named

# pastebin get 9bf3dHx4 named.lua

peripheral.find("modem", rednet.open)
os.setComputerLabel("dns-server")
filename = "dns.db"
computers = {}
rows = 1


function readDBfromFileToRAM()
    local file = fs.open(filename, "r")
    if file then
        local restored = file.readAll()
        file.close()
        return textutils.unserialise(restored)
    end
    return nil
end

function writeToDB(id,name)
    --save to array
    computers[rows] = {}
    computers[rows][1] = tostring(id)
    computers[rows][2] = name
    rows = rows + 1
    --save to file
    local file = fs.open(filename,"w")
    file.write(textutils.serialize(computers))
    file.close()
end

function searchInDB(id,name)
    for i=1,#computers do
        if (computers[i][1] == id) or (computers[i][2] == name) then
            print(("already have client %s in database"):format(computers[i][2]))
            return
        end
    end
    writeToDB(id, name)
    print(("registered id: %d with name %s"):format(id, name))
end

function querryDB(searchType,target)
    for i=1,#computers do
        if (searchType == "name") and (computers[i][2] == target) then
            return computers[i][1]
        end
        if (searchType == "id") and (computers[i][1] == target) then
            return computers[i][2]
        end
    end
    return "not found"
end

function listenForRegister()
    while true do
        local id,name = rednet.receive("dns-register")
        searchInDB(id, name)
    end
end

function listenForQuerry()
    while true do
        id, request = rednet.receive("dns-querry")
        print(("client: %d asking for type: %s target %s"):format(id, request[1], request[2]))
        result = querryDB(request[1], request[2])
        rednet.send(id, result, "dns-answer")
    end
end

--RUNTIME
---------------------------
--read saved database to ram
restoredDatabase = readDBfromFileToRAM()
if restoredDatabase then
    computers = restoredDatabase
    rows = #computers + 1
end

--write own name to db
searchInDB(os.computerID(), os.computerLabel())

--parallel start two listen jobs
parallel.waitForAny(listenForRegister, listenForQuerry)

--this should never be reached
print("Somehow the DNS server stopped")