Re: What happens when a client terminates a connection?

[Eric Wong <normalperson@yhbt.net>]

Jesse Storimer <jstorimer@gmail.com> wrote:
> Eric Wong <normalperson@yhbt.net> wrote:
> > Unicorn has 4 distinct states :

<snip>

> > 3) inside Rack dispatch (after rack.input reading)
> >    Your app has no way of knowing your client disconnected at
> >    this stage.  You can hack Unicorn to IO.select in a separate
> >    thread, but there'll always be exposed windows leading up to
> >    4) so it's not worth it...
> > 
> > 4) writing the response: Unicorn will abort whenever a socket
> >    error is detected.  Keep in mind that every single part of the
> >    Rack response array can be dynamically generated by the app.
> >    Your application can still be "running" even though the Rack app
> >    has returned its response for Unicorn to start writing.
> > 
> >    Clients/Rack middleware can be written to detect this in the
> >    response body "close" method by checking if body.each completed.
> 
> Thanks for that explanation. Just so I understand, once the Rack application 
> enters 3) then it should be unaffected by a client disconnect, or any
> socket error? I'll definitely give PrereadInput a try in that case.

Yes, however I don't think I made it clear that 3) will /always/ transition
to state 4).  So you'll be able to use body.close to detect a client
write failure.

> When you say that Unicorn lazily reads request bodies, do you mean that
> my Rails application might already be in the middle of processing the
> request but Unicorn is still reading from the client socket?

Yes.  We use http://unicorn.bogomips.org/Unicorn::TeeInput.html by
default so it gives the Rack app a chance to reject a client
if it sees something it doesnt like

> At that point won't Rails have read all of the request body? Or does
> that only apply if I stick a middleware at the front of the stack that
> does all the heavy lifting?

I'm not certain about middlewares.  Rails may attempt to read all input
ASAP anyways depending on the request Content-Type/Encoding.  Check the
Rails/Rack sources for your versions of Rails/Rack to be sure.

-- 
Eric Wong
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