send calls via an endpoint to a GenServer - asynchronous

Question

Given a running GenServer, is there a known way to send synchronous/asynchronous calls to the pid via an endpoint, without using the Phoenix framework?
Here's an example call (using python's requests library) that maps the reply term to JSON:
iex> give_genserver_endpoint(pid, 'http://mygenserverendpoint/api')
iex> {:ok, 'http://mygenserverendpoint/api'}
>>> requests.get(url='http://mygenserverendpoint/getfood/fruits/colour/red')
>>> '{ "hits" : ["apple", "plum"]}'

Answer 1

You can write a complete elixir http server using cowboy and plug:
Application Module
defmodule MyApp do
use Application
def start(_type, _args) do
import Supervisor.Spec
children = [
worker(MyGenServer, []),
Plug.Adapters.Cowboy.child_spec(:http, MyRouter, [], [port: 4001])
]
opts = [strategy: :one_for_one, name: MyApp.Supervisor]
Supervisor.start_link(children, opts)
end
end
Router Module
defmodule MyRouter do
use Plug.Router
plug :match
plug :dispatch
get "/mygenserverendpoint/getfood/fruits/colour/:colour" do
response_body = MyGenServer.get_fruit_by_colour(colour)
conn
|> put_resp_content_type("application/json")
|> send_resp(conn, 200, Poison.encode(response_body))
end
match _ do
send_resp(conn, 404, "oops")
end
end
GenServer module
defmodule MyGenServer do
use GenServer
def start_link do
GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
end
def get_fruit_by_colour(colour) do
GenServer.call(__MODULE__, {:get_by_colour, colour})
end
def handle_call({:get_by_colour, colour}, _from, state) do
{:reply, %{"hits" : ["apple", "plum"]}, state}
end
end