tcpclient receiving data incorrectly

Question

Not sure if this is the TCPClient or something else, I have used a network sniffer to check what is being sent and received from the server and the data is correct however my software is receiving the data incorrectly.

Let me explain, I transmit an enquiry byte (05) I get a acknowledgment back (06) then I transmit some data that starts with a 9B byte, once this has sent I should then receive a single 06 byte and then after that byte I should get a C5 byte, however according to my software I get another 06 byte which isn't the case according to the sniffer!

byte[] buff;
if (!this.isConnected())
    this.connect(); 

NetworkStream gs = _Socket.GetStream();

gs.Write(enq, 0, enq.Length);
gs.Flush();
outputByte(enq, "Trans"); //outputs ---> 05

buff = new byte[1];
gs.Read(buff, 0, buff.Length);
gs.Flush();
outputByte(buff, "Rec");// outputs <--- 06

if (buff[0] == 0x06)
{
    byte[] data = new byte[] {
                                            0x9B, 0x00,         0x80, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00, 0x09,         
        0x67, 0x11, 0x01, 0x49, 0x4D, 0x41, 0x47, 0x45,         0x31, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,         
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,         0x01, 0x53, 0x75, 0x6D, 0x6D, 0x61, 0x72, 0x79,         
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,         
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,         0x00, 0x00, 0x02, 0x08, 0x00, 0x00, 0x08, 0x00,         
        0x00, 0x00, 0x1F, 0x09, 0x01, 0x00, 0x04, 0x0A,         0x10, 0x00, 0x12, 0x01, 0x1F, 0x00, 0x00, 0x00,         
        0x05, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,         0x12, 0x10, 0x1E, 0x0E, 0x1E, 0x54, 0x65, 0x73,         
        0x74, 0x69, 0x6E, 0x67, 0x10, 0x00, 0x12, 0x01,         0x1F, 0x00, 0x00, 0x00, 0x05, 0x00, 0x01, 0x00,         
        0x00, 0x00, 0x00, 0x00, 0x12, 0x10, 0x0D, 0x00,         0x00, 0x90
    };
    outputByte(data, "Trans"); /outputs --> with above byte information
    gs.Write(data, 0, data.Length);
    gs.Flush();

    buff = new byte[1];
    gs.Read(buff, 0, buff.Length);
    gs.Flush();
    // this is the first receive of 06
    outputByte(buff, "Rec");//outputs <--- 06

    if (buff[0] == 0x06)
    {
        gs.Flush();
        Console.WriteLine("fdsfsdfs");
        byte[] resp = new byte[5];
        gs.Read(resp, 0, resp.Length);
        gs.Flush();
        //this outputs <--- 06 but it should be showing <--- c5000100c4
        outputByte(buff, "Rec"); 
        gs.Write(ack, 0, ack.Length);
        outputByte(ack, "Trans");
        gs.Flush();
    }
}

According to the sniffer this is what should be happening

---> 05
<--- 06
---> 9b008000000080000009671101494d414745310000000000000000000000000000000153756d6d617279000000000000000000000000000000000000000000000000000002080000080000001f090100040a100012011f000000050001000000000012101e0e1e54657374696e67100012011f000000050001000000000012100d000090
<--- 06
<--- c5000100c4

And according to the software this is what is happening

---> 05
<--- 06
---> 9b008000000080000009671101494d414745310000000000000000000000000000000153756d6d617279000000000000000000000000000000000000000000000000000002080000080000001f090100040a100012011f000000050001000000000012101e0e1e54657374696e67100012011f000000050001000000000012100d000090
<--- 06
<--- 06

Any ideas? Also if you have any suggestions on how to improve the code I'll be grateful

The first thing I'd say is: can you output the results from each of the `Read` calls. — Marc Gravell, May 14 '12 at 11:46
@MarcGravell that's what the outputByte function does and that's what the above shows! — Neo, May 14 '12 at 12:30

score 6 · Accepted Answer · answered May 14 '12 at 11:48

Here: you are outputting the wrong buffer:

    gs.Read(resp, 0, resp.Length);
    gs.Flush();

    outputByte(buff, "Rec");  <==== should be "resp"

HOWEVER!!!

all of your Read calls are broken; they MUST handle the return value, especially when reading multiple bytes. Packet fragmentation will kill your code.

A correct "read exactly [n] bytes" method would be:

public static void ReadExact(this Stream stream, byte[] buffer,
           int offset, int count) {
    int read;
    while(count > 0 && (read = stream.Read(buffer, offset, count)) > 0) {
        count -= read;
        offset += read;
    }
    if(count != 0) throw new EndOfStreamException();
}

Then:

gs.ReadExact(resp, 0, resp.Length);

will fill it correctly, or error if not enough data is in the stream.

OMG this is why I HATE working on multiple things at once, 2 c# projects a website and 2 laptops for repair, Marc thank you so much I couldn't see that error at all, changed it and now its correct and again thanks for the ReadExact function I'll implement it ASAP, would I need something for the write as well? — Neo, May 14 '12 at 12:32

tcpclient receiving data incorrectly

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