I am trying to monitor AJAX requests (requests send using XMLHttpRequest
object). I am trying to use observer service
(Components.interfaces.nsIObserverService) for the same and observing events
"http-on-examine-response" and "http-on-modify-request". I get hold of
nsIChannel (actually nsIHttpChannel) on which the requests are being sent.
>From the channel I am trying to get hold of XMLHttpRequest object which sent
the request. Code in nsXMLHttpRequest.cpp
(http://lxr.mozilla.org/mozilla/source/extensions/xmlextras/base/src/nsXMLHttpRequest.cpp)
suggests that XMLHttpRequest object itself is set as 'notificationCallbacks'
property for the channel. I am getting the following exception when I try to
access 'notificationCallbacks' property of the channel (I have given code
snippet at the end).
[Exception... "Component does not have requested interface arg 0
[nsIHttpChannel.notificationCallbacks]" nsresult: "0x80004002
(NS_NOINTERFACE)" location: "JS frame ::
file:///C:/rnd/mozilla/observertest.js :: handler_observe :: line 137"
data: no]
I tried printing the list of properties of 'channel' and it does list
'notificationCallbacks', also
channel.hasOwnProperty("notificationCallbacks") returns true. I am wondering
why mozilla throws the exception on accessing the property. Also is there
any other alternative to get hold of XMLHttpRequest from with in
"http-on-modify-request" callback? I would like to get hold of the
XMLHttpRequest object (which implements nsIDOMEventTarget) and use
addEventListener to add listeners to monitor activities on the request.
Code snippet:
handler.prototype.observe =
function handler_observe (channel, topic, data)
{
switch (topic)
{
case "http-on-examine-response":
if (channel instanceof Components.interfaces.nsIHttpChannel)
{
try
{
var ir = channel.notificationCallbacks;
}
catch (ex)
{
log(ex);
}
}
else
{
log("Subject is not instance of nsIHttpChannel");
}
break;
case "http-on-modify-request":
if (channel instanceof Components.interfaces.nsIHttpChannel)
{
try
{
var ir = channel.notificationCallbacks;
}
catch (ex)
{
log(ex);
}
}
else
{
log("Subject is not instance of nsIHttpChannel");
}
break;
}
}
-- Ajit Dhumale
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