I’ve been trying to debug this for days, and I can’t figure out what I’m doing wrong. If SSL is off, I can reload the page as fast as I want and I don’t encounter any errors. But when I turn SSL on and try refreshing the page quickly, repeatedly, I get an error after the 5th or 10th reload.

Steps to reproduce

1. Start with a fresh elixir Docker container.

docker run -it --rm -w /opt -p 4000:4000 -p 4001:4001 elixir bash

2. Generate a simple Phoenix app

apt-get update && apt-get install inotify-tools -y
mix archive.install hex phx_new --force
mix phx.new hello --no-ecto --install
cd hello

3. Generate a self-signed cert needed for SSL

mix phx.gen.cert

4. Configure the endpoint

• Change the IP to 0.0.0.0 to allow access from outside the container

  sed -i 's/{127, 0, 0, 1}/{0, 0, 0, 0}/' config/dev.exs
  

• Uncomment the self-cert https block

  sed -ie '/# \{5\}https/,/# \{5\}],/ { s/^#//; }' config/dev.exs
  

• Config Bandit to output client closures

  sed -ie '/certfile/,/],/ { s/"$/",\n       http_options: [log_client_closures: :verbose]/; s/],/]/; }' config/dev.exs
  

• Add a necessary comma after the watchers config option

  sed -zie '/watchers/,/]\n/ { s/]\n/],\n/ }' config/dev.exs
  

Endpoint config in config/dev.exs should look like this:

config :hello, HelloWeb.Endpoint,
  http: [ip: {0, 0, 0, 0}, port: 4000],
  ...
  watchers: [
    ...
  ],
  https: [
    port: 4001,
    cipher_suite: :strong,
    keyfile: "priv/cert/selfsigned_key.pem",
    certfile: "priv/cert/selfsigned.pem",
    http_options: [log_client_closures: :verbose]
  ]

5. Configure the controller

• Add a 1-second sleep to the controller home action to simulate a slow server response:

  sed -ie '/render/ { s/^/    Process.sleep(1000)\n/ }' lib/hello_web/controllers/page_controller.ex
  

The home action in lib/hello_web/controllers/page_controller.ex should now look like this:

def home(conn, _params) do
  ...
  Process.sleep(1000)
  render(conn, :home, layout: false)
end

6. Start the server

iex -S mix phx.server

7. Test with the HTTPS scheme

Visit https://localhost:4001 with your browser. It will complain about the certificates. Bypass and continue.

Now, reload the page repeatedly as fast as you can. After about the 5th or 10th reload, you should start encountering problems. With Firefox, I don’t see any errors in the console, but Firefox does eventually render a “Network protocol error” page. When I try it with Chromium and Gnome Web browsers, I see the following error in the console:

Error output

[info] Sent 500 in 1010ms
[error] ** (Bandit.TransportError) Client reset stream normally
    (bandit 1.6.1) lib/bandit/http2/stream.ex:386: Bandit.HTTPTransport.Bandit.HTTP2.Stream.do_recv_rst_stream!/2
    (bandit 1.6.1) lib/bandit/adapter.ex:230: Bandit.Adapter.send_data/3
    (bandit 1.6.1) lib/bandit/adapter.ex:113: Bandit.Adapter.send_resp/4
    (plug 1.16.1) lib/plug/conn.ex:444: Plug.Conn.send_resp/1
    (hello 0.1.0) lib/hello_web/controllers/page_controller.ex:1: HelloWeb.PageController.action/2
    (hello 0.1.0) lib/hello_web/controllers/page_controller.ex:1: HelloWeb.PageController.phoenix_controller_pipeline/2
    (phoenix 1.7.18) lib/phoenix/router.ex:484: Phoenix.Router.__call__/5
    (hello 0.1.0) lib/hello_web/endpoint.ex:1: HelloWeb.Endpoint.plug_builder_call/2
    (hello 0.1.0) deps/plug/lib/plug/debugger.ex:136: HelloWeb.Endpoint."call (overridable 3)"/2
    (hello 0.1.0) lib/hello_web/endpoint.ex:1: HelloWeb.Endpoint.call/2
    (phoenix 1.7.18) lib/phoenix/endpoint/sync_code_reload_plug.ex:22: Phoenix.Endpoint.SyncCodeReloadPlug.do_call/4
    (bandit 1.6.1) lib/bandit/pipeline.ex:127: Bandit.Pipeline.call_plug!/2
    (bandit 1.6.1) lib/bandit/pipeline.ex:36: Bandit.Pipeline.run/4
    (bandit 1.6.1) lib/bandit/http2/stream_process.ex:27: Bandit.HTTP2.StreamProcess.handle_continue/2
    (stdlib 6.1.2) gen_server.erl:2335: :gen_server.try_handle_continue/3
    (stdlib 6.1.2) gen_server.erl:2244: :gen_server.loop/7
    (stdlib 6.1.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3

Error screenshots

The forum won’t let me upload pictures, so I’ve uploaded screenshots of the error pages to Imgur.

Firefox | Chromium

8. Test with the HTTP scheme

Now visit http://localhost:4000.

Reload page repeatedly as fast as you can.

No matter how long or how fast I reload the browser, I get no errors.

Incidentals

Since it’s running in a Docker container, I’m not sure that it matters what OS I’m using, but in case it does, I’m on Debian Bookworm.