Response Filter losing data when response is buffered

Discussion in 'ASP .Net' started by Brad, Feb 18, 2004.

  1. Brad

    Brad Guest

    I have a response filter which injects "standard" html into my pages. The
    filter works fine when the initial stream is small enough not to
    buffer...or....if I have a large unbuffered stream (i.e. I set buffer=false
    on a large page). Now the problem: If I turn on buffering on a large
    page, the page output (to the browser) is correct a few times (sometines
    just once, sometime 2-3 times...on the same page) then I seem to either
    lose data or get corrputed data (I'm not sure which) in the middle of the
    stream. The problem seems to persist until the page in my local web servers
    cache (?) is cleared out i.e. I browser to some other pages then browse
    back to the problem page.

    I've compared the size of the buffer at the start and end of my filter's
    write sub on the calls when it works when it does not and the buffers are
    the same size which make it look like I'm not droping characters. The large
    page has embedded encrypted client script from a third party control and
    I've wondered if that script could be getting corrupted from the
    UTF8Encoding.UTF8.GetString and/or the later UTF8Encoding.UTF8.GetBytes in
    the write sub.

    Anyone have thoughts or suggestions as to what to look for?

    Thanks

    Brad
    Brad, Feb 18, 2004
    #1
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  2. Hi Brad,



    Thanks for posting in the community!
    From your description, you used a certain Custom Response Filter to add
    some certain html code into the response stream. However, you found the
    page which has applied the Filter will output incompleted or corrupted
    response data when the page's response content is large enough to buffer
    and the Response's Buffer is set as true, yes?
    If there is anything I misunderstood, please feel free to let me know.

    I'm not sure the detailed operations in your filter, can you repro this
    problem via certain code logic and steps? Or just a certain simple sample
    Filter class to repro this problem?
    Have you tried applied another certain filter class on the page's response
    to see whether this problem remains?
    If so , I think I can do some further tests on my side on this issue.
    Please check the above items and let me know if you have any findings.


    Regards,

    Steven Cheng
    Microsoft Online Support

    Get Secure! www.microsoft.com/security
    (This posting is provided "AS IS", with no warranties, and confers no
    rights.)

    Get Preview at ASP.NET whidbey
    http://msdn.microsoft.com/asp.net/whidbey/default.aspx
    Steven Cheng[MSFT], Feb 18, 2004
    #2
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  3. Brad

    Brad Guest

    Steven -
    I've resolved the problem. Here's what I found and how I resolved it:

    First, I simplified the filter's Write sub to the following and still had
    the problem.
    =============================
    Friend Class ResponseFilter
    Inherits Stream
    Private responseStream As Stream

    Public Overrides Sub Write(ByVal buffer() As Byte, ByVal offset As
    Integer, ByVal count As Integer)
    Dim sBuffer As String =
    System.Text.UTF8Encoding.UTF8.GetString(buffer, offset, count)

    ' Here is where code could be placed to manipulate content of
    sBuffer before writing to stream

    buffer = System.Text.UTF8Encoding.UTF8.GetBytes(sBuffer)
    responseStream.Write(buffer, offset, buffer.Length)
    End Sub

    =============================
    I resolved the problem, by appending the writes buffer content into a
    stringbuilder. When I detect </html> in the buffer I know I've received the
    last buffer (last call to write). I make my changes to the contents of the
    stringbuilder and write the entire content to the stream.

    Friend Class ResponseFilter
    Inherits Stream
    Private responseStream As Stream
    Private html As StringBuilder = New StringBuilder
    ...
    Public Overrides Sub Write(ByVal buffer() As Byte, ByVal offset As
    Integer, ByVal count As Integer)
    Dim sBuffer As String =
    System.Text.UTF8Encoding.UTF8.GetString(buffer, offset, count)
    html.Append(sBuffer)

    Dim oEndFile As Regex = New Regex("</html>",
    RegexOptions.IgnoreCase)

    If (oEndFile.IsMatch(sBuffer)) Then
    Dim tempResponse As String = html.ToString()
    buffer = System.Text.UTF8Encoding.UTF8.GetBytes(tempResponse)
    responseStream.Write(buffer, 0, buffer.Length)
    End If
    End Sub
    =============================

    If you see anything bad still or have suggestions please let me know.

    Thanks

    Brad



    "Steven Cheng[MSFT]" <> wrote in message
    news:...
    > Hi Brad,
    >
    >
    >
    > Thanks for posting in the community!
    > From your description, you used a certain Custom Response Filter to add
    > some certain html code into the response stream. However, you found the
    > page which has applied the Filter will output incompleted or corrupted
    > response data when the page's response content is large enough to buffer
    > and the Response's Buffer is set as true, yes?
    > If there is anything I misunderstood, please feel free to let me know.
    >
    > I'm not sure the detailed operations in your filter, can you repro this
    > problem via certain code logic and steps? Or just a certain simple sample
    > Filter class to repro this problem?
    > Have you tried applied another certain filter class on the page's response
    > to see whether this problem remains?
    > If so , I think I can do some further tests on my side on this issue.
    > Please check the above items and let me know if you have any findings.
    >
    >
    > Regards,
    >
    > Steven Cheng
    > Microsoft Online Support
    >
    > Get Secure! www.microsoft.com/security
    > (This posting is provided "AS IS", with no warranties, and confers no
    > rights.)
    >
    > Get Preview at ASP.NET whidbey
    > http://msdn.microsoft.com/asp.net/whidbey/default.aspx
    >
    Brad, Feb 18, 2004
    #3
  4. Hi Brad,


    Thanks for your followup. I'm glad that you've figured out this problem.
    The StringBuilder will provide high performance when doing string
    manipulation. Here is the description in MSDN:
    ----------------------------------------------------------
    The String object is immutable. Every time you use one of the methods in
    the System.String class, you create a new string object in memory, which
    requires a new allocation of space for that new object. In situations where
    you need to perform repeated modifications to a string, the overhead
    associated with creating a new String object can be costly. The
    System.Text.StringBuilder class can be used when you want to modify a
    string without creating a new object. For example, using the StringBuilder
    class can boost performance when concatenating many strings together in a
    loop.
    ----------------------------------------------------------
    Also, here are some tech articles discussing on this:
    #HOW TO: Improve String Concatenation Performance in Visual Basic .NET
    http://support.microsoft.com/?id=306821

    #Efficient String Manipulations with StringBuilder
    http://www.ondotnet.com/pub/a/dotnet/2002/07/15/string.html


    Maybe the large page with buffer turn on cause string to realloc again and
    again cause the unexpected problem. But I'm still so surprised at this
    result. Any way, thanks again for providing us your experience.


    Regards,

    Steven Cheng
    Microsoft Online Support

    Get Secure! www.microsoft.com/security
    (This posting is provided "AS IS", with no warranties, and confers no
    rights.)

    Get Preview at ASP.NET whidbey
    http://msdn.microsoft.com/asp.net/whidbey/default.aspx
    Steven Cheng[MSFT], Feb 19, 2004
    #4
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