Monitor a stream with a Supervisor in Elixir - twitter

Question

I use the ExTwitter-library to poll data using a stream like this:
stream = ExTwitter.stream_sample(receive_messages: true)
for message <- stream do
case message do
tweet = %ExTwitter.Model.Tweet{} ->
IO.puts "tweet = #{tweet.text}"
deleted_tweet = %ExTwitter.Model.DeletedTweet{} ->
IO.puts "deleted tweet = #{deleted_tweet.status[:id]}"
limit = %ExTwitter.Model.Limit{} ->
IO.puts "limit = #{limit.track}"
stall_warning = %ExTwitter.Model.StallWarning{} ->
IO.puts "stall warning = #{stall_warning.code}"
_ ->
IO.inspect message
end
end
and it's working great but now I want to monitor the stream with a Supervisor. What is the simplest way to do that?

Answer 1

The simplest way would be to put this code in a function in a new module, add a start_link function that simply invokes this function through spawn_link, and add that module as a worker to your Supervisor. Here's a simple example:
defmodule M do
use Application
def start(_type, _args) do
import Supervisor.Spec, warn: false
children = [
worker(M.Streamer, []),
]
opts = [strategy: :one_for_one, name: M.Supervisor]
Supervisor.start_link(children, opts)
end
end
defmodule M.Streamer do
def start_link do
{:ok, spawn_link(__MODULE__, :main, [])}
end
def main do
IO.inspect(self)
for i <- Stream.cycle([1, 2, 3]) do
IO.puts i
:timer.sleep(1000)
end
end
end
Demo:
#PID<0.85.0>
iex(1)> 1
2
3
1
2
3
1
2
Process.exit3pid(0, 85, 0), :kill)
#PID<0.88.0>
1
true
iex(2)> 2
3
1
2
3
1
2
3
Process.exit(pid(0, 88, 0), :kill)
#PID<0.90.0>
true
1
iex(3)> 2
3
1
2
3
This might be a little hard to follow as the output was happening while I was typing, but all the PID values were printed whenever Streamer started, the Process.exit lines are the code entered by me, and true is the return value of those calls. As you can see, whenever I killed the M.Streamer process, it was restarted by the Supervisor.