Re: [PATCH] check_client_connection: use tcp state on linux

[Simon Eskildsen <simon.eskildsen@shopify.com>]

I left out a TCPSocket check, we'll need a `socket.is_a?(TCPSocket)`
in there. I'll wait with sending an updated patch in case you have
other comments. I'm also not entirely sure we need the `socket.close`.
What do you think?

On Sat, Feb 25, 2017 at 9:03 AM, Simon Eskildsen
<simon.eskildsen@shopify.com> wrote:
> The implementation of the check_client_connection causing an early write is
> ineffective when not performed on loopback. In my testing, when on non-loopback,
> such as another host, we only see a 10-20% rejection rate with TCP_NODELAY of
> clients that are closed. This means 90-80% of responses in this case are
> rendered in vain.
>
> This patch uses getosockopt(2) with TCP_INFO on Linux to read the socket state.
> If the socket is in a state where it doesn't take a response, we'll abort the
> request with a similar error as to what write(2) would give us on a closed
> socket in case of an error.
>
> In my testing, this has a 100% rejection rate. This testing was conducted with
> the following script:
>
> 100.times do |i|
>   client = TCPSocket.new("some-unicorn", 20_000)
>   client.write("GET /collections/#{rand(10000)}
> HTTP/1.1\r\nHost:walrusser.myshopify.com\r\n\r\n")
>   client.close
> end
> ---
>  lib/unicorn/http_request.rb | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/lib/unicorn/http_request.rb b/lib/unicorn/http_request.rb
> index 0c1f9bb..b4c95fc 100644
> --- a/lib/unicorn/http_request.rb
> +++ b/lib/unicorn/http_request.rb
> @@ -31,6 +31,9 @@ class Unicorn::HttpParser
>    @@input_class = Unicorn::TeeInput
>    @@check_client_connection = false
>
> +  # TCP_TIME_WAIT: 6, TCP_CLOSE: 7, TCP_CLOSE_WAIT: 8, TCP_LAST_ACK: 9
> +  IGNORED_CHECK_CLIENT_SOCKET_STATES = (6..9)
> +
>    def self.input_class
>      @@input_class
>    end
> @@ -83,10 +86,18 @@ def read(socket)
>        false until add_parse(socket.kgio_read!(16384))
>      end
>
> -    # detect if the socket is valid by writing a partial response:
> -    if @@check_client_connection && headers?
> -      self.response_start_sent = true
> -      HTTP_RESPONSE_START.each { |c| socket.write(c) }
> +    # detect if the socket is valid by checking client connection.
> +    if @@check_client_connection
> +      if defined?(Raindrops::TCP_Info)
> +        tcp_info = Raindrops::TCP_Info.new(socket)
> +        if IGNORED_CHECK_CLIENT_SOCKET_STATES.cover?(tcp_info.state)
> +          socket.close
> +          raise Errno::EPIPE
> +        end
> +      elsif headers?
> +        self.response_start_sent = true
> +        HTTP_RESPONSE_START.each { |c| socket.write(c) }
> +      end
>      end
>
>      e['rack.input'] = 0 == content_length ?
> --
> 2.11.0