Rednet API

CHANNEL_BROADCAST = 65535

local tValidSides = {}
for n,sSide in ipairs( rs.getSides() ) do
    tValidSides[ sSide ] = true
end

function open( sSide )
    if type( sSide ) ~= "string" then
        error( "string expected" )
    end
    if not tValidSides[sSide] then
        error( "Invalid side" )
    end
    if peripheral.getType( sSide ) ~= "modem" then
        error( "No modem on "..sSide.." side" )
    end
    peripheral.call( sSide, "open", os.getComputerID() )
    peripheral.call( sSide, "open", CHANNEL_BROADCAST )
end

function close( sSide )
    if type( sSide ) ~= "string" then
        error( "string expected" )
    end
    if not tValidSides[sSide] then
        error( "Invalid side" )
    end
    if peripheral.getType( sSide ) ~= "modem" then
        error( "No modem on "..sSide.." side" )
    end
    peripheral.call( sSide, "close", os.getComputerID() )
    peripheral.call( sSide, "close", CHANNEL_BROADCAST )
end

function isOpen( sSide )
    if type( sSide ) ~= "string" then
        error( "string expected" )
    end
    if not tValidSides[sSide] then
        error( "Invalid side" )
    end
    if peripheral.getType( sSide ) == "modem" then
        return peripheral.call( sSide, "isOpen", os.getComputerID() ) and peripheral.call( sSide, "isOpen", CHANNEL_BROADCAST )
    end
    return false
end

function send( nRecipient, sMessage )
    for n,sSide in ipairs( rs.getSides() ) do
        if isOpen( sSide ) then
            peripheral.call( sSide, "transmit", nRecipient, os.getComputerID(), sMessage )
            return true
        end
    end
    error( "No open sides" )
end

function broadcast( sMessage )
    send( CHANNEL_BROADCAST, sMessage )
end

function receive( nTimeout )
    local timer = nil
    local sFilter = nil
    if nTimeout then
        timer = os.startTimer( nTimeout )
        sFilter = nil
    else
        sFilter = "rednet_message"
    end
    while true do
        local e, p1, p2, p3, p4, p5 = os.pullEvent( sFilter )
        if e == "rednet_message" then
            local nSenderID, sMessage, nDistance = p1, p2, p3
            return nSenderID, sMessage, nDistance
        elseif e == "timer" and p1 == timer then
            return nil
        end
    end
end

local bRunning = false
function run()
    if bRunning then
        error( "rednet is already running" )
    end
    bRunning = true

    while bRunning do
        local sEvent, sSide, sChannel, sReplyChannel, sMessage, nDistance = os.pullEventRaw( "modem_message" )
        if sEvent == "modem_message" and isOpen( sSide ) and (sChannel == os.getComputerID() or sChannel == CHANNEL_BROADCAST) then
            os.queueEvent( "rednet_message", sReplyChannel, sMessage, nDistance )
        end
    end
end