An example which shows how to use a Lua script to modify incoming data in an input port

Collaboration diagram for An example which shows how to use a Lua script to modify incoming data in an input port:

Description

This example demonstrates how to simply use the port monitor carrier to modify data going through a connection. The port '/write' from 'yarp write' module is connected to the '/read' port of 'yarp read' using a portmonitor plugged into the receiver side. The portmoniotr loads a Lua script ('bot_modifier.lua') in which we access and modify the data going through through the port.

Requirements

• Enable and compile portmonitor carrier (ENABLE_yarpcar_portmonitor_carrier=ON in YARP cmake).

• Compile YARP with Lua binding support (see Using YARP from python, java, ruby, C#, and other languages).

• Set LUA_CPATH to include YARP-Lua binding library (e.g., export LUA_CPATH=";;;$YARP_ROOT/build/lib/lua/?.so")

Running the example

• Open a terminal and run yarpserver

     $ yarpserver
  

• Open another terminal (lets call this the sender terminal) and type

     $ yarp write /write
  

• Open another terminal (lets call this the receiver terminal) )and change to the 'simple_modification' directory:

     $ cd $YARP_ROOT/example/portmonitor/simple_modification
     $ yarp read /read
  

• In another terminal connect the port as follow

     $ yarp connect /write /read tcp+recv.portmonitor+type.lua+file.bot_modifier
  

Now if you write something in the 'sender' terminal, you will see the text "modified from Lua" will be added to the original message. For example:

[sender terminal]
 Hello

[receiver terminal]
 Hello "modified from Lua"

As it is constrained in this PortMonitor.accept() method, If you type "ignore", the word will never be delivered to the input port.

Scripts

bot_modifier.lua

-- loading lua-yarp binding library
require("yarp")
 
--
-- accept is called when the port receives new data
-- @param thing The Things abstract data type
-- @return Boolean
-- if false is returned, the data will be ignored
-- and update() will never be called
PortMonitor.accept = function(thing)
    if thing:asBottle():toString() == "ignore" then
        return false
    end
    return true
end
 
--
-- update is called when the port receives new data
-- @param thing The Things abstract data type
-- @return Things
PortMonitor.update = function(thing)
    bt = thing:asBottle()
    bt:addString("modified from Lua :)")
    return thing
end