computercraft/lib/lns.lua

-- Desc: LNS Client
-- Auth:  Layla Manley
-- Link: https://gitea.layla.gg/layla/computercraft
local cache = {}
local cache_file = "/var/cache/lns_cache.db"

settings.define("lns_client.allow_dynamic_lns_hosts", {
    description = "Allow dynamic LNS hosts",
    type = "boolean",
    default = false
})

settings.define("lns_client.lns_server", {
    description = "LNS Server Rednet ID",
    type = "number",
    default = 8
})


function _load_cache()
    if fs.exists(cache_file) then
        db = fs.open(cache_file, "r")
        db_contents = db.readAll()
        db.close()

        cache = textutils.unserialize(db_contents)
    end
end

function _save_cache()
    db = fs.open(cache_file, "w")
    db.write(textutils.serialize(cache))
    db.close()
end

function server()
    local lns_server_id = settings.get("lns_client.lns_server")
    local allow_dynamic_lns_hosts = settings.get("lns_client.allow_dynamic_lns_hosts")

    if allow_dynamic_lns_hosts then
        lns_server_id = rednet.lookup("lns", lns_server)
        if lns_server_id == nil then
            io.write("LNS Server not found!\n")
            return nil
        end
    end

    return lns_server_id
end

function lookup(remote_hostname)

    _load_cache()
    if cache[remote_hostname] ~= nil then
        return cache[remote_hostname]
    end

    local data = {
        ["action"] = "lookup",
        ["hostname"] = remote_hostname
    }

    local lns_server_id = server()
    rednet.send(lns_server_id, data, "lns")

    while true do
        id, msg = rednet.receive("lns")
        if id == lns_server_id then
            if msg == nil then
                return nil
            else
                cache[remote_hostname] = msg
                _save_cache()
                return msg
            end
        end
    end
end

function clear_cache()
    cache = {}
    _save_cache()
    print("Cleared cache!")
end