What causing this "Invalid length for a Base-64 char array"

user_29774 0
Viewed 170660

I have very little to go on here. I can't reproduce this locally, but when users get the error I get an automatic email exception notification:

Invalid length for a Base-64 char array.

  at System.Convert.FromBase64String(String s)
  at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)
  at System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState)
  at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState)
  at System.Web.UI.HiddenFieldPageStatePersister.Load()

I'm inclined to think there is a problem with data that is being assigned to viewstate. For example:

List<int> SelectedActionIDList = GetSelectedActionIDList();
ViewState["_SelectedActionIDList"] = SelectedActionIDList;

It's difficult to guess the source of the error without being able to reproduce the error locally.

If anyone has had any experience with this error, I would really like to know what you found out.

viewstate exception asp.net .net
12 Answers

After urlDecode processes the text, it replaces all '+' chars with ' ' ... thus the error. You should simply call this statement to make it base 64 compatible again:

        sEncryptedString = sEncryptedString.Replace(' ', '+');
user_953800

I've seen this error caused by the combination of good sized viewstate and over aggressive content-filtering devices/firewalls (especially when dealing with K-12 Educational institutions).

We worked around it by storing Viewstate in SQL Server. Before going that route, I would recommend trying to limit your use of viewstate by not storing anything large in it and turning it off for all controls which do not need it.

References for storing ViewState in SQL Server:
MSDN - Overview of PageStatePersister
ASP Alliance - Simple method to store viewstate in SQL Server
Code Project - ViewState Provider Model

user_833810

My guess is that something is either encoding or decoding too often - or that you've got text with multiple lines in.

Base64 strings have to be a multiple of 4 characters in length - every 4 characters represents 3 bytes of input data. Somehow, the view state data being passed back by ASP.NET is corrupted - the length isn't a multiple of 4.

Do you log the user agent when this occurs? I wonder whether it's a badly-behaved browser somewhere... another possibility is that there's a proxy doing naughty things. Likewise try to log the content length of the request, so you can see whether it only happens for large requests.

user_226560

Take a look at your HttpHandlers. I've been noticing some weird and completely random errors over the past few months after I implemented a compression tool (RadCompression from Telerik). I was noticing errors like:

  • System.Web.HttpException: Unable to validate data.

  • System.Web.HttpException: The client disconnected.---> System.Web.UI.ViewStateException: Invalid viewstate.

and

  • System.FormatException: Invalid length for a Base-64 char array.

  • System.Web.HttpException: The client disconnected. ---> System.Web.UI.ViewStateException: Invalid viewstate.

I wrote about this on my blog.

Admin1

During initial testing for Membership.ValidateUser with a SqlMembershipProvider, I use a hash (SHA1) algorithm combined with a salt, and, if I changed the salt length to a length not divisible by four, I received this error.

I have not tried any of the fixes above, but if the salt is being altered, this may help someone pinpoint that as the source of this particular error.

user_4266220
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