Setting custom attribute value from external source like an API/JSON/DB?

[larsschwarz]

Does the current process Lua script allow retrieving "external" data from sources like an API (http request), a JSON file or similar?

Something like

local my_custom_value = getExternalDataFromThisOrThat(way:Id())
way:Attribute("some_attribute_key",my_custom_value)

No Lua guy, but I assume JSON or http requests require the use of additional modules that aren't loaded by the current script process? Is there any default/on-board Lua functionality that could be used to load external data by the process script?

[systemed]

Lua itself is fairly bare-bones but you should be able to find some libraries to do this. In a similar situation (my OSRM fork) I need to read GeoJSON from Lua. First of all I have a simple bit of code to read a local file:

function Utils.read_file(fn)
	local f = assert(io.open(fn, "rb"))
	local content = f:read("*all")
	f:close()
	return content
end

I then use LunaJSON to parse the file. It's just three files that you can install manually, you don't have to use the Luarocks package manager.

I then put that in init_function so that the parsed JSON file is available to each thread.

Another option I find useful on occasion is to preprocess the .pbf to set arbitrary tags on each way: https://github.com/systemed/tagmangle is a little C++ utility I wrote for this.

[larsschwarz]

Thanks Richard. I tested some modules installed via Lurarocks and ended up using a simple io.popen to Curl, which works just fine.