How to receive full string from server

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VB

Hello to all

i opened a socket for receiving data from server.
after that i sending command and the server sending me back a string.
The problem is to receive full string i need to connect minimum 3 times.

For example:

First result hell
second will be o world
The last and the correct one : Hello world

The Code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

    Dim serverStream As NetworkStream = clientSocket.GetStream()
    Dim outStream As Byte() = System.Text.Encoding.ASCII.GetBytes("COMMAND" & vbCrLf)
    serverStream.Write(outStream, 0, outStream.Length)
    serverStream.Flush()

    Dim myReadBuffer(1024) As Byte
    Dim numberOfBytesRead As Integer = 0
    Dim myCompleteMessage As StringBuilder = New StringBuilder()

    ' Incoming message may be larger than the buffer size.
    Do
        numberOfBytesRead = serverStream.Read(myReadBuffer, 0, myReadBuffer.Length)
        myCompleteMessage.AppendFormat("{0}", Encoding.ASCII.GetString(myReadBuffer, 0, numberOfBytesRead))
    Loop While serverStream.DataAvailable

    returndata = myCompleteMessage.ToString()

    TextBox1.Text = returndata 

End Sub

I tried to make myReadBuffer larger, the same result

the interesting thing is if i putting breaking point on Loop while its doing the job
until the string is not full its not exit the while

Do i need to change the while condition ? or is it the server

Thank you.