Transfer-Encoding header lost with EventSource

[zhongsheng]

bin/rails s works

But with thruster bin/thrust bin/rails s, transfer-encoding is missing. This cause a problem, messages returned as a whole text.

Rails 8.0.0.beta1
ruby 3.3.1 (2024-04-23 revision c56cd86388) [arm64-darwin23]

class SseController < ApplicationController
  include ActionController::Live
  def index
  end

  def events
    response.headers['Content-Type'] = 'text/event-stream'

    sse = SSE.new(response.stream, event: "message")

    5.times {
      sse.write({ message: "hello world" })
      sleep 1
    }
  ensure
    response.stream.close
  end

end

[3v0k4]

I cannot reproduce with:

• rails 8.0.0
• thruster 0.1.8
• ruby 3.3.5

I see Transfer-Encoding: chunked with and without thruster.

Could you please double check? 🙏

[zhongsheng]

I cannot reproduce with:

• rails 8.0.0
• thruster 0.1.8
• ruby 3.3.5

I see Transfer-Encoding: chunked with and without thruster.

Could you please double check? 🙏

rails new myapp
cd myapp
rails g controller sse index events
# put some code in events method
HTTP_PORT=8088 bin/thrust rails server

Then access http://localhost:8088/sse/events

[3v0k4]

My bad, I was curling the wrong port 🤦

I think there's some buffering involved with the GzipHandler.

If you change your Rails controller code as follows then it should work:

class SseController < ApplicationController
  include ActionController::Live
  def index
  end

  def events
    response.headers['Content-Type'] = 'text/event-stream'

    sse = SSE.new(response.stream, event: "message")

    5.times {
-    sse.write({ message: "hello world" })
+    sse.write({ message: "hello world" * 1000 })
      sleep 1
    }
  ensure
    response.stream.close
  end
end

[mjason]

I also encountered this problem, debugged for a long time, initially thought it was a kamal proxy issue, because there is a issues over there. Then I switched to caddy and it still occurred, so I'm sure it's not this problem.

Then I debugged rack and found no anomalies, later I reviewed the dockerfile code and found this part, and discovered that someone else had the same issue as me. I disabled thruster and found that my program was working normally.

class ChatsController < ApplicationController
  include ActionController::Live

  def index
    @prompts = Prompt.all
    @default_prompt = @prompts.first
    @fields = @default_prompt&.fields
  end


  def create
    response.headers["Content-Type"] = "text/event-stream"
    response.headers["Last-Modified"] = Time.now.httpdate

    sse = SSE.new(response.stream, retry: 300, event: "chat-output")

    prompt = Prompt.find(params[:prompt_id])

    prompt.chat(fields: params.require(:fields).permit!) do |message, html_content, accumulated, done|
      if done
        [
          turbo_stream.update("chat_output", html_content),
          turbo_stream.update("submit_button", partial: "shared/normal_button"),
          turbo_stream.update("chat-output-bottom", partial: "chats/copy", locals: { markdown_content: accumulated })
        ].join("\n").then { sse.write({ template: _1 }) }
      else
        turbo_stream.append("chat_output", message.gsub("\n", "<br>")).then {
          sse.write({ template: _1 })
        }
      end

      logger.info "message: #{message}"
    end
  ensure
    sse.close
  end
end

Dockerfile:

EXPOSE 80
# CMD ["./bin/thrust", "./bin/rails", "server"]
CMD ["bundle", "exec", "falcon", "host"]