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    nsIXMLHttpRequest

    nsIXMLHttpRequest along with nsIJSXMLHttpRequest and nsIXMLHttpRequestEventTarget are Mozilla's implementation details of the DOM XMLHttpRequest object.

    Note: If you're a web developer or a Mozilla add-on developer, please refer to the XMLHttpRequest documentation instead.

    This page contains documentation, specific to Mozilla application and add-on developers.

    The interface definition: http://mxr.mozilla.org/mozilla-central/source/dom/base/nsIXMLHttpRequest.idl

    Elevated Privileges

    As mentioned in the "Non-Standard Properties" the property of channel was read-only. When using the XPCOM interface, as seen below in Example 2, we can get access to this. The most obvious benefit is that we can set nsiRequest - Constants in the xhr.channel.loadFlags. For instance, as done in Example 2, the flag of LOAD_ANONYMOUS is added, this strips all user data (cookies, tokens, etc).

    Using event handlers from native code

    (Not sure if it's up-to-date)

    From native code, the way to set up onload and onerror handlers is a bit different. Here is a comment from Johnny Stenback <jst@netscape.com>:

    The mozilla implementation of nsIXMLHttpRequest implements the interface nsIDOMEventTarget and that's how you're supported to add event listeners. Try something like this: nsCOMPtr<nsIDOMEventTarget> target(do_QueryInterface(myxmlhttpreq)); target->AddEventListener(NS_LITERAL_STRING("load"), mylistener, PR_FALSE) where mylistener is your event listener object that implements the interface nsIDOMEventListener. The 'onload', 'onerror', and 'onreadystatechange' attributes moved to nsIJSXMLHttpRequest, but if you're coding in C++ you should avoid using those.

    Though actually, if you use addEventListener from C++ weird things will happen too, since the result will depend on what JS happens to be on the stack when you do it....

    Conclusion: Do not use event listeners on XMLHttpRequest from C++, unless you're aware of all the security implications. And then think twice about it.

    Example code

    This is a simple example code for opening a simple HTTP request from a xul application (like a Mozilla extension) without using observers:

     var req = Components.classes["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance();
     req.open('POST', "http://www.foo.bar:8080/nietzsche.do", true);
     req.send('your=data&and=more&stuff=here');
    

    Example 2

    var {Cu: utils, Cc: classes, Ci: instances} = Components;
    Cu.import('resource://gre/modules/Services.jsm');
    function xhr(url, cb) {
        let xhr = Cc["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance(Ci.nsIXMLHttpRequest);
    
        let handler = ev => {
            evf(m => xhr.removeEventListener(m, handler, !1));
            switch (ev.type) {
                case 'load':
                    if (xhr.status == 200) {
                        cb(xhr.response);
                        break;
                    }
                default:
                    Services.prompt.alert(null, 'XHR Error', 'Error Fetching Package: ' + xhr.statusText + ' [' + ev.type + ':' + xhr.status + ']');
                    break;
            }
        };
    
        let evf = f => ['load', 'error', 'abort'].forEach(f);
        evf(m => xhr.addEventListener(m, handler, false));
    
        xhr.mozBackgroundRequest = true;
        xhr.open('GET', url, true);
        xhr.channel.loadFlags |= Ci.nsIRequest.LOAD_ANONYMOUS | Ci.nsIRequest.LOAD_BYPASS_CACHE | Ci.nsIRequest.INHIBIT_PERSISTENT_CACHING;
        xhr.responseType = "arraybuffer"; //dont set it, so it returns string, you dont want arraybuffer. you only want this if your url is to a zip file or some file you want to download and make a nsIArrayBufferInputStream out of it or something
        xhr.send(null);
    }
    
    xhr('https://www.gravatar.com/avatar/eb9895ade1bd6627e054429d1e18b576?s=24&d=identicon&r=PG&f=1', data => {
        Services.prompt.alert(null, 'XHR Success', data);
        var file = OS.Path.join(OS.Constants.Path.desktopDir, "test.png");
        var promised = OS.File.writeAtomic(file, new UInt8Array(data));
        promised.then(
            function() {
                alert('succesfully saved image to desktop')
            },
            function(ex) {
                 alert('FAILED in saving image to desktop')
            }
        );
    });

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    Last updated by: ZhenboLi,