ViewState getting truncated : The Official Microsoft ASP.NET Forums

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Jason Hill

Contributor

2019 Points

494 Posts

ViewState getting truncated

May 29, 2007 06:42 AM|LINK

Hi,

We are experiencing a problem where our viewstate seems to be getting truncated, possibly by a proxy server or firewall at a client site. The error we get is:

Invalid length for a Base-64 char array.

We updated the web.config with the following setting in the <pages> element:

maxPageStateFieldLength="1000"

this seemed to mostly resolve the issue but we now intermittently get this exception instead:

Invalid viewstate: Missing field: __VIEWSTATE47

Has anyone successfully used the maxPageStateFieldLength property without getting the missing field error? I have seen other solutions that handle the viewstate chunking in code rather than using maxPageStateFieldLength and we are wondering if we should do that instead?

Cheers,

Jason

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Rex Lin - MSFT

All-Star

17422 Points

2116 Posts

Re: ViewState getting truncated

May 31, 2007 03:04 AM|LINK

HI, Jason Hill :

Yes absolutely, Firewalls can truncate viewstate if the field length is
too long. The work around isn't necessarily to limit the viewstate
(although I would recommend making this as small as possible something
like datagrid sorting / paging doesn't work so well with it turned off
:) ), instead you break the viewstate up into several fields. This is
actually pretty simple.

Just add these overrides to your base page class...

#region Modified ViewState Code
protected override object LoadPageStateFromPersistenceMedium()
{
        LosFormatter format = new LosFormatter();
        int cnt = 0;
        try
        {
                Cnt =
Convert.ToInt32(Request["__VIEWSTATE0"].ToString());
        }
        catch (System.NullReferenceException)
        {}
        catch (System.FormatException)
        {}

        System.Text.StringBuilder s     = new
System.Text.StringBuilder();
        for ( int i = 1; i <= cnt; i++ )
        try
        {
                s.Append( Request["__VIEWSTATE" +
i.ToString()].ToString() );
        }
        catch (System.NullReferenceException)
        {}

        try
        {
                object o = format.Deserialize(s.ToString());
                if (o.GetType() == typeof(Triplet))
                        return o;
                else if (o.GetType() == typeof(string) && (o as
string).Length == 0)
                        o = null;
                return o;
        }
        catch (System.Exception)
        {
        }
}

protected override void SavePageStateToPersistenceMedium(object
viewState)
{
        LosFormatter format = new LosFormatter();
        System.IO.StringWriter writer   = new System.IO.StringWriter();
        format.Serialize(writer, viewState);
        System.Text.StringBuilder s = new
System.Text.StringBuilder(writer.ToString());
        int cnt = 1;
        int left = s.Length;

        while( left > 0 )
        {
                int cut= (left > 1000) ? 1000 : left; //Change 1000 to
whatever size you need
                RegisterHiddenField("__VIEWSTATE" + cnt.ToString(),
s.ToString().Substring(0,cut));
                S = s.Remove(0,cut);
                left    -= cut;
                cnt++;
        }
        cnt--;

        RegisterHiddenField("__VIEWSTATE0", cnt.ToString());
}
#endregion

Good Luck

Best Regards,
__________________________________________________
Sincerely,
Rex Lin
Microsoft Online Community Support

If there is any question or the issue is not resolved, please feel free to mark the thread as not resolved

Reply

Jason Hill

Contributor

2019 Points

494 Posts

Re: ViewState getting truncated

May 31, 2007 03:13 AM|LINK

Thanks Rex,

This is what the maxPageStateFieldLength config attribute is supposed to do but then we get the missing field errors.

We have since worked around the problem by implementing our own PageAdapter and PageStatePersister classes so that we can persist viewstate to the database. This has actually improved the performance of our application noticably as there is less info being sent across the wire between the server and browser (especially important as we are using ajax with lots of small postbacks that still send the entire viewstate).

Jason