I am working on an Phoenix API (PUT) route that allows the upload of rather large image files (more than 1gb). So I am trying to read the request body in chunks by parsing some requests parameters, opening an io_device (with File.open/2) and hand both my conn and the device to the following function:

  defp read_body_chunked(conn, io_device) do
    IO.inspect(conn, label: "read_body_chunked called")

    read_body(conn)
    |> IO.inspect()
    |> case do
      {:ok, data, conn} ->
        IO.binwrite(io_device, data)
        {:ok, conn}

      {:more, data, conn} ->
        IO.binwrite(io_device, data)
        read_body_chunked(conn, io_device)

      error ->
        error
    end
  end

This works in general if the connection is stable.

But if I kill my client (an Electron app) deliberately while a large file is being uploaded it looks like read_body/2 is still called but never returns. I get a final log with the label “read_body_chunked called”, but then nothing afterwards and I end up with a only partially uploaded file and no apparent way to recover.

What am I missing?

I am using :plug_cowboy 2.7 and Phoenix 1.7.20.