Newbie Stream Behavior Question RSS

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  compbrat75

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  2 Posts

  Newbie Stream Behavior Question

  Dec 04, 2012 08:48 PM|LINK

  Can a Stream only be read once?

  I have a System.IO.Stream object where I store a HttpContext.Current.Request.InputStream. I need to write the stream to a log file and then process the stream later in my program. It seems that I can only read the stream once and then it disappears.

  I've tried a number of copy methods including the CopyTo method, but the second stream never populates.

  If I do this:

  Dim input As Stream = HttpContext.Current.Request.InputStream
  Dim tmpSR As StreamReader = New StreamReader(input)
  Response.Write(tmpSR.ReadToEnd())

  The stream outputs just fine, but then I can't access the stream again which leads me to believe that after its read, it's gone.

  I have tried this:

  	Dim logfile As String = "mylogfile_" & DateTime.Now.ToString("yyyyMMdd") & ".log"
  	Dim objFileStream As FileStream
  	Dim asyncResult As IAsyncResult
  	Dim writeBuffer As Byte()
  	Dim logText As String
  	
  	Dim input As Stream = HttpContext.Current.Request.InputStream
  	Dim inputSave As Stream = input
  
  	Dim tmpSR As StreamReader = New StreamReader(input)
  	Dim tmpSR2 As StreamReader = New StreamReader(inputSave)
  
  
  	logText = (DateTime.Now.ToString("yyyyMMdd HHmmss")) & "Request Method: " & Request.RequestType & " "
  
  	objFileStream = New FileStream(logfile,FileMode.Append,FileAccess.Write,Fileshare.ReadWrite,4096,True)
  
  	Using objStreamWriter As StreamWriter = New StreamWriter(objFileStream)
  		writeBuffer = Encoding.ASCII.GetBytes(logText)
  		asyncResult = objFileStream.BeginWrite(writeBuffer,0,writeBuffer.Length,Nothing,Nothing)
  		objStreamWriter.WriteLine()
  		objStreamWriter.Write(tmpSR.ReadToEnd())
  		objStreamWriter.WriteLine()
  		objFileStream.EndWrite(asyncResult)
  		objFileStream.Flush()
  		objStreamWriter.Flush()
  		objStreamWriter.Close()
  	End Using
  			
  	objFileStream.Close() 	
  	
  	Response.Write(tmpSR2.ReadToEnd())

  The log file receives the Stream data; however, the 'saved' Stream that I want to Write out to the browser returns 0 bytes. It appears to have vanished.

  I've read a bit about the CopyTo() method of the Stream class that's available in 4.0, but I haven't been able to implement that method with any success either.

  As I have said, I'm pretty new to ASP.net. I'm using VB and my framework is 4.0. Any guidance would be appreciated.

  Thanks!

  ~Maria
  
  

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  Angie xu - M...

  All-Star

  18045 Points

  1550 Posts

  Microsoft

  Re: Newbie Stream Behavior Question

  Dec 11, 2012 06:07 AM|LINK

  Hi compbrat

  compbrat75

  Dim tmpSR As StreamReader = New StreamReader(input)

  Yes, you could use Stream.CopyTo Method to read the bytes from the current stream and write them to the destination stream.

  But StreamReader is designed for character input in a particular encoding,  use StreamReader for reading lines of information from

   a standard text file.

   StreamReader is for text data. You will almost certainly lose data if you use it for arbitrary binary data.

  You could learn StreamReader here.

  kind regards

  Please mark the replies as answers if they help or unmark if not.
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  • Edited by Angie xu - MSFT on Dec 11, 2012 06:09 AM
  • Edited by Angie xu - MSFT on Dec 11, 2012 06:09 AM
  • Edited by Angie xu - MSFT on Dec 11, 2012 06:10 AM
• • Reply
  

  compbrat75

  0 Points

  2 Posts

  Re: Newbie Stream Behavior Question

  Dec 13, 2012 09:03 PM|LINK

  Hi Angie,

  Thank you for the response!

  I just figured out what I needed to do. It was so simple in the end.

  I kept thinking that the stream was disappearing and that I had to copy it off somewhere in order to read it again. In the end, all that I needed to do was reset the position of the stream to 0. For anyone else that needs this...

  Dim logfile As String = "mylogfile_" & DateTime.Now.ToString("yyyyMMdd") & ".log"
          Dim objFileStream As FileStream
          Dim asyncResult As IAsyncResult
          Dim writeBuffer As Byte()
          Dim logText As String
          
          Dim input As Stream = HttpContext.Current.Request.InputStream
          Dim inputSR As StreamReader = New StreamReader(input)
  
          logText = (DateTime.Now.ToString("yyyyMMdd HHmmss")) & " Request Method: " & Request.RequestType & " "
  
          objFileStream = New FileStream(logfile,FileMode.Append,FileAccess.Write,Fileshare.ReadWrite,4096,True)
  
          Using objStreamWriter As StreamWriter = New StreamWriter(objFileStream)
                  writeBuffer = Encoding.ASCII.GetBytes(logText)
                  asyncResult = objFileStream.BeginWrite(writeBuffer,0,writeBuffer.Length,Nothing,Nothing)
                  objStreamWriter.WriteLine()
                  objStreamWriter.Write(inputSR.ReadToEnd())
                  objStreamWriter.WriteLine()
                  objFileStream.EndWrite(asyncResult)
                  objFileStream.Flush()
                  objStreamWriter.Flush()
                  objStreamWriter.Close()
          End Using
                          
          objFileStream.Close()
          input.Position = 0
          Response.Write(inputSR.ReadToEnd())

  
  I hope this helps some other newbie!

  • Marked as answer by compbrat75 on Dec 13, 2012 09:03 PM