net.lua

SIDES = {"left", "right", "top", "bottom", "front", "back"}

local modem = nil

function connect()
    if modem ~= nil and rednet.isOpen(modem) then
        return true
    end
    for _, side in ipairs(SIDES) do
        if peripheral.getType(side) == "modem" then
            rednet.open(side)
            if rednet.isOpen() then
                modem = side
                return true
            end
        end
    end
    error("could not establish connection")
    return false
end

function broadcast(msg, proto)
    connect()
    rednet.broadcast(msg, proto)
end

function getID(host, proto)
    connect()
    id = rednet.lookup(proto, host)
    if id == nil then
        error("no such host '" .. host .. "'")
    end
    return id
end

function sendToHost(msg, proto, host)
    connect()
    id = getID(host, proto)
    rednet.send(id, msg, proto)
end

function listen(proto, id)
    connect()
    while(true) do
        local senderID, msg = rednet.receive(proto)
        if id == nil or id == senderID then
            return senderID, msg
        end
    end
end