Scratch

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I was under the impression it was a TCP connection, not UDP -- though the article doesn't actually mention that anywhere...

Actually, going through the code, I get this as a comment:

"Process incoming UDP commands."

That's in Scratch-Networking>ScratchServer>private-server>processUDPCommands

And anything I see about networking has 'UDP' in it.

It's weird how Scratch uses an UDP connection, while other things (Going to use Magnie's Little Server That Can as an example) use TCP connections.

Quite odd, isn't it?

EDIT: Here's the code for 'startHosting', which makes me certain that Scratch uses UDP and not TCP.

startHosting
"Open a socket on my port and start accepting connections."

Socket initializeNetwork.
self shutdownServer.

serverSocket _ Socket new.
serverSocket listenOn: self class portNumber backlogSize: 20.

incomingUDPSocket _ Socket newUDP setPort: self class portNumber.

Interesting, isn't it?

Last edited by DigiTechs (2013-04-09 16:47:18)

Well, the Python example is using TCP.

DigiTechs wrote:

If I use TCP, I get the error mentioned in the top.

Sounds like you're sending a malformed message    It's definitely TCP.

DigiTechs wrote:

using TCP gives me this malformed message thing.

Check your message!

I think I have encountered a problem using my TCP server.

I've found it can't receive from the port. I'll have to use a different client to do it.

OKAY, I think I have sending.. buggy but working to a small extent. Here's an error message (YAY, THE SAME.) of what I get when I send messages to scratch. Maybe the people who are better than me at Squeak can tell me what I'm doing wrong.

message too big; bad size field?

MessageSocket(Object)>>error:
[] in PasteUpMorph>>runStepMethods
[] in BlockContext>>ifError:
MessageSocket(Object)>>error:
MessageSocket>>nextMessage
ScratchServer>>processCommandFrom:
[] in ScratchServer>>processIncomingCommands
OrderedCollection>>do:
ScratchServer>>processIncomingCommands
ScratchServer>>stepServer

That's my error message. What I'm thinking is 'OH COME ON, DO I NEED TO ENCODE YOU IN MD5 OR SOMETHING?!'

UDP seems to be communicating with scratch easier.

But thanks for the info.

EDIT: Okay, so I did that but I'm still getting the error.

Here's what I send:

'\\0\\0\\0\\'..string.len('broadcast "TESTMSG"')..'broadcast "TESTMSG"'

Since \ is Lua's Escape Character, I have to double it up for it to work. But this time I'll try and just use one single one.

EDIT 2: When I use the single one I get an error... :I

EDIT 3: Okay, now this is the format of my begin code: \0\0\0\\ which DOESN'T give me the message to big error. I think another way I'll do it will be better.

EDIT 4: In fact, what I tried didn't work. I'm kinda still confused.

Last edited by DigiTechs (2013-04-12 12:23:21)

\ is usually the escape character, which is why I said '\0\0\0\0' instead of '\\0\\0\\0\\0' since it is necessary to escape the character.

\0\0\0\0 means the message is '0' characters long and basically tells Scratch that it's closing the session. Send this message exactly as it is:

\0\0\0\19broadcast "message"

And with the same code (without the double-escape) send:

'\0\0\0\'....string.len('broadcast "TESTMSG"')..'broadcast "TESTMSG"'

I don't know exactly how the length is generated, I just use this (in Python):

def add_length(cmd):
    # Defines the length of each message.
    n = len(cmd)
    a = array('c')
    a.append(chr((n >> 24) & 0xFF))
    a.append(chr((n >> 16) & 0xFF))
    a.append(chr((n >>  8) & 0xFF))
    a.append(chr(n & 0xFF))
    return (a.tostring() + cmd)

If you understand bit shifting and stuff, you should be able to recreate the function in Lua. chr() is a function that changes a character from an integer (0-255) to the character equivalent. If Lua has a built-in function like that, use this instead (Lua code):

'\0\0\0'..chr(string.len('broadcast "TESTMSG"'))..'broadcast "TESTMSG"'

since it is more likely to work correctly (since I don't know exactly how to use escape characters to get the equivalent character.

Does that make sense?

It might be. I've never even touched Lua, so I wouldn't know. 

I actually think it's supposed to be '\x13' (not sure how you get 19 into that, but that's what I have from Python). I hope it fixed your problem. The next step is decoding the string that you receive.