TCP socket programming, strange behavior when read data

Question

I'm writing tcp socket program.
When I send string, shorter than previous sending, from client and receive it on server, something strange happening. For example:
First I send '999999999' . Server receives finely.
After that, I send shorter string: '7777777' . But the data on server is '777777799' .

Why the previous data's remnant is still alive on next sending?

My code is below:

// Section: client sending data ----
NetworkStream serverStream = clientSocket.GetStream();
byte[] outStream = Encoding.ASCII.GetBytes("999999999");
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();

// Section: Server reading data ----
while ((true))
{
    NetworkStream networkStream = clientSocket.GetStream();
    networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize);
    dataFromClient = Encoding.ASCII.GetString(bytesFrom);
    networkStream.Flush();
}

Answer 1

You're ignoring the amount of data you've read, instead always converting the whole byte array into a string, including any data which is still present from a previous read (or the initial byte array elements). You should have:

int bytesRead = networkStream.Read(bytesFrom, 0, bytesFrom.Length);
dataFromClient = Encoding.ASCII.GetString(bytesFrom. 0, bytesRead);

Note that I've changed the third argument to networkStream.Read , too - otherwise if there's more data than you have space for in the array, you'll get an exception. (If you really want to use ReceiveBufferSize , then create the array for that length.)

Also, you should check that bytesRead is positive - otherwise you'll get an exception if the connection is closed.

Basically, you should pretty much never ignore the return value of Stream.Read .