FiddlerCore occasionally dropping requests

3 posts, 0 answers
  1. Louis
    Louis avatar
    2 posts
    Member since:
    Dec 2015

    Posted 15 Dec 2015 Link to this post

    To begin, let me say that this is an intermittent issue, and I'm not 100% sure it is caused by Fiddler.

    I have an application that uses the IXMLHTTPRequest2 interface to make requests. I am trying to mock network requests using FiddlerCore.dll in my tests, but every so often I'm seeing the following behavior:

    1. I issue several requests, which succeed.
    2. I set up my IXMLHTTPRequest2 object and call Send(), which returns S_OK.
    3. Nothing happens for 20 seconds.
    4. Windows calls my OnError callback with E_FAIL.

    I have added a BeforeRequest handler to FiddlerCore that logs every request seen (whether I end up mocking it out or not) and an OnLogString handler that simply passes through the logs to my test logger. The request doesn't show up anywhere. It seems to have disappeared without a trace somewhere between Windows and Fiddler.

    I can't find any information about debugging issues with IXMLHTTPRequest2 on MSDN. Do you have any ideas about what may have happened, or where I can look to understand more?


  2. Louis
    Louis avatar
    2 posts
    Member since:
    Dec 2015

    Posted 15 Dec 2015 in reply to Louis Link to this post

    Whoops, I just now realized that this should have gone in the FiddlerCore forum. I didn't see it at first. There doesn't seem to be a way to move or delete and repost this thread, can a mod do it?
  3. Eric Lawrence
    Eric Lawrence avatar
    832 posts

    Posted 16 Dec 2015 Link to this post

    Howdy, Louis--

    No worries on the classification of the post-- I see them all and I answer most of them myself :-). 

    Having said that, do you ever have this problem with Fiddler itself (not FiddlerCore)? As Fiddler's proxy engine is fundamentally the same as FiddlerCore's, it would be revealing if you only saw this in a FiddlerCore-based application and not Fiddler itself.

    Are you sending a large number of requests? Do you have a timeout set for the requests? Are the "missing" requests going to the same server as some earlier request, or to a different server? Are the "missing" requests using "POST" or another method that carries a request body? 

    If you could share the code you're using (send to fiddler, that could prove helpful.

    Eric Lawrence
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