TCP socket programming, strange behavior when read data

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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:

C#

// 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();
}

Posted 22-Feb-15 22:54pm

orgilhp

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Richard MacCutchan 23-Feb-15 5:06am

You are just seeing the previous message's data that was left in the buffer. You need to extract only the number of characters that you receive.

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sjelen · Answer 1 · 2015-02-23T02:56:00

When reading data, you need to determine how much data was really taken from the stream (buffer will not always be full).
The clientSocket.ReceiveBufferSize does not tell you how much data was buffered, it only tells how much memory is used for buffering.
Try something like this:

C#

int count = networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize);
dataFromClient = Encoding.ASCII.GetString(bytesFrom, 0, count);