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

[Eric Wong <e@80x24.org>]

Simon Eskildsen <simon.eskildsen@shopify.com> wrote:

<snip>
> I would assume you would see TIME_WAIT and CLOSE. LAST_ACK_CLOSING it
> seems pretty unlikely to hit, but not impossible. As with CLOSING,
> I've included LAST_ACK_CLOSING for completeness.

Did you mean "LAST_ACK, and CLOSING"? (not joined by underscore)

Anyways, thanks for testing and adding

> <e@80x24.org> wrote:
> > Yep, we need to account for the UNIX socket case.  I forget if
> > kgio even makes them different...
> 
> I read the implementation and verified by dumping the class when
> testing on some test boxes. You are right—it's a simple Kgio::Socket
> object, not differentiating between Kgio::TCPSocket and
> Kgio::UnixSocket at the class level. Kgio only does this if they're
> explicitly passed to override the class returned from #try_accept.
> Unicorn doesn't do this.
> 
> I've tried to find a way to determine the socket domain (INET vs.
> UNIX) on the socket object, but neither Ruby's Socket class nor Kgio
> seems to expose this. I'm not entirely sure what the simplest way to
> do this check would be. We could have the accept loop pass the correct
> class to #try_accept based on the listening socket that came back from
> #accept. If we passed the listening socket to #read after accept, we'd
> know.. but I don't like that the request knows about the listener
> either. Alternatively, we could expose the socket domain in Kgio, but
> that'll be problematic in the near-ish future as you've mentioned
> wanting to move away from Kgio as Ruby's IO library is at parity as
> per Ruby 2.4.
> 
> What do you suggest pursuing here to check whether the client socket
> is a TCP socket?

I think passing the listening socket is the best way to go about
detecting whether a socket is INET or UNIX, for now.

You're right about kgio, I'd rather not make more changes to
kgio but we will still need it to for Ruby <2.2.x users.

And #read is an overloaded name, feel free to change it :)

> Below is a patch addressing the other concerns. I had to include
> require raindrops so the `defined?` check would do the right thing, as
> the only other file that requires Raindrops is the worker one which is
> loaded after http_request. I can change the load-order or require
> raindrops in lib/unicorn.rb if you prefer.

The require is fine.  However we do not need a class variable,
below...

>  # TODO: remove redundant names
>  Unicorn.const_set(:HttpRequest, Unicorn::HttpParser)
> @@ -29,6 +30,7 @@ class Unicorn::HttpParser
>    # 2.2+ optimizes hash assignments when used with literal string keys
>    HTTP_RESPONSE_START = [ 'HTTP', '/1.1 ']
>    @@input_class = Unicorn::TeeInput
> +  @@raindrops_tcp_info_defined = defined?(Raindrops::TCP_Info)

I prefer we avoid adding this cvar, instead...

>    @@check_client_connection = false
> 
>    def self.input_class
> @@ -83,11 +85,7 @@ 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) }
> -    end
> +    check_client_connection(socket) if @@check_client_connection
> 
>      e['rack.input'] = 0 == content_length ?
>                        NULL_IO : @@input_class.new(socket, self)
> @@ -108,4 +106,27 @@ def call
>    def hijacked?
>      env.include?('rack.hijack_io'.freeze)
>    end

... we can have different methods defined:

   if defined?(Raindrops::TCP_Info) # Linux, maybe FreeBSD
     def check_client_connection(client, listener) # :nodoc:
     ...
     end
   else # portable version
     def check_client_connection(client, listener) # :nodoc:
     ...
     end
   end

And eliminate the class variable entirely.

> +
> +  private

I prefer to avoid marking methods as 'private' to ease any
ad-hoc unit testing which may come up.  Instead, rely on :nodoc:
directives to discourage people from depending on it.

Thanks.

> +  def check_client_connection(socket)
> +    if @@raindrops_tcp_info_defined
> +      tcp_info = Raindrops::TCP_Info.new(socket)
> +      raise Errno::EPIPE, "client closed connection".freeze, [] if
> closed_state?(tcp_info.state)
> +    elsif headers?
> +      self.response_start_sent = true
> +      HTTP_RESPONSE_START.each { |c| socket.write(c) }
> +    end
> +  end
> +
> +  def closed_state?(state)
> +    case state
> +    when 1 # ESTABLISHED
> +      false
> +    when 6, 7, 8, 9, 11 # TIME_WAIT, CLOSE, CLOSE_WAIT, LAST_ACK, CLOSING
> +      true
> +    else
> +      false
> +    end
> +  end
>  end

closed_state? looks good to me, good call on short-circuiting
the common case of ESTABLISHED!