[IronPython] Silverlight and Catching HttpWebRequest Errors

Dino Viehland dinov at exchange.microsoft.com
Wed Jun 25 21:22:35 PDT 2008


While it might look like those events are public they aren't really.  BrowserHttpWebRequest is an internal type so its members are not directly exposed - even if those members are public.  If it were overriding some methods on a base class or interface that were public we could then access them.  It does implement an interface which has those members, INetworkProgress, but that interface is also internal!  So even though there are public methods there is no publicly accessible way for us to get to those events :(.  If the interface was public we'd be able to access them.

-----Original Message-----
From: users-bounces at lists.ironpython.com [mailto:users-bounces at lists.ironpython.com] On Behalf Of Jimmy Schementi
Sent: Wednesday, June 25, 2008 9:09 PM
To: Discussion of IronPython
Subject: Re: [IronPython] Silverlight and Catching HttpWebRequest Errors

So, did some homework on this. Taking a look at BrowserHttpWebRequest with Reflector, it definitely has a public ProgressFailed event, but it says it's read-only.

Dino/Curt, could this behavior happen because BrowserHttpWebRequest has a methods and events by exactly the same name?

    private EventHandler<NetworkProgressChangedEventArgs> ProgressChanged;
    private EventHandler<NetworkProgressChangedEventArgs> ProgressCompleted;
    private EventHandler<NetworkProgressChangedEventArgs> ProgressFailed;

    // Events
    public event EventHandler<NetworkProgressChangedEventArgs> ProgressChanged;
    public event EventHandler<NetworkProgressChangedEventArgs> ProgressCompleted;
    public event EventHandler<NetworkProgressChangedEventArgs> ProgressFailed;

Michael, regardless, for simple downloading I'd use WebClient; the code is much more concise:

from System.Net import WebClient
from System import Uri

def Downloaded(sender, args):
    print args.Result

uri = Uri('http://localhost:2060/index.html')
req = WebClient()
req.DownloadStringCompleted += Downloaded
req.DownloadStringAsync(uri)

Do you still have time to change your book's example? =P

~Jimmy

> -----Original Message-----
> From: users-bounces at lists.ironpython.com [mailto:users-
> bounces at lists.ironpython.com] On Behalf Of Michael Foord
> Sent: Wednesday, May 14, 2008 2:58 PM
> To: Discussion of IronPython
> Subject: Re: [IronPython] Silverlight and Catching HttpWebRequest
> Errors
>
> Michael Foord wrote:
> > Michael Foord wrote:
> >> On May 12, 9:17 am, Jimmy Schementi <Jimmy.Scheme... at microsoft.com>
> >> wrote:
> >>
> >>> The actual type returned by HttpWebRequest.Create() is a
> >>> BrowserHttpWebRequest, but it's internal (not sure why). Anyway, it
> >>> has a ProgressFailed event you can hook.
> >>>
> >>
> >> Hello Jimmy,
> >>
> >> As far as I can tell it *doesn't* have the 'ProgressFailed' event.
> >>
> >
> > The actual failure I see is:
> >
> > Exception: [Arg_COMException]
> > Arguments:
> > Debugging resource strings are unavailable. Often the key and
> > arguments provide sufficient information to diagnose the problem. See
> >
> http://go.microsoft.com/fwlink/?linkid=106663&Version=2.0.30226.1&File=
> mscorlib.dll&Key=Arg_COMException
> >
> >
> >
>
> Sorry for the noise. This one is actually for the sake of google (and
> all who sail in her).
>
> Exception
>    at MS.Internal.XcpImports.GetDownloaderBytes(IntPtr element, IntPtr&
> outBytes, Int32& outSize)
>    at MS.Internal.InternalWebRequest.GetResponseStream()
>    at System.Net.BrowserHttpWebRequest.Completed(Object sender,
> EventArgs e)
>    at System.Windows.CoreInvokeHandler.InvokeEventHandler(Int32
> typeIndex, Delegate handlerDelegate, Object sender, Object args)
>    at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr
> unmanagedObjArgs, Int32 argsTypeIndex, String eventName)
>
> Michael
>
> > This is using Safari. As I'm developing on the Mac I can't use
> > debugging, nor can I test in Firefox because of the bug in Chiron.
> >
> > It looks like some people have similar errors:
> >
> >    http://silverlight.net/forums/p/12500/40967.aspx#40967
> >
> > and a guy in the comments here:
> >
> >
> > http://www.cameronalbert.com/post/2008/03/HttpWebRequest-Helper-for-
> Silverlight-2.aspx
> >
> >
> > All the best,
> >
> > Michael Foord
> > http://www.ironpythoninaction.com/
> >
> >> I need to make cross-domain POST, and although the request gets made
> >> successfully I'm getting a COM Arg Exception everytime (I think
> >> because the server is slow to respond). This is screwing me at the
> >> moment.
> >>
> >> FYI - when I execute the following code in Silverlight:
> >>
> >>   from System.Net import WebRequest
> >>   from System import Uri
> >>
> >>   u = Uri('http://www.v.com')
> >>   req = WebRequest.Create(u)
> >>   print req.ProgressFailed
> >>
> >> I get the following exception:
> >>
> >> Traceback (most recent call last):
> >>   File "None", line 6, in <undefined>
> >> AttributeError: 'BrowserHttpWebRequest' object has no attribute
> >> 'ProgressFailed'
> >>
> >> All the best,
> >>
> >> Michael Foord
> >> http://www.ironpythoninaction.com/
> >>
> >>
> >>> PS. If you REALLY want synchronous downloading, just hack on
> >>> XMLHttpRequest
> >>>
> >>> def download(url):
> >>>     request = HtmlPage.Window.CreateInstance("XMLHttpRequest")
> >>>     request.Invoke("open", "GET", url, false) # false means
> synchronous
> >>>     request.Invoke("send", "")
> >>>     return request.GetProperty("responseText")
> >>>
> >>> :)
> >>>
> >>> ~js
> >>> ________________________________________
> >>> From: users-boun... at lists.ironpython.com
> >>> [users-boun... at lists.ironpython.com] On Behalf Of Michael Foord
> >>> [fuzzy... at voidspace.org.uk]
> >>> Sent: Monday, May 12, 2008 12:58 AM
> >>> To: Discussion of IronPython
> >>> Subject: [IronPython] Silverlight and Catching HttpWebRequest
> Errors
> >>>
> >>> Hello guys,
> >>>
> >>> I have a problem with catching network errors raised by
> HttpWebRequest
> >>> in Silverlight. (Not necessarily an IronPython specific question -
> but
> >>> you guys are so intelligent you are always the first place I
> turn...)
> >>>
> >>> HttpWebRequest uses an async model for fetching resources. If there
> >>> is a
> >>> problem (triggered usually by a slow response from the server),
> then it
> >>> can happen *after* I have made the request - but before my callback
> is
> >>> invoked. This gives me nowhere to catch the exception, as
> >>> effectively it
> >>> happens 'inside Silverlight'. I wondered if there was a solution...
> ?
> >>>
> >>> def callback(asyncResult):
> >>>     ...
> >>>
> >>> uri = Uri(some_url)
> >>> req = HttpWebRequest.Create(uri)
> >>>
> >>> req.BeginGetResponse(AsyncCallback(callback), object())
> >>>
> >>> The error occurs after BeginGetResponse, but before calback. Any
> ideas
> >>> for catching it?
> >>>
> >>> Michael Foordhttp://www.ironpythoninaction.com/
> >>>
> >>> _______________________________________________
> >>> Users mailing list
> >>>
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> s-ironpython.com
> >>>
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> >>>
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