TCP/IP Socket Programming - Printable Version

TCP/IP Socket Programming - Printable Version

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RE: TCP/IP Socket Programming - Juergen - 07-27-2025

Thanks a lot for your Help, the connection to the device is running now !!! Now i want to transmit a message of 13 Bytes with the function : LDClient.SendMessage() But i am not sure what the correct format of the message is ? I tryed LDClient.SendMessage("0030500000000") and LDClient.SendMessage(0030500000000) , but i am even not sure , wether this is the right way of doing it anyway ....... once more i need a little help from you .....

RE: TCP/IP Socket Programming - litdev - 07-27-2025

Hi,

Glad the basic connection is working.

LDClient.SendMessage can take either a number or a string as input. The input is then converted into a string, then array of bytes (each byte is the ascii character code value) with trailing null terminator before sending.

I would recommend sending a string so it is clear what you are sending, e.g. LDClient.SendMessage("0030500000000"). If you send just a number LDClient.SendMessage(0030500000000) it would be interpreted as "3050000000" - conversion from number to string would loose the leading zeros. This is the extension code behind SendMessage.

Code:
                if (!tcpClient.Connected) return "NOT_CONNECTED";

                Byte[] bytes = Encoding.UTF8.GetBytes(message + '\0');

                NetworkStream networkStream = tcpClient.GetStream();

                networkStream.Write(bytes, 0, bytes.Length);

                return "SUCCESS";

Secondly, you say you want to send bytes - there is a distiction between byte values and their ascii representation. A byte is a number between 0 and 255 (in decimal and FF in hex), and each value represnets a character, so the character "0" is 48 (dec) or 30 (hex), see https://www.ascii-code.com. If you want to send pure byte numbers then you will have to form the string using Text.GetCharacter(code), where code is the byte value.

Code:
char = Text.GetCharacter(48)

TextWindow.WriteLine(char)

code = Text.GetCharacterCode("0")

TextWindow.WriteLine(code)

One suggestion is to try to read from the server first (if you know how to get it to send a message), and see what it looks like.

Code:
result = LDClient.Connect("192.168.2.20:15730", "False")

If (result = "SUCCESS") Then

  msg = "" 

  LDClient.ServerMessage = OnServerMessage

  While("True") 'Keep the program running - we would do more here later

    If (msg <> "") Then 'We have a message

      TextWindow.WriteLine("Client message received : "+msg)

      msg = "" 'Message handled

    EndIf

    Program.Delay(10)' Don't mash cpu

  EndWhile

EndIf

Sub OnServerMessage

  msg = LDClient.LastServerMessage

EndSub

If you have a link to some documentation for the server device that you can share, there may be more detailed info on the data format required and some way to check what was received by the server.

RE: TCP/IP Socket Programming - Juergen - 07-27-2025

you are right with the conversion to ascii when the LDClient.SendMessage converts all to a string. so when i want to transmit a pure
00 (HEX) the LDClient.SendMessage send 30(Hex ) , that is the wrong value in the telegram for the device .
The Functions : Text.GetCharacter() or Text.GetCharacterCode(0) will not help me with that...... i guess . I think i have a problem now ;-(

RE: TCP/IP Socket Programming - litdev - 07-27-2025

No, you can create a string of bytes of any value 0 to FF (hex)

Code:
bytes = ""

bytes = Text.Append(bytes,Text.GetCharacter(48))

bytes = Text.Append(bytes,Text.GetCharacter(0))

bytes = Text.Append(bytes,Text.GetCharacter(32))

bytes = Text.Append(bytes,Text.GetCharacter(7))

TextWindow.WriteLine(":"+bytes+":")

LDClient.SendMessage(bytes)

This is a string with bytes (dec) equal to 48, 0, 32, 7

When we print it, 48 is intepreted as chatracter 0, 0 is unprintable, 32 is a space, 7 is a machine beep

Also you can easily convert hex to decimal:

TextWindow.WriteLine(LDMath.Base2Decimal("ff",16))

EDIT

Something like this:

Code:
data = "0 0 3 0 5 0 0 CB 0 0 0 af 0" 'A space separated list of hex bytes

GetBytes()

LDClient.SendMessage(bytes)

Sub GetBytes

  dataArray = LDText.Split(data," ")

  bytes = ""

  For i = 1 To Array.GetItemCount(dataArray)

    codeHex = dataArray[i]

    codeDec = LDMath.Base2Decimal(codeHex,16)

    TextWindow.WriteLine("Byte "+i+" Hex="+codeHex+" Dec="+codeDec)

    char = Text.GetCharacter(codeDec)

    bytes = Text.Append(bytes,char)

  EndFor

EndSub

RE: TCP/IP Socket Programming - Juergen - 07-28-2025

LDClient.SendMessage(bytes)

Sub GetBytes
dataArray = LDText.Split(data," ")
bytes = ""

Hello, i understand the example, but how works ..... bytes = "" ..... ? how comes the converted result from ....dataArray.... into .... bytes .... ?

RE: TCP/IP Socket Programming - litdev - 07-28-2025

Hi, not sure which bit you don't follow.

A string is in fact just an array of characters, so we can create a string by appending characters to the end of a string, this is what ' bytes = Text.Append(bytes,char) ' is doing.

So char is a single character.

A character is internally stored as a byte (00 to FF in hex), so a string as an array of bytes. When we print a string, the char (byte) value corresponds to the character defined by the ascii code for the given byte value, so a string with byte value of 0x20 (or 32 decimal) will print a space. Not all of the 256 ascii values are characters, some are control characters (originally derived from typewriters and mechanical input, like Line Feed, Cariage Return, Backspace, Beep etc.

So the key is to get the character (char) that corresponds to a given ascii code number, that is simply what ' Text.GetCharacter(7) ' does (7 is a machine beep).

So in the end we form a string (array of bytes) with each byte being the byte value corresponding to a character obtained from a byte value (in decimal, so we use the hex to decimal conversion ' LDMath.Base2Decimal ' for convenience).

Hope this helps.

RE: TCP/IP Socket Programming - WhTurner - 07-28-2025

In posting #14:
bytes="" is used to clear the string before starting to append the chars.

RE: TCP/IP Socket Programming - Juergen - 08-23-2025

Hello, I send you a protocol of the wireshark sniffer tool. I send from 169.254.22.62 ( my PC ) with

LDClient.Connect( "169.254.5.166:15471" , "False" ) a Connection Command to my Device.

The Response was :

4 0.010297 169.254.5.166 169.254.22.62 TCP 66 15471 → 59024 [SYN, ACK] Seq=0 Ack=1 Win=29200 Len=0 MSS=1460 SACK_PERM
5 0.010505 169.254.22.62 169.254.5.166 TCP 54 59024 → 15471 [ACK] Seq=1 Ack=1 Win=131328 Len=0
6 0.010940 169.254.22.62 169.254.5.166 TCP 54 59024 → 15471 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0

In Line 6 the PC send a RST , i think that mean "Reset" to my Device 169.254.5.166 .....
Can you explain why this happens ?

The Protocol is in Attachment.

RE: TCP/IP Socket Programming - litdev - 08-23-2025

Hi,

I don't know anything about the device you are connecting to, or what SB code you are using apart from the connect command.

I am guessing that you connect to some device, and I guess that 'wireshark sniffer tool' records network traffic - I've never heard of or used it.

It sees some traffic (line 6) and your question is this being sent by the connection?

This is a lot of guessing by me. Under the hood the extension LDCLient.Connect calls this connection command:

https://learn.microsoft.com/en-gb/dotnet/api/system.net.sockets.tcpclient.connect?view=net-9.0

I don't know in detail exactly what this does at a low level.

Maybe this helps (a bit of googling) - looks like maybe the device was sent something it didn't understand (line5?), but I'm not an expert at all on TCP:

https://www.pico.net/kb/what-is-a-tcp-reset-rst/

Or

https://www.howtouselinux.com/post/tcp-flags

Maybe someone else here has some experience with low level TCP

EDIT, maybe the SB program ended and the connection was closed?

RE: TCP/IP Socket Programming - stevantosic - 08-24-2025

It is hard to say what Protocol means. Or what is "application" protocol in this case? Pure TCP/IP is only a stream of data like a file read/write. "Application" protocol is a logic how applications (devices) talk to each other.

Links which can help:

https://serverfault.com/questions/645025/tcp-dump-cannot-understand-these-4-lines

https://networkengineering.stackexchange.com/questions/2012/why-do-i-see-a-rst-ack-packet-instead-of-a-rst-packet