client.lua

local port = 0x7AC0 -- port for 'TACO' delivery
local waypoint = "station_1"

local component = require("component")

local modem = component.modem

modem.open(port)

-- simple test program: ask for delivery to the configured waypoint
modem.broadcast(port, "DELIVER_TACO", waypoint)

drone.lua

local modem = component.proxy(component.list("modem")())
local nav = component.proxy(component.list("navigation")())
local drone = component.proxy(component.list("drone")())

local range = nav.getRange()
local port = 0x7AC0 -- port for 'TACO' delivery

modem.open(port)

local function pickUpTaco()
    -- attempt to retrieve 1 taco from storage, then check if we got one
    drone.suck(0, 1)
    return drone.count() >= 1
end

local function getWaypointsByName()
    local got_waypoints = nav.findWaypoints(range)
    local waypoints = {}
    for i,waypoint in ipairs(got_waypoints) do
        local label = waypoint.label
        local pos = waypoint.position
        -- discards waypoints with no name
        if label ~= "" then
            waypoints[label] = pos
        end
    end

    return waypoints
end

drone.setStatusText("BOOTING\n")
local waypoints = getWaypointsByName()
drone.setStatusText("READY\n")

local function deliverToWaypoint(waypoint_name)
    local pos = waypoints[waypoint_name]
    if not pos == nil then
        drone.setStatusText("Delivering taco...")
        -- TODO: change to some kind of error message
        if not pickUpTaco() then return end
        -- move to waypoint and store position to return later
        local dx, dy, dz = pos
        drone.move(dx, dy + 1, dz)
        -- drop off the taco
        drone.drop(0, 1)
        -- return home
        drone.setStatusText("Returning home...")
        drone.move(-dx, -dy, -dz)
    else
        return false
        -- TODO: change to some kind of error message
    end
    drone.setStatusText("")
    return true
end

local function loop()
    local evt,_,sender,_,dist,message,destination = computer.pullSignal()
    -- verify that this message was meant for us
    if evt == "modem_message" and message == "DELIVER_TACO" then
        -- argument checking
        if dist > range then
            return
        elseif destination == nil then
            return
        end
        
        -- attempt delivery to the destination
        if not deliverToWaypoint(destination) then
            return false
        end
    end
    return true
end

while true do
    loop()
end