Re: How is this conditional able to execute?

Thanks Stephany. This is super helpful.

Why is this part out of the loop:
Dim networkStream As NetworkStream = tcpClient.GetStream()

Also, your first IF:
If networkStream.DataAvailable then

didn't have an ending END IF. I put on just before the catch. Is that
correct?

This conditional is still being executed when returndata = ""
If returndata <> "" AndAlso returndata <>
ClientForm.ReturnData Then
ClientForm.ReturnData = returndata
End If
Maybe I just don't understand the returndata = "" because of the byte array.
But it seems you are testing the same conditions I did before. So the above
will always execute because the array always has 8192 length and somehow
that makes returndata pass on returndata <> "".

How can I read the string in :
Dim returndata As String = Encoding.UTF8.GetString(bytes, 0, bytesread)
returndata gets the empty string here, although it really isn't, as have
seen previously.

thanks,
brett

"Stephany Young" <noone@localhost> wrote in message
news:eJau0ZURFHA.576@xxxxxxxxxxxxxxxxxxxxxxx
> The mist is clearing.
>
> If I've misunderstood anything please let me know because I'm still making
> some assumptions.
>
> I suspect that your starting point for the Try ... Catch ... End Try
> section is the example shown in the documentation on the
> TcpClient.GetStream method.
>
> What you have done is wrapped it in a loop and added some embellishments
> and that example was not quite designed for that to be done to it. The
> example was designed for a one-time run and to drop through the logic to
> whatever followed. In your case you want the loop to continue until
> certain conditions are met or the program ends. To meet this need you need
> to do things just a little differently.
>
> I assume that ClientForm.utility is also a shared reference to some sort
> of utiliy class and that ClientForm.Packet is declared in a similar
> fashion to ClientForm.ReturnData.
>
> If I am correct in that ConnectInit is outside the thread then you
> shouldn't be attempting to reinstate a 'broken' connection within the
> thread. If a 'broken' connection is detected you should allow the thread
> to 'die', then reconnect, then start a new instance of the thread.
>
> Before the start of loop you are obtaining a reference to the
> NetworkStream object of the TcpClient object. In addidition, on each
> iteration of the loop you are obtaining a fresh reference to the
> NetworkStream object of the TcpClient object. There is no reason to do
> this. Don't quote me on this but I suspect that doing so will cause you
> problems.
>
> The declaration of the 'bytes' array should not need to be inside the
> loop. Creating a new array on every iteration is not necessary. When you
> read the NetworkStream object, the data will overwrite what is already in
> the array. of course the array should be created with 8192 elements by
> using tcpClient.ReceiveBufferSize - 1 rather than the 8193 elements you
> will get if you simply use tcpClient.ReceiveBufferSize.
>
> The NetworkStream.Read method, as well as filling the array, also returns
> an integer indicating the number of bytes successfully read into the
> array. You should make use of this to control what you are dealing with.
> Remember that tcpClient.ReceiveBufferSize is the maximum number of bytes
> that can be read at any one time rather than the number of bytes that are
> actually read.
>
> For the third parameter to the NetworkStream.Read method, it is, in my
> opinion, better to use bytes.Length rather than
> tcpClient.ReceiveBufferSize because bytes.Length is the actual number of
> elements in the array.
>
> I think that the tests of the NetworkStream.CanWrite and
> NetworkStream.CanRead are probably redundant, unless you are opening the
> sockets at either end with specfic read/write restrictions.
>
> Another important point is that the NetworkStream.Read method will block
> until data is available. This is probably undesirable but can be
> circumvented by using the NetworkStream.DataAvailable property. This will
> allow your loop to iterate in a timely manner.
>
> Now that we know exactly how many bytes were read from the NetworkStream
> object, we can use the appropriate Encoding.GetString overload to make
> sure that our string is a representation of only those bytes. This should
> do away with the need for any 'trimming' of the resulting string.
>
> Where you have the test for NetworkStream.DataAvailable is inappropriate
> and I get the impression that you might not fully understand it's use.
>
> On the test of returndata, the .ToString is redundant because returndata
> is already a string. The parenthesis are also redundant. In addition,
> using AndAlso will be better than And here because if returndata is an
> empty string then the second part of the test will not be evaluated if
> AndAlso is used whereas it will be evaluated if just And is used. The
> logic is that if the evaluation of first part fails then why bother
> evaluating the second part at all. This is clled 'short-circuiting' and is
> a very useful technique when used appropriately. Setting returndata to
> Nothing is redundant because returndata is going to be created anew on the
> next iteration of the loop. Likewise, the 'Else' that does nothing is also
> redundant.
>
> As you can see, the resulting code is more compact and now, that the
> appropriate techniques are being used, should work quite happily.
>
> What is left to do, of course, is for you to add the appropriate code to
> 'tear-down' the thread in a friendly fashion when the program needs to
> terminate or you need to stop the thread for some other reason.
>
>
> Code as supplied by Brett
> -------------------------
>
> In ClientForm
> -------------
> Public Shared ReturnData As String
> Public Shared Packet As String ' or something like that
> Public Shared utility As UtilityClass = New UtilityClass ' or something
> like that
> -------------
>
>
> Dim ConnectAttempts As Integer = 0
> Dim t As Thread
>
> Dim Packet As String
> Dim InitialIDSent As Boolean = False
>
> Dim tsGap As TimeSpan
> Dim dtStart As DateTime = Now
>
> ConnectInit()
>
> Within thread
> -------------
> Dim networkStream As NetworkStream = tcpClient.GetStream()
>
> While True
> Try
>
> If networkStream.CanWrite And networkStream.CanRead Then
>
> networkStream = tcpClient.GetStream()
>
> Dim bytes(tcpClient.ReceiveBufferSize) As Byte
> networkStream.Read(bytes, 0, tcpClient.ReceiveBufferSize)
> Dim returndata As String =
> Trim(Encoding.UTF8.GetString(bytes).Trim(Char.MinValue))
>
> If InitialIDSent Then
> Packet = "Nothing to Write from: " & Thread.CurrentThread.Name
> Else
> Packet = "Connected: " & ClientForm.Packet
> InitialIDSent = True
> 'write to log file
>
> ClientForm.utility.WriteToFile(ClientForm.CurrentDirectory.GetCurrentDirectory,
> ClientForm.LogFileExec, ClientForm.utility.CurrentDateTime(0) & " -
> Connected: " & ClientForm.Packet)
> End If
>
> ' Do a simple write.
> Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes(Packet.TrimEnd)
> networkStream.Write(sendBytes, 0, sendBytes.Length)
>
> If networkStream.DataAvailable() Then
> If (returndata <> "") And returndata.ToString <>
> ClientForm.ReturnData Then
> ClientForm.ReturnData = returndata
> returndata = Nothing
>
> Else
> End If
> End If
>
> End If
>
> Catch ex As Exception
>
> If ex.Message = "Operation not allowed on non-connected sockets."
> Then
> ConnectInit()
> ConnectAttempts = +1
>
> If ConnectAttempts > 5 Then
> Exit Sub
> End If
> Else
> End If
> Exit While
> End Try
>
> Thread.CurrentThread.Sleep(500)
> End While
> -------------
>
>
> Code as modified by Stephany
> ----------------------------
>
> In ClientForm
> -------------
> Public Shared ReturnData As String
> Public Shared Packet As String ' or something like that
> Public Shared utility As UtilityClass = New UtilityClass ' or something
> like that
> -------------
>
>
> Dim ConnectAttempts As Integer = 0
> Dim t As Thread
>
> Dim Packet As String
> Dim InitialIDSent As Boolean = False
>
> Dim tsGap As TimeSpan
> Dim dtStart As DateTime = Now
>
> ConnectInit()
>
> Within thread
> -------------
> Dim networkStream As NetworkStream = tcpClient.GetStream()
>
> Dim bytes(tcpClient.ReceiveBufferSize - 1) As Byte
>
> Dim bytesread As Integer
>
> While True
> Try
> If networkStream.DataAvailable then
> bytesread = networkStream.Read(bytes, 0, bytes.Length)
> Dim returndata As String = Encoding.UTF8.GetString(bytes, 0,
> bytesread)
> If InitialIDSent Then
> Packet = "Nothing to Write from: " & Thread.CurrentThread.Name
> Else
> Packet = "Connected: " & ClientForm.Packet
> InitialIDSent = True
> 'write to log file
>
> ClientForm.utility.WriteToFile(ClientForm.CurrentDirectory.GetCurrentDirectory,
> ClientForm.LogFileExec, ClientForm.utility.CurrentDateTime(0) & " -
> Connected: " & ClientForm.Packet)
> End If
> ' Do a simple write.
> Dim sendBytes() As Byte = Encoding.ASCII.GetBytes(Packet.TrimEnd)
> networkStream.Write(sendBytes, 0, sendBytes.Length)
> If returndata <> "" AndAlso returndata <> ClientForm.ReturnData
> Then ClientForm.ReturnData = returndata
> End If
> Catch ex As Exception
> Exit While
> End Try
> Thread.CurrentThread.Sleep(500)
> End While
> -------------
>
>
>


.

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