update-bat-hosts - get the list of neighbours from the meshviewer to see in batctlcd

update-bat-hosts.lua

#!/usr/bin/lua
-- SPDX-FileCopyrightText: Florian Maurer
-- SPDX-License-Identifier: MIT

local jsonc = require("jsonc")

local function truncate_hostname(hostname, max_length)
    -- If the hostname is already within the maximum length, return it as is
    if #hostname <= max_length then
        return hostname
    end

    -- Define the number of characters to keep at the start and end
    local keep_start = math.floor((max_length - 3) / 2)
    local keep_end = max_length - 3 - keep_start

    -- Concatenate the start, ellipses, and end of the hostname
    return hostname:sub(1, keep_start) .. "..." .. hostname:sub(-keep_end)
end

-- Function to fetch JSON data using wget
local function fetch_json_from_url(url)
    local tmpfile = "/tmp/nodes.json" -- Temporary file to store the downloaded JSON data
    local success = os.execute("wget -q -O " .. tmpfile .. " " .. url)
    if success > 0 then
        error("Failed to download JSON file from" .. url)
    end
    local file = io.open(tmpfile, "r")
    if not file then
        error("Failed to open the downloaded JSON file")
    end

    local json_data = file:read("*all")
    file:close()

    return json_data
end

-- Function to parse the JSON data and output MAC addresses with hostnames
local function parse_and_print_mac_addresses(json_data, gateway_only)
    gateway_only = gateway_only or true
    local data = jsonc.parse(json_data)
    if not data then
        error("Failed to parse JSON data")
    end
    local seen_hostnames = {} -- Table to keep track of seen hostnames

    local file = io.open("/tmp/bat-hosts", "w")
    if not file then
        error("Failed to open /tmp/bat-hosts")
    end

    -- Iterate over nodes and extract MAC addresses with corresponding hostnames
    for _, node in ipairs(data.nodes) do
        local hostname = truncate_hostname(node.nodeinfo.hostname:gsub("%s", "-"), 30)
        local mesh = node.nodeinfo.network.mesh

        -- only parse if gateway filter is off or is gateway
        -- and if mesh info exists and host was not seen yet (otherwise this would give warnings)
        if (not gateway_only or node.flags.gateway) and mesh and not seen_hostnames[hostname] then
            seen_hostnames[hostname] = true
            for _, mesh_interface in pairs(mesh) do
                local interfaces = mesh_interface.interfaces
                -- Loop through wireless, other, and tunnel interfaces
                for iface, mac_list in pairs(interfaces) do
                    for idx, mac in ipairs(mac_list) do
                        file:write(mac .. " " .. hostname .. "-" .. iface .. "" .. idx .. "\n")
                    end
                end
            end
        end
    end
end

local url = arg[1]
local json_data = fetch_json_from_url(url)
parse_and_print_mac_addresses(json_data)
os.execute("ln -s /tmp/bat-hosts /etc/bat-hosts")

Cool script to test /etc/bat-hosts. Didn't know about that one.

I noticed two things:

If run again the symlink creation fails: ln: /etc/bat-hosts: File exists

Also it could be good not to get a traceback if the url is ommited but some more helpfull error message.