XML.getValue(id)); // Prints "Result: myContent"
          XML.close(id); // Free all resources associated to the DOM
        }
      "
    }
  ]
}

XML libary can load data without use HTTP library, via the open method.
Method: XML.open (url, XML.URL, callback);
Callback function: parseXml(url, responseCode, id, now)
With id the identity of XML result.

Previous example without use HTTP library:

Group {
  children [
    Script {
      url "javascript:
      	function initialize() {
      	  XML.open ('http://my_xml_service/', XML.URL, parseXml);
      	}
        //HTTP request response processing    
        function parseXml(url, responseCode, id, now) {
          XML.find(id, '/result');
          Browser.print('Result: '+XML.getValue(id)); // Prints "Result: myContent"
          XML.close(id); // Free all resources associated to the DOM
        }
      "
    }
  ]
}