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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
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<html> |
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<head> |
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<script type="text/javascript"> |
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<!-- |
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// Mozilla only implementation! |
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|
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// Constructor for generic HTTP client |
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function HTTPClient() {}; |
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|
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// Add methods and properties as array |
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HTTPClient.prototype = { |
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url: null, |
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|
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// Instance of XMLHttpRequest |
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xmlhttp: null, |
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|
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// Used to make sure multiple calls are not placed |
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// with the same client object while another in progress |
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callinprogress: false, |
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|
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// The user defined handler - see MyHandler below |
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userhandler: null, |
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|
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init: function(url) { |
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this.url = url; |
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this.xmlhttp = new XMLHttpRequest(); |
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}, |
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|
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// handler argument is a user defined object to be called |
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asyncGET: function (handler) { |
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|
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// Prevent multiple calls |
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if (this.callinprogress) { |
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throw "Call in progress"; |
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}; |
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|
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this.userhandler = handler; |
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|
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// Open an async request - third argument makes it async |
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this.xmlhttp.open(‘GET‘,this.url,true); |
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|
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// Have to assign "this" to a variable - not sure why can‘t use directly |
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var self = this; |
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|
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// Assign a closure to the onreadystatechange callback |
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this.xmlhttp.onreadystatechange = function() { |
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self.stateChangeCallback(self); |
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} |
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|
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// Send the request |
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this.xmlhttp.send(null); |
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}, |
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|
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stateChangeCallback: function(client) { |
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switch (client.xmlhttp.readyState) { |
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|
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// Request not yet made |
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case 1: |
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try { |
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client.userhandler.onInit(); |
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} catch (e) { /* Handler method not defined */ } |
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break; |
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|
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// Contact established with server but nothing downloaded yet |
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case 2: |
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try { |
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// Check for HTTP status 200 |
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if ( client.xmlhttp.status != 200 ) { |
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client.userhandler.onError( |
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client.xmlhttp.status, |
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client.xmlhttp.statusText |
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); |
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|
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// Abort the request |
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client.xmlhttp.abort(); |
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|
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// Call no longer in progress |
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client.callinprogress = false; |
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} |
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} catch (e) { |
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/* Handler method not defined */ |
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} |
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break; |
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|
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// Called multiple while downloading in progress |
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case 3: |
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// Notify user handler of download progress |
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try { |
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// Get the total content length |
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// -useful to work out how much has been downloaded |
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try { |
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var contentLength = |
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client.xmlhttp.getResponseHeader("Content-Length"); |
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} catch (e) { |
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var contentLength = NaN; |
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} |
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|
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// Call the progress handler with what we‘ve got |
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client.userhandler.onProgress( |
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client.xmlhttp.responseText, |
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contentLength |
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); |
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|
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} catch (e) { /* Handler method not defined */ } |
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break; |
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|
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// Download complete |
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case 4: |
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try { |
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client.userhandler.onLoad(client.xmlhttp.responseText); |
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} catch (e) { |
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/* Handler method not defined */ |
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} finally { |
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// Call no longer in progress |
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client.xmlhttp.callinprogress = false; |
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} |
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break; |
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} |
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} |
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} |
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|
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// A user defined handler to response to the XMLHTTPRequest |
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var MyHandler = { |
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onInit: function() { |
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echo("About to send request<br>"); |
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}, |
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onError: function(status,statusText) { |
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echo("Error: "+status+": "+statusText+"<br>"); |
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}, |
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onProgress: function(responseText,length) { |
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echo("Downloaded "+responseText.length+" of "+length+"<br>"); |
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}, |
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onLoad: function(result) { |
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echo("<pre>"+result+"</pre>"); |
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}, |
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} |
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|
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// Just a function to help display results |
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function echo(string) { |
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document.getElementById("results").innerHTML += string; |
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} |
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|
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// Invoke the client |
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function getPage() { |
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// Modify this to some page |
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var url = "http://localhost/test/test.txt"; |
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var client = new HTTPClient(); |
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client.init(url); |
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|
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try { |
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client.asyncGET(MyHandler); |
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} catch (e) { |
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alert(e); |
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} |
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echo("Async request so still able to do stuff here<br>"); |
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} |
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</script> |
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</head> |
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<body> |
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<a href="javascript:getPage();">getPage</a> |
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<div id="results"> |
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</div> |
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</body> |
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</html> |
