unexpected characters in TCP-communication

[Peter Pippinger]

Hello NG,

i have 2 functions to read and write strings on a TCP-socket.
The strange thing is, that sometimes there are unexpected characters
in the string.

First of all, have i understood it right,
- that i say in the first byte of the string - i want to send - the
number of chars, that i will send?
- that the fist byte of a string - i recieve - declares the number of
chars, i´ll get?

One example of my problem:
I expect one string "UNBEKANNTE R PROZESS".
Sometimes i get for example "#UNBEKANNT ER PROZESS".
Which gets me into trouble when working with this string...

Does someone have an idea, what goes wrong with this?

*** There is no cleaning-personal in the server-room which could
stumble over cables ;-) ***

The functions i use:

///
*************** *************** *************** *************** ***************
*************** **************
/// <summary>
/// Gibt den Wert eines ASCII-Zeichens zurück
/// </summary>
/// <param name="src">ASCI I-Zeichen</param>
/// <returns>ASCI I-Wert</returns>
///
*************** *************** *************** *************** ***************
*************** **************
public static byte Asc(char src)
{
// ASCII Wert eines Zeichens zurückgeben
return (System.Text.AS CIIEncoding.ASC II.GetBytes(src +
"")
[0]);
}


///
*************** *************** *************** *************** ***************
*************** **************
/// <summary>
/// Gibt ein ASCII-Zeichen für einen Wert zurück
/// </summary>
/// <param name="src">ASCI I-Wert</param>
/// <returns>ASCI I-Zeichen</returns>
///
*************** *************** *************** *************** ***************
*************** **************
public static char Chr(byte src)
{
// Zeichen zu einem ASCII Wert zurückgeben
return (System.Text.AS CIIEncoding.ASC II.GetChars(new
byte[] { src })[0]);
}


///
*************** *************** *************** *************** ***************
*************** **************
/// <summary>
/// Sendet einen String über einen Socket
/// </summary>
/// <param name="socket">S ocket</param>
/// <param name="stringDat a">String</param>
///
*************** *************** *************** *************** ***************
*************** **************
public void write_string_on _socket(Socket socket, String
stringData)
{
// Länge des Strings festlegen, die übertragen wird
stringData = Chr((byte)strin gData.Length).T oString() +
stringData;


// Nachricht an Server senden
socket.Send(Enc oding.ASCII.Get Bytes(stringDat a));
}


///
*************** *************** *************** *************** ***************
*************** **************
/// <summary>
/// Liest einen Sting über einen Socket
/// </summary>
/// <param name="socket">S ocket</param>
/// <returns>String </returns>
///
*************** *************** *************** *************** ***************
*************** **************
public string read_string_fro m_socket(Socket socket)
{
// Empfangspuffer
byte[] data = new byte[1024];


// ermitteln, wieviele Bytes uns der Server schicken
möchte
int recv = socket.Receive( data);
int byte_anzahl = (int)data[0];


// jetzt den eigentlichen String mit der vorher
ermittelten Länge holen
recv = socket.Receive( data);
string stringData = Encoding.ASCII. GetString(data, 0,
byte_anzahl);


// empfangene Nachricht zurückgeben
return stringData;
}

[Chris Dunaway]

Re: unexpected characters in TCP-communication

On Mar 27, 8:58 am, Peter Pippinger <peter.pippin.. .@gmx.dewrote:

Hello NG,
>
>
First of all, have i understood it right,
- that i say in the first byte of the string - i want to send - the
number of chars, that i will send?
- that the fist byte of a string - i recieve - declares the number of
chars, i´ll get?

No, I don't believe this is correct. When sending an array of bytes,
the entire array is sent so there is no need to specify the number of
bytes to send in the array.

When receiving, the return value from the Receive command indicates
the number of bytes received.

[Peter Pippinger]

Re: unexpected characters in TCP-communication

No, I don't believe this is correct.  When sending an array of bytes,

the entire array is sent so there is no need to specify the number of
bytes to send in the array.
>
When receiving, the return value from the Receive command indicates
the number of bytes received.

But if i connect my service for example with telnet the first "HELLO"
of the handshake only appears in telnet, if i my fist byte of the
sended string has the Value 5 (5 + "HELLO"). If the first Byte of the
Sting is 4 then only "HELL" will apear in telnet...

So i think its right, first to send how many characters there will be
send.

[Ignacio Machin ( .NET/ C# MVP )]

Re: unexpected characters in TCP-communication

On Mar 27, 9:58 am, Peter Pippinger <peter.pippin.. .@gmx.dewrote:

Hello NG,
>
i have 2 functions to read and write strings on a TCP-socket.
The strange thing is, that sometimes there are unexpected characters
in the string.

Most probably cause of the encoding.

First of all, have i understood it right,
- that i say in the first byte of the string - i want to send - the
number of chars, that i will send?

Yes, that is ok, I would use Int32 instead of byte but that's ok

- that the fist byte of a string - i recieve - declares the number of
chars, i´ll get?

Humm, I think that both cases are the same no?
If you are sending a variable amount of data you should send
previously the number of bytes you are going to send next.

[Barry Kelly]

Re: unexpected characters in TCP-communication

Barry Kelly wrote:

Silly bug:

---8<---

int length = chars.Length 255 ? 255 : 0;

int length = chars.Length 255 ? 255 : chars.Length;

int resultLen;
--->8---

-- Barry

--

http://barrkel.blogspot.com/

[Peter Duniho]

Re: unexpected characters in TCP-communication

On Thu, 27 Mar 2008 07:18:12 -0700, Chris Dunaway <dunawayc@gmail .com>
wrote:

>First of all, have i understood it right,
>- that i say in the first byte of the string - i want to send - the
>number of chars, that i will send?
>- that the fist byte of a string - i recieve - declares the number of
>chars, i´ll get?

>
No, I don't believe this is correct. When sending an array of bytes,
the entire array is sent so there is no need to specify the number of
bytes to send in the array.

The Socket.Send() method only sends the bytes you ask it to. It sends no
other meta-data, such as the length of the transmission, and thus the
receiver obviously receives no such meta-data that it could use to
reconstruct the array.

When receiving, the return value from the Receive command indicates
the number of bytes received.

It does indicate the number of bytes received. But that doesn't tell you
how many bytes were sent.

Pete

[Chris Dunaway]

Re: unexpected characters in TCP-communication

On Mar 27, 10:29 am, "Peter Duniho" <NpOeStPe...@nn owslpianmk.com>
wrote:

On Thu, 27 Mar 2008 07:18:12 -0700, Chris Dunaway <dunaw...@gmail .com>
wrote:
>

First of all, have i understood it right,
- that i say in the first byte of the string - i want to send - the
number of chars, that i will send?
- that the fist byte of a string - i recieve - declares the number of
chars, i´ll get?

>

No, I don't believe this is correct. When sending an array of bytes,
the entire array is sent so there is no need to specify the number of
bytes to send in the array.

>
The Socket.Send() method only sends the bytes you ask it to. It sends no
other meta-data, such as the length of the transmission, and thus the
receiver obviously receives no such meta-data that it could use to
reconstruct the array.
>

When receiving, the return value from the Receive command indicates
the number of bytes received.

>
It does indicate the number of bytes received. But that doesn't tell you
how many bytes were sent.
>
Pete

Thanks,

I was just going by the docs for Send and Receive. I didn't realize
that a Pascal string was being sent (as alluded by Barry in another
response) where the string is preceded by the length.

Cheers,

Chris