Request/Response streaming for Finch adapter, SSE middleware

[teamon]

• Request streaming support #506
• First take on response streaming support #271

The implementation requires spawning a process, I'm not sure there's a way to implement streaming without it given Finch.stream/5 only returns after all data has been streamed and the idea for tesla response streaming is to return Tesla.Env with status & headers and body as a stream.

Example streaming OpenAI client:

defmodule OpenAI do
  def new(token) do
    middleware = [
      {Tesla.Middleware.BaseUrl, "https://api.openai.com/v1"},
      {Tesla.Middleware.BearerAuth, token: token},
      # decode text/event-stream response
      {Tesla.Middleware.JSON, decode_content_types: ["text/event-stream"]},
      # decode SSE and return stream of data only (to be decoded by JSON)
      {Tesla.Middleware.SSE, only: :data}
    ]
    # use Finch as adapter
    Tesla.client(middleware, {Tesla.Adapter.Finch, name: MyFinch})
  end

  def completion(client, prompt) do
    data = %{
      model: "gpt-3.5-turbo",
      messages: [
        %{role: "user", content: prompt}
      ],
      # tell OpenAI to stream the response
      stream: true
    }
    # use the new [response: :stream] adapter option
    Tesla.post(client, "/chat/completions", data, opts: [adapter: [response: :stream]])
  end
end

{:ok, pid} = Finch.start_link(name: MyFinch)

client = OpenAI.new("<token>")

{:ok, env} = OpenAI.completion(client, "Count to 5, with a comma between each number and no newlines.")

env.body
|> Stream.each(&IO.inspect(&1, label: "chunk"))
|> Stream.run()

Output:

chunk: %{
  "choices" => [
    %{"delta" => %{"role" => "assistant"}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => "1"}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => ","}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => " "}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => "2"}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => ","}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => " "}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => "3"}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => ","}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => " "}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => "4"}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => ","}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => " "}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [
    %{"delta" => %{"content" => "5"}, "finish_reason" => nil, "index" => 0}
  ],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: %{
  "choices" => [%{"delta" => %{}, "finish_reason" => "stop", "index" => 0}],
  "created" => 1681734469,
  "id" => "chatcmpl-76IFRG54YaoTcpb7bPEw5SvJZT5N6",
  "model" => "gpt-3.5-turbo-0301",
  "object" => "chat.completion.chunk"
}
chunk: "[DONE]"

[hodak]

Love it, would like to use it, here's a PR with error handling fix: https://github.com/elixir-tesla/tesla/pull/573

[cliftonmcintosh]

Thanks for this. I'd love to be able to use the streaming. This would allow me to move away from HTTPoison for streaming a response. Are there plans for this to be merged soon?

[atomkirk]

Please merge!! 😄