Best way to listen from outside?

i don't know if is the best way to do it , but i will show you what i do!
We already know pure lua don't have any synchronized functions , sokets or listeners, so the only way is to check always any data change from outside!
so far the example logic you put here is good, but you can speed up and improve catch error, sothing like try/catch!

so first we gonna secure our http request

local http_get_status, http_get_result = pcall(httpGet, "https://example.com/my-path")
if http_get_status then
   print("Host data\n"..http_get_result)
else
   print("Host connection error\nERROR\n\n" .. http_get_result)
end

so far is easy , you get data from host if success or error on fail

Now we need to check the returned data and see if is valid!
For what i saw in your example you use json data structure, for that you need a json lib to read/convert the data to table! i recommend this lib, is pure lua https://gist.github.com/tylerneylon/59f4bcf316be525b30ab


-- http try/catch
local http_get_status, http_data = pcall(httpGet, "https://example.com/my-path")
if http_get_status then
   print("Host data\n" .. http_data)

   -- json try/catch
   local json_status, json_data = pcall(function()
       return Json.parse(http_data)
   end)

   if json_status then
       -- json_data at this stage is a lua table
       print(json_data.action)
   else
       print("Data bad format\n" .. json_data)
   end
else
   print("Host connection error\nERROR\n\n" .. http_data)
end

now from here you can apply any new condition from returned data

       
...
if json_data.action == "stop" then
   scriptExit("Script stopped from outside")
end
...

The end , The basics is this, checks if we can connect to given url and validate parsed data,
but in your case i would create a module just for this, this way we can re-use or modify data received, from multiples sources, in different ways instead of creating new functions for different scenarios!
Something like this

httpRequest.lua
local Json = require "Json"
local M = {}
M.__index = M


-- private function
local _sanitizeUrl;
local _getHttpData;
local _jsonToLua;

-- ---------------------------------------------------
-- init
function M:new(url, init_http_timeout, max_http_timeout)
   local _self = {}
   setmetatable(_self, M)
   _self.url = _sanitizeUrl(url)
   _self.data = {}
   _self.init_http_timeout = init_http_timeout or 15
   _self.max_http_timeout = max_http_timeout or 30
   return _self
end

-- ---------------------------------------------------
-- you can put any conditions to sanitize the url
-- for now we only see if is not empty
_sanitizeUrl = function(url)
   if string.len(url) > 0 then
       return url
   end
   scriptExit("url is empty")
end

-- ---------------------------------------------------
-- Private
-- try to connect until timeout
-- returns data from http request or stop script if fail
_getHttpData = function(self)
   local http_status, http_data, http_timeout = nil, nil, self.init_http_timeout

   repeat
       setHttpTimeout(http_timeout)
       http_status, http_data = pcall(httpGet, self.url)
       if http_timeout > self.max_http_timeout then
           scriptExit("Host Connection\nRetrieving data - Timeout")
       end
       -- increase 5 sec
       http_timeout = http_timeout + 5
   until http_status

   return http_data
end

-- ---------------------------------------------------
-- Private
-- try to convert json to lua table
-- return data table from json data on success or a empty table on fail
_jsonToLua = function(http_data)
   local json_status, json_data = pcall(function()
       return Json.parse(http_data)
   end)

   if json_status then
       if typeOf(json_data) == "table" then
           return json_data
       else
           print("Json Data bad format, should be a table instead of " .. typeOf(json_data))
       end
   else
       print("Json to table fail \n status = " .. json_status .. "\n data = " .. json_data)
   end
   return {}
end

-- ---------------------------------------------------
-- Public
-- get http data
-- resturn data
function M:getData()
   self.data = _jsonToLua(_getHttpData(self))
   return self.data
end

-- ---------------------------------------------------
-- Public
-- print data for simple tables
function M:showData()
   for k, v in pairs(self.data) do
       print("Key - " .. k .. " | Value - " .. v)
   end
end

-- ---------------------------------------------------
-- Public
-- example to get company field from json data
function M:getCompany()
   if #self.data > 0 then
       return self.data[1].company
   end

   return false
end

return M



main.lua
-- load luaLib
-- we only need PRINT function from this lib for data show
dofile(scriptPath() .. "luaLib.lua")

-- updates modules path
package.path = scriptPath() .. '?.lua;' .. package.path

-- if you use a folder for your modules/class add this line too
-- package.path = scriptPath() .. 'YOUR_FOLDER_CLASS/?.lua;' .. package.path

-- load module
local httpRequest = require("httpRequest")

-- New request
-- httpRequest:new(url, init_http_timeout, max_http_timeout)
local http = httpRequest:new("https://raw.githubusercontent.com/mercobots/ankulua_http_test/main/json_data")
local http2 = httpRequest:new("SOURCE2")

http:getData()

print(http:getCompany())
print(http.data)

-- in a loop Example
while true do
   http:getData()
   if http:getCompany() == 'exit' then
       break
   end
   print(http:getCompany())


   -- ALTERNATIVE but i don't recommend
   if http.data[1].company == 'exit' then
       break
   end
   print(http.data[1].company)
end

-- in a loop Example
while true do
   http:getData()
   if http:getCompany() then
       http2:getData()
       
   end
end



dependencies
Json to lua - https://gist.github.com/tylerneylon/59f4bcf316be525b30ab
LuaLib ankulua.boards.net/thread/481/lib-lualib-ankulua-scripts
Json data example - github.com/mercobots/ankulua_http_test/blob/main/json_data

structure

- root/
-- httpRequest.lua
-- Json.lua
-- luaLib.lua
-- main.lua

I just ran a few simple tests, you may need to re-work httpRequest.lua returned values or add some new conditions to avoid issues!
Hope this helps you
Best Regards