Archive for May, 2009

POST and HTTP Protocol Violation Resolution in

Good Morning! My daughter played volleyball last night and was once again outstanding. MY eldest daughter has been released. Unfortunately that has not gone so well. She is moving out of our house no later than next Monday and to be honest I am ok with that.

Today’s topic is one that has plagued me for a while and isn’t really a coded solution but a hack. I thought I would share it in case some of you run into the same problem. Basically we want to POST data to the server, and the server saves the file and its response is a tar archive. Making the request works fine. Where I ran into trouble was the saving of the binary response to a variable and eventually a file. First some of the code to give you an idea of what happened:

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‘ Download a single binary file from a server and save it to a local folder
    Public Sub DownloadAndSaveFile(ByVal Url As String, ByVal Filename As String, ByVal User As String, ByVal Pass As String, ByVal Debug As Integer)

        ‘ The post data template
        Dim PostdataTemplate As String = _

        Dim PostdataArray As Byte() = Encoding.ASCII.GetBytes(Postdata)

        ‘ Create a new NetworkCredential object
        Dim NetworkCredential As New NetworkCredential(User, Pass)

            ‘ Create a new WebClient instance
            Dim myWebClient As New WebClient

            ‘ Set Preauthenticate property to true
            ‘myWebClient.PreAuthenticate = True

            ‘ Associate the NetworkCrbedential object with the ‘WebRequest’ object
            myWebClient.Credentials = NetworkCredential

            ‘ Add required HTTP headers to request
            myWebClient.Headers.Add("Accept", "*/*")
            myWebClient.Headers.Add("Content-Type", "application/x-www-form-urlencoded")

            ‘ UploadData method implicitly sets HTTP POST as the request method
            Dim responseArray As Byte() = myWebClient.UploadData(Url, PostdataArray)
            ‘ The response array as byte generates an exception!

        Catch Ex As Exception
            WriteLine("Error: " & Ex.Message)

        End Try
    End Sub

I get an exception when saving the response as a byte:

Error: The underlying connection was closed: The server committed an HTTP protocol violation.

The problem was that the .NET Framework detected the server did not comply with HTTP 1.1 RFC. This problem may occur when the response contains incorrect headers or incorrect header delimiters.


S0 what to do? I don’t have control of the production server so I can’t fix it on that end. So here is where the hack came in. I modified the app.exe.config file in the following way. You can also modify the machine.config file this way but don’t do that.I should note that I know that the server inserting a header with no name or value is against RFC2616.  But I don’t have the ability to modify the server’s response in the production environment. Make it a great day! 

<httpWebRequest useUnsafeHeaderParsing="true" />


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