add nic option config for json response

[BuckarooBanzay]

This PR adds the ability to pass a config object to the nic as well as json parsing and header settings.
The message can still be a plain url as text or an object in the form:

{
 url = "http://x.y",
 parse_json = true
)

I've tested it and it works well but there may be some crash vectors, not sure 🤷

Example

Luacontroller

if event.type == "program" then
 digiline_send("nic", {
  url = "http://api.icndb.com/jokes/random",
  parse_json = true
 })
end

if event.type == "digiline" then
 print(event.msg)
end

Console

{
	completed = true,
	timeout = false,
	succeeded = true,
	data = {
		value = {
			id = 34,
			categories = {
				
			},
			joke = "The opening scene of the movie "Saving Private Ryan" is loosely based on games of dodgeball Chuck Norris played in second grade."
		},
		type = "success"
	},
	code = 200
}

[S-S-X]

Should check type of headers before using it.

[S-S-X]

Also contents, if you send headers = {false} it will crash server.
Probably something like:

if type(msg.headers) == "table" and #msg.headers > 0 and #msg.headers < 50 then
  headers = {}
  for _, header in ipairs(msg.headers) do
    header = (tostring(header)):gmatch("%C+")()
    if header ~= "" then
      table.insert(headers, header)
    end
  end
end

ipairs is intended over pairs to drop hash keys.

[S-S-X]

Tested above with this crap:

local msg = { headers =
{ 1, 2, 3, false, true, {"woo"}, function()quit()end, "Authorization: Ajadshk:dasjhghja", [[
And what
			about			!!!
this
crap????
]]
}
}
table.insert(msg.headers, msg.headers)
msg.headers.really = msg.headers[#msg.headers]

local headers
if type(msg.headers) == "table" and #msg.headers > 0 and #msg.headers < 50 then
  headers = {}
  for _, header in ipairs(msg.headers) do
    header = (tostring(header)):gmatch("%C+")()
    if header ~= "" then
      table.insert(headers, header)
    end
  end
end

http.fetch({
		url="http://127.0.0.1:10101/?hello",
		timeout=5,
		user_agent="Minetest Digilines Modem",
		extra_headers = headers
	},
	function(r) print(dump(r)) end,
	1
)

Headers after running through filter was:

{
	"1",
	"2",
	"3",
	"false",
	"true",
	"table: 0x555983663440",
	"function: 0x555983663490",
	"Authorization: Ajadshk:dasjhghja",
	"And what",
	"table: 0x5559836633f0"
}

[S-S-X]

Also for complete test, request I get for that is:

GET /?hello HTTP/1.1
Host: 127.0.0.1:10101
User-Agent: Minetest Digilines Modem
Accept: */*
Accept-Encoding: gzip
table: 0x555983663440
function: 0x555983663490
Authorization: Ajadshk:dasjhghja
table: 0x5559836633f0

[BuckarooBanzay]

i've removed the headers option completely, not worth the trouble IMO.

Also: some fixed headers could be set in the future, for example if POST would be implemented with a json-object, the headers could be just `Content-Type: application/json``

[OgelGames]

luacontroller_json.lua 👀

Though really the ideal solution would be to include minetest.parse_json and minetest.write_json in the luacontroller sandbox, instead of having it only be for the nic.

There is a PR open to add them, along with a heap of other helper functions: minetest-mods/mesecons#507, though this other one looks like it's more likely to get merged: minetest-mods/mesecons#557, and would allow for even more functionality.

EDIT: then again, there is the huge benefit of the parsing being done outside of the luacontroller sandbox, so still 👍 for this PR :)

[OgelGames]

I don't see any objections to this, so merging it.