Difference between revisions of "Modem (API)"

From ComputerCraft Wiki
Jump to: navigation, search
(Re-opened the page due to changes in modem behavior which I thought would fit appropriately here.)
 
(Keep in Mind...)
Line 59: Line 59:
 
* Sending messages does not require you to open any channels prior to sending it.
 
* Sending messages does not require you to open any channels prior to sending it.
 
* If you aren't receiving a message when you think you should, check to make sure that you have opened the channel first!
 
* If you aren't receiving a message when you think you should, check to make sure that you have opened the channel first!
 +
* Modems and channels are not secure! If you are sending a message over rednet, it is available to any computer listening on the sent channel.

Revision as of 08:07, 7 March 2013

With the advent of ComputerCraft 1.5, the behavior of modems has changed somewhat drastically. Although the rednet api still has the same functionality, it is really just a wrapper for what is a completely different system underneath.

The major change introduced to modems in this version of ComputerCraft is channels: Channels are essentially open networks which can be opened, closed, and listened on by any computer within range. To interact with channels, one must directly wrap the peripheral as opposed to the previous interaction with the rednet API.

Here is a list of functions available from modems:

Function Parameters Description
isOpen integer channel Check to see if the specified channel is open
open integer channel (under 65535) Opens the specified channel to allow for listening
close integer channel Closes an open channel to disallow listening
closeAll None Closes all open channels
transmit integer channel, integer replyChannel, string message Transmits a message on the specified channel

Sending Messages

Sending messages is simple and does not require that you open any channels. Simply use the transmit function like so:

 
 local modem = peripheral.wrap("right") --Wraps the modem on the right side.
 modem.transmit(3, 1, "Hello world!")  
 

What did that do? First I wrapped the peripheral in order to interact with it. Second, I used modem.transmit(channel, replyChannel, message) in order to send my message. In case you were wondering, the reply channel is captured by the listening computer and suggests which channel they should reply on.

Receiving Messages

Receiving messages requires that you be familiar with events. As of this moment, there is no api which cuts out events from the process. Here is an example of how to receive messages:

 
 local modem = peripheral.wrap("left")
 modem.open(3)--Open channel 3 so that we can listen on it
 local event, modemSide, senderChannel, 
   replyChannel, message, senderDistance = os.pullEvent("modem_message")
 print("I just received a message from: "..senderChannel)
 print("I should apparently reply on: "..replyChannel)
 print("The modem receiving this is located on the "..modemSide.." side")
 print("The message was: "..message)
 print("The sender is: "..senderDistance.." blocks away from me.")
 

So what did I do? Quite simply, I called os.pullEvent() with the string argument "modem_message", which blocks all other events from being returned. When the "modem_message" event is captured, it returns the arguments: event, modemSide, senderChannel, replyChannel, message, senderDistance. I captured these and then printed them out.

Keep in Mind...

  • You can only open 128 channels at any given time.
  • The max channel you can open is 65535.
  • You can listen on more than one channel at a time. For example, if I have channel 3 and channel 5 open and somebody sends a message on channel 5, I will still receive it. If they send a message on channel 3, I will receive that.
  • Sending messages does not require you to open any channels prior to sending it.
  • If you aren't receiving a message when you think you should, check to make sure that you have opened the channel first!
  • Modems and channels are not secure! If you are sending a message over rednet, it is available to any computer listening on the sent channel.