Using Elixir's Stream for API endpoints that require pagination

[sinni800]

I have tried to get all reactions to a message, but Api.get_reactions only returns the first 25.

So I thought, yeah, this needs pagination.

I have implemented a way to get all reactions to a message and have used Elixir's own Streams for this.

Here's my example code, it's a dirty "proof of concept" that is copypasted together a little, but here:

defmodule Bot.Library.ReactionsStream do
    require Logger

    def handle_request_with_decode(response)
    def handle_request_with_decode({:ok, body}), do: {:ok, Jason.decode!(body, keys: :atoms)}
    def handle_request_with_decode({:error, _} = error), do: error
  
    def handle_request_with_decode(response, type)
    # add_guild_member/3 can return both a 201 and a 204
    def handle_request_with_decode({:ok}, _type), do: {:ok}
    def handle_request_with_decode({:error, _} = error, _type), do: error
  
    def handle_request_with_decode({:ok, body}, type) do
      convert =
        body
        |> Jason.decode!(keys: :atoms)
        |> Nostrum.Util.cast(type)
  
      {:ok, convert}
    end

    def request(channel_id, message_id, emoji, after_id \\ 0) do
        
        params = 
            case after_id do
                   0 -> [limit: 100]
                   num -> [after: num, limit: 100]
            end
            
            
        route = Nostrum.Constants.channel_reactions_get(channel_id, message_id, emoji)
        Nostrum.Api.request(:get, route, "", params: params)
        |> handle_request_with_decode
    end

    defp start(channel_id, message_id, emoji) do
        fn -> 
            {[], channel_id, message_id, emoji, 0} 
        end
    end

    defp next_item({items, channel_id, message_id, emoji, after_id}) when length(items) == 0 do
        {:ok, list} = request(channel_id, message_id, emoji, after_id)
        Logger.info("fetched new items" <> inspect length(list))
        case Enum.count(list) do
            0 -> {:halt, {[], channel_id, message_id, emoji, after_id}}
            _ -> next_item({list, channel_id, message_id, emoji, List.last(list).id})
        end
    end

    defp next_item({items, channel_id, message_id, emoji, after_id}) when length(items) > 0 do
        {item, items} = List.pop_at(items, 0)
        {[item], {items, channel_id, message_id, emoji, after_id}}
    end

    defp stop(_acc) do 

    end

    def get_reactions_stream(channel_id, message_id, emoji) do
        Stream.resource(start(channel_id, message_id, emoji), &next_item/1, &stop/1)
    end
end

Usage is like this, for example:

Bot.Library.ReactionsStream.get_reactions_stream(channel_id, message_id, "emoji") |> Enum.take(10)

Should we add enumerable streams to the API package for paginated queries?

[jchristgit]

I like this idea a lot.

@Kraigie @jb3 what are your thoughts on this?