Elixir 流向所有订阅者

Question

我正在尝试在 Elixir 中实现无线电服务器

一个进程始终在工作并读取文件 (mp3) 并发布到主题“:radio”，目前用于测试目的，当它完成时重新开始

每个连接都订阅主题“:radio”

我不明白如何将块发送到所有订阅的连接，连接在 2 或 3 个块后关闭

defmodule Plugtest do
  import Plug.Conn

  def init(opts), do: opts

  def start() do
    Plug.Adapters.Cowboy.http(Plugtest, [])
    {:ok, _pid} = PubSub.start_link()
    spawn(fn -> stream_from_file("./song.mp3", 128) end)
  end

  def call(conn, _opts) do
    conn = conn
    |> send_chunked(200)
    |> put_resp_content_type("audio/mpeg")

    :ok = PubSub.subscribe(spawn(fn -> send_chunk_to_connection(conn) end), :radio)
#    File.stream!("./song.mp3", [], 128) |> Enum.into(conn) # test purpose only
  end

  defp send_chunk_to_connection(conn) do
    receive do
      {:radio_data, data} ->
        IO.inspect "* #{inspect self()} * [ #{inspect conn.owner} ] [ #{inspect data} ]"
#        Enum.into(data, conn) # not working TODO send chunk to connection
        {:ok, conn} = chunk(conn, data)
        send_chunk_to_connection(conn)
    end
  end

  defp stream_from_file(fpath, bytes) do
    File.stream!(fpath, [], bytes)
    |> Enum.each(fn chunk ->
      PubSub.publish(:radio, {:radio_data, chunk})
    end)
    stream_from_file(fpath, bytes)
  end

end

堆栈跟踪：

[error] Process #PID<0.274.0> raised an exception
        ** (MatchError) no match of right hand side value: {:error, :closed}    
            (plugtest) lib/plugtest.ex:26: Plugtest.send_chunk_to_connection/1

依赖：

  defp deps do
    [{:plug, "~> 1.0"}, {:cowboy, "~> 1.0"}, {:pubsub, "~> 0.0.2"}]
  end

在@maxdec 评论后编辑

defmodule Plugtest do
  import Plug.Conn

  @file_path "./song.mp3"
  @port 4000
  @chunk_size 128

  def init(opts), do: opts

  def start() do
    Plug.Adapters.Cowboy.http Plugtest, [], port: @port
    {:ok, _pid} = PubSub.start_link()
    spawn fn ->
        stream_from_file(@file_path, @chunk_size)
    end
  end

  def call(conn, _opts) do
    conn = conn
    |> send_chunked(200)
    |> put_resp_content_type("audio/mpeg")

    :ok = PubSub.subscribe(spawn(fn -> send_chunk_to_connection(conn) end), :radio)
#    File.stream!("./song.mp3", [], 128) |> Enum.into(conn) # test purpose only
    conn
  end
  defp send_chunk_to_connection(conn) do
    receive do
      {:radio_data, data} ->
        case chunk(conn, data) do
          {:ok, conn} -> send_chunk_to_connection(conn)
          {:error, err} -> IO.puts err # do nothing, as something went wrong (client disconnection or something else...)
        end
    end
  end

  defp stream_from_file(fpath, bytes) do
    File.stream!(fpath, [], bytes)
    |> Enum.each(fn chunk ->
      PubSub.publish(:radio, {:radio_data, chunk})
    end)
    stream_from_file(fpath, bytes)
  end

end

Answer 1

快速浏览后，我认为您应该解决两件事：

1. PlugTest 是 Plug 所以 call/2 应该返回 conn （虽然这不是你的问题）。它还应该在等待事件时阻塞 (receive)：

    def call(conn, _opts) do
      conn = conn
      |> send_chunked(200)
      |> put_resp_content_type("audio/mpeg")

      :ok = PubSub.subscribe(self(), :radio)
      send_chunk_to_connection(conn)
    end

1. 在send_chunk_to_connection 你应该这样做：

    defp send_chunk_to_connection(conn) do
      receive do
        {:radio_data, data} ->
          case chunk(conn, data) do
            {:ok, conn} -> send_chunk_to_connection(conn)
            {:error, err} -> IO.puts err; conn # do nothing, as something went wrong (client disconnection or something else...)
          end
      end
    end