Lua for Network Engineers

-- Set leader key
vim.g.mapleader = " "

-- Line numbers
vim.opt.number = true
vim.opt.relativenumber = true

-- Tabs
vim.opt.tabstop = 4
vim.opt.shiftwidth = 4
vim.opt.expandtab = true

-- Keybinding
vim.keymap.set("n", "<leader>w", ":w<CR>", { desc = "Save file" })

-- Register custom protocol
local myproto = Proto("myproto", "My Custom Protocol")

-- Define fields
myproto.fields.command = ProtoField.uint8("myproto.cmd", "Command", base.HEX)
myproto.fields.length = ProtoField.uint16("myproto.len", "Length", base.DEC)

-- Dissector function
function myproto.dissector(buffer, pinfo, tree)
    pinfo.cols.protocol = "MYPROTO"
    local subtree = tree:add(myproto, buffer(), "My Protocol Data")
    subtree:add(myproto.fields.command, buffer(0,1))
    subtree:add(myproto.fields.length, buffer(1,2))
end

-- Register on TCP port
local tcp_table = DissectorTable.get("tcp.port")
tcp_table:add(9999, myproto)

description = [[
Checks for default IPMI credentials
]]

author = "EvanusModestus"
categories = {"auth", "default"}

local ipmi = require "ipmi"
local shortport = require "shortport"

portrule = shortport.port_or_service(623, "asf-rmcp", "udp")

action = function(host, port)
    local default_users = {"ADMIN", "admin", "root"}
    local default_pass = {"ADMIN", "admin", "password"}

    for _, user in ipairs(default_users) do
        for _, pass in ipairs(default_pass) do
            local status, err = ipmi.login(host.ip, user, pass)
            if status then
                return string.format("DEFAULT CREDS: %s/%s", user, pass)
            end
        end
    end
    return "No default credentials found"
end

-- Triggered when interface goes down
-- File: flash:eem_interface_down.lua

function main()
    local cli = require("cli")
    local syslog = require("syslog")

    -- Get interface from event
    local intf = eem.event_data("interface")

    -- Log event
    syslog.info("Interface " .. intf .. " went down - running recovery")

    -- Attempt recovery
    cli.exec("configure terminal")
    cli.exec("interface " .. intf)
    cli.exec("shutdown")
    cli.exec("no shutdown")
    cli.exec("end")

    syslog.info("Recovery attempt complete for " .. intf)
end

main()

-- /etc/nginx/lua/auth.lua
local jwt = require "resty.jwt"

local function authenticate()
    local token = ngx.var.http_authorization
    if not token then
        ngx.status = 401
        ngx.say("Missing token")
        return ngx.exit(401)
    end

    local verified = jwt:verify("secret", token:gsub("Bearer ", ""))
    if not verified.verified then
        ngx.status = 403
        ngx.say("Invalid token")
        return ngx.exit(403)
    end

    -- Set user for downstream
    ngx.var.authenticated_user = verified.payload.sub
end

return { authenticate = authenticate }

-- Variables (global by default, use 'local')
local name = "kvm-02"
local ip = "10.50.1.111"
local port = 22
local enabled = true
local nothing = nil

-- Tables (arrays AND dictionaries)
local hosts = {"kvm-01", "kvm-02", "kvm-03"}
local config = {
    hostname = "kvm-02",
    ip = "10.50.1.111",
    ports = {22, 443, 5900}
}

-- Access
print(hosts[1])           -- "kvm-01" (1-indexed!)
print(config.hostname)    -- "kvm-02"
print(config["ip"])       -- "10.50.1.111"

-- If/else
if status == "up" then
    print("Online")
elseif status == "degraded" then
    print("Warning")
else
    print("Down")
end

-- For loops
for i = 1, 10 do
    print(i)
end

-- Iterate table
for key, value in pairs(config) do
    print(key .. " = " .. tostring(value))
end

-- Iterate array
for index, host in ipairs(hosts) do
    print(index .. ": " .. host)
end

-- Basic function
local function greet(name)
    return "Hello, " .. name
end

-- Multiple returns
local function get_host_info(hostname)
    return "10.50.1.111", 22, "Rocky Linux"
end

local ip, port, os = get_host_info("kvm-02")

-- Anonymous function
local process = function(x) return x * 2 end

-- Closures
local function counter()
    local count = 0
    return function()
        count = count + 1
        return count
    end
end

local c = counter()
print(c())  -- 1
print(c())  -- 2

local host = "kvm-02.inside.domusdigitalis.dev"

-- Concatenation
local msg = "Host: " .. host

-- Length
print(#host)  -- 33

-- Pattern matching (like regex-lite)
local name = host:match("^([^.]+)")  -- "kvm-02"
local domain = host:match("%.(.+)$")  -- "inside.domusdigitalis.dev"

-- Split (manual, no built-in)
local function split(str, sep)
    local result = {}
    for part in str:gmatch("([^" .. sep .. "]+)") do
        table.insert(result, part)
    end
    return result
end

local parts = split(host, ".")  -- {"kvm-02", "inside", "domusdigitalis", "dev"}